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Martin, Louis, Jacques Bertaux, Thierry Corrège, Marie-Pierre Ledru, Philippe Mourguiart, Abdelfettah Sifeddine, François Soubiès, Denis Wirrmann, Kenitiro Suguio, and Bruno Turcq. "Astronomical Forcing of Contrasting Rainfall Changes in Tropical South America between 12,400 and 8800 cal yr B.P." Quaternary Research 47, no. 1 (January 1997): 117–22. http://dx.doi.org/10.1006/qres.1996.1866.
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AbstractToday, precipitation over tropical South America is largely controlled by the seasonal movements of the Inter-Tropical Convergence Zone (ITCZ). During the summer, the ITCZ is shifted southward due to the warming of the continent. Paleoclimate data from southeastern Amazonia and the central Andes indicate that these two areas evolved similarly during the last 30,000 yr. However, between 12,400 and 8800 cal yr B.P., eastern Amazonia received substantial moisture whereas the Bolivian Altiplano was arid. This suggests that the ITCZ during summer was then farther north than it is today.
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Sum, Lai Shan, and Brent Wilson. "The influence of the inter-tropical convergence zone on the Orinoco River and Late Quaternary tropical planktonic foraminiferal assemblages." Micropaleontology 68, no. 4 (2022): 413–25. http://dx.doi.org/10.47894/mpal.68.4.05.
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Although deep-water oil and gas exploration offshore eastern Trinidad is becoming prevalent, the use of ecostratigraphy around eastern Trinidad are limited mostly to neritic water depths. Changes in planktonic foraminiferal assemblages of Core BGT086, offshore eastern Trinidad, are used here to indicate biozonal events useful for deep-water (>1000 m water depth) exploration. Decreased proportional abundances of Globigerinella obesa and Globigerina bulloides mark the southward migration of the inter-tropical convergence zone (ITCZ) during the Younger Dryas (YD). A decrease in species richness and Globigerinoides ruberwhite proportional abundance is consistent with rising temperature during the YD. During Biozone Z2, nutrient-preferring species (G. bulloides, Neogloboquadrina dutertrei) declined in proportional abundance, while G. ruberpink increased in proportional abundance, reflecting the arrival of the ITCZ in the area. Decreases in mean diversity (measured using the Shannon Function, H) and evenness (equitability index, E), and an increase in mean dominance (max pi) support the claim that the ITCZ arrived in the area after the YD. A sudden increase in Globorotalia menardii proportional abundance marked the start of Biozone Z1, at which time there was a change from a stressed community to a less stressed one. Boundaries of SHE abundance biozones coincided with noticeably enhanced assemblage changes, being consistent with the southward migration of the ITCZ and the onset of Biozone Z1. The mean value of the pairwise assemblage turnover index (ATIs) is here used as a proxy for what we term 'assemblage stability'. Comparisons of mean planktonic foraminiferal ATIs from Core BGT086 and six other nearby tropical piston cores (Cores 1, 2 and 3 off NW Tobago, and En20-2, En20-10 and En20-16 from the Leeward Islands, Lesser Antilles) showed no statistical difference in assemblage stabilities within similar planktonic foraminiferal biozones. Kruskal-Wallis tests determined a significant difference in median ATIs values when all seven cores' ATIs were used, but the difference was not significant when data above the YD boundary (i.e., Biozone Z) were used. The lowered nutrient influx from the Orinoco River due to the arrival of the ITCZ in the area after the YD would have triggered a stable environment for planktonic foraminiferal assemblages. This implies that caution must be used to ensure data from the same biozone is used when analyzing assemblage stabilities of planktonic foraminifera.
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Zappalà, Dario A., Marcelo Barreiro, and Cristina Masoller. "Quantifying changes in spatial patterns of surface air temperature dynamics over several decades." Earth System Dynamics 9, no. 2 (April 18, 2018): 383–91. http://dx.doi.org/10.5194/esd-9-383-2018.
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Abstract. We study daily surface air temperature (SAT) reanalysis in a grid over the Earth's surface to identify and quantify changes in SAT dynamics during the period 1979–2016. By analysing the Hilbert amplitude and frequency we identify the regions where relative variations are most pronounced (larger than ±50 % for the amplitude and ±100 % for the frequency). Amplitude variations are interpreted as due to changes in precipitation or ice melting, while frequency variations are interpreted as due to a northward shift of the inter-tropical convergence zone (ITCZ) and to a widening of the rainfall band in the western Pacific Ocean. The ITCZ is the ascending branch of the Hadley cell, and thus by affecting the tropical atmospheric circulation, ITCZ migration has far-reaching climatic consequences. As the methodology proposed here can be applied to many other geophysical time series, our work will stimulate new research that will advance the understanding of climate change impacts.
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Voarintsoa, Ny Riavo G., George A. Brook, Fuyuan Liang, Eugene Marais, Ben Hardt, Hai Cheng, R. Lawrence Edwards, and L. Bruce Railsback. "Stalagmite multi-proxy evidence of wet and dry intervals in northeastern Namibia: Linkage to latitudinal shifts of the Inter-Tropical Convergence Zone and changing solar activity from AD 1400 to 1950." Holocene 27, no. 3 (July 28, 2016): 384–96. http://dx.doi.org/10.1177/0959683616660170.
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Multiple proxies using variation in δ18O, δ13C, mineralogy, and petrography in a newly generated high-resolution record of Stalagmite DP1 from Dante Cave indicate a linkage between changes in hydroclimate in northeastern Namibia and changes in solar activity and changes in global temperatures. The record suggests that during solar minima and globally cooler conditions (ca. 1660–1710 and ca. 1790–1830), wetter periods (reflecting longer summer seasons) in northeastern Namibia were linked to advances of the Inter-Tropical Convergence Zone (ITCZ) and the Inter-Ocean Convergence Zone (IOCZ) southwestward. A slight southward push of the Angola–Benguela Front (ABF) during such intervals could also be expected, bringing more rainfall inland. On the other hand, drier and warmer periods in northeastern Namibia, inferred from the increasing δ18O trend in Stalagmite DP1 after AD 1715, coincide with globally warmer conditions, and thus a northeastward migration of the ITCZ, specifically with more warming of the Northern Hemisphere (NH). This finding agrees with reducing precipitation observed in the summer rainfall zone of southern Africa since ca. 1900. Therefore, predictions of warming in high-latitude regions of the NH in the next century should suggest that the presently semi-arid climate of northern Namibia may become even drier.
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Margalef, O., I. Cacho, S. Pla-Rabes, N. Cañellas-Boltà, J. J. Pueyo, A. Sáez, L. D. Pena, B. L. Valero-Garcés, V. Rull, and S. Giralt. "Millennial-scale precipitation variability over Easter Island (South Pacific) during MIS 3: inter-hemispheric teleconnections with North Atlantic abrupt cold events." Climate of the Past Discussions 11, no. 2 (April 17, 2015): 1407–35. http://dx.doi.org/10.5194/cpd-11-1407-2015.
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Abstract. Marine Isotope Stage 3 (MIS 3, 59.4–27.8 kyr BP) is characterized by the occurrence of rapid millennial-scale climate oscillations known as Dansgaard–Oeschger cycles (DO) and by abrupt cooling events in the North Atlantic known as Heinrich events. Although both the timing and dynamics of these events have been broadly explored in North Atlantic records, the response of the tropical and subtropical latitudes to these rapid climatic excursions, particularly in the Southern Hemisphere, still remains unclear. The Rano Aroi peat record (Easter Island, 27° S) provides a unique opportunity to understand atmospheric and oceanic changes in the South Pacific during these DO cycles because of its singular location, which is influenced by the South Pacific Anticyclone (SPA), the Southern Westerlies (SW), and the Intertropical Convergence Zone (ITCZ) linked to the South Pacific Convergence Zone (SPCZ). The Rano Aroi sequence records 6 major events of enhanced precipitation between 38 and 65 kyr BP. These events are compared with other hydrological records from the tropical and subtropical band supporting a coherent regional picture, with the dominance of humid conditions in Southern Hemisphere tropical band during Heinrich Stadials (HS) 5, 5a and 6 and other Stadials while dry conditions prevailed in the Northern tropics. This antiphased hydrological pattern between hemispheres has been attributed to ITCZ migration, which in turn might be associated with an eastward expansion of the SPCZ storm track, leading to an increased intensity of cyclogenic storms reaching Easter Island. Low Pacific Sea Surface Temperature (SST) gradients across the Equator were coincident with the here-defined Rano Aroi humid events and consistent with a reorganization of Southern Pacific atmospheric and oceanic circulation also at higher latitudes during Heinrich and Dansgaard–Oeschger stadials.
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Lau, William K. M., Kyu-Myong Kim, Jiun-Dar Chern, W. K. Tao, and L. Ruby Leung. "Structural changes and variability of the ITCZ induced by radiation–cloud–convection–circulation interactions: inferences from the Goddard Multi-scale Modeling Framework (GMMF) experiments." Climate Dynamics 54, no. 1-2 (October 5, 2019): 211–29. http://dx.doi.org/10.1007/s00382-019-05000-y.
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Abstract In this paper, we have investigated the impact of radiation–cloud–convection–circulation interaction (RC3I) on structural changes and variability of the Inter-tropical Convergence Zone (ITCZ) using the Goddard Multi-scale Modeling Framework, where cloud processes are super-parameterized, i.e., explicitly resolved with 2-D cloud resolving models embedded in each coarse grid of the host Goddard Earth Observing System-Version 5 global climate model. Experiments have been conducted under prescribed sea surface temperature conditions for 10 years (2007–2016), with and without cloud radiation feedback in the atmosphere, respectively. Diagnostic analyses separately for January and July show that RC3I leads to an enhanced and expanded Hadley Circulation characterized by (1) a quasi-uniform warming and moistening of the tropical atmosphere and a sharpening of the ITCZ with enhanced deep convection, more intense precipitation and higher clouds, (2) extended drying of the tropical marginal convective zones, and extratropical mid- to lower troposphere, and (3) a cooling of the polar regions, with increased baroclinicity and midlatitude storm track activities. Computations based on the zonal mean thermodynamic energy balance equation show that the radiative warming and cooling are strongly balanced by local adiabatic processes associated with changes in large-scale vertical motions, as well as horizontal atmospheric heat transport. In the tropics, enhanced short-wave absorption and longwave water vapor greenhouse effects by high clouds play key roles in providing strong positive feedback to the tropospheric warming. In the extratropics, increased atmospheric heat transport associated with changes in the Hadley circulation is balanced by strong longwave cooling above, and warming below due to increased high clouds. We also find a strong positive correlation between daily and pentad heavy rain in the ITCZ core, and expansion of the drier zones coupled to a contraction of the highly convective zones in the ITCZ, indicating a strong tendency RC3I-induced convective aggregation in tropical clouds i.e., wet-regions-get-wetter and contracted, and dry-areas-get-drier and expanded.
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Lashkari, Hassan, Zainab Mohammadi, and Ghassem Keikhosravi. "Annual Fluctuations and Displacements of Inter Tropical Convergence Zone (ITCZ) within the Range of Atlantic Ocean-India." Open Journal of Ecology 07, no. 01 (2017): 12–33. http://dx.doi.org/10.4236/oje.2017.71002.
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Norman, M., C. Leck, and H. Rodhe. "Differences across the ITCZ in the chemical characteristics of the Indian Ocean MBL aerosol during INDOEX." Atmospheric Chemistry and Physics 3, no. 3 (May 28, 2003): 563–79. http://dx.doi.org/10.5194/acp-3-563-2003.
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Abstract. The water soluble inorganic part of the sub-micrometer aerosol was measured from two research vessels over the Indian Ocean during the winter monsoon season (February and March) as part of the INDOEX project in 1998 and 1999. Additional measurements were made of gas phase SO2 from one of the vessels in 1999. All samples collected north of the Inter Tropical Convergence Zone, ITCZ, were clearly affected by continental, anthropogenic sources. A sharp transition occurred across the ITCZ with concentrations of nss-SO42-, NH4+ and nss-K+ being lower by a factor of 7-15, >20 and >40, respectively, on the southern side of the ITCZ. The contribution from DMS to the sub-micrometer nss-SO42- was estimated to be up to 40% in clean air north of the ITCZ but less than 10% in polluted air originating from India. South of the ITCZ virtually all nss-SO42- was likely to be derived from oxidation of DMS. The concentration of SO2 decreased rapidly with distance from the Indian coast, the molar ratio SO2/nss-SO42- reaching values below 5% after 35 h travel time over the ocean. Surprisingly, MSA, which is derived from DMS, also showed higher concentrations in the sub-micrometer aerosol north of the ITCZ than south of it. This could be explained by the larger sub-micrometer surface area available north of the ITCZ for the condensation of MSA. South of the ITCZ a major part of the MSA was found on the super-micrometer particles. An analysis based on the air trajectories showed that systematic variation in the observed concentrations was associated with variations in the transport from source regions. For example, differences in time since air parcels left the Arabian or Indian coasts was shown to be an important factor for explaining the substantial differences in absolute concentrations.
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McCarthy, M. P., J. Sanjay, B. B. B. Booth, K. Krishna Kumar, and R. A. Betts. "The influence of vegetation on the ITCZ and South Asian monsoon in HadCM3." Earth System Dynamics 3, no. 1 (June 22, 2012): 87–96. http://dx.doi.org/10.5194/esd-3-87-2012.
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Abstract. The role of global vegetation on the large-scale tropical circulation is examined in the version 3 Hadley Centre climate model (HadCM3). Alternative representations of global vegetation cover from observations and a dynamic global vegetation model (DGVM) were used as the land-cover component for a number of HadCM3 experiments under a nominal present day climate state, and compared to the simulations using the standard land cover map of HadCM3. The alternative vegetation covers result in a large scale cooling of the Northern Hemisphere extra-tropics relative to the HadCM3 standard, resulting in a southward shift in the location of the inter-tropical convergence zone (ITCZ). A significant reduction in Indian monsoon precipitation is also found, which is related to a weakening of the South Asian monsoon circulation, broadly consistent with documented mechanisms relating to temperature and snow perturbations in the Northern Hemisphere extra-tropics in winter and spring, delaying the onset of the monsoon. The role of the Northern Hemisphere extra-tropics on tropical climate is demonstrated, with an additional representation of vegetation cover based on DGVM simulated changes in Northern Hemisphere vegetation from the end of the 21st Century. This experiment shows that through similar processes the simulated extra-tropical vegetation changes in the future contribute to a strengthening of the South Asian monsoon in this model. These findings provide renewed motivation to give careful consideration to the role of global scale vegetation feedbacks when looking at climate change, and its impact on the tropical circulation and South Asian monsoon in the latest generation of Earth System models.
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Anderson, R. Charles. "Do dragonflies migrate across the western Indian Ocean?" Journal of Tropical Ecology 25, no. 4 (July 2009): 347–58. http://dx.doi.org/10.1017/s0266467409006087.
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Abstract:In the tropical Indian Ocean, the Maldive Islands lack surface freshwater, so are unsuitable for dragonfly reproduction. Nevertheless, millions of dragonflies (Insecta, Odonata; mostly globe skimmer, Pantala flavescens) appear suddenly every year starting in October. Arrival dates in the Maldives and India demonstrate that the dragonflies travel from southern India, a distance of some 500–1000 km. Dates of arrival and occurrence coincide with the southward passage of the Inter-tropical Convergence Zone (ITCZ). Circumstantial evidence suggests that the dragonflies fly with north-easterly tail winds, within and behind the ITCZ, at altitudes over 1000 m. It is proposed that this massive movement of dragonflies is part of an annual migration across the western Indian Ocean from India to East Africa. Arrival dates in the Seychelles support this hypothesis. Dragonflies also appear (in smaller numbers) in the Maldives in May, with the onset of the southwest monsoon, suggesting a possible return migration from Africa. These proposed migrations of dragonflies, regularly crossing 3500 km or more of open ocean, were previously unknown. It is known that these dragonflies exploit ephemeral rain pools for reproduction; the monsoons and ITCZ bring not only alternating, seasonal rains to India and Africa, but also appropriate winds for dragonflies to follow those rains. Several bird species migrate from India across the western Indian Ocean to wintering grounds in Africa. They do so at the same time as the dragonflies, presumably taking advantage of the same seasonal tail winds. Many of these birds also eat dragonflies; the possible significance of this was not previously appreciated.
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Vergados, P., A. J. Mannucci, C. O. Ao, J. H. Jiang, and H. Su. "On the comparisons of tropical relative humidity in the lower and middle troposphere among COSMIC radio occultations, MERRA and ECMWF data sets." Atmospheric Measurement Techniques Discussions 8, no. 1 (January 15, 2015): 517–40. http://dx.doi.org/10.5194/amtd-8-517-2015.
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Abstract. The spatial variability of the tropical tropospheric relative humidity (RH) throughout the vertical extent of the troposphere is examined using Global Positioning System Radio Occultation (GPSRO) observations from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) mission. These high vertical resolution observations capture the detailed structure and moisture budget of the Hadley Cell circulation. We compare the COSMIC observations with the European Center for Medium-range Weather Forecast (ECMWF) Re-Analysis Interim (ERA-Interim) and the Modern-Era Retrospective analysis for Research and Applications (MERRA) climatologies. Qualitatively, the spatial pattern of RH in all data sets matches up remarkably well, capturing distinct features of the general circulation. However, RH discrepancies exist between ERA-Interim and COSMIC data sets, which are noticeable across the tropical boundary layer. Specifically, ERA-Interim shows a drier Inter Tropical Convergence Zone (ITCZ) by 15–20% compared both to COSMIC and MERRA data sets, but this difference decreases with altitude. Unlike ECMWF, MERRA shows an excellent agreement with the COSMIC observations except above 400 hPa, where GPSRO observations capture drier air by 5–10%. RH climatologies were also used to evaluate intraseasonal variability. The results indicate that the tropical middle troposphere at ±5–25° is most sensitive to seasonal variations. COSMIC and MERRA data sets capture the same magnitude of the seasonal variability, but ERA-Interim shows a weaker seasonal fluctuation up to 10% in the middle troposphere inside the dry air subsidence regions of the Hadley Cell. Over the ITCZ, RH varies by maximum 9% between winter and summer.
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Shikwambana, Lerato. "Global Distribution of Clouds over Six Years: A Review Using Multiple Sensors and Reanalysis Data." Atmosphere 13, no. 9 (September 16, 2022): 1514. http://dx.doi.org/10.3390/atmos13091514.
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A six-year global study of cloud distribution and cloud properties obtained from observations of the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), the Atmospheric Infrared Sounder (AIRS), and the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) data is presented in this study. From the CALIPSO observations, the highest clouds for both daytime and night-time were found in the Inter Tropical Convergence Zone (ITCZ) region. The lowest cloud heights were found towards the poles due to the decrease in the tropopause height. Seasonal studies also revealed a high dominance of clouds in the 70 °S–80 °S (Antarctic) region in the June–July–August (JJA) season and a high dominance of Arctic clouds in the December–January–February (DJF) and September–October–November (SON) seasons. The coldest cloud top temperatures (CTT) were mostly observed over land in the ITCZ and the polar regions, while the warmest CTTs were mostly observed in the mid-latitudes and over the oceans. Regions with CTTs greater than 0 °C experienced less precipitation than regions with CTTs less than 0 °C.
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Sepulcre, S., L. Vidal, K. Tachikawa, F. Rostek, and E. Bard. "Sea-surface salinity variations in the northern Caribbean Sea across the Mid-Pleistocene Transition." Climate of the Past 7, no. 1 (February 11, 2011): 75–90. http://dx.doi.org/10.5194/cp-7-75-2011.
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Abstract. By reconstructing past hydrologic variations in the Northern Caribbean Sea and their influence on the stability of the Atlantic Meridional Overturning Circulation (AMOC) during the last 940 ka, we seek to document climate changes in this tropical area in response to the Mid-Pleistocene Transition (MPT). Using core MD03-2628, we estimated past changes in sea surface salinity (SSS) using Δδ18O, the difference between the modern, and the past δ18O of seawater (obtained by combining alkenone thermometer data with the δ18O of the planktonic foraminifera Globigerinoides rube (white) and corrected for ice-sheet volume effects). Today, the lowest SSS values in the area studied are associated with the northernmost location of the Inter-Tropical Convergence Zone (ITCZ). The Δδ18O record obtained from core MD03-2628 exhibits glacial/interglacial cyclicity with higher values during all glacial periods spanning the last 940 ka, indicating increased SSS. A long-term trend was also observed in the Δδ18O values that exhibited a shift toward lower values for interglacial periods during the last 450 ka, as compared to interglacial stages older than 650 ka. A rise in SSS during glacial stages may be related to the southernmost location of the ITCZ, which is induced by a steeper cross-equator temperature gradient and associated with reduced northward cross-equatorial oceanic transport. Therefore, the results suggest a permanent link between the tropical salinity budget and the AMOC during the last 940 ka. Following the MPT, lower salinities during the last five interglacial stages indicated a northernmost ITCZ location that was forced by changes in the cross-equator temperature gradient and that was associated with the poleward position of Southern Oceanic Fronts that amplify the transport of heat and moisture to the North Atlantic. These processes may have contributed to the amplification of the climate cycles that followed the MPT.
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Sepulcre, S., L. Vidal, K. Tachikawa, F. Rostek, and E. Bard. "Sea-surface salinity variations in the Northern Caribbean Sea across the mid-Pleistocene transition." Climate of the Past Discussions 6, no. 3 (June 29, 2010): 1229–65. http://dx.doi.org/10.5194/cpd-6-1229-2010.
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Abstract. This study aimed at documenting climate changes in tropical area in response to the Mid-Pleistocene Transition (MPT) by reconstructing past hydrologic variations in the Northern Caribbean Sea and its influence on the stability of the Atlantic Meridional Overturning Circulation (AMOC) during the last 940 kyr. Using core MD03-2628, we estimated past changes in sea surface salinity (SSS) using Δδ18O, the difference between the modern and the past δ18O of seawater (obtained by combining alkenone thermometer data with the δ18O of the planktonic foraminifera Globigerinoides ruber (white) and corrected for ice-sheet volume effects). Today, the lowest SSS values in the studied area are associated with the northernmost location of the Inter-Tropical Convergence Zone (ITCZ). The Δδ18O record exhibits glacial/interglacial cyclicity with higher values during all glacial periods spanning the last 940 kyr, indicating increased SSS. At a longer timescale, the Δδ18O exhibits a shift toward lower values for interglacial periods during the last 450 kyr, when compared to interglacial stages older than 650 kyr. A rise in SSS during glacial stages may be related to the southernmost location of the ITCZ, which is induced by a steeper interhemispheric temperature gradient and associated with reduced northward cross equatorial oceanic transport. Therefore, the results suggest a permanent link between the tropical salinity budget and the AMOC during the last 940 kyr. Following the MPT, lower salinities during the last five interglacial stages indicate a northernmost ITCZ location, forced by changes in the interhemispheric temperature gradient that is associated with the poleward position of Southern Oceanic Fronts that amplified the transport of heat and moisture to the North Atlantic. These processes may have contributed to amplification of the climate cycles that followed the MPT.
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McCarthy, M. P., J. Sanjay, B. B. B. Booth, K. Krishna Kumar, and R. A. Betts. "The influence of vegetation on the ITCZ and South Asian Monsoon in HadCM3." Earth System Dynamics Discussions 3, no. 1 (February 6, 2012): 91–111. http://dx.doi.org/10.5194/esdd-3-91-2012.
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Abstract. The role of extra-tropical vegetation on the large-scale tropical circulation is examined in the version 3 Hadley Centre Climate Model (HadCM3). Alternative representations of present day vegetation from observations and a dynamic vegetation model were used as the land-cover component for a number of HadCM3 experiments under a nominal present day climate state, and are shown to induce perturbations to the simulated global dynamics. This results in a shift in the location of the Inter Tropical Convergence Zone (ITCZ) and changes in the South Asian monsoon circulation. This has a significant impact on the Indian land precipitation compared to the standard configuration of HadCM3. This large-scale forcing is consistent with documented mechanisms relating to temperature and snow perturbations in the Northern Hemisphere extra-tropics. This analysis demonstrates that uncertainties in the representation of present day vegetation cover can result in significant perturbations to the simulated climate. The role of the Northern Hemisphere extra-tropics is further demonstrated with a fourth representation of vegetation cover produced by imposing simulated changes in Northern Hemisphere extra-tropical vegetation from the end of the 21st century on the present day climate. This experiment shows that through similar processes extra-tropical vegetation changes in the future contribute to a strengthening of the South Asian monsoon in this model, with a particular influence on the monsoon onset. These findings provide renewed motivation to give careful consideration to the role of global scale vegetation feedbacks when looking at climate change and its impact on the tropics and South Asian monsoon in the latest generation of Earth System models.
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Nurmohamed, R. J., and S. Naipal. "Variability of rainfall in Suriname and the relation with ENSO-SST and TA-SST." Advances in Geosciences 6 (January 9, 2006): 77–82. http://dx.doi.org/10.5194/adgeo-6-77-2006.
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Abstract. Spatial correlations in the annual rainfall anomalies are analyzed using principle component analyses (PCA). Cross correlation analysis and composites are used to measure the influence of sea surface temperatures anomalies (SSTAs) in the tropical Atlantic and tropical Pacific Ocean with the seasonal rainfall in Suriname. The spatial and time variability in rainfall is mainly determined by the meridional movement of the Inter-tropical Convergence Zone (ITCZ). Rainfall anomalies tend to occur fairly uniformly over the whole country. In December-January (short wet season), there is a lagged correlation with the SSTAs in the Pacific region (clag3Nino1+2=-0.63). The strongest correlation between the March-May rainfall (beginning long wet season) and the Pacific SSTAs is found with a correlation coefficient of ckNino1+2=0.59 at lag 1 month. The June-August rainfall (end part of long wet season) shows the highest correlation with SSTAs in the TSA region and is about c=-0.52 for lag 0. In the September-November long dry season there is also a lagged correlation with the TSA SSTAs of about clag3=0.66. The different correlations and predictors can be used for seasonal rainfall predictions.
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Okello, Ochieng, Guirong Tan, Victor Ongoma, and Isaiah Nyandega. "Influence of convectively coupled equatorial Kelvin waves on March-May precipitation over East Africa." Geographica Pannonica 25, no. 1 (2021): 24–34. http://dx.doi.org/10.5937/gp25-31132.
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Convectively coupled equatorial Kelvin waves (CCEKWs) are those types of equatorially trapped disturbances that propagate eastward and are among the most common intra-seasonal oscillations in the tropics. There exists two-way feedback between the inter-tropical convergence zone (ITCZ) and these equatorially trapped disturbances. Outgoing Longwave Radiation (OLR) was utilized as a proxy for deep convection. For CCEKWs, the modes are located over the West Atlantic, equatorial West Africa, and the Indian Ocean. The influence of other circulations and climate dynamics is studied for finding other drivers of climate within East Africa. The results show a positive relationship between Indian and Atlantic Oceans Sea Surface Temperatures and March-May rainfall over equatorial East Africa over the period of 1980 to 2010. This influence is driven by the Walker circulation and anomalous moisture influx enhanced by winds. Composite analysis reveals strong lower-tropospheric westerlies during the active phase of the CCKWs activities over Equatorial East Africa. The winds are in the opposite direction with the upper-tropospheric winds, which are easterlies. Singular Value Decomposition shows a strong coupling interaction between rainfall over equatorial East Africa and CCKWs. This study concludes that Kelvin waves are not the main factors that influence rainfall during the rainy season. Previous studies show that the main influencing factors are ITCZ, El-Nino Southern Oscillation (ENSO), and tropical anticyclones that borders the African continent. However, CCKWs are a significant factor during the dry seasons.
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King, Gregory P., Marcos Portabella, Wenming Lin, and Ad Stoffelen. "Correlating Extremes in Wind Divergence with Extremes in Rain over the Tropical Atlantic." Remote Sensing 14, no. 5 (February 25, 2022): 1147. http://dx.doi.org/10.3390/rs14051147.
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Air–sea fluxes are greatly enhanced by the winds and vertical exchanges generated by mesoscale convective systems (MCSs). In contrast to global numerical weather prediction models, space-borne scatterometers are able to resolve the small-scale wind variability in and near MCSs at the ocean surface. Downbursts of heavy rain in MCSs produce strong gusts and large divergence and vorticity in surface winds. In this paper, 12.5 km wind fields from the ASCAT-A and ASCAT-B tandem mission, collocated with short time series of Meteosat Second Generation 3 km rain fields, are used to quantify correlations between wind divergence and rain in the Inter-Tropical Convergence Zone (ITCZ) of the Atlantic Ocean. We show that when there is extreme rain, there is extreme convergence/divergence in the vicinity. Probability distributions for wind divergence and rain rates were found to be heavy-tailed: exponential tails for wind divergence (P∼e−αδ with slopes that flatten with increasing rain rate), and power-law tails for rain rates (P∼(R*)−β with a slower and approximately equal decay for the extremes of convergence and divergence). Co-occurring points are tabulated in two-by-two contingency tables from which cross-correlations are calculated in terms of the odds and odds ratio for each time lag in the collocation. The odds ratio for extreme convergence and extreme divergence both have a well-defined peak. The divergence time lag is close to zero, while it is 30 min for the convergence peak, implying that extreme rain generally appears after (lags) extreme convergence. The temporal scale of moist convection is thus determined by the slower updraft process, as expected. A structural analysis was carried out that demonstrates consistency with the known structure of MCSs. This work demonstrates that (tandem) ASCAT winds are well suited for air–sea exchange studies in moist convection.
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Anderson, James R., and Peter Crozier. "Microstructure of Climate-Forcing Aerosols: Aircraft Traverses from Clean to Polluted Conditions in the Indian Ocean." Microscopy and Microanalysis 7, S2 (August 2001): 480–81. http://dx.doi.org/10.1017/s1431927600028476.
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The Indian Ocean Experiment (INDOEX) was conducted in Feb.-Mar. 1999 in a large area of the Indian Ocean, Bay of Bengal, and Arabian Sea to investigate climate forcing produced by pollutant aerosol particles being transported out of India, Pakistan, and Indochina during the Northeast (“Dry“) Monsoon2. Pollutant aerosols can be transported a thousand km or more by prevailing winds as far south as the Inter-tropical Convergence Zone (ITCZ), the convective band that separates Northern and Southern Hemisphere tropospheric air. We present here results from TEM examination of aerosol particles collected on INDOEX research flights of the NCAR C-130 aircraft.The climate forcing properties of sulfate aerosols over the oceans have long been recognized2. Sulfate and other particles scatter incoming solar radiation, reducing the amount of light (and heat) incident on the ocean surface and thus causing a cooling effect which may locally counter some of the warming effect due to greenhouse gases.
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Hassler, Birgit, and Axel Lauer. "Comparison of Reanalysis and Observational Precipitation Datasets Including ERA5 and WFDE5." Atmosphere 12, no. 11 (November 5, 2021): 1462. http://dx.doi.org/10.3390/atmos12111462.
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Precipitation is a key component of the hydrological cycle and one of the most important variables in weather and climate studies. Accurate and reliable precipitation data are crucial for determining climate trends and variability. In this study, eleven different precipitation datasets are compared, six reanalysis and five observational datasets, including the reanalysis datasets ERA5 and WFDE5 from the ECMWF family, to quantify the differences between the widely used precipitation datasets and to identify their particular strengths and shortcomings. The comparisons are focused on the common time period 1983 through 2016 and on monthly, seasonal, and inter-annual times scales in regions representing different precipitation regimes, i.e., the Tropics, the Pacific Inter Tropical Convergence Zone (ITCZ), Central Europe, and the South Asian Monsoon region. For the analysis, satellite-gauge precipitation data from the Global Precipitation Climatology Project (GPCP-SG) are used as a reference. The comparison shows that ERA5 and ERA5-Land are a clear improvement over ERA-Interim and show in most cases smaller biases than the other reanalysis datasets (e.g., around 13% high bias in the Tropics compared to 17% for MERRA-2 and 36% for JRA-55). ERA5 agrees well with observations for Central Europe and the South Asian Monsoon region but underestimates very low precipitation rates in the Tropics. In particular, the tropical ocean remains challenging for reanalyses with three out of four products overestimating precipitation rates over the Atlantic and Indian Ocean.
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Pinault, Jean-Louis, and Ligia Pereira. "What Speleothems Tell Us about Long-Term Rainfall Oscillation throughout the Holocene on a Planetary Scale." Journal of Marine Science and Engineering 9, no. 8 (August 8, 2021): 853. http://dx.doi.org/10.3390/jmse9080853.
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Within the context of anthropogenic warming, rainfall oscillations may induce especially important societal impacts worldwide. In this article, we propose to study potential underlying mechanisms related to precipitation changes on a planetary scale by taking advantage of the recent theory of Rossby waves of long periods winding around subtropical gyres, the Gyral Rossby Waves (GRWs). The stable oxygen isotopic compositions of speleothems are used to regionalize and reconstruct the evolution of long-term rainfall oscillation during the Holocene. The method applied here consists in estimating the wavelet power of dated series of stable oxygen isotopic composition (δ18O) in speleothems within period bands representative of subharmonic modes. Our findings highlight: (1) hydrological processes resulting from friction between the North Equatorial Current (NEC) and the North Equatorial Counter Current (NECC) to explain the weakening of ENSO activity in mid-Holocene, and (2) the quasi-resonance of the equatorward migration of the summer Inter Tropical Convergence Zone (ITCZ) during the Holocene, because of the progressive decrease of the thermal gradient between the low and high latitudes of the gyres. The results of this study suggest that the spatial and temporal variations in the amplitude of the rainfall oscillations are related both on the acceleration/deceleration phases of the western boundary currents and on the shrinkage of the Hadley cell. The latitudinal shift of the summer ITCZ in response to changes in the thermal gradient is of the utmost importance in predicting the expansion of deserts resulting from anthropogenic warming.
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Gray, Lesley J., James A. Anstey, Yoshio Kawatani, Hua Lu, Scott Osprey, and Verena Schenzinger. "Surface impacts of the Quasi Biennial Oscillation." Atmospheric Chemistry and Physics 18, no. 11 (June 13, 2018): 8227–47. http://dx.doi.org/10.5194/acp-18-8227-2018.
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Abstract. Teleconnections between the Quasi Biennial Oscillation (QBO) and the Northern Hemisphere zonally averaged zonal winds, mean sea level pressure (mslp) and tropical precipitation are explored. The standard approach that defines the QBO using the equatorial zonal winds at a single pressure level is compared with the empirical orthogonal function approach that characterizes the vertical profile of the equatorial winds. Results are interpreted in terms of three potential routes of influence, referred to as the tropical, subtropical and polar routes. A novel technique is introduced to separate responses via the polar route that are associated with the stratospheric polar vortex, from the other two routes. A previously reported mslp response in January, with a pattern that resembles the positive phase of the North Atlantic Oscillation under QBO westerly conditions, is confirmed and found to be primarily associated with a QBO modulation of the stratospheric polar vortex. This mid-winter response is relatively insensitive to the exact height of the maximum QBO westerlies and a maximum positive response occurs with westerlies over a relatively deep range between 10 and 70 hPa. Two additional mslp responses are reported, in early winter (December) and late winter (February/March). In contrast to the January response the early and late winter responses show maximum sensitivity to the QBO winds at ∼ 20 and ∼ 70 hPa respectively, but are relatively insensitive to the QBO winds in between (∼ 50 hPa). The late winter response is centred over the North Pacific and is associated with QBO influence from the lowermost stratosphere at tropical/subtropical latitudes in the Pacific sector. The early winter response consists of anomalies over both the North Pacific and Europe, but the mechanism for this response is unclear. Increased precipitation occurs over the tropical western Pacific under westerly QBO conditions, particularly during boreal summer, with maximum sensitivity to the QBO winds at 70 hPa. The band of precipitation across the Pacific associated with the Inter-tropical Convergence Zone (ITCZ) shifts southward under QBO westerly conditions. The empirical orthogonal function (EOF)-based analysis suggests that this ITCZ precipitation response may be particularly sensitive to the vertical wind shear in the vicinity of 70 hPa and hence the tropical tropopause temperatures.
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Fischel, Andrea, Marit-Solveig Seidenkrantz, Dirk Nürnberg, Michal Kucera, and Antoon Kuijpers. "Upper water mass variability in the Anegada–Jungfern Passage, NE Caribbean, during the last 11,100 cal. yr." Holocene 27, no. 9 (January 18, 2017): 1291–307. http://dx.doi.org/10.1177/0959683616687378.
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Using qualitative and quantitative analyses of planktonic foraminifera assemblages, δ18O measurements, Mg/Ca–temperature relationship ( Globigerinoides ruber pink sensu stricto) data and sea-surface temperatures (SSTs) derived from artificial neural network (ANN) transfer functions, a reconstruction was made of upper water mass variability in the Anegada–Jungfern Passage (AJP), northeastern Caribbean Sea, over the last c. 11,100 years. Our record is based on the study of two marine sediment cores and reveals three main circulation stages during the Holocene. In the early-Holocene (11,100–6300 cal. yr BP), ANN-based SST estimations indicate moderately cooler than present winter condition in the NE Caribbean with SSTs of ~25.5°C. These conditions presumably reflect advection of well-mixed upper water masses from the Guyana upwelling area associated with a strong Atlantic Meridional Overturning Circulation (AMOC) and enhanced trade wind activity, linked to a more northerly location of the inter-tropical convergence zone (ITCZ). Between 6300 and 3700 cal. yr BP, a relative warming of winter SSTs (~26.5°C) was probably related to a weaker circulation and upper water mass mixing because of less intense trade wind activity, as the ITCZ moved southwards. From 3700 cal. yr BP to the present, the region was characterised by small seasonal SST variations and generally stable winter and summer SSTs. The data suggest a minor shift in the (sub)surface inflow pattern during the last 2000 years, possibly related to changes in Northern Hemisphere large-scale atmospheric circulation also observed at higher latitude. The ANN-based temperature pattern is supported by fluctuations in the Mg/Ca-derived temperature record, although temperature maxima derived from the Mg/Ca ratio appear anomalously high. On a Holocene timescale, we conclude that the northeastern Caribbean SST and circulation regime have been mainly dependent on the position of the ITCZ, which, in turn, is controlled by changes in hemispheric solar insolation.
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Trachte, Katja. "Atmospheric Moisture Pathways to the Highlands of the Tropical Andes: Analyzing the Effects of Spectral Nudging on Different Driving Fields for Regional Climate Modeling." Atmosphere 9, no. 11 (November 19, 2018): 456. http://dx.doi.org/10.3390/atmos9110456.
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Atmospheric moisture pathways to the highlands of the tropical Andes Mountains were investigated using the Weather Research and Forecasting (WRF) model, as well as back-trajectory analysis. To assess model uncertainties according to the initial and lateral boundary conditions (ILBCs), the effects of spectral nudging and different driving fields on regional climate modeling were tested. Based on the spatio-temporal patterns of the large-scale atmospheric features over South America, the results demonstrated that spectral nudging compared to traditional long-term integration generally produced greater consistency with the reference data (ERA5). These WRF simulations further revealed that the location of the inter-tropical convergence zone (ITCZ), as well as the precipitation over the Andes Mountains were better reproduced. To investigate the air mass pathways, the most accurate WRF simulation was used as atmospheric conditions for the back-trajectory calculations. Three subregions along the tropical Andean chain were considered. Based on mean cluster trajectories and the water vapor mixing ratio along the pathways, the contributions of eastern and western water sources were analyzed. In particular, the southernmost subregion illustrated a clear frequency of occurrences of Pacific trajectories mostly during September–November (40%) when the ITCZ is shifted to the Northern Hemisphere and the Bolivian high pressure system is weakened. In the northernmost subregion, Pacific air masses as well reached the Andes highlands with rather low frequencies regardless of the season (2–12%), but with a moisture contribution comparable to the eastern trajectories. Cross-sections of the equivalent-potential temperature as an indicator of the moisture and energy content of the atmosphere revealed a downward mixing of the moisture aloft, which was stronger in the southern subregion. Additionally, low-level onshore breezes, which developed in both subregions, indicated the transport of warm-moist marine air masses to the highlands, highlighting the importance of the representation of the terrain and, thus, the application of dynamical downscaling using regional climate models.
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Tang, Y., H. Pang, W. Zhang, Y. Li, S. Wu, and S. Hou. "Effects of changes in moisture source and the upstream rainout on stable isotopes in precipitation – a case study in Nanjing, eastern China." Hydrology and Earth System Sciences 19, no. 10 (October 22, 2015): 4293–306. http://dx.doi.org/10.5194/hess-19-4293-2015.
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Abstract. In the Asian monsoon region, variations in the stable isotopic composition of speleothems have often been attributed to the "amount effect". However, an increasing number of studies suggest that the "amount effect" in local precipitation is insignificant or even non-existent. To explore this issue further, we examined the variability of daily stable isotopic composition (δ18O) in precipitation from September 2011 to November 2014 in Nanjing, eastern China. We found that intra-seasonal variations of δ18O during summer were not significantly correlated with local rainfall amount but could be linked to changes in the moisture source location and rainout processes in the source regions. Our findings suggest that the stable isotopes in summer precipitation could signal the location shift of precipitation source regions in the inter-tropical convergence zone (ITCZ) over the course of the monsoon season. As a result, changes in moisture source location and upstream rainout effect should be taken into account when interpreting the stable isotopic composition of speleothems in the Asian monsoon region. In addition, the temperature effect on isotopic variations in non-monsoonal precipitation should also be considered because precipitation in the non-monsoon season accounts for about half of its annual precipitation.
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Yang, Ji-Woong, Jinho Ahn, Edward J. Brook, and Yeongjun Ryu. "Atmospheric methane control mechanisms during the early Holocene." Climate of the Past 13, no. 9 (September 22, 2017): 1227–42. http://dx.doi.org/10.5194/cp-13-1227-2017.
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Abstract. Understanding processes controlling the atmospheric methane (CH4) mixing ratio is crucial to predict and mitigate future climate changes in this gas. Despite recent detailed studies of the last ∼ 1000 to 2000 years, the mechanisms that control atmospheric CH4 still remain unclear, partly because the late Holocene CH4 budget may be comprised of both natural and anthropogenic emissions. In contrast, the early Holocene was a period when human influence was substantially smaller, allowing us to elucidate more clearly the natural controls under interglacial conditions more clearly. Here we present new high-resolution CH4 records from Siple Dome, Antarctica, covering from 11.6 to 7.7 thousands of years before 1950 AD (ka). We observe four local CH4 minima on a roughly 1000-year spacing, which correspond to cool periods in Greenland. We hypothesize that the cooling in Greenland forced the Intertropical Convergence Zone (ITCZ) to migrate southward, reducing rainfall in northern tropical wetlands. The inter-polar difference (IPD) of CH4 shows a gradual increase from the onset of the Holocene to ∼ 9.5 ka, which implies growth of boreal source strength following the climate warming in the northern extratropics during that period.
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Verma, S., O. Boucher, M. S. Reddy, S. K. Deb, H. C. Upadhyaya, P. Le Van, F. S. Binkowski, and O. P. Sharma. "Tropospheric distribution of sulphate aerosol mass and number concentration during INDOEX-IFP and its transport over the Indian Ocean: a GCM study." Atmospheric Chemistry and Physics Discussions 5, no. 1 (January 31, 2005): 395–436. http://dx.doi.org/10.5194/acpd-5-395-2005.
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Abstract. An interactive sulphate aerosol chemistry module has been incorporated in the Laboratoire de Météorologie Dynamique General Circulation Model (LMD-GCM) to simulate the sulphur chemistry during the Indian Ocean Experiment (INDOEX) Intensive Field Phase-1999 (INDOEX-IFP). The originality of this module is its ability to predict particle mass and number concentration for the Aitken and accumulation modes. The model qualitatively reproduces the spatial patterns of observations on sulphate aerosol during INDOEX. On the basis of size distribution retrieved from the observations made along the cruise route during 1998 and 1999, the model successfully simulates the order of magnitude and the general north-south gradient in aerosol number concentration. The result shows the southward migration of minimum concentrations, which follows ITCZ (Inter Tropical Convergence Zone) migration. Sulphate surface concentration during INDOEX-IFP at Kaashidhoo (73.46° E, 4.96° N) gives an agreement within a factor of 2 to 3. Predicted sulphate aerosol optical depth (AOD) matches reasonably with measured values, indicating the capability of this model to predict the vertically integrated column sulphate burden. The Indian contribution to estimated sulphate burden over India is more than 60% with values upto 40% over the Arabian Sea.
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Taschetto, A. S., and I. Wainer. "The impact of the subtropical South Atlantic SST on South American precipitation." Annales Geophysicae 26, no. 11 (November 10, 2008): 3457–76. http://dx.doi.org/10.5194/angeo-26-3457-2008.
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Abstract. The Community Climate Model (CCM3) from the National Center for Atmospheric Research (NCAR) is used to investigate the effect of the South Atlantic sea surface temperature (SST) anomalies on interannual to decadal variability of South American precipitation. Two ensembles composed of multidecadal simulations forced with monthly SST data from the Hadley Centre for the period 1949 to 2001 are analysed. A statistical treatment based on signal-to-noise ratio and Empirical Orthogonal Functions (EOF) is applied to the ensembles in order to reduce the internal variability among the integrations. The ensemble treatment shows a spatial and temporal dependence of reproducibility. High degree of reproducibility is found in the tropics while the extratropics is apparently less reproducible. Austral autumn (MAM) and spring (SON) precipitation appears to be more reproducible over the South America-South Atlantic region than the summer (DJF) and winter (JJA) rainfall. While the Inter-tropical Convergence Zone (ITCZ) region is dominated by external variance, the South Atlantic Convergence Zone (SACZ) over South America is predominantly determined by internal variance, which makes it a difficult phenomenon to predict. Alternatively, the SACZ over western South Atlantic appears to be more sensitive to the subtropical SST anomalies than over the continent. An attempt is made to separate the atmospheric response forced by the South Atlantic SST anomalies from that associated with the El Niño – Southern Oscillation (ENSO). Results show that both the South Atlantic and Pacific SSTs modulate the intensity and position of the SACZ during DJF. Particularly, the subtropical South Atlantic SSTs are more important than ENSO in determining the position of the SACZ over the southeast Brazilian coast during DJF. On the other hand, the ENSO signal seems to influence the intensity of the SACZ not only in DJF but especially its oceanic branch during MAM. Both local and remote influences, however, are confounded by the large internal variance in the region. During MAM and JJA, the South Atlantic SST anomalies affect the magnitude and the meridional displacement of the ITCZ. In JJA, the ENSO has relatively little influence on the interannual variability of the simulated rainfall. During SON, however, the ENSO seems to counteract the effect of the subtropical South Atlantic SST variations on convection over South America.
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Johnson, Markes E., Ricardo Ramalho, and Carlos Marques da Silva. "Storm-Related Rhodolith Deposits from the Upper Pleistocene and Recycled Coastal Holocene on Sal Island (Cabo Verde Archipelago)." Geosciences 10, no. 11 (October 23, 2020): 419. http://dx.doi.org/10.3390/geosciences10110419.
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This project examines the role of tropical storms in the northeast Atlantic Ocean related to the post-mortem deposition of rhodoliths in coastal settings during Neogene to Holocene time with primary emphasis on Sal Island in the Cabo Verde Archipelago located 600 km off the coast of Senegal in northwest Africa. Fossil rhodoliths from 10 to 15 cm in diameter are equal in size to contemporary rhodoliths that survive for a century or more at water depths undisturbed by all but the most energetic storms. The shape of large rhodoliths makes them susceptible to rare disturbances with sufficient energy to export them beyond their preferred habitat into extreme environments that include supratidal settings. The methodology of this study gauges the relative sphericity of rhodoliths based on measurements across three axes perpendicular to one another, plots size variations on bar graphs, and considers whether or not individual nodules are nucleated around rock cores eroded from proximal rocky shores. Sal Island is impacted on a steady basis by wave swell generated from the Northeast Trade Winds, but Pleistocene and Holocene deposits with large rhodoliths on the Island’s windward coast are interpreted as the result of major storms of hurricane intensity. Comparison of Sal Island rhodoliths with Pliocene and Miocene examples from other insular localities in the Northeast Atlantic considers evidence for displacement of the Inter-Tropical Convergence Zone (ITCZ) into more northern latitudes as an influence on past hurricane tracks that are less common today.
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Bovalo, C., C. Barthe, and N. Bègue. "A lightning climatology of the South-West Indian Ocean." Natural Hazards and Earth System Sciences 12, no. 8 (August 22, 2012): 2659–70. http://dx.doi.org/10.5194/nhess-12-2659-2012.
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Abstract. The World Wide Lightning Location Network (WWLLN) data have been used to perform a lightning climatology in the South-West Indian Ocean (SWIO) region from 2005 to 2011. Maxima of lightning activity were found in the Maritime Continent and southwest of Sri Lanka (>50 fl km−2 yr−1) but also over Madagascar and above the Great Lakes of East Africa (>10–20 fl km−2 yr−1). Lightning flashes within tropical storms and tropical cyclones represent 50 % to 100 % of the total lightning activity in some oceanic areas of the SWIO (between 10° S and 20° S). The SWIO is characterized by a wet season (November to April) and a dry season (May to October). As one could expect, lightning activity is more intense during the wet season as the Inter Tropical Convergence Zone (ITCZ) is present over all the basin. Flash density is higher over land in November–December–January with values reaching 3–4 fl km−2 yr−1 over Madagascar. During the dry season, lightning activity is quite rare between 10° S and 25° S. The Mascarene anticyclone has more influence on the SWIO resulting in shallower convection. Lightning activity is concentrated over ocean, east of South Africa and Madagascar. A statistical analysis has shown that El Niño–Southern Oscillation mainly modulates the lightning activity up to 56.8% in the SWIO. The Indian Ocean Dipole has a significant contribution since ~49% of the variability is explained by this forcing in some regions. The Madden–Julian Oscillation did not show significative impact on the lightning activity in our study.
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MacCracken, M. C., H. J. Shin, K. Caldeira, and G. A. Ban-Weiss. "Climate response to imposed solar radiation reductions in high latitudes." Earth System Dynamics 4, no. 2 (September 2, 2013): 301–15. http://dx.doi.org/10.5194/esd-4-301-2013.
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Abstract. With human-induced climate change leading to amplified warming in high latitudes, mitigation alone is unlikely to be rapid enough to prevent significant, even irreversible, impacts. Model simulations in which solar insolation was arbitrarily reduced poleward of 51, 61, or 71° latitude in one or both hemispheres not only cooled those regions, but also drew energy from lower latitudes, exerting a cooling influence over much of the particular hemisphere in which the reduction was imposed. The simulations, conducted using the National Center for Atmospheric Research's CAM3.1 atmospheric model coupled to a slab ocean, indicated that high-latitude reductions in absorbed solar radiation have a significantly larger cooling influence than solar reductions of equivalent magnitude spread evenly over the Earth. This amplified influence occurred primarily because concentrated high-latitude reductions in solar radiation led to increased sea ice fraction and surface albedo, thereby amplifying the energy deficit at the top of the atmosphere as compared to the response for an equivalent reduction in solar radiation spread evenly over the globe. Reductions in incoming solar radiation in one polar region (either north or south) resulted in increased poleward energy transport during that hemisphere's cold season and shifted the Inter-Tropical Convergence Zone (ITCZ) away from that pole, whereas comparable solar reductions in both polar regions resulted in increased poleward energy transport, but tended to leave the ITCZ approximately in place. Together, these results suggest that, until emissions reductions are sufficient to limit the warming influence of increasing greenhouse gas concentrations, polar reductions in solar radiation, if they could be efficiently and effectively implemented, warrant further research as an approach to moderating the early stages of both high-latitude and global warming.
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MacCracken, M. C., H. J. Shin, K. Caldeira, and G. A. Ban-Weiss. "Climate response to imposed solar radiation reductions in high latitudes." Earth System Dynamics Discussions 3, no. 2 (July 26, 2012): 715–57. http://dx.doi.org/10.5194/esdd-3-715-2012.
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Abstract. Increasing concentrations of greenhouse gases are the primary contributor to the 0.8 °C increase in the global average temperature since the late 19th century, shortening cold seasons and lengthening warm seasons. The warming is amplified in polar regions, causing retreat of sea ice, snow cover, permafrost, mountain glaciers, and ice sheets, while also modifying mid-latitude weather, amplifying global sea level rise, and initiating high-latitude carbon feedbacks. Model simulations in which we reduced solar insolation over high latitudes not only cooled those regions, but also drew energy from lower latitudes, exerting a cooling influence over much of the hemisphere in which the reduction was imposed. Our simulations, which used the National Center for Atmospheric Research's CAM3.1 atmospheric model coupled to a slab ocean, indicated that, on a normalized basis, high-latitude reductions in absorbed solar radiation have a significantly larger cooling influence than equivalent solar reductions spread evenly over the Earth. This amplified influence occurred because high-latitude surface cooling preferentially increased sea ice fraction and, therefore, surface albedo, leading to a larger deficit in the radiation budget at the top of the atmosphere than from an equivalent global reduction in solar radiation. Reductions in incoming solar radiation in one polar region (either north or south) resulted in increased poleward energy transport during that hemisphere's cold season and shifted the Inter-Tropical Convergence Zone (ITCZ) away from that pole, whereas equivalent reductions in both polar regions tended to leave the ITCZ approximately in place. Together, these results suggest that, until emissions reductions are sufficient to limit the warming influence of greenhouse gas concentrations, polar reductions in solar radiation, if they can be efficiently and effectively implemented, might, because of fewer undesirable side effects than for global solar radiation reductions, be a preferred approach to limiting both high-latitude and global warming.
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Verma, S., O. Boucher, M. Shekar Reddy, H. C. Upadhyaya, P. Le Van, F. S. Binkowski, and O. P. Sharma. "Tropospheric distribution of sulphate aerosols mass and number concentration during INDOEX-IFP and its transport over the Indian Ocean: a GCM study." Atmospheric Chemistry and Physics 12, no. 14 (July 18, 2012): 6185–96. http://dx.doi.org/10.5194/acp-12-6185-2012.
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Abstract. The sulphate aerosols mass and number concentration during the Indian Ocean Experiment (INDOEX) Intensive Field Phase-1999 (INDOEX-IFP) has been simulated using an interactive chemistry GCM. The model considers an interactive scheme for feedback from chemistry to meteorology with internally resolving microphysical properties of aerosols. In particular, the interactive scheme has the ability to predict both particle mass and number concentration for the Aitken and accumulation modes as prognostic variables. On the basis of size distribution retrieved from the observations made along the cruise route during IFP-1999, the model successfully simulates the order of magnitude of aerosol number concentration. The results show the southward migration of minimum concentrations, which follows ITCZ (Inter Tropical Convergence Zone) migration. Sulphate surface concentration during INDOEX-IFP at Kaashidhoo (73.46° E, 4.96° N) gives an agreement within a factor of 2 to 3. The measured aerosol optical depth (AOD) from all aerosol species at KCO was 0.37 ± 0.11 while the model simulated sulphate AOD ranged from 0.05 to 0.11. As sulphate constitutes 29% of the observed AOD, the model predicted values of sulphate AOD are hence fairly close to the measured values. The model thus has capability to predict the vertically integrated column sulphate burden. Furthermore, the model results indicate that Indian contribution to the estimated sulphate burden over India is more than 60% with values upto 40% over the Arabian Sea.
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Ardi, R. D. W., Aswan, K. A. Maryunani, E. Yulianto, P. S. Putra, and S. H. Nugroho. "Australian–Indonesian monsoon rainfall responses to the northern hemisphere climatic changes prior to the Last Glacial Maximum: an early indication." IOP Conference Series: Earth and Environmental Science 1047, no. 1 (July 1, 2022): 012031. http://dx.doi.org/10.1088/1755-1315/1047/1/012031.
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Abstract The evidences of Australian-Indonesian monsoon (AIM) rainfall response to the northern hemisphere climatic changes from both marine and terrestrial proxies are well established for the Last Glacial Maximum (LGM) – Deglaciation time interval but not in the previous time interval. Sediment cores from off south Sumba (ST10) and off north Sumba (Sumba strait) (ST14) were analyzed using X-Ray Fluorescence method to obtain elemental proxies. Elemental ratios which reflect terrigenous input (Ti/Ca and K/Ca) are used to infer the AIM rainfall changes since ~42 ka BP. AIM rainfall changes indicate a clear response to the Heinrich Events prior to the LGM (H2, H3, and H4). H2 and H3 are corroborated with the AIM rainfall increases in off south Sumba (~24 – 26 ka BP and ~30 – 31 ka BP) while the AIM rainfall increase (~39 – 41 ka BP) in the Sumba strait indicates a response to H4. The cooler temperature during the Heinrich Events could enhance the Northern Hemisphere (NH) cold surges which eventually pushed the Austral summer Intertropical Convergence Zone (ITCZ) southward in a similar fashion to the Last Deglaciation period (~18 – 11 ka BP). The southward movement of Austral summer ITCZ should increase the research area’s exposure time to the Tropical Rain Belt (TRB) during the Australian – Indonesian summer monsoon (AISM) which eventually triggers the AIM rainfall increase. The Sumba strait AIM rainfall unresponsiveness to H2 and H3 could be related to the constant exposure time to the TRB which indicates that the southern limit of Austral summer ITCZ during its northernmost shift didn’t reach the latitude of Sumba Strait. Comparison with other proxies from the same site and other rainfall proxies from southern Indonesia and the northern Australia regions is needed to confirm the spatial extend of those responses.
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Guevara-Murua, Alvaro, Caroline A. Williams, Erica J. Hendy, and Pablo Imbach. "300 years of hydrological records and societal responses to droughts and floods on the Pacific coast of Central America." Climate of the Past 14, no. 2 (February 15, 2018): 175–91. http://dx.doi.org/10.5194/cp-14-175-2018.
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Abstract. The management of hydrological extremes and impacts on society is inadequately understood because of the combination of short-term hydrological records, an equally short-term assessment of societal responses and the complex multi-directional relationships between the two over longer timescales. Rainfall seasonality and inter-annual variability on the Pacific coast of Central America is high due to the passage of the Inter Tropical Convergence Zone (ITCZ) and the El Niño–Southern Oscillation (ENSO). Here we reconstruct hydrological variability and demonstrate the potential for assessing societal impacts by drawing on documentary sources from the cities of Santiago de Guatemala (now Antigua Guatemala) and Guatemala de la Asunción (now Guatemala City) over the period from 1640 to 1945. City and municipal council meetings provide a rich source of information dating back to the beginning of Spanish colonisation in the 16th century. We use almost continuous sources from 1640 AD onwards, including > 190 volumes of Actas de Cabildo and Actas Municipales (minutes of meetings of the city and municipal councils) held by the Archivo Histórico de la Municipalidad de Antigua Guatemala (AHMAG) and the Archivo General de Centro América (AGCA) in Guatemala City. For this 305-year period (with the exception of a total of 11 years during which the books were either missing or damaged), information relating to Catholic rogation ceremonies and reports of flooding events and crop shortages were used to classify the annual rainy season (May to October) on a five-point scale from very wet to very dry. In total, 12 years of very wet conditions, 25 years of wetter than usual conditions, 34 years of drier conditions and 21 years of very dry conditions were recorded. An extended drier period from the 1640s to the 1740s was identified and two shorter periods (the 1820s and the 1840s) were dominated by dry conditions. Wetter conditions dominated the 1760s–1810s and possibly record more persistent La Niña conditions that are typically associated with higher precipitation over the Pacific coast of Central America. The 1640s–1740s dry period coincides with the Little Ice Age and the associated southward displacement of the ITCZ.
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Melgarejo, Ana E., Paulina Ordoñez, Raquel Nieto, Cristina Peña-Ortiz, Ricardo García-Herrera, and Luis Gimeno. "Mechanisms for Severe Drought Occurrence in the Balsas River Basin (Mexico)." Atmosphere 12, no. 3 (March 11, 2021): 368. http://dx.doi.org/10.3390/atmos12030368.
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This work provides an assessment of the two most intense seasonal droughts that occurred over the Balsas River Basin (BRB) in the period 1980–2017. The detection of the drought events was performed using the 6 month scale standardized precipitation–evapotranspiration index (SPEI-6) and the 6 month standardized precipitation index (SPI-6) in October. Both indices were quite similar during the studied period, highlighting the larger contribution of precipitation deficits vs. temperature excess to the drought occurrence in the basin. The origin of the atmospheric water arriving to the BRB (1 May 1980–31 October 2017) was investigated by using a Lagrangian diagnosis method. The BRB receives moisture from the Caribbean Sea and the rest of the tropical Atlantic, the Gulf of Mexico, the eastern north Pacific and from three terrestrial evaporative sources: the region north of BRB, the south of BRB and the BRB itself. The terrestrial evaporative source of the BRB itself is by far the main moisture source. The two most intense drought events that occurred in the studied period were selected for further analysis. During the severe drought of 2005, the summertime sea surface temperature (SST) soared over the Caribbean Sea, extending eastward into a large swathe of tropical North Atlantic, which was accompanied by the record to date of hurricane activity. This heating generated a Rossby wave response with westward propagating anticyclonic/cyclonic gyres in the upper/lower troposphere. A cyclonic low-level circulation developed over the Gulf of Mexico and prevented the moisture from arriving to the BRB, with a consequent deficit in precipitation. Additionally, subsidence also prevented convection in most of the months of this drought period. During the extreme drought event of 1982, the Inter Tropical Convergence Zone (ITCZ) remained southern and stronger than the climatological mean over the eastern tropical Pacific, producing an intense regional Hadley circulation. The descent branch of this cell inhibited the development of convection over the BRB, although the moisture sources increased their contributions; however, these were bounded to the lower levels by a strong trade wind inversion.
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Liu, Qian, Long S. Chiu, Xianjun Hao, and Chaowei Yang. "Spatiotemporal Trends and Variations of the Rainfall Amount, Intensity, and Frequency in TRMM Multi-satellite Precipitation Analysis (TMPA) Data." Remote Sensing 13, no. 22 (November 17, 2021): 4629. http://dx.doi.org/10.3390/rs13224629.
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The spatiotemporal mean rain rate (MR) can be characterized by the rain frequency (RF) and the conditional rain rate (CR). We computed these parameters for each season using the TMPA 3-hourly, 0.25° gridded data for the 1998–2017 period at a quasi-global scale, 50°N~50°S. For the global long-term average, MR, RF, and CR are 2.83 mm/d, 10.55%, and 25.05 mm/d, respectively. The seasonal time series of global mean RF and CR show significant decreasing and increasing trends, respectively, while MR depicts only a small but significant trend. The seasonal anomaly of RF decreased by 5.29% and CR increased 13.07 mm/d over the study period, while MR only slightly decreased by −0.029 mm/day. The spatiotemporal patterns in MR, RF, and CR suggest that although there is no prominent trend in the total precipitation amount, the frequency of rainfall events becomes smaller and the average intensity of a single event becomes stronger. Based on the co-variability of RF and CR, the paper optimally classifies the precipitation over land and ocean into four categories using K-means clustering. The terrestrial clusters are consistent with the dry and wet climatology, while categories over the ocean indicate high RF and medium CR in the Inter Tropical Convergence Zone (ITCZ) region; low RF with low CR in oceanic dry zones; and low RF and high CR in storm track areas. Empirical Orthogonal Function (EOF) analysis was then performed, and these results indicated that the major pattern of MR is characterized by an El Niño-Southern Oscillation (ENSO) signal while RF and CR variations are dominated by their trends.
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Chakraborty, A., S. K. Satheesh, R. S. Nanjundiah, and J. Srinivasan. "Impact of absorbing aerosols on the simulation of climate over the Indian region in an atmospheric general circulation model." Annales Geophysicae 22, no. 5 (April 8, 2004): 1421–34. http://dx.doi.org/10.5194/angeo-22-1421-2004.
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Abstract. The impact of anthropogenic absorbing aerosols (such as soot) on the climate over the Indian region has been studied using the NCMRWF general circulation model. The absorbing aerosols increase shortwave radiative heating of the lower troposphere and reduce the heating at the surface. These effects have been incorporated as heating of the lower troposphere (up to 700hPa) and cooling over the continental surface based on INDOEX measurements. The heating effect is constant in the pre-monsoon season and reduces to zero during the monsoon season. It is shown that even in the monsoon season when the aerosol forcing is zero, there is an overall increase in rainfall and a reduction in surface temperature over the Indian region. The rainfall averaged over the Tropics shows a small reduction in most of the months during the January to September period. The impact of aerosol forcing, the model's sensitivity to this forcing and its interaction with model-physics has been studied by changing the cumulus parameterization from the Simplified Arakawa-Schubert (SAS) scheme to the Kuo scheme. During the pre-monsoon season the major changes in precipitation occur in the oceanic Inter Tropical Convergence Zone (ITCZ), where both the schemes show an increase in precipitation. This result is similar to that reported in Chung2002. On the other hand, during the monsoon season the changes in precipitation in the continental region are different in the SAS and Kuo schemes. It is shown that the heating due to absorbing aerosols changes the vertical moist-static stability of the atmosphere. The difference in the precipitation changes in the two cumulus schemes is on account of the different responses in the two parameterization schemes to changes in vertical stability. Key words. Atmospheric composition and structure (aerosols and particles) – Meteorology and atmospheric dynamics (tropical meteorology; precipitation)
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Guo, Z. T., A. Berger, Q. Z. Yin, and L. Qin. "Strong asymmetry of hemispheric climates during MIS-13 inferred from correlating China loess and Antarctica ice records." Climate of the Past 5, no. 1 (February 18, 2009): 21–31. http://dx.doi.org/10.5194/cp-5-21-2009.
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Abstract. We correlate the China loess and Antarctica ice records to address the inter-hemispheric climate link over the past 800 ka. The results show a broad coupling between Asian and Antarctic climates at the glacial-interglacial scale. However, a number of decoupled aspects are revealed, among which marine isotope stage (MIS) 13 exhibits a strong anomaly compared with the other interglacials. It is characterized by unusually positive benthic oxygen (δ18O) and carbon isotope (δ13C) values in the world oceans, cooler Antarctic temperature, lower summer sea surface temperature in the South Atlantic, lower CO2 and CH4 concentrations, but by extremely strong Asian, Indian and African summer monsoons, weakest Asian winter monsoon, and lowest Asian dust and iron fluxes. Pervasive warm conditions were also evidenced by the records from northern high-latitude regions. These consistently indicate a warmer Northern Hemisphere and a cooler Southern Hemisphere, and hence a strong asymmetry of hemispheric climates during MIS-13. Similar anomalies of lesser extents also occurred during MIS-11 and MIS-5e. Thus, MIS-13 provides a case that the Northern Hemisphere experienced a substantial warming under relatively low concentrations of greenhouse gases. It suggests that the global climate system possesses a natural variability that is not predictable from the simple response of northern summer insolation and atmospheric CO2 changes. During MIS-13, both hemispheres responded in different ways leading to anomalous continental, marine and atmospheric conditions at the global scale. The correlations also suggest that the marine δ18O record is not always a reliable indicator of the northern ice-volume changes, and that the asymmetry of hemispheric climates is one of the prominent factors controlling the strength of Asian, Indian and African monsoon circulations, most likely through modulating the position of the inter-tropical convergence zone (ITCZ) and land-sea thermal contrasts.
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Fattore, F., T. Bertolini, S. Materia, S. Gualdi, A. Thongo M'Bou, G. Nicolini, R. Valentini, A. De Grandcourt, D. Tedesco, and S. Castaldi. "Seasonal trends of dry and bulk concentration of nitrogen compounds over a rain forest in Ghana." Biogeosciences Discussions 10, no. 9 (September 17, 2013): 15225–55. http://dx.doi.org/10.5194/bgd-10-15225-2013.
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Abstract. African tropical forests of the equatorial belt might receive significant input of extra nitrogen derived from biomass burning occurring in the north savanna belt and transported equator wards by NE winds. In order to test this hypothesis an experiment was set up in a tropical rain forest in the National park of Ankasa (Ghana) aiming at: quantifying magnitude and seasonal variability of concentrations of N compounds, present as gas and aerosol (dry nitrogen) or in the rainfall (bulk nitrogen), over the studied forest; relating their seasonal variability to trends of local and regional winds and rainfall and to variations of fire events in the region. Three Delta systems, implemented for monthly measurements of NO2, were mounted over a tower at 45 m height, 20 m above forest canopy to sample gas (NH3, NO2, HNO3, HCl, SO2) and aerosol (NH4+, NO3−, and several ions), together with three tanks for bulk rainfall collection (to analyze NH4+, NO3− and ion concentration). The tower was provided with a sonic anemometer to estimate local wind data. The experiment started in October 2011 and data up to October 2012 are presented. To interpret the observed seasonal trends of measured compounds, local and regional meteo data and regional satellite fire data were analyzed. The concentration of N compounds significantly increased from December to April, during the drier period, peaking in December-February when North Eastern winds (Harmattan) were moving dry air masses over the West central African region and the inter tropical convergence zone (ITCZ) was at its minimum latitude over the equator. This period also coincided with peaks of fire in the whole region. On the contrary, N concentration in gas, aerosol and rain decreased from May to October when prevalent winds arrived from the sea (South-East), during the Monsoon period. Both ionic compositions of rain and analysis of local wind direction showed a significant and continuous presence of see-breeze at site. The ionic composition of rain water resulted much closer to see water and poorer in N compounds from May to October.
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Wells, Christopher D., Matthew Kasoar, Nicolas Bellouin, and Apostolos Voulgarakis. "Local and remote climate impacts of future African aerosol emissions." Atmospheric Chemistry and Physics 23, no. 6 (March 23, 2023): 3575–93. http://dx.doi.org/10.5194/acp-23-3575-2023.
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Abstract. The potential future trend in African aerosol emissions is uncertain, with a large range found in future scenarios used to drive climate projections. The future climate impact of these emissions is therefore uncertain. Using the Shared Socioeconomic Pathway (SSP) scenarios, transient future experiments were performed with the UK Earth System Model (UKESM1) to investigate the effect of African emissions following the high emission SSP370 scenario as the rest of the world follows the more sustainable SSP119, relative to a global SSP119 control. This isolates the effect of Africa following a relatively more polluted future emissions pathway. Compared to SSP119, SSP370 projects higher non-biomass-burning (non-BB) aerosol emissions, but lower biomass burning emissions, over Africa. Increased shortwave (SW) absorption by black carbon aerosol leads to a global warming, but the reduction in the local incident surface radiation close to the emissions is larger, causing a local cooling effect. The local cooling persists even when including the higher African CO2 emissions under SSP370 than SSP119. The global warming is significantly higher by 0.07 K when including the non-BB aerosol increases and higher still (0.22 K) when including all aerosols and CO2. Precipitation also exhibits complex changes. Northward shifts in the Inter-tropical Convergence Zone (ITCZ) occur under relatively warm Northern Hemisphere land, and local rainfall is enhanced due to mid-tropospheric instability from black carbon absorption. These results highlight the importance of future African aerosol emissions for regional and global climate and the spatial complexity of this climate influence.
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Kageyama, M., J. Mignot, D. Swingedouw, C. Marzin, R. Alkama, and O. Marti. "Glacial climate sensitivity to different states of the Atlantic Meridional Overturning Circulation: results from the IPSL model." Climate of the Past Discussions 5, no. 2 (March 18, 2009): 1055–107. http://dx.doi.org/10.5194/cpd-5-1055-2009.
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Abstract. Numerous records from the North Atlantic and the surrounding continents have shown rapid and large amplitude climate variability during the last glacial period. This variability has often been associated to changes in the Atlantic Meridional Overturning Circulation (AMOC). Rapid climate change on the same time scales has also been reconstructed for sites far away from the North Atlantic, such as the tropical Atlantic, the East Pacific and Asia. The mechanisms explaining these climatic responses to the state of the AMOC are far from being completely understood, especially in a glacial context. Here we study three glacial simulations characterised by different AMOC strengths: 18, 15 and 2 Sv. With these simulations, we analyse the global climate sensitivity to a weak (18 to 15 Sv) and a strong (15 to 2 Sv) decrease in the AMOC strength. A weak decrease in the AMOC is associated, in our model simulations, to the classical North Atlantic and European cooling, but this cooling is not homogeneous over this region. We investigate the reasons for a lesser cooling (or even slight warming in some cases) over the Norwegian Sea and Northwestern Europe. It appears that the convection site in this area is active in both simulations, but that convection is unexpectedly stronger in the 15 Sv simulation. Due to the large variability of the atmosphere, it is difficult to definitely establish what is the origin of this climatic difference, but it appears that the atmospheric circulation anomaly helps sustaining the activity of this convection sites. Far from the North Atlantic, the climatic response is of small amplitude, the only significant change appearing in summer over the tropical Atlantic, where the Inter-Tropical Convergence Zone (ITCZ) shifts southward. The climate differences between the 15 Sv and 2 Sv simulations are much larger and our analyses focus on three areas: the North Atlantic and surrounding regions, the Tropics and the Indian monsoon region. We study the timing of appearance of these responses to the AMOC shutdown, which gives some clues about the mechanisms for these teleconnections. We show that the North Atlantic cooling associated with the collapse of the AMOC induces a cyclonic atmospheric circulation anomaly centered over the North Atlantic, which modulates the eastward advection of the cold anomaly over the Eurasian continent. It can explain that the cooling is not as strong over Western Europe as over the North Atlantic and the rest of the Eurasian continent. Another modification in the northern extratropical stationary waves occurs over the Eastern Pacific, explaining a warming over Northwestern America. In the Tropics, the ITCZ southward shift in this simulation appears to be strongest over the Atlantic and Eastern Pacific and results from an ajustment of the atmospheric and oceanic transports. Finally, the Indian monsoon weakening also appears to be connected to the tropospheric cooling over Eurasia.
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Singh, Ram, Kostas Tsigaridis, Allegra N. LeGrande, Francis Ludlow, and Joseph G. Manning. "Investigating hydroclimatic impacts of the 168–158 BCE volcanic quartet and their relevance to the Nile River basin and Egyptian history." Climate of the Past 19, no. 1 (January 27, 2023): 249–75. http://dx.doi.org/10.5194/cp-19-249-2023.
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Abstract. The Ptolemaic era (305–30 BCE) is an important period of Ancient Egyptian history known for its material and scientific advances, but also intermittent political and social unrest in the form of (sometimes widespread) revolts against the Ptolemaic elites. While the role of environmental pressures has long been overlooked in this period of Egyptian history, ice-core-based volcanic histories have identified the period as experiencing multiple notable eruptions, and a repeated temporal association between explosive volcanism and revolt has recently been noted. Here we analyze the global and regional (Nile River basin) hydroclimatic response to a unique historical sequence of four large and closely timed volcanic eruptions (first a tropical one, followed by three extratropical northern hemispheric events) between 168 and 158 BCE, a particularly troubled period in Ptolemaic history for which we now provide a more detailed hydroclimatic context. The NASA (National Aeronautics and Space Administration) GISS (Goddard Institute for Space Studies) ModelE2.1 Earth system model simulates a strong radiative response with a radiative forcing (top of atmosphere) of −7.5 W m−2 (following the first eruption) and −2.5 W m−2 (after each of the three remaining eruptions) at a global scale. Associated with this, we observe a global surface cooling of the order of 1.5 ∘C following the first (tropical) eruption, with the following three extratropical eruptions extending the cooling period for more than 15 years. Consequently, this series of eruptions is observed to constrain the northward migration of the inter-tropical convergence zone (ITCZ) during the Northern Hemisphere summer monsoon season, and major monsoon zones (African, South Asian, and East Asian) were seen to experience a suppression of rainfall of >1 mm d−1 during the monsoon (JJAS) season averaged for 2 years after each eruption. A substantial suppression of the Indian and North African summer monsoon (over the Nile River headwater region) was seen to strongly affect the modeled river flow in the catchment and discharge at river mouth. River mass flow over the basin was observed to decrease by 29 % and 38 % relative to an unperturbed (non-volcanic) annual mean flow in the first and second year, respectively, after the first (i.e., tropical) eruption. A moderate decrease ranging between 5 % and 18 % was observed after the third and fourth (extratropical) eruptions. These results indicate, in sum, that the first eruption likely produced a strong hydroclimate response, with the following extratropical eruptions prolonging this. These results also support the recently hypothesized association between ice-core-based signals of explosive volcanism and hydroclimatic variability during the Ptolemaic era, including the suppression of the agriculturally critical Nile summer flooding.
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Kucieńska, B., G. B. Raga, and O. Rodríguez. "Cloud-to-ground lightning over Mexico and adjacent oceanic regions: a preliminary climatology using the WWLLN dataset." Annales Geophysicae 28, no. 11 (November 9, 2010): 2047–57. http://dx.doi.org/10.5194/angeo-28-2047-2010.
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Abstract. This work constitutes the first climatological study of lightning over Mexico and adjacent oceanic areas for the period 2005–2009. Spatial and temporal distributions of cloud to ground lightning are presented and the processes that contribute to the lightning variability are analysed. The data are retrieved from the World Wide Lightning Location Network (WWLLN) dataset. The current WWLL network includes 40 stations which cover much of the globe and detect very low frequency radiation ("spherics") associated with lightning. The spatial distribution of the average yearly lightning over the continental region of Mexico shows the influence of orographic forcing in producing convective clouds with high lightning activity. However, a very high number of strikes is also observed in the States of Tabasco and Campeche, which are low-lying areas. This maximum is related to the climatological maximum of precipitation for the country and it may be associated with a region of persistent low-level convergence and convection in the southern portion of the Gulf of Mexico. The maps of correlation between rainfall and lightning provide insight into the microphysical processes occurring within the clouds. The maritime clouds close to the coastline exhibit similar properties to continental clouds as they produce very high lightning activity. The seasonal cycle of lightning registered by WWLLN is consistent with the LIS/OTD dataset for the selected regions. In terms of the annual distribution of cloud-to-ground strikes, July, August and September exhibit the highest number of strikes over continental Mexico. The diurnal cycle indicates that the maximum number of strikes over the continent is observed between 6 and 9 p.m. LT. The surrounding oceanic regions were subdivided into four distinct sectors: Gulf of Mexico, Caribbean, Sub-tropical Pacific and Tropical Pacific. The Gulf of Mexico has the broadest seasonal distribution, since during winter lightning associated with mid-latitude systems also affects the region. The diurnal distribution of lightning for the Gulf of Mexico exhibits the highest number of strokes at 9 a.m. The Caribbean seasonal distribution is slightly biased towards early fall, with a clear maximum observed during October. The diurnal distribution of lightning over the Caribbean is quite uniform with a slight increase near midnight. The Subtropical Pacific has the narrowest seasonal distribution, associated with the convection observed during the "North American Monsoon", with the maximum number of strikes during August and September. In contrast, the Tropical Pacific has a broader seasonal cycle, associated with convection in the Inter-Tropical Convergence Zone (ITCZ), starting in May and lasting till October. In both adjacent Pacific regions, the strikes present a maximum in the early morning, the time of the highest frequency of land breeze.
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Jeong, G. R., and C. Wang. "Climate effects of seasonally varying biomass burning emitted carbonaceous aerosols (BBCA)." Atmospheric Chemistry and Physics Discussions 10, no. 4 (April 15, 2010): 9431–62. http://dx.doi.org/10.5194/acpd-10-9431-2010.
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Abstract. The climate impact of the seasonality of Biomass Burning emitted Carbonaceous Aerosols (BBCA) has been studied using an aerosol-climate model coupled with a slab ocean model in a set of 60-year long simulations driven by BBCA emission data with and without seasonal variation, respectively. The model run with seasonally varying emission of BBCA leads to an increase in external mixture of carbonaceous aerosols and a decrease in internal mixtures of carbonaceous aerosols relative to those in the run with constant annual BBCA emissions, resulting from different strengths of source/sink processes. We find that the differences in atmospheric direct radiative forcing (DRF) caused by BBCA seasonality are in phase with the differences in column concentrations of an external mixture of carbonaceous aerosols in space and time; thus, the differences in surface temperature and heat fluxes are limited to the biomass burning source regions. In contrast, the differences in all-sky radiative forcing at the top of the atmosphere and at the earth's surface extend beyond the BBCA source regions due to climate feedback through cloud distribution and precipitation. The seasonality of biomass burning emissions uniquely affects the global distributions of high-level clouds and convective precipitation, which indicate an impact on atmospheric circulation. We especially find that the Inter-Tropical Convergence Zone (ITCZ) shifts northward when the seasonality of BBCA emissions is included in the model, compared to the case otherwise configured. In addition, the climate response to the periodic climate forcing of BBCA is not static in biomass burning seasons but dynamically extends into non-biomass seasons as well. The climate effects in contrasting biomass burning seasons occur in the springtime in northern Tropics with the largest difference in precipitation and mixed aerosol abundance caused by the seasonality of BBCA.
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Nsubuga, Francis Wasswa, and Hannes Rautenbach. "Climate change and variability: a review of what is known and ought to be known for Uganda." International Journal of Climate Change Strategies and Management 10, no. 5 (November 19, 2018): 752–71. http://dx.doi.org/10.1108/ijccsm-04-2017-0090.
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Purpose In view of the consensus that climate change is happening, scientists have documented several findings about Uganda’s recent climate, as well as its variability and change. The purpose of this study is to review what has been documented, thus it gives an overview of what is known and seeks to explain the implications of a changing climate, hence what ought to be known to create a climate resilient environment. Design/methodology/approach Terms such as “climate”, “climate change” and “climate variability” were identified in recent peer-reviewed published literature to find recent climate-related literature on Uganda. Findings from independent researchers and consultants are incorporated. Data obtained from rainfall and temperature observations and from COSMO-CLM Regional Climate Model-Coordinated Regional Climate Downscaling Experiment (CCLM CORDEX) data, European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-Interim) data and Global Precipitation Climatology Centre (GPCC) have been used to generate spatial maps, seasonal outputs and projections using GrADS 2.02 and Geographic Information System (GIS) software for visualization. Findings The climate of Uganda is tropical in nature and influenced by the Inter-Tropical Convergence Zone (ITCZ), varied relief, geo-location and inland lakes, among other factors. The impacts of severe weather and climate trends and variability have been documented substantially in the past 20-30 years. Most studies indicated a rainfall decline. Daily maximum and minimum temperatures are on the rise, while projections indicate a decrease in rainfall and increase in temperature both in the near and far future. The implication of these changes on society and the economy are discussed herein. Cost of inaction is expected to become huge, given factors like, the growing rate of the population and the slow expanding economy experienced in Uganda. Varied forms of adaptation to the impacts of climate change are being implemented, especially in the agricultural sector and at house hold level, though not systematically. Originality/value This review of scientific research findings aims to create a better understanding of the recent climate change and variability in Uganda and provides a baseline of summarized information for use in future research and actions.
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Loidi, Javier, Gonzalo Navarro-Sánchez, and Denys Vynokurov. "Climatic definitions of the world’s terrestrial biomes." Vegetation Classification and Survey 3 (December 19, 2022): 231–71. http://dx.doi.org/10.3897/vcs.86102.
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Question: Is it feasible to establish a classification of large biotic units of the world related to climatic types? Study area: The world. Methods: A total of 616 localities have been selected, their climatic parameters calculated and subjected to a PCA. The climatic characterization of biomes and subbiomes has been completed after data analysis. Results: A hierarchical classification is proposed for the biotic units within four main domains: Cryocratic, Mesocratic, Xerocratic and Thermocratic, divided into 7 ecozones, 9 biomes and 20 subbiomes linked to climatically defined territories. Most of the units are intercontinental. The mountains represent an abbreviated version of the latitudinal zonation and the altitudinal belts are related to the corresponding units of the lowlands. For the bioclimatic units, a parallel classification is proposed to fit with that of the biotic units: 4 Macrobioclimates and 10 bioclimates. Furthermore, 7 ombrotypes and 7 thermotypes are recognized to frame the climatic variation within each climatic territory due to terrain ruggedness, particularly in relation to large or medium sized mountains. Conclusions: The southern hemisphere is substantially more oceanic than the northern hemisphere. This is due to the distribution of the land masses and the modifying effect they have on the flow of air and marine currents. As a result, there is one biome and one subbiome exclusively found in the northern hemisphere (6. Biome of the steppe, and 5.b Continental scrub and woodlands subbiome) and two others which are almost confined to it (2. Biome of the boreal forest, and 3. Biome of the temperate deciduous forests). The 7. Biome of the deserts and 5. Biome of the temperate aridiestival evergreen forests and shrublands occur on the western side of the continents and expand in their interior favoured by rain shadow and continentality effects. Taxonomic reference: The Plant List (2013). Abbreviations: ITCZ = Inter Tropical Convergence Zone; NH = Northern Hemisphere; PCA = Principal Component Analysis; SH = Southern Hemisphere.
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Hällberg, Petter L., Frederik Schenk, Kweku A. Yamoah, Xueyuen Kuang, and Rienk H. Smittenberg. "Seasonal aridity in the Indo-Pacific Warm Pool during the Late Glacial driven by El Niño-like conditions." Climate of the Past 18, no. 7 (July 18, 2022): 1655–74. http://dx.doi.org/10.5194/cp-18-1655-2022.
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Abstract. Island South-East Asia (ISEA) is a highly humid region that hosts the world's largest tropical peat deposits. Most of this peat accumulated only relatively recently during the Holocene, suggesting that the climate was drier and/or more seasonal during earlier times. Although there is evidence for savanna expansion and drier conditions during the Last Glacial Maximum (LGM, 21 ka BP), the mechanisms behind hydroclimatic changes during the ensuing deglacial period have received much less attention and are poorly understood. Here we use CESM1 climate model simulations to investigate the key drivers behind ISEA climate at the end of the Late Glacial (14.7–11.7 ka BP), with a focus on the last stadial of the Younger Dryas (12 ka BP). We further simulate the preceding Allerød (13 ka BP) interstadial climate and perform a sensitivity experiment to disentangle the climate impacts due to orbital forcing and Late Glacial boundary conditions against a slowdown of the Atlantic Meridional Overturning Circulation (AMOC). A transient simulation (TRACE) is used to track the climate seasonality and orbitally driven change over time during the deglaciation into the Holocene. In agreement with proxy evidence, CESM1 simulates overall drier conditions during the Younger Dryas and Allerød. More importantly, ISEA experienced extreme seasonal aridity, in stark contrast to the ever-wet modern climate. We identify that the simulated drying and enhanced seasonality in the Late Glacial is mainly the result of a combination of three factors: (1) large orbital insolation difference on the Northern Hemisphere (NH) between summer and winter, in contrast to the LGM and the present day, (2) a stronger (dry) East Asian winter monsoon caused by a larger meridional thermal gradient and (3) a major reorganization of the Indo-Pacific Walker Circulation with an inverted land-sea circulation and a complete breakdown of deep convection over ISEA in NH winters. The altered atmospheric circulation, sea surface temperature and sea level pressure patterns led to conditions resembling extreme El Niño events in the modern climate and a dissolution of the Intertropical Convergence Zone (ITCZ) over the region. From these results we infer that terrestrial cooling of ISEA and at least a seasonal reversal of land-sea circulation likely played a major role in delaying tropical peat formation until at least the onset of the Holocene period. Our results also suggest that centennial to millennial shifts in AMOC strength modifies the Pacific Ocean hydroclimate via alteration of the position of the ITCZ, and a modulation of the Pacific Walker Circulation. However, Late Glacial AMOC shifts are overall less important than hydroclimate changes due to orbital forcing and boundary condition changes relative to the modern climate.
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Martínez-Abarca, Rodrigo, Michelle Abstein, Frederik Schenk, David Hodell, Philipp Hoelzmann, Mark Brenner, Steffen Kutterolf, et al. "Millennial hydrological variability in the continental northern Neotropics during Marine Isotope Stages (MISs) 3–2 (59–15 cal ka BP) inferred from sediments of Lake Petén Itzá, Guatemala." Climate of the Past 19, no. 7 (July 18, 2023): 1409–34. http://dx.doi.org/10.5194/cp-19-1409-2023.
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Abstract. Lake Petén Itzá (Guatemala) possesses one of the longest lacustrine sediment records in the northern Neotropics, which enabled study of paleoclimate variability in the region during the last ∼400 000 years. We used geochemical (Ti, Ca/(Ti+Fe) and Mn/Fe) and mineralogical (carbonates, gypsum, quartz, clay) data from sediment core PI-2 to infer past changes in runoff, lake evaporation, organic matter sources and redox conditions in the water column, caused by hydrological changes in the northern Neotropics during Marine Isotope Stages (MISs) 3–2. From 59 to 39 cal ka BP climate conditions were relatively wet, and the lake was marked by higher primary productivity and anoxic bottom waters. This wet environment was interrupted for two periods of possible low water level at 52 and 46 cal ka BP, when our data suggest higher evaporation, high terrestrial organic matter input and persistent oxic conditions. Between 39 and 23 cal ka BP, evaporation and input of terrestrial organic matter increased considerably, lake level declined, and lake bottom waters generally became oxic. These conditions reversed during the Last Glacial Maximum (23.5–18.0 cal ka BP), when runoff and lake productivity increased, and rising lake level caused bottom waters to again become anoxic. Comparison of our hydrologic proxy data with sea surface temperature anomalies between the eastern Pacific and the Caribbean suggests that changes in the intensity of the Caribbean Low-Level Jet (CLLJ) may have influenced long-term changes in runoff during MISs 3–2. Higher intensity of the CLLJ during the onset of MIS 3 and the LGM might have led to greater runoff into the lake, whereas the MIS 3–2 transition experienced a weaker CLLJ and consequently less runoff. A refined, high-resolution age–depth model for the PI-2 sediment core enabled us to identify millennial-scale Greenland interstadials (GIs) 14–2, Greenland stadials (GSs) 14–2 and Heinrich stadials (HSs) 5–1. In general, HSs and GSs were characterized by drier conditions. In contrast to GSs and HSs, GIs were characterized by greater runoff and overall wetter conditions, with the most pronounced GI peaks between 40 and 30 cal ka BP. Whereas GSs 9, 8, 7 and 6 began with abrupt increases in evaporation and ended with gradual increases in humidity, GSs 11 and 10 showed reversed patterns. The Lake Petén Itzá paleohydrology record, along with other regional paleoclimate records, led us to conclude that shifts in the position of the Intertropical Convergence Zone (ITCZ) altered moisture delivery to the lake on millennial timescales. During GSs and HSs, high evaporation from Petén Itzá (dry climate conditions) was associated with a more southerly position of the ITCZ, whereas wetter GIs prevailed during a more northerly ITCZ position. Although abrupt millennial-scale shifts in ITCZ and hydroclimate between GSs/HSs and GIs can be linked to instabilities in the Atlantic Meridional Overturning Circulation (AMOC), longer-term changes were additionally influenced by changes in atmospheric convection linked to modulations of the CLLJ in response to ΔSST between the equatorial Pacific and tropical Atlantic.
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Wolters, E. L. A., B. J. J. M. van den Hurk, and R. A. Roebeling. "Evaluation of rainfall retrievals from SEVIRI reflectances over West Africa using TRMM-PR and CMORPH." Hydrology and Earth System Sciences 15, no. 2 (February 3, 2011): 437–51. http://dx.doi.org/10.5194/hess-15-437-2011.
Full textAbstract:
Abstract. This paper describes the evaluation of the KNMI Cloud Physical Properties – Precipitation Properties (CPP-PP) algorithm over West Africa. The algorithm combines condensed water path (CWP), cloud phase (CPH), cloud particle effective radius (re), and cloud-top temperature (CTT) retrievals from visible, near-infrared and thermal infrared observations of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) onboard the Meteosat Second Generation (MSG) satellites to estimate rain occurrence frequency and rain rate. For the 2005 and 2006 monsoon seasons, it is investigated whether the CPP-PP algorithm is capable of retrieving rain occurrence frequency and rain rate over West Africa with sufficient accuracy, using Tropical Monsoon Measurement Mission Precipitation Radar (TRMM-PR) as reference. As a second goal, it is assessed whether SEVIRI is capable of monitoring the seasonal and daytime evolution of rainfall during the West African monsoon (WAM), using Climate Prediction Center Morphing Technique (CMORPH) rainfall observations. The SEVIRI-detected rainfall area agrees well with TRMM-PR, with the areal extent of rainfall by SEVIRI being ~10% larger than from TRMM-PR. The mean retrieved rain rate from CPP-PP is about 8% higher than from TRMM-PR. Examination of the TRMM-PR and CPP-PP cumulative frequency distributions revealed that differences between CPP-PP and TRMM-PR are generally within +/−10%. Relative to the AMMA rain gauge observations, CPP-PP shows very good agreement up to 5 mm h−1. However, at higher rain rates (5–16 mm h−1) CPP-PP overestimates compared to the rain gauges. With respect to the second goal of this paper, it was shown that both the accumulated precipitation and the seasonal progression of rainfall throughout the WAM is in good agreement with CMORPH, although CPP-PP retrieves higher amounts in the coastal region of West Africa. Using latitudinal Hovmüller diagrams, a fair correspondence between CPP-PP and CMORPH was found, which is reflected by high correlation coefficients (~0.7) for both rain rate and rain occurrence frequency. The daytime cycle of rainfall from CPP-PP shows distinctly different patterns for three different regions in West Africa throughout the WAM, with a decrease in dynamical range of rainfall near the Inter Tropical Convergence Zone (ITCZ). The dynamical range as retrieved from CPP-PP is larger than that from CMORPH. It is suggested that this results from both the better spatio-temporal resolution of SEVIRI, as well as from thermal infrared radiances being partly used by CMORPH, which likely smoothes the daytime precipitation signal, especially in case of cold anvils from convective systems. The promising results show that the CPP-PP algorithm, taking advantage of the high spatio-temporal resolution of SEVIRI, is of added value for monitoring daytime precipitation patterns in tropical areas.