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1
Boyard-Micheau, Joseph, and Pierre Camberlin. "Reconstitution de séries de pluies quotidiennes en Afrique de l’est : application aux caractéristiques des saisons des pluies." Climatologie 12 (2015): 83–105. http://dx.doi.org/10.4267/climatologie.1142.
Анотація:
La reconstitution de données de pluies manquantes au pas de temps quotidien et à l’échelle stationnelle est parfois nécessaire pour l’étude de changements climatiques ou des travaux de climatologie appliquée. C’est le cas, en domaine tropical, de l’analyse des variations des caractéristiques des saisons des pluies (dates de démarrage et de fin, durée, etc.). A partir d’une approche méthodologique classique fondée sur une régression linéaire multiple pas à pas, mais appliquée pour tirer le meilleur parti possible des données disponibles et incluant une correction des biais, les performances de la reconstitution des pluies obtenues sont évaluées en considérant différents descripteurs de la structure temporelle des saisons des pluies est-africaines. L’Afrique de l’Est, par sa topographie contrastée et ses deux saisons des pluies forcées par des mécanismes d’échelles spatiales différentes, constitue une zone pertinente pour tester la méthodologie de reconstitution. Les résultats montrent que l’occurrence des jours de pluies ainsi que les quantités précipitées sont reproduites correctement dans les espaces où les précipitations sont les plus abondantes et où le nombre de pluviomètres est plus important. Si au pas de temps journalier, les performances des reconstitutions restent parfois modestes, elles sont bien plus satisfaisantes lorsqu’on les évalue à partir des caractéristiques saisonnières ou intra-saisonnières comme le cumul saisonnier, le nombre de jours de pluie, ou les dates de début et de fin des saisons des pluies. L’impact du comblement des lacunes est directement associé à la proportion de lacunes dans les séries temporelles de pluie, sans qu’il soit possible d’identifier un pourcentage de lacunes au-delà duquel les performances de la méthode de reconstitution se détériorent significativement. La distribution temporelle des valeurs manquantes a également un impact non négligeable sur la qualité de la reconstitution de la saison des pluies : ainsi, lorsque l’absence de données de pluie concerne de longues périodes continues, les caractéristiques de la saison des pluies sont mal reproduites.
2
Koffi, Yao Blaise. "Modélisation pluie-débit en région tropicale humide : application des réseaux de neurones sur quatre stations hydrométriques du Bandama Blanc (Bada, Marabadiassa, Tortiya et Bou) situées au Nord de la Côte d'Ivoire. Thèse de l'Universit." Physio-Géo, Volume 3 (January 1, 2009): 1–3. http://dx.doi.org/10.4000/physio-geo.940.
3
McGuirk, James P., Aylmer H. Thompson, and James R. Schaefer. "An Eastern Pacific Tropical Plume." Monthly Weather Review 116, no. 12 (December 1988): 2505–21. http://dx.doi.org/10.1175/1520-0493(1988)116<2505:aeptp>2.0.co;2.
4
Ffield, Amy. "Amazon and Orinoco River Plumes and NBC Rings: Bystanders or Participants in Hurricane Events?" Journal of Climate 20, no. 2 (January 15, 2007): 316–33. http://dx.doi.org/10.1175/jcli3985.1.
Анотація:
Abstract The Amazon and Orinoco River plumes and North Brazil Current (NBC) rings are investigated during the 1 June through 30 November Atlantic hurricane season to identify their impact on upper-ocean temperatures in the region and to draw attention to their potential role in hurricane maintenance and intensification. The analysis uses ocean temperature and salinity stratification data, infrared and microwave satellite-derived sea surface temperature (SST) data, and Atlantic tropical storm and hurricane tracks data. The Amazon–Orinoco River plume spreads into the western equatorial Atlantic Ocean forming an extensive (0°–20°N, 78°–33°W) 10–60-m-thick buoyant surface layer associated with the warmest surface temperatures (up to +3°C) in the region due to the freshwater barrier layer effect. At times the warm Amazon–Orinoco River plume is bisected by cool-surface NBC rings. For the 1960 to 2000 time period, 68% of all category 5 hurricanes passed directly over the historical region of the plume, revealing that most of the most destructive hurricanes may be influenced by ocean–atmosphere interaction with the warm plume just prior to reaching the Caribbean. Statistical analyses of tropical Atlantic SSTs and tropical cyclone wind speeds reveal a significant and unique relationship between warm (cool) SSTs in the Amazon–Orinoco River plume and stronger (weaker) tropical cyclone wind speeds between 35° and 55°W. This implies that warmer (cooler) plume SSTs due to increased (decreased) river discharge may directly contribute to a more (less) vigorous hurricane season.
5
Mandret, Gilles, A. Ourry, and Guy Roberge. "Effet des facteurs température et nutrition azotée sur la croissance des plantes fourragères tropicales. I. Variation saisonnière de la croissance d'une graminée tropicale, Brachiaria mutica, au Sénégal." Revue d’élevage et de médecine vétérinaire des pays tropicaux 43, no. 1 (January 1, 1990): 119–24. http://dx.doi.org/10.19182/remvt.8879.
Анотація:
La croissance en climat sahélien subcanarien d'une graminée tropicale, Brachiaria mutica, a été étudiée pendant la saison sèche froide (novembre-m a rs), la saison sèche chaude (mars-mi-juillet) et la saison des pluies (mi-juillet-octobre). L'essentiel des résultats montre que cette graminée a une faible productivité en saison sèche froide, du fait de températures minimales très basses, contrairement à celles obtenues en saisons des pluies. Par ailleurs, il semble qu'il y ait une déplacement du facteur limitant (températures minimales basses) vers un effet azoté qui témoigne de la faible disponibilité en azote du sol pendant la saison froide et de l'importance d'une fertilisation azotée. Cette étude souligne l'intérêt d'introduire, lors de la saison sèche froide, des plantes fourragères des régions tempérées, moins exigeantes vis-à-vis de la température.
6
Bamory, Kamagaté, Séguis Luc, Goné Droh Lanciné, Favreau Guillaume, and Koffi Kouadio. "Processus hydrogéochimiques et séparation d’hydrogrammes de crue sur un bassin versant en milieu soudano-tropical de socle au Bénin (Donga, haute vallée de l’Ouémé)." Revue des sciences de l'eau 21, no. 3 (September 10, 2008): 363–72. http://dx.doi.org/10.7202/018782ar.
Анотація:
Résumé Le projet international et pluridisciplinaire AMMA (Analyse Multidisciplinaire de la Mousson Africaine) a été initié en vue de mieux comprendre les variabilités climatiques de l’Afrique de l’Ouest et leur impact hydrologique. La haute vallée de l’Ouémé au Bénin (10 000 km2) a été retenue et instrumentée (pluie, débit et nappe) depuis 1997. Le sous-bassin de la Donga (586 km2), cadre d’observations intensives depuis 2003, permet de préciser les processus majeurs et quantifier les termes du bilan hydrologique. Le travail vise à déterminer le fonctionnement hydrogéochimique du bassin de la Donga, et à identifier et quantifier les composantes majeures de l’écoulement de surface par traçage géochimique naturel. Le caractère temporaire des eaux de surface, la très faible minéralisation des écoulements ainsi que l’asynchronisme entre le tarissement des rivières et la vidange de la nappe phréatique traduisent une origine superficielle des débits et un échange de flux négligeable entre cette nappe et le réseau hydrographique. L’écoulement à l’exutoire, limité à la saison des pluies, apparaît être essentiellement formé d’un flux rapide (ruissellement Hortonien et écoulement sur surfaces saturées) et d’un flux lent de subsurface (vidange de nappes perchées saisonnières), sans contribution significative de la nappe phréatique. En accord avec ce fonctionnement, une séparation géochimique de l’hydrogramme de trois crues a été réalisée.
7
Zender, C. S., A. G. Krolewski, M. G. Tosca, and J. T. Randerson. "Tropical biomass burning smoke plume size, shape, reflectance, and age based on 2001–2009 MISR imagery of Borneo." Atmospheric Chemistry and Physics 12, no. 7 (April 11, 2012): 3437–54. http://dx.doi.org/10.5194/acp-12-3437-2012.
Анотація:
Abstract. Land clearing for crops, plantations and grazing results in anthropogenic burning of tropical forests and peatlands in Indonesia, where images of fire-generated aerosol plumes have been captured by the Multi-angle Imaging SpectroRadiometer (MISR) since 2001. Here we analyze the size, shape, optical properties, and age of distinct fire-generated plumes in Borneo from 2001–2009. The local MISR overpass at 10:30 a.m. misses the afternoon peak of Borneo fire emissions, and may preferentially sample longer plumes from persistent fires burning overnight. Typically the smoke flows with the prevailing southeasterly surface winds at 3–4 m s−1, and forms ovoid plumes whose mean length, height, and cross-plume width are 41 km, 708 m, and 27% of the plume length, respectively. 50% of these plumes have length between 24 and 50 km, height between 523 and 993 m and width between 18% and 30% of plume length. Length and cross-plume width are lognormally distributed, while height follows a normal distribution. Borneo smoke plume heights are similar to previously reported plume heights, yet Borneo plumes are on average nearly three times longer than previously studied plumes. This could be due to sampling or to more persistent fires and greater fuel loads in peatlands than in other tropical forests. Plume area (median 169 km2, with 25th and 75th percentiles at 99 km2 and 304 km2, respectively) varies exponentially with length, though for most plumes a linear relation provides a good approximation. The MISR-estimated plume optical properties involve greater uncertainties than the geometric properties, and show patterns consistent with smoke aging. Optical depth increases by 15–25% in the down-plume direction, consistent with hygroscopic growth and nucleation overwhelming the effects of particle dispersion. Both particle single-scattering albedo and top-of-atmosphere reflectance peak about halfway down-plume, at values about 3% and 10% greater than at the origin, respectively. The initially oblong plumes become brighter and more circular with time, increasingly resembling smoke clouds. Wind speed does not explain a significant fraction of the variation in plume geometry. We provide a parameterization of plume shape that can help atmospheric models estimate the effects of plumes on weather, climate, and air quality. Plume age, the age of smoke furthest down-plume, is lognormally distributed with a median of 2.8 h (25th and 75th percentiles at 1.3 h and 4.0 h), different from the median ages reported in other studies. Intercomparison of our results with previous studies shows that the shape, height, optical depth, and lifetime characteristics reported for tropical biomass burning plumes on three continents are dissimilar and distinct from the same characteristics of non-tropical wildfire plumes.
8
Bègue, Nelson, Hassan Bencherif, Fabrice Jégou, Hélène Vérèmes, Sergey Khaykin, Gisèle Krysztofiak, Thierry Portafaix, et al. "Transport and Variability of Tropospheric Ozone over Oceania and Southern Pacific during the 2019–20 Australian Bushfires." Remote Sensing 13, no. 16 (August 5, 2021): 3092. http://dx.doi.org/10.3390/rs13163092.
Анотація:
The present study contributes to the scientific effort for a better understanding of the potential of the Australian biomass burning events to influence tropospheric trace gas abundances at the regional scale. In order to exclude the influence of the long-range transport of ozone precursors from biomass burning plumes originating from Southern America and Africa, the analysis of the Australian smoke plume has been driven over the period December 2019 to January 2020. This study uses satellite (IASI, MLS, MODIS, CALIOP) and ground-based (sun-photometer, FTIR, ozone radiosondes) observations. The highest values of aerosol optical depth (AOD) and carbon monoxide total columns are observed over Southern and Central Australia. Transport is responsible for the spatial and temporal distributions of aerosols and carbon monoxide over Australia, and also the transport of the smoke plume outside the continent. The dispersion of the tropospheric smoke plume over Oceania and Southern Pacific extends from tropical to extratropical latitudes. Ozone radiosonde measurements performed at Samoa (14.4°S, 170.6°W) and Lauder (45.0°S, 169.4°E) indicate an increase in mid-tropospheric ozone (6–9 km) (from 10% to 43%) linked to the Australian biomass burning plume. This increase in mid-tropospheric ozone induced by the transport of the smoke plume was found to be consistent with MLS observations over the tropical and extratropical latitudes. The smoke plume over the Southern Pacific was organized as a stretchable anticyclonic rolling which impacted the ozone variability in the tropical and subtropical upper-troposphere over Oceania. This is corroborated by the ozone profile measurements at Samoa which exhibit an enhanced ozone layer (29%) in the upper-troposphere. Our results suggest that the transport of Australian biomass burning plumes have significantly impacted the vertical distribution of ozone in the mid-troposphere southern tropical to extratropical latitudes during the 2019–20 extreme Australian bushfires.
9
Ahmed, Fiaz, and J. David Neelin. "Reverse Engineering the Tropical Precipitation–Buoyancy Relationship." Journal of the Atmospheric Sciences 75, no. 5 (May 2018): 1587–608. http://dx.doi.org/10.1175/jas-d-17-0333.1.
Анотація:
The tropical precipitation–moisture relationship, characterized by rapid increases in precipitation for modest increases in moisture, is conceptually recast in a framework relevant to plume buoyancy and conditional instability in the tropics. The working hypothesis in this framework links the rapid onset of precipitation to integrated buoyancy in the lower troposphere. An analytical expression that relates the buoyancy of an entraining plume to the vertical thermodynamic structure is derived. The natural variables in this framework are saturation and subsaturation equivalent potential temperatures, which capture the leading-order temperature and moisture variations, respectively. The use of layer averages simplifies the analytical and subsequent numerical treatment. Three distinct layers, the boundary layer, the lower free troposphere, and the midtroposphere, adequately capture the vertical variations in the thermodynamic structure. The influence of each environmental layer on the plume is assumed to occur via lateral entrainment, corresponding to an assumed mass-flux profile. The fractional contribution of each layer to the midlevel plume buoyancy (i.e., the layer weight) is estimated from TRMM 3B42 precipitation and ERA-Interim thermodynamic profiles. The layer weights are used to “reverse engineer” a deep-inflow mass-flux profile that is nominally descriptive of the tropical atmosphere through the onset of deep convection. The layer weights—which are nearly the same for each of the layers—constitute an environmental influence function and are also used to compute a free-tropospheric integrated buoyancy measure. This measure is shown to be an effective predictor of onset in conditionally averaged precipitation across the global tropics—over both land and ocean.
10
Zender, C. S., A. G. Krolewski, M. G. Tosca, and J. T. Randerson. "Tropical biomass burning smoke plume size, shape, reflectance, and age based on 2001–2009 MISR imagery of Borneo." Atmospheric Chemistry and Physics Discussions 11, no. 11 (November 22, 2011): 30989–1030. http://dx.doi.org/10.5194/acpd-11-30989-2011.
Анотація:
Abstract. Land clearing for crops and plantations and grazing results in anthropogenic burning of tropical forests and peatlands in Indonesia, where images of fire-generated aerosol plumes have been captured by the Multi-angle Imaging SpectroRadiometer (MISR) since 2001. Our modeling studies show this smoke increases atmospheric heating, and reduces regional SST and dry-season precipitation, causing a potential feedback that increases drought-stress and air quality problems during El Niño years. Here we analyze the size, shape, optical properties, and age of fire-generated plumes in Borneo from 2001–2009. Most smoke flows with the prevailing southeasterly surface winds at 3–4 m s−1, and forms ovoid plumes whose mean length, height, and cross-plume width are 41 ± 1.4 (mean ± std. error) km, 708 ± 13 m, and 27 ± 0.75% of the plume length, respectively. Borneo smoke plume heights are similar to previously reported plume heights, yet Borneo plumes are nearly three times longer than previously studied plumes, possibly due to more persistent fires and greater fuel loads in peatlands than in other tropical forests. Plume area (median 169 ± 15 km2) varies exponentially with length, though for most plumes a linear relation provides a good approximation. The MISR-estimated plume optical properties involve greater uncertainties than the geometric properties, and show patterns consistent with smoke aging. Optical depth increases by 15–25% in the down-plume direction, consistent with hygroscopic growth and nucleation overwhelming the effects of particle dispersion. Both particle single-scattering albedo and top-of-atmosphere albedo peak about halfway down-plume, at values about 3% and 10% greater than at the origin, respectively. The initially oblong plumes become brighter and more circular with time, increasingly resembling smoke clouds. Wind speed does not explain a significant fraction of the variation in plume geometry. We provide a parameterization of plume shape that can help atmospheric models estimate the effects of plumes on weather, climate, and air quality. Plume age, the age of smoke furthest down-plume, is lognormally distributed with a median of 2.8 ± 0.3 h, significantly different than median ages reported in other studies. Intercomparison of our results with previous studies shows that the shape, height, optical depth, and lifetime characteristics reported for tropical biomass burning plumes on three continents are dissimilar and distinct from the same characteristics of wildfire plumes from the extratropics.
11
Montoya, Joseph P., Jason P. Landrum, and Sarah C. Weber. "Amazon River influence on nitrogen fixation in the western tropical North Atlantic." Journal of Marine Research 77, no. 2 (December 15, 2019): 191–213. http://dx.doi.org/10.1357/002224019828474278.
Анотація:
We measured rates of N- and C-fixation with a direct tracer method in regions of the western tropical North Atlantic influenced by the Amazon River plume during the high flow period of 2010 (May–June 2010). We found distinct regional variations in N-fixation activity, with the lowest rates in the plume proper and the highest rates in the plume margins and in offshore waters. A comparison of our N- and C-fixation measurements showed that the relative contribution of N-fixation to total primary production increased from the plume core toward oceanic waters, and that most of the C-fixation in this system was supported by sources of nitrogen other than those derived from biological N-fixation, or diazotrophy. We complemented these rate experiments with measurements of the δ15N of suspended particles (δ15PN), which documented the important and often dominant role of diazotrophs in supplying nitrogen to particulate organic matter in the water column. These coupled measurements revealed that small phytoplankton contributed more new nitrogen to the particulate nitrogen pool than larger phytoplankton. We used a habitat classification method to assess the fac- tors that control diazotrophic activity and contribution to the suspended particle pool, both of which increased from the plume toward oceanic waters. Our findings provide an important constraint on the role of the Amazon plume in creating distinct niches and roles for diazotrophs in the nutrient and carbon budgets of the western tropical North Atlantic.
12
Wu, Xue, Sabine Griessbach, and Lars Hoffmann. "Equatorward dispersion of a high-latitude volcanic plume and its relation to the Asian summer monsoon: a case study of the Sarychev eruption in 2009." Atmospheric Chemistry and Physics 17, no. 21 (November 13, 2017): 13439–55. http://dx.doi.org/10.5194/acp-17-13439-2017.
Анотація:
Abstract. Tropical volcanic eruptions have been widely studied for their significant contribution to stratospheric aerosol loading and global climate impacts, but the impact of high-latitude volcanic eruptions on the stratospheric aerosol layer is not clear and the pathway of transporting aerosol from high latitudes to the tropical stratosphere is not well understood. In this work, we focus on the high-latitude volcano Sarychev (48.1° N, 153.2° E), which erupted in June 2009, and the influence of the Asian summer monsoon (ASM) on the equatorward dispersion of the volcanic plume. First, the sulfur dioxide (SO2) emission time series and plume height of the Sarychev eruption are estimated with SO2 observations of the Atmospheric Infrared Sounder (AIRS) and a backward trajectory approach using the Lagrangian particle dispersion model Massive–Parallel Trajectory Calculations (MPTRAC). Then, the transport and dispersion of the plume are simulated using the derived SO2 emission time series. The transport simulations are compared with SO2 observations from AIRS and validated with aerosol observations from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). The MPTRAC simulations show that about 4 % of the sulfur emissions were transported to the tropical stratosphere within 50 days after the beginning of the eruption, and the plume dispersed towards the tropical tropopause layer (TTL) through isentropic transport above the subtropical jet. The MPTRAC simulations and MIPAS aerosol data both show that between the potential temperature levels of 360 and 400 K, the equatorward transport was primarily driven by anticyclonic Rossby wave breaking enhanced by the ASM in boreal summer. The volcanic plume was entrained along the anticyclone flows and reached the TTL as it was transported southwestwards into the deep tropics downstream of the anticyclone. Further, the ASM anticyclone influenced the pathway of aerosols by isolating an aerosol hole inside of the ASM, which was surrounded by aerosol-rich air outside. This transport barrier was best indicated using the potential vorticity gradient approach. Long-term MIPAS aerosol detections show that after entering the TTL, aerosol from the Sarychev eruption remained in the tropical stratosphere for about 10 months and ascended slowly. The ascent speed agreed well with the ascent speed of the water vapor tape recorder. Furthermore, a hypothetical MPTRAC simulation for a wintertime eruption was carried out. It is shown that under winter atmospheric circulations, the equatorward transport of the plume would be suppressed by the strong subtropical jet and weak wave breaking events. In this hypothetical scenario, a high-latitude volcanic eruption would not be able to contribute to the tropical stratospheric aerosol layer.
13
Wu, Xue, Sabine Griessbach, and Lars Hoffmann. "Long-range transport of volcanic aerosol from the 2010 Merapi tropical eruption to Antarctica." Atmospheric Chemistry and Physics 18, no. 21 (November 6, 2018): 15859–77. http://dx.doi.org/10.5194/acp-18-15859-2018.
Анотація:
Abstract. Volcanic sulfate aerosol is an important source of sulfur for Antarctica, where other local sources of sulfur are rare. Midlatitude and high-latitude volcanic eruptions can directly influence the aerosol budget of the polar stratosphere. However, tropical eruptions can also enhance polar aerosol load following long-range transport. In the present work, we analyze the volcanic plume of a tropical eruption, Mount Merapi in 2010, and investigate the transport pathway of the volcanic aerosol from the tropical tropopause layer (TTL) to the lower stratosphere over Antarctica. We use the Lagrangian particle dispersion model Massive-Parallel Trajectory Calculations (MPTRAC) and Atmospheric Infrared Sounder (AIRS) SO2 measurements to reconstruct the altitude-resolved SO2 injection time series during the explosive eruption period and simulate the transport of the volcanic plume using the MPTRAC model. AIRS SO2 and aerosol measurements, the aerosol cloud index values provided by Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), are used to verify and complement the simulations. The Lagrangian transport simulation of the volcanic plume is compared with MIPAS aerosol measurements and shows good agreement. Both the simulations and the observations presented in this study suggest that volcanic plumes from the Merapi eruption were transported to the south of 60∘ S 1 month after the eruption and even further to Antarctica in the following months. This relatively fast meridional transport of volcanic aerosol was mainly driven by quasi-horizontal mixing from the TTL to the extratropical lower stratosphere, and most of the quasi-horizontal mixing occurred between the isentropic surfaces of 360 to 430 K. When the plume went to Southern Hemisphere high latitudes, the polar vortex was displaced from the South Pole, so that the volcanic plume was carried to the South Pole without penetrating the polar vortex. Although only 4 % of the sulfur injected by the Merapi eruption was transported into the lower stratosphere south of 60∘ S, the Merapi eruption contributed up to 8800 t of sulfur to the Antarctic lower stratosphere. This indicates that the long-range transport under favorable meteorological conditions enables a moderate tropical volcanic eruption to be an important remote source of sulfur for the Antarctic stratosphere.
14
Knippertz, Peter. "Tropical–Extratropical Interactions Associated with an Atlantic Tropical Plume and Subtropical Jet Streak." Monthly Weather Review 133, no. 9 (September 1, 2005): 2759–76. http://dx.doi.org/10.1175/mwr2999.1.
Анотація:
Abstract Tropical plumes (TPs) are elongated bands of upper- and midlevel clouds stretching from the Tropics poleward and eastward into the subtropics, typically accompanied by a subtropical jet (STJ) streak and a trough on their poleward side. This study uses ECMWF analyses and high-resolution University of Wisconsin–Nonhydrostatic Modeling System trajectories to analyze the multiscale complex tropical–extratropical interactions involved in the genesis of a pronounced TP and STJ over the NH Atlantic Ocean in late March 2002 that was associated with extreme precipitation in arid northwest Africa. Previous concepts for TP genesis from the literature are discussed in the light of this case study. Analysis of the upper-level flow prior to the TP formation shows a northeastward propagation and a continuous acceleration of the STJ over the Atlantic Ocean equatorward of a positively tilted upper-level trough to the west of northwest Africa. Both dynamic and advective processes contribute to the generation of the accompanying cloud band. The northern portion of the TP consists of parcels that exit a strong STJ streak over North America, enter the deep Tropics over South America, and then accelerate into the Atlantic STJ, accompanied by strong cross-jet ageostrophic motions, rising, and cloud formation. The southern portion is formed by parcels originating in the divergent outflow from strong near-equatorial convection accompanying the TP genesis. A local increase in the Hadley overturning is found over the tropical Atlantic and east Pacific/South America and appears to be related to low inertial stability at the outflow level and to low-level trade surges associated with the cold advection, sinking, and lower-level divergence underneath two strong upper-level convergence centers in the eastern portions of both a subtropical ridge over North America and an extratropical ridge over the North Atlantic Ocean. Evidence is presented that the convective response lags the trade surge by several days.
15
Gonzalez-Alonso, Laura, Maria Val Martin, and Ralph A. Kahn. "Biomass-burning smoke heights over the Amazon observed from space." Atmospheric Chemistry and Physics 19, no. 3 (February 8, 2019): 1685–702. http://dx.doi.org/10.5194/acp-19-1685-2019.
Анотація:
Abstract. We characterise the vertical distribution of biomass-burning emissions across the Amazon during the biomass-burning season (July–November) with an extensive climatology of smoke plumes derived from MISR and MODIS (2005–2012) and CALIOP (2006–2012) observations. Smoke plume heights exhibit substantial variability, spanning a few hundred metres up to 6 km above the terrain. However, the majority of the smoke is located at altitudes below 2.5 km. About 60 % of smoke plumes are observed in drought years, 40 %–50 % at the peak month of the burning season (September) and 94 % over tropical forest and savanna regions, with respect to the total number of smoke plume observations. At the time of the MISR observations (10:00–11:00 LT), the highest plumes are detected over grassland fires (with an averaged maximum plume height of ∼1100 m) and the lowest plumes occur over tropical forest fires (∼800 m). A similar pattern is found later in the day (14:00–15:00 LT) with CALIOP, although at higher altitudes (2300 m grassland vs. 2000 m tropical forest), as CALIOP typically detects smoke at higher altitudes due to its later overpass time, associated with a deeper planetary boundary layer, possibly more energetic fires, and greater sensitivity to thin aerosol layers. On average, 3 %–20 % of the fires inject smoke into the free troposphere; this percentage tends to increase toward the end of the burning season (November: 15 %–40 %). We find a well-defined seasonal cycle between MISR plume heights, MODIS fire radiative power and atmospheric stability across the main biomes of the Amazon, with higher smoke plumes, more intense fires and reduced atmospheric stability conditions toward the end of the burning season. Lower smoke plume heights are detected during drought (800 m) compared to non-drought (1100 m) conditions, in particular over tropical forest and savanna fires. Drought conditions favour understory fires over tropical forest, which tend to produce smouldering combustion and low smoke injection heights. Droughts also seem to favour deeper boundary layers and the percentage of smoke plumes that reach the free troposphere is lower during these dry conditions. Consistent with previous studies, the MISR mid-visible aerosol optical depth demonstrates that smoke makes a significant contribution to the total aerosol loading over the Amazon, which in combination with lower injection heights in drought periods has important implications for air quality. This work highlights the importance of biome type, fire properties and atmospheric and drought conditions for plume dynamics and smoke loading. In addition, our study demonstrates the value of combining observations of MISR and CALIOP constraints on the vertical distribution of smoke from biomass burning over the Amazon.
16
Schiro, Kathleen A., J. David Neelin, David K. Adams, and Benjamin R. Lintner. "Deep Convection and Column Water Vapor over Tropical Land versus Tropical Ocean: A Comparison between the Amazon and the Tropical Western Pacific." Journal of the Atmospheric Sciences 73, no. 10 (September 23, 2016): 4043–63. http://dx.doi.org/10.1175/jas-d-16-0119.1.
Анотація:
Abstract The relationships between the onset of tropical deep convection, column water vapor (CWV), and other measures of conditional instability are analyzed with 2 yr of data from the DOE Atmospheric Radiation Measurement (ARM) Mobile Facility in Manacapuru, Brazil, as part of the Green Ocean Amazon (GOAmazon) campaign, and with 3.5 yr of CWV derived from global positioning system meteorology at a nearby site in Manaus, Brazil. Important features seen previously in observations over tropical oceans—precipitation conditionally averaged by CWV exhibiting a sharp pickup at high CWV, and the overall shape of the CWV distribution for both precipitating and nonprecipitating points—are also found for this tropical continental region. The relationship between rainfall and CWV reflects the impact of lower-free-tropospheric moisture variability on convection. Specifically, CWV over land, as over ocean, is a proxy for the effect of free-tropospheric moisture on conditional instability as indicated by entraining plume calculations from GOAmazon data. Given sufficient mixing in the lower troposphere, higher CWV generally results in greater plume buoyancies through a deep convective layer. Although sensitivity of buoyancy to other controls in the Amazon is suggested, such as boundary layer and microphysical processes, the CWV dependence is consistent with the observed precipitation onset. Overall, leading aspects of the relationship between CWV and the transition to deep convection in the Amazon have close parallels over tropical oceans. The relationship is robust to averaging on time and space scales appropriate for convective physics but is strongly smoothed for averages greater than 3 h or 2.5°.
17
Chu, Wenchao, Yanluan Lin, and Ming Zhao. "Implementation and Evaluation of a Double-Plume Convective Parameterization in NCAR CAM5." Journal of Climate 35, no. 2 (January 15, 2022): 617–37. http://dx.doi.org/10.1175/jcli-d-21-0267.1.
Анотація:
Abstract Performance of global climate models (GCMs) is strongly affected by the cumulus parameterization (CP) used. Similar to the approach in GFDL AM4, a double-plume CP, which unifies the deep and shallow convection in one framework, is implemented and tested in the NCAR Community Atmospheric Model version 5 (CAM5). Based on the University of Washington (UW) shallow convection scheme, an additional plume was added to represent the deep convection. The shallow and deep plumes share the same cloud model, but use different triggers, fractional mixing rates, and closures. The scheme was tested in single-column, short-term hindcast, and AMIP simulations. Compared with the default combination of the Zhang–McFarlane scheme and UW scheme in CAM5, the new scheme tends to produce a top-heavy mass flux profile during the active monsoon period in the single-column simulations. The scheme increases the intensity of tropical precipitation, closer to TRMM observations. The new scheme increased subtropical marine boundary layer clouds and high clouds over the deep tropics, both in better agreement with observations. Sensitivity tests indicate that regime-dependent fractional entrainment rates of the deep plume are desired to improve tropical precipitation distribution and upper troposphere temperature. This study suggests that a double-plume approach is a promising way to combine shallow and deep convections in a unified framework.
18
Zhou, Wenyu, and Shang-Ping Xie. "A Conceptual Spectral Plume Model for Understanding Tropical Temperature Profile and Convective Updraft Velocities." Journal of the Atmospheric Sciences 76, no. 9 (August 27, 2019): 2801–14. http://dx.doi.org/10.1175/jas-d-18-0330.1.
Анотація:
Abstract The tropical tropospheric temperature is close to but typically cooler than that of the moist adiabat. The negative temperature deviation from the moist adiabat manifests a C-shape profile and is projected to increase and stretch upward under warming in both comprehensive climate models and idealized radiative–convective equilibrium (RCE) simulations. The increased temperature deviation corresponds to a larger convective available potential energy (CAPE) under warming. The extreme convective updraft velocity in RCE increases correspondingly but at a smaller fractional rate than that of CAPE. A conceptual model for the tropical temperature deviation and convective updraft velocities is formulated to understand these features. The model builds on the previous zero-buoyancy model but replaces the bulk zero-buoyancy plume by a spectrum of entraining plumes that have distinct entrainment rates and are positively buoyant until their levels of neutral buoyancy. Besides the negative temperature deviation and its increasing magnitude with warming, this allows the spectral plume model to further predict the C-shape profile as well as its upward stretch with warming. By representing extreme convective updrafts as weakly entraining plumes, the model is able to reproduce the smaller fractional increase in convective velocities with warming as compared to that of CAPE. The smaller fractional increase is mainly caused by the upward stretch in the temperature deviation profile with warming, which reduces the ratio between the integrated plume buoyancy and CAPE. The model thus provides a useful tool for understanding the tropical temperature profile and convective updraft velocities.
19
Rudzin, Johna E., Lynn K. Shay, and Benjamin Jaimes de la Cruz. "The Impact of the Amazon–Orinoco River Plume on Enthalpy Flux and Air–Sea Interaction within Caribbean Sea Tropical Cyclones." Monthly Weather Review 147, no. 3 (March 1, 2019): 931–50. http://dx.doi.org/10.1175/mwr-d-18-0295.1.
Анотація:
Abstract The influence of the Amazon–Orinoco River plume in the Caribbean Sea on latent and sensible heat flux (enthalpy flux) and tropical cyclone (TC) intensity is investigated for Hurricanes Ivan (2004), Emily (2005), Dean (2007), and Felix (2007) using dropwindsonde data, satellite sea surface temperature (SST), and the SMARTS climatology. Relationships among enthalpy fluxes, ocean heat content relative to the 26°C isotherm depth (OHC), and SST during storm passage are diagnosed. Results indicate that sea surface cooling in the river plume, a low-OHC region, is comparable to that in the warm eddy region, which has high OHC. An isothermal layer heat budget shows that upper-ocean cooling in the river plume can be explained predominantly by sea-to-air heat flux, rather than by entrainment flux from the thermocline. The latter two findings suggest that relatively large upper-ocean stratification in the plume regime limited entrainment cooling, sustaining SST and enthalpy flux. Inspection of atmospheric variables indicates that deep moderate wind shear is prevalent, and equivalent potential temperature is enhanced over the river plume region for most of these storms. Thus, sustained surface fluxes in this region may have provided warm, moist boundary layer conditions, which may have helped these storms to rapidly intensify even over relatively low-OHC waters and moderate shear. These findings are important because several Caribbean Sea TCs, including these cases, have been underforecast with respect to intensity and/or rapid intensifications, yet minimal upper-ocean observations exist to understand air–sea interaction during TCs in the salinity-stratified Amazon–Orinoco plume regime.
20
Stanichny, Sergey V., Elena A. Kubryakova, and Arseny A. Kubryakov. "Quasi-tropical cyclone caused anomalous autumn coccolithophore bloom in the Black Sea." Biogeosciences 18, no. 10 (May 26, 2021): 3173–88. http://dx.doi.org/10.5194/bg-18-3173-2021.
Анотація:
Abstract. A quasi-tropical cyclone (QTC) observed over the Black Sea on 25–29 September 2005 caused an exceptionally strong anomalous autumn coccolithophore bloom that lasted for more than 1.5 months. The QTC induced intense upwelling, causing a decrease in sea surface temperature of 15 ∘C and an acceleration of the cyclonic Rim Current up to extreme values of 0.75 m s−1. The Rim Current transported nutrient-rich Danube plume waters from the northwestern shelf to the zone of the cyclone action. Baroclinic instabilities of the plume boundary caused intense submesoscale processes, accompanied by mixing of the shelf and upwelling of the waters. These processes triggered the initial growth of remote sensing reflectance (Rrs) on the offshore front of the plume, indicating the beginning of the coccolithophore bloom. Furthermore, the bloom shifted to the zone of the strongest upwelling in the western cyclonic gyre. Intense vertical entrainment of nutrients in this area caused the increase in chlorophyll a concentration (Chl), which was then followed by a strong bloom of coccolithophores. Advection by the Rim Current spread the bloom over the entire southern part of the Black Sea, more than 1000 km from its initial source. A month after the QTC action, Rrs in these areas reached a value of 0.018 sr−1, corresponding to an estimate of a coccolithophore concentration of 107 cells per liter.
21
Cheng, Peng, Ming Li, and Yun Li. "Generation of an estuarine sediment plume by a tropical storm." Journal of Geophysical Research: Oceans 118, no. 2 (February 2013): 856–68. http://dx.doi.org/10.1002/jgrc.20070.
22
Varona, H. L., D. Veleda, M. Silva, M. Cintra, and M. Araujo. "Amazon River plume influence on Western Tropical Atlantic dynamic variability." Dynamics of Atmospheres and Oceans 85 (March 2019): 1–15. http://dx.doi.org/10.1016/j.dynatmoce.2018.10.002.
23
Yokelson, R. J., T. Karl, P. Artaxo, D. R. Blake, T. J. Christian, D. W. T. Griffith, A. Guenther, and W. M. Hao. "The Tropical Forest and Fire Emissions Experiment: overview and airborne fire emission factor measurements." Atmospheric Chemistry and Physics 7, no. 19 (October 9, 2007): 5175–96. http://dx.doi.org/10.5194/acp-7-5175-2007.
Анотація:
Abstract. The Tropical Forest and Fire Emissions Experiment (TROFFEE) used laboratory measurements followed by airborne and ground based field campaigns during the 2004 Amazon dry season to quantify the emissions from pristine tropical forest and several plantations as well as the emissions, fuel consumption, and fire ecology of tropical deforestation fires. The airborne campaign used an Embraer 110B aircraft outfitted with whole air sampling in canisters, mass-calibrated nephelometry, ozone by UV absorbance, Fourier transform infrared spectroscopy (FTIR), and proton-transfer mass spectrometry (PTR-MS) to measure PM10, O3, CO2, CO, NO, NO2, HONO, HCN, NH3, OCS, DMS, CH4, and up to 48 non-methane organic compounds (NMOC). The Brazilian smoke/haze layers extended to 2–3 km altitude, which is much lower than the 5–6 km observed at the same latitude, time of year, and local time in Africa in 2000. Emission factors (EF) were computed for the 19 tropical deforestation fires sampled and they largely compare well to previous work. However, the TROFFEE EF are mostly based on a much larger number of samples than previously available and they also include results for significant emissions not previously reported such as: nitrous acid, acrylonitrile, pyrrole, methylvinylketone, methacrolein, crotonaldehyde, methylethylketone, methylpropanal, "acetol plus methylacetate," furaldehydes, dimethylsulfide, and C1-C4 alkyl nitrates. Thus, we recommend these EF for all tropical deforestation fires. The NMOC emissions were ~80% reactive, oxygenated volatile organic compounds (OVOC). Our EF for PM10 (17.8±4 g/kg) is ~25% higher than previously reported for tropical forest fires and may reflect a trend towards, and sampling of, larger fires than in earlier studies. A large fraction of the total burning for 2004 likely occurred during a two-week period of very low humidity. The combined output of these fires created a massive "mega-plume" >500 km across that we sampled on 8 September. The mega-plume contained high PM10 and 10–50 ppbv of many reactive species such as O3, NH3, NO2, CH3OH, and organic acids. This is an intense and globally important chemical processing environment that is still poorly understood. The mega-plume or "white ocean" of smoke covered a large area in Brazil, Bolivia, and Paraguay for about one month. The smoke was transported >2000 km to the southeast while remaining concentrated enough to cause a 3–4-fold increase in aerosol loading in the São Paulo area for several days.
24
Yokelson, R. J., T. Karl, P. Artaxo, D. R. Blake, T. J. Christian, D. W. T. Griffith, A. Guenther, and W. M. Hao. "The Tropical Forest and fire emissions experiment: overview and airborne fire emission factor measurements." Atmospheric Chemistry and Physics Discussions 7, no. 3 (May 23, 2007): 6903–58. http://dx.doi.org/10.5194/acpd-7-6903-2007.
Анотація:
Abstract. The Tropical Forest and Fire Emissions Experiment (TROFFEE) used laboratory measurements followed by airborne and ground based field campaigns during the 2004 Amazon dry season to quantify the emissions from pristine tropical forest and several plantations as well as the emissions, fuel consumption, and fire ecology of tropical deforestation fires. The airborne campaign used an Embraer 110B aircraft outfitted with whole air sampling in canisters, mass-calibrated nephelometry, ozone by uv absorbance, Fourier transform infrared spectroscopy (FTIR), and proton-transfer mass spectrometry (PTR-MS) to measure PM10, O3, CO2, CO, NO, NO2, HONO, HCN, NH3, OCS, DMS, CH4, and up to 48 non-methane organic compounds (NMOC). The Brazilian smoke/haze layers extended to 2–3 km altitude, which is much lower than the 5–6 km observed at the same latitude, time of year, and local time in Africa in 2000. Emission factors (EF) were computed for the 19 tropical deforestation fires sampled and they largely compare well to previous work. However, the TROFFEE EF are mostly based on a much larger number of samples than previously available and they also include results for significant emissions not previously reported such as: nitrous acid, acrylonitrile, pyrrole, methylvinylketone, methacrolein, crotonaldehyde, methylethylketone, methylpropanal, "acetol plus methylacetate," furaldehydes, dimethylsulfide, and C1-C4 alkyl nitrates. Thus, we recommend these EF for all tropical deforestation fires. The NMOC emissions were ~80% reactive, oxygenated volatile organic compounds (OVOC). Our EF for PM10 (17.8±4 g/kg) is ~25% higher than previously reported for tropical forest fires and may reflect a trend towards, and sampling of, larger fires than in earlier studies. A large fraction of the total burning for 2004 likely occurred during a two-week period of very low humidity. The combined output of these fires created a massive "mega-plume" >500 km across that we sampled on September 8. The mega-plume contained high PM10 and 10–50 ppbv of many reactive species such as O3, NH3, NO2, CH3OH, and organic acids. This is an intense and globally important chemical processing environment that is still poorly understood. The mega-plume or "white ocean" of smoke covered a large area in Brazil, Bolivia, and Paraguay for about one month. The smoke was transported >2000 km to the southeast while remaining concentrated enough to cause a 3-4-fold increase in aerosol loading in the São Paulo area for several days.
25
Y GOYA, SAMARA CAZZOLI, MOYSÉS GONSALEZ TESSLER, and MARCELO RODRIGUES. "Caracterização do Transporte Sedimentar Litorâneo junto à foz do Rio Itanhaém sob ação do Anticiclone Tropical Continental e dos Ciclones Extra-Tropicais." Pesquisas em Geociências 28, no. 2 (December 31, 2001): 141. http://dx.doi.org/10.22456/1807-9806.20280.
Анотація:
The study of the shore and beach environment is one of the most investigated issues in the last decades on the Brazilian coast. This kind of research involves scientists from several areas due to the large amount of variables interfering into this kind of environment. Meteorological studies, for instance are essential to the comprehension of beach evolution. The foreshore is the less known compartment among the existent beach compartment in such terms of complexity and difficulty that involves this kind of study. This work had as objective the monitoring of the foreshore under the influence of the Continental Tropical Anticyclone (ATC). The monitoring was made in the region of Itanhaém, central coast of São Paulo state. Near the outlet of Itanhaém River suspension material were collected and profiles of currentmetry and thermosalinometry were made. The meteorological specifications were obtained from properly literature. The observation of waves was done visually. The results showed that the ATC effects were punctual, causing the increase of the local rainfall without change of the incident wave trains characteristics. The plume of suspended material was inducted by the river discharge due to the rains, causing the increasing of the transport capacity from Itanhaém River.
26
McFarlane, Sally A., Charles N. Long, and Donna M. Flynn. "Impact of Island-Induced Clouds on Surface Measurements: Analysis of the ARM Nauru Island Effect Study Data." Journal of Applied Meteorology 44, no. 7 (July 1, 2005): 1045–65. http://dx.doi.org/10.1175/jam2241.1.
Анотація:
Abstract An Atmospheric Radiation and Cloud Station (ARCS) was established on the island of Nauru by the Atmospheric Radiation Measurement (ARM) Program. Analysis of the Nauru99 field experiment data indicated that measurements at the ARCS were affected by a cloud plume that was induced by diurnal heating of the island. During the Nauru Island Effects Study, instrumentation was installed at a second site to develop criteria for identifying when the cloud plume occurs and to quantify its effect on ARCS measurements. The plume directional heading and frequency of occurrence are affected by the large-scale tropical circulation. During the present study, in which an El Niño was developing, Nauru was in a region of active convection, and easterly trade winds were not dominant; plumes were observed in 25% of satellite images, and only one-half of the observed plumes were downwind of the ARCS site. Surface wind direction, surface air temperature, and downwelling solar radiation at the two sites were used to identify periods when the cloud plume affected surface measurements. Differences in low-cloud frequency and surface radiation between plume-affected and non-plume-affected periods were examined. Existence of the cloud plume increased the average low-cloud frequency of occurrence from 20% to 35%, decreased the average downwelling shortwave radiation by 50–60 W m−2, and increased the average downwelling longwave radiation by 5–10 W m−2. Installing a suite of surface meteorological instruments and a global shortwave radiometer at a second site will allow for the long-term quantification of the cloud plume effect on the radiation field at the ARCS site.
27
Pohl, K., M. Cantwell, P. Herckes, and R. Lohmann. "Black carbon concentrations and sources in the marine boundary layer of the tropical Atlantic Ocean using four methodologies." Atmospheric Chemistry and Physics 14, no. 14 (July 18, 2014): 7431–43. http://dx.doi.org/10.5194/acp-14-7431-2014.
Анотація:
Abstract. Combustion-derived aerosols in the marine boundary layer have been poorly studied, especially in remote environments such as the open Atlantic Ocean. The tropical Atlantic has the potential to contain a high concentration of aerosols, such as black carbon, due to the African emission plume of biomass and agricultural burning products. Atmospheric particulate matter samples across the tropical Atlantic boundary layer were collected in the summer of 2010 during the southern hemispheric dry season when open fire events were frequent in Africa and South America. The highest black carbon concentrations were detected in the Caribbean Sea and within the African plume, with a regional average of 0.6 μg m−3 for both. The lowest average concentrations were measured off the coast of South America at 0.2 to 0.3 μg m−3. Samples were quantified for black carbon using multiple methods to provide insights into the form and stability of the carbonaceous aerosols (i.e., thermally unstable organic carbon, soot like, and charcoal like). Soot-like aerosols composed up to 45% of the carbonaceous aerosols in the Caribbean Sea to as little as 4% within the African plume. Charcoal-like aerosols composed up to 29% of the carbonaceous aerosols over the oligotrophic Sargasso Sea, suggesting that non-soot-like particles could be present in significant concentrations in remote environments. To better apportion concentrations and forms of black carbon, multiple detection methods should be used, particularly in regions impacted by biomass burning emissions.
28
Mecikalski, John R., and Gregory J. Tripoli. "Inertial Available Kinetic Energy and the Dynamics of Tropical Plume Formation." Monthly Weather Review 126, no. 8 (August 1998): 2200–2216. http://dx.doi.org/10.1175/1520-0493(1998)126<2200:iakeat>2.0.co;2.
29
de Santana, Claudeilton Severino, Simone Maria de Albuquerque Lira, Humberto L. Varona, Sigrid Neumann-Leitão, Moacyr Araujo, and Ralf Schwamborn. "Amazon river plume influence on planktonic decapods in the tropical Atlantic." Journal of Marine Systems 212 (December 2020): 103428. http://dx.doi.org/10.1016/j.jmarsys.2020.103428.
30
Nara, Hideki, Hiroshi Tanimoto, Yukihiro Nojiri, Hitoshi Mukai, Jiye Zeng, Yasunori Tohjima, and Toshinobu Machida. "CO emissions from biomass burning in South-east Asia in the 2006 El Niño year: shipboard and AIRS satellite observations." Environmental Chemistry 8, no. 2 (2011): 213. http://dx.doi.org/10.1071/en10113.
Анотація:
Environmental contextAtmospheric carbon monoxide greatly affects the abundance of environmentally important gases, including methane, hydrochlorofluorocarbons and tropospheric ozone. We present evidence for episodes of CO pollution over the tropical Pacific Ocean resulting from intensive biomass burning in South-east Asia and Northern Australia during the 2006 El Niño year. We discuss the locations of the CO emissions and their long-range transport. AbstractBiomass burning is often associated with climate oscillations. For example, biomass burning in South-east Asia is strongly linked to El Niño–southern oscillation activity. During October and November of the 2006 El Niño year, a substantial increase in CO mixing ratios was detected over the Western tropical Pacific Ocean by shipboard observations routinely operated between Japan and Australia and New Zealand. Combining in-situ measurements, satellite observations, and an air trajectory model simulation, two high CO episodes were identified originating from biomass burning in Borneo, Sumatra, New Guinea, and Northern Australia. Between 15°N and the Equator, marked CO enhancements were encountered associated with a significant correlation between CO and CO2 and between CO and O3. The ΔCO/ΔCO2 ratio observed in the fire plume was considerably high (171 ppbv ppmv–1), suggesting substantial contributions from peat soil burning in Indonesia. In contrast, the ΔO3/ΔCO ratio was only 0.05 ppbv ppbv–1, indicating that net photochemical production of O3 in the plume was negligible during long-range transport in the lower troposphere over the Western tropical North Pacific.
31
Moura, Rodrigo L., Gilberto M. Amado-Filho, Fernando C. Moraes, Poliana S. Brasileiro, Paulo S. Salomon, Michel M. Mahiques, Alex C. Bastos, et al. "An extensive reef system at the Amazon River mouth." Science Advances 2, no. 4 (April 2016): e1501252. http://dx.doi.org/10.1126/sciadv.1501252.
Анотація:
Large rivers create major gaps in reef distribution along tropical shelves. The Amazon River represents 20% of the global riverine discharge to the ocean, generating up to a 1.3 × 106–km2plume, and extensive muddy bottoms in the equatorial margin of South America. As a result, a wide area of the tropical North Atlantic is heavily affected in terms of salinity, pH, light penetration, and sedimentation. Such unfavorable conditions were thought to imprint a major gap in Western Atlantic reefs. We present an extensive carbonate system off the Amazon mouth, underneath the river plume. Significant carbonate sedimentation occurred during lowstand sea level, and still occurs in the outer shelf, resulting in complex hard-bottom topography. A permanent near-bottom wedge of ocean water, together with the seasonal nature of the plume’s eastward retroflection, conditions the existence of this extensive (~9500 km2) hard-bottom mosaic. The Amazon reefs transition from accretive to erosional structures and encompass extensive rhodolith beds. Carbonate structures function as a connectivity corridor for wide depth–ranging reef-associated species, being heavily colonized by large sponges and other structure-forming filter feeders that dwell under low light and high levels of particulates. The oxycline between the plume and subplume is associated with chemoautotrophic and anaerobic microbial metabolisms. The system described here provides several insights about the responses of tropical reefs to suboptimal and marginal reef-building conditions, which are accelerating worldwide due to global changes.
32
Liao, Xiaomei, Yan Du, Tianyu Wang, Shuibo Hu, Haigang Zhan, Huizeng Liu, and Guofeng Wu. "High-Frequency Variations in Pearl River Plume Observed by Soil Moisture Active Passive Sea Surface Salinity." Remote Sensing 12, no. 3 (February 8, 2020): 563. http://dx.doi.org/10.3390/rs12030563.
Анотація:
River plumes play an important role in the cross-margin transport of phytoplankton and nutrients, which have profound impacts on coastal ecosystems. Using recently available Soil Moisture Active Passive (SMAP) sea surface salinity (SSS) data and high-resolution ocean color products, this study investigated summertime high-frequency variations in the Pearl River plume of China and its biological response. The SMAP SSS captures the intraseasonal oscillations in the offshore transport of the Pearl River plume well, which has distinct 30–60 day variations from mid-May to late September. The offshore transport of freshwater varies concurrently with southwesterly wind anomalies and is roughly in phase with the Madden–Julian Oscillation (MJO) index in phases 1–5, thus implying that the MJO exerts a significant influence. During MJO phases 1–2, the southwest wind anomalies in the northeastern South China Sea (SCS) enhanced cross-shore Ekman transport, while the northeast wind anomalies during MJO phases 3–5 favored the subsequent southwestward transport of the plume. The high chlorophyll-a concentration coincided well with the low-salinity water variations, emphasizing the important role of the offshore transport of the Pearl River plume in sustaining biological production over the oligotrophic northern SCS. The strong offshore transport of the plume in June 2015 clearly revealed that the proximity of a cyclonic eddy plays a role in the plume’s dispersal pathway. In addition, heavy rainfall related to the landfall of tropical cyclones in the Pearl River Estuary region contributed to the episodic offshore transport of the plume.
33
Holloway, Christopher E., and J. David Neelin. "Moisture Vertical Structure, Column Water Vapor, and Tropical Deep Convection." Journal of the Atmospheric Sciences 66, no. 6 (June 1, 2009): 1665–83. http://dx.doi.org/10.1175/2008jas2806.1.
Анотація:
Abstract The vertical structure of the relationship between water vapor and precipitation is analyzed in 5 yr of radiosonde and precipitation gauge data from the Nauru Atmospheric Radiation Measurement (ARM) site. The first vertical principal component of specific humidity is very highly correlated with column water vapor (CWV) and has a maximum of both total and fractional variance captured in the lower free troposphere (around 800 hPa). Moisture profiles conditionally averaged on precipitation show a strong association between rainfall and moisture variability in the free troposphere and little boundary layer variability. A sharp pickup in precipitation occurs near a critical value of CWV, confirming satellite-based studies. A lag–lead analysis suggests it is unlikely that the increase in water vapor is just a result of the falling precipitation. To investigate mechanisms for the CWV–precipitation relationship, entraining plume buoyancy is examined in sonde data and simplified cases. For several different mixing schemes, higher CWV results in progressively greater plume buoyancies, particularly in the upper troposphere, indicating conditions favorable for deep convection. All other things being equal, higher values of lower-tropospheric humidity, via entrainment, play a major role in this buoyancy increase. A small but significant increase in subcloud layer moisture with increasing CWV also contributes to buoyancy. Entrainment coefficients inversely proportional to distance from the surface, associated with mass flux increase through a deep lower-tropospheric layer, appear promising. These yield a relatively even weighting through the lower troposphere for the contribution of environmental water vapor to midtropospheric buoyancy, explaining the association of CWV and buoyancy available for deep convection.
34
Nugent, Alison D., Ronald B. Smith, and Justin R. Minder. "Wind Speed Control of Tropical Orographic Convection." Journal of the Atmospheric Sciences 71, no. 7 (June 20, 2014): 2695–712. http://dx.doi.org/10.1175/jas-d-13-0399.1.
Анотація:
Abstract This study compares observations from the Dominica Experiment (DOMEX) field campaign with 3D and 2D Weather Research and Forecasting Model (WRF) simulations to understand how ambient upstream wind speed controls the transition from thermally to mechanically forced moist orographic convection. The environment is a conditionally unstable, tropical atmosphere with shallow trade wind cumulus clouds. Three flow indices are defined to quantify the convective transition: horizontal divergence aloft, cloud location, and island surface temperature. As wind speed increases, horizontal airflow divergence from plume detrainment above the mountain changes to convergence associated with plunging flow, convective clouds relocate from the leeward to the windward side of the mountain as mechanically triggered convection takes over, and the daytime mountaintop temperature decreases because of increased ventilation and cloud shading. Possible mechanisms by which wind speed controls island precipitation are also discussed. The result is a clearer understanding of orographic convection in the tropics.
35
Martin, S. T., P. Artaxo, L. Machado, A. O. Manzi, R. A. F. Souza, C. Schumacher, J. Wang, et al. "The Green Ocean Amazon Experiment (GoAmazon2014/5) Observes Pollution Affecting Gases, Aerosols, Clouds, and Rainfall over the Rain Forest." Bulletin of the American Meteorological Society 98, no. 5 (May 1, 2017): 981–97. http://dx.doi.org/10.1175/bams-d-15-00221.1.
Анотація:
Abstract The Observations and Modeling of the Green Ocean Amazon 2014–2015 (GoAmazon2014/5) experiment took place around the urban region of Manaus in central Amazonia across 2 years. The urban pollution plume was used to study the susceptibility of gases, aerosols, clouds, and rainfall to human activities in a tropical environment. Many aspects of air quality, weather, terrestrial ecosystems, and climate work differently in the tropics than in the more thoroughly studied temperate regions of Earth. GoAmazon2014/5, a cooperative project of Brazil, Germany, and the United States, employed an unparalleled suite of measurements at nine ground sites and on board two aircraft to investigate the flow of background air into Manaus, the emissions into the air over the city, and the advection of the pollution downwind of the city. Herein, to visualize this train of processes and its effects, observations aboard a low-flying aircraft are presented. Comparative measurements within and adjacent to the plume followed the emissions of biogenic volatile organic carbon compounds (BVOCs) from the tropical forest, their transformations by the atmospheric oxidant cycle, alterations of this cycle by the influence of the pollutants, transformations of the chemical products into aerosol particles, the relationship of these particles to cloud condensation nuclei (CCN) activity, and the differences in cloud properties and rainfall for background compared to polluted conditions. The observations of the GoAmazon2014/5 experiment illustrate how the hydrologic cycle, radiation balance, and carbon recycling may be affected by present-day as well as future economic development and pollution over the Amazonian tropical forest.
36
Tarya, A., M. van der Vegt, and A. J. F. Hoitink. "Wind forcing controls on river plume spreading on a tropical continental shelf." Journal of Geophysical Research: Oceans 120, no. 1 (January 2015): 16–35. http://dx.doi.org/10.1002/2014jc010456.
37
Matthews, Stuart, Jörg M. Hacker, Jason Cole, Jeffrey Hare, Charles N. Long, and R. Michael Reynolds. "Modification of the Atmospheric Boundary Layer by a Small Island: Observations from Nauru." Monthly Weather Review 135, no. 3 (March 1, 2007): 891–905. http://dx.doi.org/10.1175/mwr3319.1.
Анотація:
Abstract Nauru, a small island in the tropical Pacific, generates cloud plumes that may grow to over 100-km lengths. This study uses observations to examine the mesoscale disturbance of the marine atmospheric boundary layer by the island that produces these cloud plumes. Observations of the surface layer were made from two ships in the vicinity of Nauru and from instruments on the island. The structure of the atmospheric boundary layer over the island was investigated using aircraft flights. Cloud production over Nauru was examined using remote sensing instruments. The diurnal cycles of surface meteorology and radiation are characterized at a point near the west (downwind) coast of Nauru. The spatial variation of surface meteorology and radiation are also examined using surface and aircraft measurements. During the day, the island surface layer is warmer than the marine surface layer and wind speed is lower than over the ocean. Surface heating forces the growth of a thermal internal boundary layer, within which a plume of cumulus clouds forms. Cloud production begins early in the morning over the ocean near the island’s lee shore; as heating intensifies during the day, cloud production moves upwind over Nauru. These clouds form a plume that may extend over 100 km downwind of Nauru. Aircraft observations showed that a plume of warm, dry air develops over the island that extends 15–20 km downwind before dissipating. Limited observations suggest that the cloud plume may be sustained farther downwind of Nauru by a pair of convective rolls. Suggestions for further investigation of the cloud plume are made.
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Darbyshire, Eoghan, William T. Morgan, James D. Allan, Dantong Liu, Michael J. Flynn, James R. Dorsey, Sebastian J. O'Shea, et al. "The vertical distribution of biomass burning pollution over tropical South America from aircraft in situ measurements during SAMBBA." Atmospheric Chemistry and Physics 19, no. 9 (May 3, 2019): 5771–90. http://dx.doi.org/10.5194/acp-19-5771-2019.
Анотація:
Abstract. We examine processes driving the vertical distribution of biomass burning pollution following an integrated analysis of over 200 pollutant and meteorological profiles measured in situ during the South AMerican Biomass Burning Analysis (SAMBBA) field experiment. This study will aid future work examining the impact of biomass burning on weather, climate and air quality. During the dry season there were significant contrasts in the composition and vertical distribution of haze between western and eastern regions of tropical South America. Owing to an active or residual convective mixing layer, the aerosol abundance was similar from the surface to ∼1.5 km in the west and ∼3 km in the east. Black carbon mass loadings were double as much in the east (1.7 µg m−3) than the west (0.85 µg m−3), but aerosol scattering coefficients at 550 nm were similar (∼120 Mm−1), as too were CO near-surface concentrations (310–340 ppb). We attribute these contrasts to the more flaming combustion of Cerrado fires in the east and more smouldering combustion of deforestation and pasture fires in the west. Horizontal wind shear was important in inhibiting mixed layer growth and plume rise, in addition to advecting pollutants from the Cerrado regions into the remote tropical forest of central Amazonia. Thin layers above the mixing layer indicate the roles of both plume injection and shallow moist convection in delivering pollution to the lower free troposphere. However, detrainment of large smoke plumes into the upper free troposphere was very infrequently observed. Our results reiterate that thermodynamics control the pollutant vertical distribution and thus point to the need for correct model representation so that the spatial distribution and vertical structure of biomass burning smoke is captured. We observed an increase of aerosol abundance relative to CO with altitude both in the background haze and plume enhancement ratios. It is unlikely associated with thermodynamic partitioning, aerosol deposition or local non-fire sources. We speculate it may be linked to long-range transport from West Africa or fire combustion efficiency coupled to plume injection height. Further enquiry is required to explain the phenomenon and explore impacts on regional climate and air quality.
39
Salerno, G. G., C. Oppenheimer, V. I. Tsanev, A. J. Sutton, T. J. Roberts, and T. Elias. "Enhancement of the volcanogenic "bromine explosion" via reactive nitrogen chemistry (Kīlauea volcano, Hawai'i)." Atmospheric Chemistry and Physics Discussions 10, no. 4 (April 20, 2010): 10313–34. http://dx.doi.org/10.5194/acpd-10-10313-2010.
Анотація:
Abstract. Since the first detection of bromine monoxide in volcanic plumes attention has focused on the atmospheric synthesis and impact of volcanogenic reactive halogens. We report here new measurements of BrO in the volcanic plume emitted from Kīlauea volcano – the first time reactive halogens have been observed in emissions from a hotspot volcano. Observations were carried out by ground-based Differential Optical Absorption Spectroscopy in 2007 and 2008 at Pu'u'O'o crater, and at the 2008 magmatic vent that opened within Halema'uma'u crater. BrO was readily detected in the Halema'uma'u plume (average column amount of 3×1015 molec cm−2) and its abundance was strongly correlated with that of SO2. However, anticorrelation between NO2 and SO2 (and BrO) abundances in the same plume strongly suggest an active role of NOx in reactive halogen chemistry. The calculated SO2/BrO molar ratio of ~1600 is comparable to observations at other volcanoes, although the BrO mixing ratio is roughly double that observed elsewhere. While BrO was not observed in the Pu'u'O'o plume this was probably merely a result of the detection limit of our measurements and based on understanding of the Summit and East Rift magmatic system we expect reactive halogens to be formed also in the Pu'u'O'o emissions. If this is correct then based on the long term SO2 flux from Pu'u'O'o we calculate that Kīlauea emits ~480 Mg yr−1 of reactive bromine and may thus represent an important source to the tropical Pacific troposphere.
40
Federico, S., and C. Bellecci. "The 11−12 December 2003 storm in Southern Italy." Advances in Geosciences 7 (January 23, 2006): 37–44. http://dx.doi.org/10.5194/adgeo-7-37-2006.
Анотація:
Abstract. We review an intense and heavy impact storm that occurred over Calabria, southern Italy, during the 11 and 12 December 2003. The event is traced back, at synoptic and planetary scales, up to 5 December 2003 by National Centre for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) reanalysis fields and backtrajectories. The role of tropical storm Odette is clearly shown as well as that of the Azores high. Even if non negligible water vapour sources are expected from the Mediterranean sea, unusually large precipitable water was present over the Atlantic mid-latitudes. It is shown that tropical storm Odette determined large evaporation from Atlantic Tropics and the cooperative action of synoptic scale and planetary scale pressure centres focused this humidity into a plume and conveyed it into the Mediterranean area.
41
Zhao, Junpeng, Wenping Gong, and Jian Shen. "The effect of wind on the dispersal of a tropical small river plume." Frontiers of Earth Science 12, no. 1 (March 24, 2017): 170–90. http://dx.doi.org/10.1007/s11707-016-0628-6.
42
Ziv, B. "A subtropical rainstorm associated with a tropical plume overAfrica and the Middle-East." Theoretical and Applied Climatology 69, no. 1-2 (June 1, 2001): 91–102. http://dx.doi.org/10.1007/s007040170037.
43
Soulat, Patrick, Stephen Bonnet, Mathieu Le Floch, Bernard Tardieu, Daniel Billaux, Claudio Carvajal, Géraldine Rougier, and Alain Pecker. "L’utilisation de sols résiduels tropicaux dans la construction du barrage de Moreau (Guadeloupe)." Revue Française de Géotechnique, no. 160 (2019): 3. http://dx.doi.org/10.1051/geotech/2019015.
Анотація:
Le barrage de Moreau est un barrage en remblai actuellement en construction sur la commune de Goyave en Guadeloupe. Le barrage est fondé sur des roches résiduelles d’origine volcanique. Ces roches se sont formées sur place par altération in situ, c’est-à-dire sans transport. Cette altération, qui pénètre profondément dans la roche, est accélérée par la pluie et la température. L’altération produit des matériaux argileux en passant, à des stades d’altération intermédiaires, par des matériaux aux caractéristiques et aux comportements inhabituels, en particulier l’allophane, l’halloysite et la kaolinite. Dans le cas du barrage de Moreau, les matériaux résiduels sont proches de l’halloysite. Sensibles à l’eau, ils ont aussi été utilisés pour les remblais du corps du barrage. L’article traite du comportement peu courant de ces matériaux, de leurs caractéristiques géotechniques, et des particularités de leur mise en œuvre en remblai sur le barrage de Moreau.
44
Demetriou, Jakovos, Christos Kazilas, Evangelos Koutsoukos та Konstantinos Kalaentzis. "Α new tropical invader in Greece: The lantana plume moth Lantanophaga pusillidactylus (Lepidoptera: Pterophoridae)". ENTOMOLOGIA HELLENICA 29, № 1 (12 лютого 2020): 1. http://dx.doi.org/10.12681/eh.21907.
Анотація:
This study documents the first known record of the lantana plume moth Lantanophaga pusillidactylus (Walker, 1864) in Greece. The moth was observed in four localities from April 2018 to November 2019, and four individuals were collected and deposited in the Zoological Museum of the University of Athens (ZMUA). All specimens were identified as L. pusillidactylus, an alien species in Europe, that has been recently introduced in Spain, Italy (Sicily), Portugal, and Malta. The possible pathways of its introduction, as well as potential ecological implications, are discussed.
45
Chen, Yixiang, Shiquan Lin, Chunsheng Wang, Juan Yang, and Dong Sun. "Response of size and trophic structure of zooplankton community to marine environmental conditions in the northern South China Sea in winter." Journal of Plankton Research 42, no. 3 (May 2020): 378–93. http://dx.doi.org/10.1093/plankt/fbaa022.
Анотація:
Abstract The South China Sea (SCS) is a semi-enclosed marginal sea. And in the northern SCS (NSCS), the Pearl River plume, mesoscale eddies and Kuroshio intrusion may influence the structure of pelagic ecosystems. Here, based on mesozooplankton samples collected in the NSCS from December 2014 to January 2015, spatial variations of mesozooplankton biomass, abundance, normalized biomass size spectra (NBSS), size structure and trophic structure were analyzed to study the response of mesozooplankton community to the influence of highly variable oceanographic environment. High biomass, abundance and intercept of NBSS for the mesozooplankton community were observed in highly productive regions (net primary production > 400 mg C m−2 day−1), such as river plume and cold eddy. No consistent spatial variation was observed for the slope of NBSS, probably because of highly dynamic marine environment in the NSCS. For the trophic structure of mesozooplankton community, the ratio of total chaetognaths biovolume to herbivores/omnivores biovolume (RTCH) was significantly high in river plume and Kuroshio intrusion. The high RTCH indicated unstable trophic structures, which may be due to extreme high proportion of smaller size individuals supported by discharge of river and transport of warm water species from the tropical western Pacific by Kuroshio intrusion, respectively.
46
Gressent, A., B. Sauvage, D. Cariolle, M. Evans, M. Leriche, C. Mari, and V. Thouret. "Modeling lightning-NO<sub><i>x</i></sub> chemistry at sub-grid scale in a global chemical transport model." Atmospheric Chemistry and Physics Discussions 15, no. 23 (December 4, 2015): 34091–147. http://dx.doi.org/10.5194/acpd-15-34091-2015.
Анотація:
Abstract. For the first time, a plume-in-grid approach is implemented in a chemical transport model (CTM) to parameterize the effects of the non-linear reactions occurring within high concentrated NOx plumes from lightning NOx emissions (LNOx) in the upper troposphere. It is characterized by a set of parameters including the plume lifetime, the effective reaction rate constant related to NOx-O3 chemical interactions and the fractions of NOx conversion into HNO3 within the plume. Parameter estimates were made using the DSMACC chemical box model, simple plume dispersion simulations and the mesoscale 3-D Meso-NH model. In order to assess the impact of the LNOx plume approach on the NOx and O3 distributions at large scale, simulations for the year 2006 were performed using the GEOS-Chem global model with a horizontal resolution of 2° × 2.5°. The implementation of the LNOx parameterization implies NOx and O3 decrease at large scale over the region characterized by a strong lightning activity (up to 25 and 8 %, respectively, over Central Africa in July) and a relative increase downwind of LNOx emissions (up to 18 and 2 % for NOx and O3, respectively, in July) are derived. The calculated variability of NOx and O3 mixing ratios around the mean value according to the known uncertainties on the parameter estimates is maximum over continental tropical regions with ΔNOx [−33.1; +29.7] ppt and ΔO3 [−1.56; +2.16] ppb, in January, and ΔNOx [−14.3; +21] ppt and ΔO3 [−1.18; +1.93] ppb, in July, mainly depending on the determination of the diffusion properties of the atmosphere and the initial NO mixing ratio injected by lightning. This approach allows (i) to reproduce a more realistic lightning NOx chemistry leading to better NOx and O3 distributions at the large scale and (ii) focus on other improvements to reduce remaining uncertainties from processes related to NOx chemistry in CTM.
47
Resgalla Junior, Charrid, Vitor Gonçalves Coutinho de Souza, Leonardo Rubi Rörig, and Carlos Augusto França Schettini. "Spatial and temporal variation of the zooplankton community in the area of influence of the Itajaí-açu River, SC (BRAZIL)." Brazilian Journal of Oceanography 56, no. 3 (September 2008): 211–24. http://dx.doi.org/10.1590/s1679-87592008000300006.
Анотація:
On the north coast of the State of Santa Catarina (Brazil), the Itajaí-Açu River mouth shows a low-saline water plume on the internal shelf with strong density gradients. This oceanographic condition has a possible influence over the pelagic community, and it has been little investigated on the Brazilian coast. The present work seeks to evaluate the spatial and temporal variations of the zooplankton community in the area of influence of the Itajaí-açu River, and its relations with the abiotic forces of temperature (seasonal variation) and salinity of the river plume. For this purpose, 14 monthly oceanographic cruises were carried out during the years 2002 and 2003, to obtain physical and chemical parameters, and zooplankton hauls in 9 sampling points. The zooplankton analyses were carried out at the lowest taxon possible to characterize the resident community of the river mouth. It was observed that the zooplankton presented the highest densities in winter and spring. The species with higher densities and frequencies of occurrence were Paracalanus quasimodo, Parvocalanus crassirostris, Acartia lilijeborgi, Temora stylifera, T. turbinata, and Penilia avirostris, indicating a prevalence in this region, of Tropical Water from the Brazil Current and greater similarity with the coastal community of the Southeast region of Brazil. However, even for the species typical of Tropical Water, there were alterations in dominance of the species, due to the seasonality and level of flow rate of the river on the salinity of the internal shelf of the study area.
48
Romps, David M. "An Analytical Model for Tropical Relative Humidity." Journal of Climate 27, no. 19 (September 24, 2014): 7432–49. http://dx.doi.org/10.1175/jcli-d-14-00255.1.
Анотація:
Abstract An analytical model is derived for tropical relative humidity using only the Clausius–Clapeyron relation, hydrostatic balance, and a bulk-plume water budget. This theory is constructed for radiative–convective equilibrium and compared against a cloud-resolving model. With some reinterpretation of variables, it can be applied more generally to the entire tropics. Given four variables—pressure, temperature, and the fractional entrainment and detrainment rates—the equations predict the relative humidity (RH) and the temperature lapse rate analytically. The RH is a simple ratio involving the fractional detrainment rate and the water-vapor lapse rate. When integrated upward in height, the equations give profiles of RH and temperature for a convecting atmosphere. The theory explains the magnitude of RH and the “C” shape of the tropospheric RH profile. It also predicts that RH is an invariant function of temperature as the atmosphere warms, and this behavior matches what has been seen in global climate models and what is demonstrated here with cloud-resolving simulations. Extending the theory to include the evaporation of hydrometeors, a lower bound is derived for the precipitation efficiency (PE) at each height: PE > 1 − RH. In a cloud-resolving simulation, this constraint is obeyed with the PE profile taking the shape of an inverted C shape.
49
Glatthor, N., M. Höpfner, G. P. Stiller, T. von Clarmann, B. Funke, S. Lossow, E. Eckert, et al. "Seasonal and interannual variations in HCN amounts in the upper troposphere and lower stratosphere observed by MIPAS." Atmospheric Chemistry and Physics 15, no. 2 (January 16, 2015): 563–82. http://dx.doi.org/10.5194/acp-15-563-2015.
Анотація:
Abstract. We present a HCN climatology of the years 2002–2012, derived from FTIR limb emission spectra measured with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on the ENVISAT satellite, with the main focus on biomass burning signatures in the upper troposphere and lower stratosphere. HCN is an almost unambiguous tracer of biomass burning with a tropospheric lifetime of 5–6 months and a stratospheric lifetime of about 2 years. The MIPAS climatology is in good agreement with the HCN distribution obtained by the spaceborne ACE-FTS experiment and with airborne in situ measurements performed during the INTEX-B campaign. The HCN amounts observed by MIPAS in the southern tropical and subtropical upper troposphere have an annual cycle peaking in October–November, i.e. 1–2 months after the maximum of southern hemispheric fire emissions. The probable reason for the time shift is the delayed onset of deep convection towards austral summer. Because of overlap of varying biomass burning emissions from South America and southern Africa with sporadically strong contributions from Indonesia, the size and strength of the southern hemispheric plume have considerable interannual variations, with monthly mean maxima at, for example, 14 km between 400 and more than 700 pptv. Within 1–2 months after appearance of the plume, a considerable portion of the enhanced HCN is transported southward to as far as Antarctic latitudes. The fundamental period of HCN variability in the northern upper troposphere is also an annual cycle with varying amplitude, which in the tropics peaks in May after and during the biomass burning seasons in northern tropical Africa and southern Asia, and in the subtropics peaks in July due to trapping of pollutants in the Asian monsoon anticyclone (AMA). However, caused by extensive biomass burning in Indonesia and by northward transport of part of the southern hemispheric plume, northern HCN maxima also occur around October/November in several years, which leads to semi-annual cycles. There is also a temporal shift between enhanced HCN in northern low and mid- to high latitudes, indicating northward transport of pollutants. Due to additional biomass burning at mid- and high latitudes, this meridional transport pattern is not as clear as in the Southern Hemisphere. Upper tropospheric HCN volume mixing ratios (VMRs) above the tropical oceans decrease to below 200 pptv, presumably caused by ocean uptake, especially during boreal winter and spring. The tropical stratospheric tape recorder signal with an apparently biennial period, which was detected in MLS and ACE-FTS data from mid-2004 to mid-2007, is corroborated by MIPAS HCN data. The tape recorder signal in the whole MIPAS data set exhibits periodicities of 2 and 4 years, which are generated by interannual variations in biomass burning. The positive anomalies of the years 2003, 2007 and 2011 are caused by succession of strongly enhanced HCN from southern hemispheric and Indonesian biomass burning in boreal autumn and of elevated HCN from northern tropical Africa and the AMA in subsequent spring and summer. The anomaly of 2005 seems to be due to springtime emissions from tropical Africa followed by release from the summertime AMA. The vertical transport time of the anomalies is 1 month or less between 14 and 17 km in the upper troposphere and 8–11 months between 17 and 25 km in the lower stratosphere.
50
Zébazé Togouet, S. H., T. Njiné, N. Kemka, M. Nola, S. Foto Menbohan, A. Monkiedje, D. Niyitegka, T. Simke-Ngando, and L. B. Jugnia. "Variations spatiales et temporelles de la richesse et de l'abondance des rotifères (Brachionidae et Trichocercidae) et des cladocères dans un petit lac artificiel eutrophe situé en zone tropicale." Revue des sciences de l'eau 18, no. 4 (April 12, 2005): 485–505. http://dx.doi.org/10.7202/705569ar.
Анотація:
Les communautés de rotifères (Brachionidae et Trichocercidae) et de cladocères peuplant les eaux du lac Municipal de Yaoundé situé en zone tropicale (Cameroun), ont été examinés en relation avec quelques variables physico-chimiques du milieu. Des 26 espèces et sous-espèces de rotifères (Brachionidae et Trichocercidae) et 15 espèces de cladocères inventoriées, environ 16 sont identifiées pour la première fois au Cameroun. Parmi les espèces quantitativement dominantes, les espèces fréquemment rencontrées sont Brachionus angularis angularis, B. falcatus falcatus, et B. calyciflorus chez les Brachionidae, Trichocerca elongata elongata, et T. bicristata bicristata chez les Trichocercidae, et Ceriodaphnia cornuta et Chydorus eurynotus chez les cladocères. Plus de 75% des espèces répertoriées sont des espèces périphytiques communément considérées comme littorales, dont le développement important a été observé dans la zone pélagique du lac qui, sans doute, offre de nombreuses ressources et constitue un refuge vis-à-vis notamment de la prédation. L'absence de corrélations entre les communautés zooplanctoniques étudiés et les quelques variables physico-chimiques suivies, nous a amenés à considérer que le développement de ces communautés est sous la dépendance d'autres facteurs. D'ailleurs, une analyse canonique de correspondance indique que les stations, profondeurs et mois de prélèvement expliqueraient respectivement 3%, 5% et 36% de la variance totale associée à l'abondance des espèces prises en compte. Ce qui nous a permis d'émettre l'hypothèse selon laquelle les principales conditions environnementales qui affectent le développement potentiel des espèces analysées et le déroulement de leurs cycles biologiques, seraient dépendantes des deux saisons (la saison des pluies et la saison sèche) caractérisant les climats tropicaux.