Journal articles: 'Equatorial East Africa'

1

Hastenrath, Stefan. "Diagnosing the decaying glaciers of equatorial East Africa." Meteorologische Zeitschrift 15, no. 3 (2006): 265–71. http://dx.doi.org/10.1127/0941-2948/2006/0106.

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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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Mahaney, William C., and Stefan Hastenrath. "The Glaciers of Equatorial East Africa." Arctic and Alpine Research 17, no. 2 (1985): 221. http://dx.doi.org/10.2307/1550856.

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Grove, J. M., and Stefan Hastenrath. "The Glaciers of Equatorial East Africa." Geographical Journal 152, no. 1 (1986): 93. http://dx.doi.org/10.2307/632951.

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Hastenrath, Stefan, Dierk Polzin, and Charles Mutai. "Diagnosing the 2005 Drought in Equatorial East Africa." Journal of Climate 20, no. 18 (2007): 4628–37. http://dx.doi.org/10.1175/jcli4238.1.

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Abstract Equatorial East Africa suffered severe drought during its 2005 “short rains,” centered on October–November. The circulation mechanisms of such precipitation anomalies are examined, using long-term upper-air and surface datasets, and based on diagnostic findings from earlier empirical investigations. The steep eastward pressure gradient is conducive to fast westerlies over the central-equatorial Indian Ocean, surface manifestation of a powerful zonal circulation cell with subsidence over East Africa, and ascending motion over Indonesia. With fast westerlies, rainfall in East Africa is deficient and they tend to be accompanied by anomalously cold waters in the northwestern and warm anomalies in the southeastern extremity of the equatorial Indian Ocean Basin, without any seesaw between these domains. In October–November 2005, pressure in the west was anomalously high, entailing a steep eastward pressure gradient along the equator, conducive to fast westerlies and, further symptomatic of the zonal circulation cell, subsidence in the west and ascending motion in the east were enhanced. Overall, the chain of causalities can be traced to anomalously high pressure in the west.

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Abiriga, Faustine, Emirant B. Amabayo, Edward Jurua, and Pierre J. Cilliers. "Statistical characterization of equatorial plasma bubbles over East Africa." Journal of Atmospheric and Solar-Terrestrial Physics 200 (April 2020): 105197. http://dx.doi.org/10.1016/j.jastp.2020.105197.

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Bolaji, Olawale, Oluwafisayo Owolabi, Elijah Falayi, et al. "Observations of equatorial ionization anomaly over Africa and Middle East during a year of deep minimum." Annales Geophysicae 35, no. 1 (2017): 123–32. http://dx.doi.org/10.5194/angeo-35-123-2017.

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Abstract. In this work, we investigated the veracity of an ion continuity equation in controlling equatorial ionization anomaly (EIA) morphology using total electron content (TEC) of 22 GPS receivers and three ground-based magnetometers (Magnetic Data Acquisition System, MAGDAS) over Africa and the Middle East (Africa–Middle East) during the quietest periods. Apart from further confirmation of the roles of equatorial electrojet (EEJ) and integrated equatorial electrojet (IEEJ) in determining hemispheric extent of EIA crest over higher latitudes, we found some additional roles played by thermospheric meridional neutral wind. Interestingly, the simultaneous observations of EIA crests in both hemispheres of Africa–Middle East showed different morphology compared to that reported over Asia. We also observed interesting latitudinal twin EIA crests domiciled at the low latitudes of the Northern Hemisphere. Our results further showed that weak EEJ strength associated with counter electrojet (CEJ) during sunrise hours could also trigger twin EIA crests over higher latitudes.

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Ummenhofer, Caroline C., Alexander Sen Gupta, Matthew H. England, and Chris J. C. Reason. "Contributions of Indian Ocean Sea Surface Temperatures to Enhanced East African Rainfall." Journal of Climate 22, no. 4 (2009): 993–1013. http://dx.doi.org/10.1175/2008jcli2493.1.

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Abstract Links between extreme wet conditions over East Africa and Indian Ocean sea surface temperatures (SST) are investigated during the core of the so-called short rain season in October–November. During periods of enhanced East African rainfall, Indian Ocean SST anomalies reminiscent of a tropical Indian Ocean dipole (IOD) event are observed. Ensemble simulations with an atmospheric general circulation model are used to understand the relative effect of local and large-scale Indian Ocean SST anomalies on above-average East African precipitation. The importance of the various tropical and subtropical IOD SST poles, both individually and in combination, is quantified. In the simulations, enhanced East African “short rains” are predominantly driven by the local warm SST anomalies in the western equatorial Indian Ocean, while the eastern cold pole of the tropical IOD is of lesser importance. The changed East African rainfall distribution can be explained by a reorganization of the atmospheric circulation induced by the SST anomalies. A reduction in sea level pressure over the western half of the Indian Ocean and converging wind anomalies over East Africa lead to moisture convergence and increased convective activity over the region. The pattern of large-scale circulation changes over the tropical Indian Ocean and adjacent landmasses is consistent with an anomalous strengthening of the Walker cell. The seasonal cycle of various indices related to the SST and the atmospheric circulation in the equatorial Indian Ocean are examined to assess their potential usefulness for seasonal forecasting.

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Seba, Ephrem Beshir, Melessew Nigussie, and Mark B. Moldwin. "The relationship between equatorial ionization anomaly and nighttime equatorial spread F in East Africa." Advances in Space Research 62, no. 7 (2018): 1737–52. http://dx.doi.org/10.1016/j.asr.2018.06.029.

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Pestriakov, Aleksandr P., Olga M. Grigorieva та Yulia V. Pelenitsyna. "Краниологический аспект генезиса населения тропической транссахарской Африки". Вестник антропологии (Herald of Anthropology) 51, № 3 (2020): 261–79. http://dx.doi.org/10.33876/2311-0546/2020-51-3/261-279.

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This article continues a study of cranial growth on the example of the population of tropical Trans-Saharan Africa. The cranial samples of Gabon, basin of the Congo River (the Western part), and East African farmers and Capoids – Bushmen and Hottentots (the Eastern part) were analyzed. Male and female cranial samples were studied separately. Crania of some samples clustered according to the type of growth processes in the crania. Comparative analysis showed that the cranial samples (and clusters inside them) from the West of the studied region, as a whole, differ significantly from those from the East in the shape of the skull. This is clearly seen in the male sample, but less obvious in the female one. The overall size of the cranium in the West is significantly more variable than in the East. This is because of a Pygmy admixture in the population of equatorial rainforest, which are associated with a small size of the cranium. There is no such difference between East African farmers and the craniologically similar Capoids (Bushmen and Hottentots). This leads to two main conclusions. First, the population of the Western (humid) part of Equatorial Africa formed as a mixture of larger-headed agricultural groups with Pygmies, who had smaller crania. Second, the agricultural population of the Eastern (more arid) part of the studied territory is almost identical in craniological terms to the Capoids (Bushmen and Hottentots) of South Africa, while differs significantly from the pastoralist population of this territory.

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11

Dumont, Henri J., and Sibylle Maas. "On nine Tropodiaptomus-species (Copepoda, Calanoida) from equatorial East Africa." Hydrobiologia 167-168, no. 1 (1988): 415–27. http://dx.doi.org/10.1007/bf00026334.

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12

Hirons, Linda, and Andrew Turner. "The Impact of Indian Ocean Mean-State Biases in Climate Models on the Representation of the East African Short Rains." Journal of Climate 31, no. 16 (2018): 6611–31. http://dx.doi.org/10.1175/jcli-d-17-0804.1.

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The role of the Indian Ocean dipole (IOD) in controlling interannual variability in the East African short rains, from October to December, is examined in state-of-the-art models and in detail in one particular climate model. In observations, a wet short-rainy season is associated with the positive phase of the IOD and anomalous easterly low-level flow across the equatorial Indian Ocean. A model’s ability to capture the teleconnection to the positive IOD is closely related to its representation of the mean state. During the short-rains season, the observed low-level wind in the equatorial Indian Ocean is westerly. However, half of the models analyzed exhibit mean-state easterlies across the entire basin. Specifically, those models that exhibit mean-state low-level equatorial easterlies in the Indian Ocean, rather than the observed westerlies, are unable to capture the latitudinal structure of moisture advection into East Africa during a positive IOD. Furthermore, the associated anomalous easterly surface wind stress causes upwelling in the eastern Indian Ocean. This upwelling draws up cool subsurface waters, enhancing the zonal sea surface temperature gradient between west and east and strengthening the positive IOD pattern, further amplifying the easterly wind stress. This positive Bjerknes coupled feedback is stronger in easterly mean-state models, resulting in a wetter East African short-rain precipitation bias in those models.

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Dezfuli, Amin K., Benjamin F. Zaitchik, and Anand Gnanadesikan. "Regional Atmospheric Circulation and Rainfall Variability in South Equatorial Africa." Journal of Climate 28, no. 2 (2015): 809–18. http://dx.doi.org/10.1175/jcli-d-14-00333.1.

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Abstract This study examines daily precipitation data during December–March over south equatorial Africa (SEA) and proposes a new zonal asymmetric pattern (ZAP) that explains the leading mode of weather-scale precipitation variability in the region. The eastern and western components of the ZAP, separated at about 30°E, appear to be a consequence of an anomalous zonal atmospheric cell triggered by enhanced low-level westerly winds. The enhanced westerlies are generated by a diagonal interhemispheric pressure gradient between the southwestern Indian and north tropical Atlantic Oceans. In eastern SEA these winds hit the East African Plateau, producing low-level convergence and convection that further intensifies the westerlies. In western SEA a subsiding branch develops in response, closing the circulation cell. The system gradually dissipates as the pressure gradient weakens. Through this mechanism, simultaneous changes in two hemispheres generate a regional zonally oriented circulation that relies on climatic communication between eastern and western equatorial Africa.

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Hastenrath, Stefan, Dierk Polzin, and Charles Mutai. "Circulation Mechanisms of Kenya Rainfall Anomalies." Journal of Climate 24, no. 2 (2011): 404–12. http://dx.doi.org/10.1175/2010jcli3599.1.

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Abstract Expanding earlier studies on the boreal spring and autumn rainy seasons in equatorial East Africa, pending challenges on the mechanisms of rainfall variability, are investigated. Eastward pressure gradient and slack south Indian Ocean trade winds allow surface equatorial westerlies in spring and autumn. Complementing that, upper-tropospheric easterlies are required for the development of a zonal vertical circulation cell along the Indian Ocean equator. Because of the summer warming and high stand of upper-tropospheric topography over South Asia, strong upper-tropospheric easterlies over the tropical northern and equatorial Indian Ocean persist from summer into autumn, thus allowing the development of a zonal vertical circulation cell. By contrast, the winter cooling entails low stand of upper-tropospheric topography in the north, thus hindering easterlies over the equator. Consequently, an equatorial zonal circulation cell does not develop in boreal spring. The equatorial zonal circulation cell, with subsidence over East Africa, strongly controls the boreal autumn rains, as evidenced in their tight correlation with the equatorial westerlies. In a related vein, rain gauge stations show much shared variance in boreal autumn as compared to spring. Plausibly consistent with this, boreal autumn rather than spring has brought the extreme flood and drought disasters in the course of the past half-century.

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15

Hastenrath, Stefan, Dierk Polzin, and Charles Mutai. "Diagnosing the Droughts and Floods in Equatorial East Africa during Boreal Autumn 2005–08." Journal of Climate 23, no. 3 (2010): 813–17. http://dx.doi.org/10.1175/2009jcli3094.1.

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Abstract Building on an earlier report on the 2005 drought in equatorial East Africa, this short note examines the circulation mechanisms of the anomalies in the boreal autumn “short rains” season in the subsequent three years. Westerlies during this season are the surface manifestation of a powerful zonal–vertical circulation cell along the Indian Ocean equator. The surface equatorial westerlies were fast during the 2005 and 2008 droughts, near average during the near-average 2007 short rains, and slack during the 2006 floods, consistent with the known circulation diagnostics.

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Janicot, Serge, Ali Harzallah, Bernard Fontaine, and Vincent Moron. "West African Monsoon Dynamics and Eastern Equatorial Atlantic and Pacific SST Anomalies (1970–88)." Journal of Climate 11, no. 8 (1998): 1874–82. http://dx.doi.org/10.1175/1520-0442-11.8.1874.

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Abstract The Laboratoire de Météorologie Dynamique atmospheric GCM is used to investigate relationships between West African monsoon dynamics and SST anomalies in the eastern equatorial Atlantic and Pacific for the period 1970–88. Positive SST anomalies in the eastern equatorial Pacific, mainly associated with a larger east–west divergent circulation over the tropical Atlantic, are found to coincide with negative rainfall anomalies over West Africa. This is the case for the composite ENSO warm episodes of 1972, 1976, 1982, and 1983. By contrast, positive SST anomalies in the eastern equatorial Atlantic are accompanied by a southward shift of the intertropical convergence zone along with negative rainfall anomalies in the Sahel and positive rainfall anomalies in the Guinean region. This was the case in 1987. The ENSO warm event during this year had apparently no significant impact on West African monsoon dynamics. A zonal atmospheric coupling associated with differences of SST anomalies between the eastern equatorial Pacific and the Atlantic is evident in the period 1970–88. Positive (negative) phases of this coupling could enhance the impact of ENSO warm (cold) events on West African monsoon dynamics.

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17

Bessems, Ilse, Dirk Verschuren, James M. Russell, Jozef Hus, Florias Mees, and Brian F. Cumming. "Palaeolimnological evidence for widespread late 18th century drought across equatorial East Africa." Palaeogeography, Palaeoclimatology, Palaeoecology 259, no. 2-3 (2008): 107–20. http://dx.doi.org/10.1016/j.palaeo.2007.10.002.

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18

Verschuren, Dirk, Kathleen R. Laird, and Brian F. Cumming. "Rainfall and drought in equatorial east Africa during the past 1,100 years." Nature 403, no. 6768 (2000): 410–14. http://dx.doi.org/10.1038/35000179.

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Faith, J. Tyler, Christian A. Tryon, Daniel J. Peppe, and David L. Fox. "The fossil history of Grévy's zebra (Equus grevyi) in equatorial East Africa." Journal of Biogeography 40, no. 2 (2012): 359–69. http://dx.doi.org/10.1111/j.1365-2699.2012.02796.x.

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20

Ongoma, Victor, Haishan Chen, and Chujie Gao. "Evaluation of CMIP5 twentieth century rainfall simulation over the equatorial East Africa." Theoretical and Applied Climatology 135, no. 3-4 (2018): 893–910. http://dx.doi.org/10.1007/s00704-018-2392-x.

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21

Mounier, Flore, George N. Kiladis, and Serge Janicot. "Analysis of the Dominant Mode of Convectively Coupled Kelvin Waves in the West African Monsoon." Journal of Climate 20, no. 8 (2007): 1487–503. http://dx.doi.org/10.1175/jcli4059.1.

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Abstract The dominant mode of convectively coupled Kelvin waves has been detected over the Atlantic and Africa during northern summer by performing composite analyses on observational fields based on an EOF reconstructed convection index over West Africa. Propagating eastward, many waves originate from the Pacific sector, interact with deep convection of the marine ITCZ over the Atlantic and the continental ITCZ over West and central Africa, and then weaken over East Africa and the Indian Ocean. It has been shown that they are able to modulate the life cycle and track of individual westward-propagating convective systems. Their mean kinematic characteristics comprise a wavelength of 8000 km, and a phase speed of 15 m s−1, leading to a period centered on 6 to 7 days. The African Kelvin wave activity displays large seasonal variability, being highest outside of northern summer when the ITCZ is close to the equator, facilitating the interactions between convection and these equatorially trapped waves. The convective and dynamical patterns identified over the Atlantic and Africa show some resemblance to the theoretical equatorially trapped Kelvin wave solution on an equatorial β plane. Most of the flow is in the zonal direction as predicted by theory, and there is a tendency for the dynamical fields to be symmetric about the equator, even though the ITCZ is concentrated well north of the equator at the full development of the African monsoon. In the upper troposphere and the stratosphere, the temperature contours slope sharply eastward with height, as expected from an eastward-moving heat source that forces a dry Kelvin wave response. It is finally shown that the mean impact of African Kelvin waves on rainfall and convection is of the same level as African easterly waves.

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22

Tian, Zhiping, Tim Li, and Dabang Jiang. "Strengthening and Westward Shift of the Tropical Pacific Walker Circulation during the Mid-Holocene: PMIP Simulation Results." Journal of Climate 31, no. 6 (2018): 2283–98. http://dx.doi.org/10.1175/jcli-d-16-0744.1.

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Based on the zonal mass streamfunction, the mid-Holocene annual and seasonal changes in the tropical Pacific Walker circulation (PWC) are examined using numerical simulations from the Paleoclimate Modelling Intercomparison Project Phases 2 and 3. Compared to the preindustrial period, the annual mean of the PWC intensity strengthened (with an average increase of 0.26 × 1014 kg2 m−2 s−1 or 5%), and both the western edge and center of the PWC cell shifted westward (by an average of 4° and 3°, respectively) in the majority of the 29 models used for analysis during the mid-Holocene. Those changes were closely related to an overall increase in the equatorial Indo-Pacific east–west sea level pressure difference and low-level trade winds over the equatorial Pacific. Annual mean PWC changes come mainly from boreal warm seasons. In response to the mid-Holocene orbital forcing, Asian and North African monsoon rainfall was strengthened due to large-scale surface warming in the Northern Hemisphere in boreal warm seasons, which led to an intensified large-scale thermally direct east–west circulation, resulting in the enhancement and westward shift of the tropical PWC. The opposite occurred during the mid-Holocene boreal cold seasons. Taken together, the change in the monsoon rainfall over the key tropical regions of Asia and North Africa and associated large-scale east–west circulation, rather than the equatorial Pacific SST change pattern, played a key role in affecting the mid-Holocene PWC strength.

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Paznukhov, V. V., C. S. Carrano, P. H. Doherty, et al. "Equatorial plasma bubbles and L-band scintillations in Africa during solar minimum." Annales Geophysicae 30, no. 4 (2012): 675–82. http://dx.doi.org/10.5194/angeo-30-675-2012.

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Abstract. We report on the longitudinal, local time and seasonal occurrence of equatorial plasma bubbles (EPBs) and L band (GPS) scintillations over equatorial Africa. The measurements were made in 2010, as a first step toward establishing the climatology of ionospheric irregularities over Africa. The scintillation intensity is obtained by measuring the standard deviation of normalized GPS signal power. The EPBs are detected using an automated technique, where spectral analysis is used to extract and identify EPB events from the GPS TEC measurements. Overall, the observed seasonal climatology of the EPBs as well as GPS scintillations in equatorial Africa is adequately explained by geometric arguments, i.e., by the alignment of the solar terminator and local geomagnetic field, or STBA hypothesis (Tsunoda, 1985, 2010a). While plasma bubbles and scintillations are primarily observed during equinoctial periods, there are longitudinal differences in their seasonal occurrence statistics. The Atlantic sector has the most intense, longest lasting, and highest scintillation occurrence rate in-season. There is also a pronounced increase in the EPB occurrence rate during the June solstice moving west to east. In Africa, the seasonal occurrence shifts towards boreal summer solstice, with fewer occurrences and shorter durations in equinox seasons. Our results also suggest that the occurrence of plasma bubbles and GPS scintillations over Africa are well correlated, with scintillation intensity depending on depletion depth. A question remains about the possible physical mechanisms responsible for the difference in the occurrence phenomenology of EPBs and GPS scintillations between different regions in equatorial Africa.

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24

Livingston, William. "Geostationary Satellite over East Africa Observed from Kitt Peak, Arizona." Bulletin of the American Meteorological Society 100, no. 10 (2019): 1877–80. http://dx.doi.org/10.1175/bams-d-18-0296.1.

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AbstractGeo-stats are geostationary communication satellites in nearly circular orbits, in the equatorial plane of the Earth, and with an orbital period of one sidereal day. If these three conditions are met, an artificial satellite will be stationary above the Earth. They are usually invisible to the unaided eye (limit of magnitude 6), since the geo-stat’s average brightness is magnitude 12. At night, stars will trail through a fixed camera time exposure of this scene. We have learned how to photograph them using a fixed simple camera from Kitt Peak Mountain in Arizona. We give examples from 30 years of annual observations with identifications from the European Space Agency. One example is over East Africa—yes, seen from Arizona.

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Wei, Ho-Hsuan, and Simona Bordoni. "On the Role of the African Topography in the South Asian Monsoon." Journal of the Atmospheric Sciences 73, no. 8 (2016): 3197–212. http://dx.doi.org/10.1175/jas-d-15-0182.1.

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Abstract The Somali jet, a strong low-level cross-equatorial flow concentrated in a narrow longitudinal band near the coast of Somalia, is a key feature of the South Asian monsoon (SAM) circulation. Previous work has emphasized the role of the East African highlands in strengthening and concentrating the jet. However, the fundamental dynamics of the jet remains debated, as does its relation to the SAM precipitation. In this study, numerical experiments with modified topography over Africa are conducted with the GFDL atmospheric model, version 2.1 (AM2.1), general circulation model (GCM) to examine the influence of topography on the Somali jet and the SAM precipitation. It is found that when the African topography is removed, the SAM precipitation moderately increases in spite of a weakening of the cross-equatorial Somali jet. The counterintuitive precipitation increase is related to lower-level cyclonic wind anomalies, and associated meridional moisture convergence, which develop over the Arabian Sea in the absence of the African topography. Potential vorticity (PV) budget analyses along particle trajectories show that this cyclonic anomaly primarily arises because, in the absence of the blocking effect by the African topography and with weaker cross-equatorial flow, air particles originate from higher latitudes with larger background planetary vorticity and thus larger PV.

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Koech, Kiprop Vincent. "Atmospheric divergence over equatorial East Africa and its influence on distribution of rainfall." Weather 70, no. 5 (2015): 158–62. http://dx.doi.org/10.1002/wea.2447.

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Verschuren, D., D. O. Olago, S. M. Rucina, and P. O. Odhengo. "DeepCHALLA: Two Glacial Cycles of Climate and Ecosystem Dynamics from Equatorial East Africa." Scientific Drilling 15 (March 1, 2013): 72–76. http://dx.doi.org/10.5194/sd-15-72-2013.

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Pohl, Benjamin, Julien Crétat, and Pierre Camberlin. "Testing WRF capability in simulating the atmospheric water cycle over Equatorial East Africa." Climate Dynamics 37, no. 7-8 (2011): 1357–79. http://dx.doi.org/10.1007/s00382-011-1024-2.

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Hastenrath, Stefan. "Circulation mechanisms of climate anomalies in East Africa and the equatorial Indian Ocean." Dynamics of Atmospheres and Oceans 43, no. 1-2 (2007): 25–35. http://dx.doi.org/10.1016/j.dynatmoce.2006.06.002.

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30

Faith, J. Tyler, David B. Patterson, Nick Blegen, et al. "Size variation in Tachyoryctes splendens (East African mole-rat) and its implications for late Quaternary temperature change in equatorial East Africa." Quaternary Science Reviews 140 (May 2016): 39–48. http://dx.doi.org/10.1016/j.quascirev.2016.03.017.

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Mounier, Flore, Serge Janicot, and George N. Kiladis. "The West African Monsoon Dynamics. Part III: The Quasi-Biweekly Zonal Dipole." Journal of Climate 21, no. 9 (2008): 1911–28. http://dx.doi.org/10.1175/2007jcli1706.1.

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Abstract This paper presents an investigation of the mechanisms giving rise to the main intraseasonal mode of convection in the African monsoon during northern summer, here identified as the quasi-biweekly zonal dipole (QBZD). The QBZD is primarily characterized by a quasi-stationary zonal dipole of convection whose dimension is larger than the West African monsoon domain, with its two poles centered along the Guinean coast and between 30° and 60°W in the equatorial Atlantic. The QBZD dynamical processes within the Atlantic–Africa domain are examined in some detail. The QBZD has a dipole pattern associated with a Walker-type circulation in the near-equatorial zonal plane. It is controlled both by equatorial atmospheric dynamics through a Kelvin wave–like disturbance propagating eastward between its two poles and by land surface processes over Africa, inducing combined fluctuations in surface temperatures, surface pressure, and low-level zonal winds off the coast of West Africa. When convection is at a minimum over central and West Africa, a lack of cloud cover results in higher net shortwave flux at the surface, which increases surface temperatures and lowers surface pressures. This creates an east–west pressure gradient at the latitude of both the ITCZ (10°N) and the Saharan heat low (20°N), leading to an increase in eastward moisture advection inland. The arrival from the Atlantic of the positive pressure signal associated with a Kelvin wave pattern amplifies the low-level westerly wind component and the moisture advection inland, leading to an increase in convective activity over central and West Africa. Then the opposite phase of the dipole develops. Propagation of the QBZD convective envelope and of the associated 200 high-level velocity potential anomalies is detected from the eastern Pacific to the Indian Ocean. When the effect of the Kelvin wave propagation is removed by filtering, the stationary character of the QBZD is highlighted. The impact of the QBZD in combination with a Kelvin wave is illustrated by a case study of the monsoon onset in 1984.

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James, Rachel, Richard Washington, and David P. Rowell. "Implications of global warming for the climate of African rainforests." Philosophical Transactions of the Royal Society B: Biological Sciences 368, no. 1625 (2013): 20120298. http://dx.doi.org/10.1098/rstb.2012.0298.

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African rainforests are likely to be vulnerable to changes in temperature and precipitation, yet there has been relatively little research to suggest how the regional climate might respond to global warming. This study presents projections of temperature and precipitation indices of relevance to African rainforests, using global climate model experiments to identify local change as a function of global temperature increase. A multi-model ensemble and two perturbed physics ensembles are used, one with over 100 members. In the east of the Congo Basin, most models (92%) show a wet signal, whereas in west equatorial Africa, the majority (73%) project an increase in dry season water deficits. This drying is amplified as global temperature increases, and in over half of coupled models by greater than 3% per °C of global warming. Analysis of atmospheric dynamics in a subset of models suggests that this could be partly because of a rearrangement of zonal circulation, with enhanced convection in the Indian Ocean and anomalous subsidence over west equatorial Africa, the Atlantic Ocean and, in some seasons, the Amazon Basin. Further research to assess the plausibility of this and other mechanisms is important, given the potential implications of drying in these rainforest regions.

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Ivory, Sarah J., and James Russell. "Lowland forest collapse and early human impacts at the end of the African Humid Period at Lake Edward, equatorial East Africa." Quaternary Research 89, no. 1 (2017): 7–20. http://dx.doi.org/10.1017/qua.2017.48.

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AbstractIn Africa, the early Holocene was characterized by wetter, warmer conditions than today, followed by rapid aridification at ~5.2 ka. However, a lack of lowland vegetation records has prevented a detailed evaluation of forest response to Holocene climate change. Additionally, although modern vegetation communities are linked to human disturbance, few studies have addressed how prehistoric human activities helped engineer the character of modern African ecosystems. Understanding the architecture of lowland and highland forests is important to prevent further degradation from climate/land-use change. We present an 11,000 yr fossil pollen record from Lake Edward, Uganda. We show that Guineo-Congolian forests dominated the highlands and lowlands in equatorial East Africa in the early Holocene, highlighting the importance of rainfall and temperature in controlling forest communities. These forests remained until ~5.2 ka, when the climate became drier. The lacustrine ecosystem response to aridification was abrupt; however, forest decreased gradually, replaced by deciduous woodlands. Woodlands dominated until after an arid period at 2 ka; however, forest did not recover. Increased disturbance indicators and grasses suggest that the arrival of Iron Age people resulted in the modern fire-tolerant vegetation. Although late Holocene climate played a role in vegetation opening, the modern ecosystem architecture in East Africa is linked to early human activities.

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Stager, J. Curt, Christine Cocquyt, Raymonde Bonnefille, Constanze Weyhenmeyer, and Nicole Bowerman. "A late Holocene paleoclimatic history of Lake Tanganyika, East Africa." Quaternary Research 72, no. 1 (2009): 47–56. http://dx.doi.org/10.1016/j.yqres.2009.04.003.

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AbstractA nearshore core (LT03-05) from the north basin of Lake Tanganyika provides diatom, pollen, and sedimentary time series covering the last ca. 3800 yr at 15–36 yr resolution. A chronology supported by 21 AMS dates on terrestrial and lacustrine materials allows us to account for ancient carbon effects on 14C ages and to propose refinements of the region's climatic history. Conditions drier than those of today were followed after ca. 3.30 ka by an overall wetting trend. Several century-scale climate variations were superimposed upon that trend, with exceptionally rainy conditions occurring 1.70–1.40 ka, 1.15–0.90 ka, 0.70–0.55 ka, and 0.35–0.20 ka. Around 0.55–0.35 ka, during the Spörer sunspot minimum, drier conditions developed in the northern Tanganyika basin while more humid conditions were registered at Lakes Victoria and Naivasha. This indicates significant variability in the nature and distribution of near-equatorial rainfall anomalies during much of the Little Ice Age.

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Yang, Gui-Ying, John Methven, Steve Woolnough, Kevin Hodges, and Brian Hoskins. "Linking African Easterly Wave Activity with Equatorial Waves and the Influence of Rossby Waves from the Southern Hemisphere." Journal of the Atmospheric Sciences 75, no. 6 (2018): 1783–809. http://dx.doi.org/10.1175/jas-d-17-0184.1.

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Abstract A connection is found between African easterly waves (AEWs), equatorial westward-moving mixed Rossby–gravity (WMRG) waves, and equivalent barotropic Rossby waves (RWs) from the Southern Hemisphere (SH). The amplitude and phase of equatorial waves is calculated by projection of broadband-filtered ERA-Interim data onto a horizontal structure basis obtained from equatorial wave theory. Mechanisms enabling interaction between the wave types are identified. AEWs are dominated by a vorticity wave that tilts eastward below the African easterly jet and westward above: the tilt necessary for baroclinic wave growth. However, a strong relationship is identified between amplifying vorticity centers within AEWs and equatorial WMRG waves. Although the waves do not phase lock, positive vorticity centers amplify whenever the cross-equatorial motion of the WMRG wave lies at the same longitude in the upper troposphere (southward flow) and east of this in the lower troposphere (northward flow). Two mechanisms could explain the vorticity amplification: vortex stretching below the upper-tropospheric divergence and ascent associated with latent heating in convection in the lower-tropospheric moist northward flow. In years of strong AEW activity, SH and equatorial upper-tropospheric zonal winds are more easterly. Stronger easterlies have two effects: (i) they Doppler shift WMRG waves so that their period varies little with wavenumber (3–4 days) and (ii) they enable westward-moving RWs to propagate into the tropical waveguide from the SH. The RW phase speeds can match those of WMRG waves, enabling sustained excitation of WMRG. The WMRG waves have an eastward group velocity with wave activity accumulating over Africa and invigorating AEWs at similar frequencies through the vorticity amplification mechanism.

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Fagbayibo, Babatunde. "Common Problems Affecting Supranational Attempts in Africa: An Analytical Overview." Potchefstroom Electronic Law Journal/Potchefstroomse Elektroniese Regsblad 16, no. 1 (2017): 31. http://dx.doi.org/10.17159/1727-3781/2013/v16i1a2303.

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Ever since the colonial era, attempts have been made throughout the various regions of Africa at building supranational units chiefly for administrative and legal convenience. Examples of such attempts include the Federation of Rhodesia and Nyasaland, the East African High Commission and the federations in former French West and Equatorial Africa, all of which were attempts at forging a supranational nation state. These experiments laid the foundation for further supranational initiatives in post-colonial Africa. In this respect, every region in Africa has either experimented with or is currently experimenting with the idea of supranational regional organisations. This article aims at investigating selected attempts at supranationalism on the continent, the successes and failures of such experiments, and the lessons to be learnt from them. As Africa embarks on the journey of solidifying its unity through the establishment of leviathan continental institutions, efforts should be geared towards building on the experiences of past and present experiments at the sub-regional level. Such experiments offer instructive lessons as they are rooted in similar historical and social contexts.

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MIZUSAKI, ANA MARIA PIMENTEL, ANTONIO THOMAZ FILHO, and PEDRO DE CESERO. "Ages of the Magmatism and the Opening of the South Atlantic Ocean." Pesquisas em Geociências 25, no. 2 (1998): 47. http://dx.doi.org/10.22456/1807-9806.21166.

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The analysis of published and unpublished 368 K/Ar radiometric ages of basic, intermediate and alkaline volcanic rocks, related to the post-Paleozoic magmatism linked to the opening of the South Atlantic Ocean, yields some important evidence concerning the break up of the Gondwana supercontinent. At the Brazilian Equatorial margin, the Gondwana break up started in the Permo-Triassic, when the opening of the Equatorial South Atlantic Ocean began and spread out south-eastward up to the present day Amazon River mouth. During the middle Jurassic/lower Cretaceous (pre-Aptian), the continuity of this separation, towards the Potiguar Basin, was coeval with the northward opening of the south-east Brazilian margin, up to the Espírito Santo State latitude. The relationship between large volcanic events in the basins and the resistance to the rifting process development offered by the cratonic area was shown by the trend of the magmatic age. Along the equatorial margin, the fragmentation resistance caused by the São Luis / West African craton is manifested by a large basic magmatism described in the Tacutu, Acre, Solimões, Amazonas and Parnaíba basins. A similar mechanism along the south-east margin, is proposed for the magmatism described in the Paraná Basin which is associated with the fracturing resistance offered by the São Francisco/Congo cratonic area. The integration of geochronological, micropalentological, sedimentological and geochemical data from the basins of the east Brazilian continental margin supports a model to explain the final disruption between South America and Africa during Cenonian/Turonian time. This model implies that 90 Ma basic magmatic rocks, related to the oceanic crust formation, probably occur offshore from the present-day eastern Brazilian coast line.

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Kelly, M. A., J. M. Russell, M. B. Baber, et al. "Expanded glaciers during a dry and cold Last Glacial Maximum in equatorial East Africa." Geology 42, no. 6 (2014): 519–22. http://dx.doi.org/10.1130/g35421.1.

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Nelson, David M., Dirk Verschuren, Michael A. Urban, and Feng Sheng Hu. "Long‐term variability and rainfall control of savanna fire regimes in equatorial East Africa." Global Change Biology 18, no. 10 (2012): 3160–70. http://dx.doi.org/10.1111/j.1365-2486.2012.02766.x.

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Ongoma, Victor, Haishan Chen, Chujie Gao, Aston Matwai Nyongesa, and Francis Polong. "Future changes in climate extremes over Equatorial East Africa based on CMIP5 multimodel ensemble." Natural Hazards 90, no. 2 (2017): 901–20. http://dx.doi.org/10.1007/s11069-017-3079-9.

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Zhang, Qiong, Karin Holmgren, and Hanna Sundqvist. "Decadal Rainfall Dipole Oscillation over Southern Africa Modulated by Variation of Austral Summer Land–Sea Contrast along the East Coast of Africa." Journal of the Atmospheric Sciences 72, no. 5 (2015): 1827–36. http://dx.doi.org/10.1175/jas-d-14-0079.1.

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Abstract A rainfall dipole mode characterized by negative correlation between subtropical southern Africa and equatorial eastern Africa is identified in instrumental observation data in the recent 100 years. The dipole mode shows a pronounced oscillation signal at a time scale of about 18 years. This study investigates the underlying dynamical mechanisms responsible for this dipole pattern. It is found that the southern African rainfall dipole index is highly correlated to the land–sea contrast along the east coast of Africa. When the land–sea thermal contrast strengthens, the easterly flow toward the continent becomes stronger. The stronger easterly flow, via its response to east coast topography and surface heating, leads to a low pressure circulation anomaly over land south of the maximum easterly flow anomalies and thus causes more rainfall in the south. On a decadal time scale, an ENSO-like SST pattern acts to modulate this land–sea contrast and the consequent rainfall dipole. During a “wet in the south and dry in the north” dipole, there are warm SSTs over the central Indian Ocean and cold SSTs over the western Indian Ocean. The cold SSTs over the western Indian Ocean further enhance the land–sea contrast during austral summer. Moreover, these cold western Indian Ocean SSTs also play an important role in regulating land temperature, thereby suppressing clouds and warming the land via increased shortwave radiation over the less-cloudy land. This cloud–SST coupling acts to further strengthen the land–sea contrast.

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HADDAD, CHARLES R. "A revision of the spider genus Echinax Deeleman-Reinhold, 2001 (Araneae: Corinnidae) in the Afrotropical Region." Zootaxa 3450, no. 1 (2012): 33. http://dx.doi.org/10.11646/zootaxa.3450.1.6.

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The cryptic arboreal castianeirine genus Echinax Deeleman-Reinhold, 2001 (Araneae: Corinnidae), previously known only from South-East Asia, is recorded from the Afrotropical Region for the first time. The female of Copa longespina Simon, 1909 is redescribed, the male is described for the first time, and the species is transferred to Echinax as E. longespina (Simon, 1909) comb. nov. It occurs widely throughout equatorial Africa, from Kenya and Tanzania in the east to Liberia in the west. Six new species are described from both sexes: E. clara sp. nov. from D.R. Congo and Ghana, E. hesperis sp. nov. from Ivory Coast, E. natalensis sp. nov. and E. similis sp. nov. from South Africa, E. scharffi sp. nov. from Tanzania, and E. spatulata sp. nov., widespread across tropical Africa. The available ecological data indicates that all seven species are mainly arboreal and represent a prominent component of corinnid assemblage collected by canopy fogging, especially in forests.

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Blaauw, Maarten, Bas van Geel, Iris Kristen, et al. "High-resolution 14C dating of a 25,000-year lake-sediment record from equatorial East Africa." Quaternary Science Reviews 30, no. 21-22 (2011): 3043–59. http://dx.doi.org/10.1016/j.quascirev.2011.07.014.

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Liu, Xiting, Rebecca Rendle-Bühring, Inka Meyer, and Rüdiger Henrich. "Holocene shelf sedimentation patterns off equatorial East Africa constrained by climatic and sea-level changes." Sedimentary Geology 331 (January 2016): 1–11. http://dx.doi.org/10.1016/j.sedgeo.2015.10.009.

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Rietti-Shati, Miri, Ruth Yam, Wibjorn Karlen, and Aldo Shemesh. "Stable isotope composition of tropical high-altitude fresh-waters on Mt. Kenya, Equatorial East Africa." Chemical Geology 166, no. 3-4 (2000): 341–50. http://dx.doi.org/10.1016/s0009-2541(99)00233-8.

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Kelly, Meredith A., James M. Russell, Margaret B. Baber, et al. "ERRATUM: Expanded glaciers during a dry and cold Last Glacial Maximum in equatorial East Africa." Geology 45, no. 12 (2017): 1145. http://dx.doi.org/10.1130/g35421e.1.

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Shilenje, ZW, V. Ongoma, and BA Ogwang. "Upper Tropospheric and Stratospheric Ozone Over Equatorial East Africa; Case Study of Nairobi County, Kenya." Ethiopian Journal of Environmental Studies and Management 8, no. 3 (2015): 290. http://dx.doi.org/10.4314/ejesm.v8i3.6.

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Camberlin, Pierre, Vincent Moron, Raphael Okoola, Nathalie Philippon, and Wilson Gitau. "Components of rainy seasons’ variability in Equatorial East Africa: onset, cessation, rainfall frequency and intensity." Theoretical and Applied Climatology 98, no. 3-4 (2009): 237–49. http://dx.doi.org/10.1007/s00704-009-0113-1.

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Juo, A. S. R., and L. P. Wilding. "Soils of the lowland forests of West and Central Africa." Proceedings of the Royal Society of Edinburgh. Section B. Biological Sciences 104 (1996): 15–29. http://dx.doi.org/10.1017/s0269727000006102.

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The forest zone of West and Central Africa comprises the coastal and adjacent inland regions bounded the semi-deciduous forests in the west and the equatorial forests in central Africa and the Congo basin. Sedimentary plains, developed mostly on weathered sandy materials, lie along the coastal stretches and cover vast areas of the Congo basin. Behind the coast the plain rises gradually to hills and plateaus of much lower elevation than those of the highlands of East Africa. Two great rivers, the Niger and the Congo, which discharge huge volumes of fresh water to the Atlantic Ocean, are major contributors to the hydrological cycles of the rain forests ecosystems of the Guinea–Congo Region. The Niger originates from the forested highlands of Guinea and discharges its waters into the Bight of Benin by way of a large delta in southern Nigeria. The Congo basin occupies an immense area of 750 000 km2, surrounded by Pre-Cambrian uplands. The alluvial floor of the saucer-shaped basin is flat, and marshes and swamps comprise a large proportion of the total area. The highlands and plateaus along the rim are low to the west and north and higher to the south. To the east, they merge with the mountains of the Great Rift Valley of East Africa (Gann & Duignan 1972; Hance 1975; Grove 1978; Hamilton 1989).

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Zuluaga, Manuel D., and Robert A. Houze. "Extreme Convection of the Near-Equatorial Americas, Africa, and Adjoining Oceans as seen by TRMM." Monthly Weather Review 143, no. 1 (2015): 298–316. http://dx.doi.org/10.1175/mwr-d-14-00109.1.

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Abstract This study documents the preferred location and diurnal cycle of extreme convective storms that occur in the tropical band containing the east Pacific Ocean, Central and South America, the Atlantic Ocean, and northern Africa. Data from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar show three types of convective-stratiform structures that constitute extreme convective events: deep convective cores (DCCs), wide convective cores (WCCs), and broad stratiform regions (BSRs). Interim ECMWF Re-Analysis (ERA-Interim) data show the associated synoptic environmental factors associated with the occurrence of extreme convective features. The DCC, WCC, and BSR echoes are associated with early, middle, and late stages of convective system development, respectively, and the statistics and timing of their occurrence are related to topography and life cycle behavior of the convection. Storms containing DCC occur primarily over the Sudanian savannas of Africa and near the mountains in northern South America, being diurnally controlled. Storms with WCC manifest over land, in the same regions as the DCC, but also over oceanic regions. They appear around the clock but with maximum frequency at night. They are favored in regions of midlevel synoptic-scale low pressure systems, which over the sub-Sahara are the troughs of easterly waves. Storms containing BSR maximize over oceanic regions west of Africa and South America, where they exhibit a weak diurnal cycle with a slight midmorning maximum. Off the west coast of South America, the storms with WCC and BSR have longer lifetimes enhanced by orographic lifting over the Andes. The storms with BSR in the east Pacific Ocean often develop into tropical cyclones.

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Journal articles on the topic 'Equatorial East Africa'

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