Rainfall Characteristics and Trends—and the Role of Congo Westerlies—in the Western Uganda Transition Zone of Equatorial Africa From 1983 to 2017
Rainfall Characteristics and Trends—and the Role of Congo Westerlies—in the Western Uganda Transition Zone of Equatorial Africa From 1983 to 2017
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DOI：
10.1029/2019jd031243
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发表时间：
2019-10
期刊：
影响因子：
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通讯作者：
J. Diem;Hae Seung Sung;B. Konecky;M. Palace;J. Salerno;J. Hartter
中科院分区：
文献类型：
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作者：
J. Diem;Hae Seung Sung;B. Konecky;M. Palace;J. Salerno;J. Hartter
虽然在过去几十年里对赤道非洲的长期降雨趋势和相关的大气动力学进行了研究，但对乌干达西部的降雨知之甚少，乌干达西部是非洲大陆中部的过渡区。利用1983年至2017年的卫星降水和再分析数据，本研究考察了季节的大气特征和降雨的多年代际趋势。该地区大部分地区一年两次降雨（即第一次降雨在3 - 5月，第二次降雨在8 - 11月）。在雨季（旱季），在乌干达西部观测到上升（下降）空气和增加（减少）比湿度。除了第一个旱季（即12月至2月）外，东南气流环流在乌干达西部任何时候都很常见。在所有季节，乌干达西部潮湿的日子的特点是上升空气和比湿度的增加，以及西风气流的异常。在大多数季节的潮湿天气中，西风背部轨迹延伸到刚果盆地上空的频率也高得不成比例。与其他轨迹相比，这些刚果西风带与更多的垂直上升和更潮湿的对流层中部有关。整个乌干达西部的雨季，尤其是初雨，变得越来越长，越来越潮湿。35年来初雨持续时间增加了约1个月；反过来，总降雨量增加了大约70%。除了12月至2月，气候季节的降雨量也有所增加。随着时间的推移，对流层中层比湿度的增加和垂直上升为卫星降水数据得出的湿润趋势提供了支持。
While long‐term rainfall trends and related atmospheric dynamics have been researched over the past several decades across equatorial Africa, little is known about rainfall in western Uganda, a transition zone in the middle of the continent. Using satellite‐derived rainfall and reanalysis data from 1983 to 2017, this study examines atmospheric characteristics of seasons and multidecadal trends in rainfall. Most of the region has a biannual rainfall regime (i.e., the first rains within March–May and the second rains during August–November). Ascending (descending) air and increased (decreased) specific humidity are observed over western Uganda during the rainy (dry) seasons. Southeasterly air‐parcel back trajectories are common throughout western Uganda at all times except for the first dry season (i.e., December–February). For all seasons, wet days in western Uganda are characterized by increases in ascending air and specific humidity in addition to westerly flow anomalies. Wet days in most seasons also have a disproportionately high frequency of westerly back trajectories extending over the Congo Basin. These Congo westerlies are associated with more vertical ascent and a more humid middle troposphere compared to the other trajectories. Rainy seasons, especially the first rains, have gotten longer and wetter throughout western Uganda. The duration of the first rains increased by about 1 month over the 35 years; in turn, the rainfall total increased by approximately 70%. Rainfall also has increased for climatological seasons, with the exception being December–February. Increases in middle‐troposphere specific humidity and vertical ascent over time provide support for the wetting trends derived from the satellite‐derived rainfall data.