Changes in March to May rainfall over Tanzania during 1978–2017,International Journal of Climatology

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Changes in March to May rainfall over Tanzania during 1978–2017
International Journal of Climatology ( IF 3.5 ) Pub Date : 2021-04-21 , DOI: 10.1002/joc.7146
Exavery Kisesa Makula _{1,

2,

3} , Botao Zhou _{1,

2}

Affiliation

This study assessed the change in March to May (MAM) rainfall over Tanzania during 1978–2017. It is revealed that the MAM rainfall experienced more years of negative (positive) anomalies after (before) the late 1990s. The atmospheric and oceanic background underlying such a change in MAM rainfall was addressed. The results show that the recent decrease in MAM rainfall is associated with the reduction of water vapour transport from the Indian Ocean to Tanzania, the enhancement of tropospheric moisture divergence, and the decrease of convective activities over Tanzania. Changes of sea surface temperature (SST) in the 1990s from a cold phase to a warm phase over the southwestern Indian Ocean and western tropical Pacific Ocean and that from a warm phase to a cold phase over the southern Atlantic Ocean also have a significant contribution. Associated with the SST warming over the southwestern Indian Ocean, an anomalous cyclonic circulation prevails over the tropical Indian Ocean in the upper level, favourable for the increase of subsidence in Tanzania. Concurrently, the Mascarene High shifts eastward, which may weaken the water vapour transport from the southern Indian Ocean toward Tanzania. The warming of SST over the western tropical Pacific Ocean is linked to a Walker-like circulation with the descending limb over the western Indian Ocean and Tanzania, conducive to the subsidence over Tanzania. Related to the SST cooling over the southern Atlantic Ocean, anomalous atmospheric convergence in the upper level is dominant over Tanzania, concurrent with the easterly outflow toward the Congo basin and the westerly and northerly outflow toward the western Indian Ocean from Tanzania in the low level, favouring the decrease of MAM rainfall.

中文翻译：

1978-2017 年坦桑尼亚 3 月至 5 月降雨量变化

本研究评估了 1978 年至 2017 年坦桑尼亚 3 月至 5 月 (MAM) 降雨量的变化。结果表明，在1990年代后期（之前）之后，MAM降雨经历了更多年的负（正）异常。解决了 MAM 降雨变化背后的大气和海洋背景。结果表明，近期MAM降雨量减少与从印度洋到坦桑尼亚的水汽输送减少、对流层水分辐散度增强以及坦桑尼亚上空对流活动减少有关。1990年代西南印度洋和热带太平洋西部海面温度(SST)由冷相向暖相的变化以及南大西洋由暖相向冷相的变化也有显着贡献。与印度洋西南部海温升高相关，热带印度洋上层异常气旋环流盛行，有利于坦桑尼亚的沉降增加。与此同时，马斯卡林高压向东移动，这可能会削弱从南印度洋向坦桑尼亚的水汽输送。西热带太平洋海温升高与西印度洋和坦桑尼亚上空的下降支路形成类似沃克的环流有关，有利于坦桑尼亚的下沉。与南大西洋的海温变冷有关，坦桑尼亚上层的异常大气辐合占主导地位，

更新日期：2021-04-21

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