Modulation of Daily Precipitation over East Africa by the Madden-Julian Oscillation
Modulation of Daily Precipitation over East Africa by the Madden-Julian Oscillation
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DOI：
10.1175/jcli-d-13-00693.1
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发表时间：
2014-08-01
影响因子：
4.9
通讯作者：
Zaitchik, Benjamin
中科院分区：
文献类型：
--
作者：
Berhane, Fisseha;Zaitchik, Benjamin
东非降水量的时空变化影响到数千万人的生计。从洪水、暴旱和农业的角度来看，季节内时间尺度上的变率是总变率的关键组成部分。本研究的主要目的是探讨亚季节的影响，对流层环流影响东非（EA）在长（3月至5月）和短（12月至12月）降雨和相关的降水变化的Madden-Julian振荡（MJO）。对1979-2012年的动力学和1998-2012年的降水量进行了分析。与以前的研究一致，在长时间和短时间的降雨过程中，发现了显著的MJO影响。然而，这种影响在每个季节都有所不同。具体而言，在70度-80度E和120度W的MJO对流指数与EA大部分地区的降水变化在早期（3月）和后期（5月）长雨季和中期和后期（11月至12月）短雨季有很强的相关性。在早期短暂的降雨（10月）出现了不同的模式，其中MJO强度在120度E（10度W）与沿海EA的干（湿）期有关，但与内陆无关。在4月，MJO对降水的影响是模糊的，但可以诊断的提前时间协会。这种影响的多样性反映了MJO影响机制的多样性，包括与大尺度大气环流和与索马里低空急流MJO调制相关的局部动力学相关的动力学和热力学机制。这些差异与EA的亚季节天气预报和气候预测问题有关。
Spatiotemporal variability in East African precipitation affects the livelihood of tens of millions of people. From the perspective of floods, flash droughts, and agriculture, variability on intraseasonal time scales is a critical component of total variability. The principal objective of this study is to explore subseasonal impacts of the Madden-Julian oscillation (MJO) on tropospheric circulations affecting East Africa (EA) during the long (March-May) and short (October-December) rains and associated variability in precipitation. Analyses are performed for 1979-2012 for dynamics and 1998-2012 for precipitation. Consistent with previous studies, significant MJO influence is found on wet and dry spells during the long and short rains. This influence, however, is found to vary within each season. Specifically, indices of MJO convection at 70 degrees-80 degrees E and 120 degrees W are strongly associated with precipitation variability across much of EA in the early (March) and late (May) long rainy season and in the middle and late (November-December) short rainy season. In the early short rains (October) a different pattern emerges, in which MJO strength at 120 degrees E (10 degrees W) is associated with dry (wet) spells in coastal EA but not the interior. In April the MJO influence on precipitation is obscured but can be diagnosed in lead time associations. This diversity of influences reflects a diversity of mechanisms of MJO influence, including dynamic and thermodynamic mechanisms tied to large-scale atmospheric circulations and localized dynamics associated with MJO modulation of the Somali low-level jet. These differences are relevant to problems of subseasonal weather forecasts and climate projections for EA.