Sahel Rainfall–Tropical Easterly Jet Relationship on Synoptic to Intraseasonal Time Scales
Sahel Rainfall–Tropical Easterly Jet Relationship on Synoptic to Intraseasonal Time Scales
复制标题
萨赫勒降雨与热带东急流在天气和季节内时间尺度上的关系
作者：
Alexander Lemburg;J. Bader;M. Claussen
热带偏东急流（TEJ）是西非季风（WAM）环流的一个典型高层特征。此外，在年际和年代际尺度上，西非上空的TEJ与夏季萨赫勒地区的降雨量呈显著相关。相比之下，萨赫勒地区降雨与区域TEJ在天气到季节内时间尺度上的关系尚不清楚。因此，这种关系是通过多重统计分析的方法来研究的，这些统计分析使用了时间上高分辨率的测量和再分析数据。结果表明，在所有天气到季节内的时间尺度上，对流活动与区域TEJ强度的平均相关系数保持在0.3以下。特别是在天气时间尺度上，TEJ明显滞后于对流活动异常1 ~ 2天，说明对流异常更可能驱动区域TEJ的变化，反之则相反。为了进一步阐明TEJ对西非降雨的作用，我们更仔细地研究了先前提出的TEJ诱导的高层辐散对中尺度对流系统（MCSs）发展的影响。对近300个萨赫勒mcs的分析表明，它们的形成通常与显著的TEJ异常或射流引起的高层辐散无关。此外，没有统计学上显著的证据表明，先前存在的与tej相关的上层辐散异常影响mcs的强度、大小和寿命。本研究的一个限制因素是对tej诱发的高层辐散的关注。因此，不能排除TEJ通过其他机制对萨赫勒地区降雨可能产生的影响，应该由未来的研究来确定。
The tropical easterly jet (TEJ) is a characteristic upper-level feature of the West African monsoon (WAM) circulation. Moreover, the TEJ over West Africa is significantly correlated with summer Sahel rainfall on interannual and decadal time scales. In contrast, the relationship between Sahel rainfall and the regional TEJ on synoptic to intraseasonal time scales is unclear. Therefore, this relationship is investigated by means of multiple statistical analyses using temporally highly resolved measurement and reanalysis data. It is shown that average correlations between convective activity and regional TEJ intensity remain below 0.3 for all synoptic to intraseasonal time scales. Especially on the synoptic time scale, the TEJ significantly lags anomalies in convective activity by one or two days, which indicates that convection anomalies are more likely to drive changes in the regional TEJ than vice versa. To further shed light on the role of the TEJ for rainfall over West Africa, a previously proposed effect of TEJ-induced upper-level divergence on the development of mesoscale convective systems (MCSs) is examined more closely. An analysis of nearly 300 Sahelian MCSs shows that their initiation is generally not associated with significant TEJ anomalies or jet-induced upper-level divergence. Furthermore, no statistically significant evidence is found that preexisting TEJ-related upper-level divergence anomalies affect intensity, size, and lifetime of MCSs. A limiting factor of this study is the focus on TEJ-induced upper-level divergence. Therefore, a possible effect of the TEJ on Sahel rainfall via other mechanisms cannot be ruled out and should be subject to future studies.
影响因子：
3.1
作者：
Yang G
通讯作者：
Yang G
影响因子：
3.1
作者：
Yang, Gui-Ying;Methven, John;Hoskins, Brian
通讯作者：
Hoskins, Brian