Internal processes within the African Easterly Wave system
Internal processes within the African Easterly Wave system
复制标题
非洲东波系统内的内部过程
DOI：
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
F. Couvreux
中科院分区：
文献类型：
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作者：
D. E. Poan;J. Lafore;R. Roehrig;F. Couvreux
使用ERA-I再分析研究了非洲东风波（AEW）系统内的内部过程，包括质量场、动力场和水汽场，以突出对流与AEW之间的相互作用。根据Poan等人（2013年）的建议，使用天气尺度可降水量异常对AEW的不同阶段进行了分析。萨赫勒地区存在的强气候学水汽纬向梯度影响了表观热源和湿汇的形状。萨赫勒上空的AEW事件与热带辐合带（ITCZ）的纬向移动有关。低层和中层之间的小尺度对流输送也突出了大的动量交换，有助于加强600 hPa的AEW环流和季风气流的阻尼。这也似乎是与AEW相关的纬向风垂直倾斜的可能机制。在西非热低（HL）地区的南侧，这种AEW发生的热收支计算表明，加热异常主要是由水平平流驱动的。垂直环流作为一种前兆，启动了对流层低层的热量输送。然而，较弱的湍流混合也参与了这些异常的发展，特别是在边界层中。这些预算最终允许不同的非绝热和绝热过程的贡献被确定。
The internal processes within an African Easterly Wave (AEW) system, involving mass, dynamic and water vapour fields are investigated using ERA‐I reanalysis, in order to highlight the interactions between convection and AEWs. The budgets of heat, moisture and momentum are analysed during the different phases of AEWs detected using synoptic‐scale precipitable water anomalies as proposed by Poan et al. (2013). The strong climatological meridional gradient of moisture present in the Sahel impacts the shape of the apparent heat source and humidity sink. AEW events over the Sahel are associated with a meridional shift of the intertropical convergence zone (ITCZ). Large exchanges of momentum by small‐scale convective transport are also highlighted between the low‐ and mid‐levels, contributing to the reinforcement of the AEW circulation at 600 hPa and the damping of the monsoon flow. This also appears as a possible mechanism for the vertical tilt of the meridional wind associated with AEWs. Heat budget computation, in the southern flank of the West African Heat‐Low (HL) region where such AEWs occur, reveals that the heating anomalies are mainly driven by the horizontal advections. The vertical circulation acts as a precursor, which initiates the heat transport in the lower troposphere. However, weaker, turbulent mixing also participates in the development of these anomalies, especially in the boundary layer. These budgets ultimately allow the distinct contributions of diabatic and adiabatic processes to be determined.