A quasi-geostrophic analysis of summertime southern African linear-regime westerly waves
A quasi-geostrophic analysis of summertime southern African linear-regime westerly waves
复制标题
夏季南部非洲线性型西风波的准地转分析
DOI：
10.1007/s00382-023-07067-0
复制
发表时间：
2024
期刊：
影响因子：
4.6
通讯作者：
Ndarana T
中科院分区：
文献类型：
--
作者：
Ndarana T
在南非域传播的线性西风波通常与众所周知的降雨产生系统有关，如热带温带槽和天气尺度热带低压系统，以及表面的南大西洋反气旋。人们普遍认为，斜压波传播的域提供了提升机制，导致所需的垂直运动的降雨发生。这项研究表明，有一个急流条纹嵌入在这些波位于槽轴的下游，东部的垂直向上运动预计将发生。当波传播经过该区域时，急流的入口正好经过该国的南部。研究进一步表明，对于这类波，垂直运动，导致降雨的发生是由热直接横向非地转环流，位于这个射流入口。这是代替传统的高空辐散，位于槽轴以东的拐点。本文采用将Q矢量分解为横向分量和切变分量的方法，用这两个分量的散度场分别将垂直运动分解为相应的分量，即，和，结果表明，前者比后者更能解释南非上空的垂直运动。因此，全国的隆升和位于海槽以东的感染点的隆升是动力学上不同的过程。考虑到准地转框架的局限性，本文认为，在线性波通过过程中，可能导致降水的垂直运动是由急流入口处的环流引起的，而不是斜压波的辐散引起的。
Linear-regime westerly waves that propagate across the South African domain are often linked to well-known rainfall producing systems such as tropical temperate troughs and synoptic scale tropical low-pressure systems, and ridging South Atlantic Ocean anticyclones at the surface. It is accepted that the baroclinic waves that propagate across the domain provide the lifting mechanism that causes the required vertical motion for rainfall to occur. This study shows that there exists a jet streak embedded in these waves that is located downstream of the trough axis, to the east of which vertically upward motion is expected to occur. The entrance of the jet streak passes just south of the country, as the waves propagate past the domain. The study further shows that for this class of waves, the vertical motion that causes rainfall to occur is induced by the thermally direct transverse ageostrophic circulation that is located at this jet entrance. This is instead of the conventional upper air divergence that is located at the inflection point east of the trough axis. Using a method of decomposing theQ-vector into its transverse () and shear () components, the divergence fields of which are used to decompose the vertical motion into the corresponding components, i.eand, respectively; it was shown that the vertical motion over South Africa is explained more by the former than the latter. Therefore, the uplift over the country and that located at the infection point east of the trough are dynamically distinct processes. Taking the limitations of the quasi-geostrophic framework into consideration, the study concludes that during the passage of linear-regime waves vertical motion that might lead to rainfall is caused by the circulation at the jet entrance and not the divergence in the baroclinic wave.
登录
查看更多内容
南部非洲副热带地区截止低压系统特征的变化
DOI：
--
发表时间：
2007
期刊：
影响因子：
--
作者：
A. Singleton;C. Reason
通讯作者：
C. Reason
非洲南部副热带夏季与南大西洋反气旋脊相关的流量和水分通量
DOI：
--
发表时间：
2020
期刊：
International Journal of Climatology
影响因子：
--
作者：
T. Ndarana;Siyabonga Mpati;Mary;F. Engelbrecht;H. Chikoore
通讯作者：
H. Chikoore
DOI：
10.1002/joc.6644
发表时间：
2020
期刊：
International Journal of Climatology
影响因子：
--
作者：
N. Crespo;R. P. da Rocha;M. Sprenger;H. Wernli
通讯作者：
H. Wernli
涡度平流对高空急流锋系统发展影响的准地转诊断
影响因子：
8.9
作者：
Jonathan E. Martin
通讯作者：
Jonathan E. Martin
东南太平洋截止低点的能量
影响因子：
4.6
作者：
M. Gan;E. D. Piva
通讯作者：
E. D. Piva