A global climatology of monsoon low-pressure systems
A global climatology of monsoon low-pressure systems
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DOI：
10.1002/qj.2447
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发表时间：
2015-04-01
影响因子：
8.9
通讯作者：
Boos, William R.
中科院分区：
文献类型：
--
作者：
Hurley, John V.;Boos, William R.
本文介绍了基于ERA中期再分析的季风低压系统的第一个全球气候学。低压系统被分为三个强度类别，并特别关注的是系统中的一个传统定义的季风低压。使用自动化算法识别1979-2012年850 hPa相对涡度、海平面气压和地面风速的分布。在当地夏季，北方半球形成的季风低压系统大约是南半球的两到三倍。成因的频率通常在当地夏季达到峰值，但在每个季风区全年都有低压系统形成。年际变化很弱，夏季计数的标准差通常低于长期夏季平均值的10%。区域合成显示，季风低压在印度，西太平洋和北方澳大利亚有一个共同的结构，包括一个温暖的冷核心和一个头重脚轻的潜在涡柱，从地面延伸到对流层上部。另一类季风低压系统在西非和澳大利亚西部的干旱地区发展，具有浅层复合结构，在对流层低层有一个温暖的核心，气旋性位涡局限于薄的近地表层。据估计，几乎所有季风区的低压系统占夏季降水的很大一部分，从大约40%到80%以上，在气候平均降水最大值的向极边缘。
The first global climatology of monsoon low-pressure systems is presented here, based on the ERA-Interim reanalysis. Low-pressure systems are classified into three intensity categories and particular focus is given to systems in the category corresponding to a traditional definition of monsoon depressions. Vortex tracks are identified using an automated algorithm applied to the distributions of 850 hPa relative vorticity, sea-level pressure and surface wind speed for 1979-2012. Roughly two to three times as many monsoon low-pressure systems form in the Northern Hemisphere as in the Southern Hemisphere during local summer. The frequency of genesis typically peaks in local summer, but low-pressure systems form throughout the year in every monsoon region. Interannual variability is weak, with standard deviations of summer counts typically being below 10% of the long-term summer mean. Regional composites reveal that monsoon depressions in India, the western Pacific and northern Australia share a common structure, consisting of a warm-over-cold core and a top-heavy column of potential vorticity that extends from the surface to the upper troposphere. A separate class of monsoon low-pressure systems develops over dry regions of West Africa and western Australia, with a shallow composite structure having a warm core in the lower troposphere and cyclonic potential vorticity confined to a thin near-surface layer. Low-pressure systems in nearly all monsoon regions are estimated to account for a large fraction, from about 40% to more than 80%, of summer precipitation on the poleward edge of the climatological mean precipitation maxima.