The four regional varieties of South Asian monsoon low-pressure systems and their modulation by tropical intraseasonal variability
The four regional varieties of South Asian monsoon low-pressure systems and their modulation by tropical intraseasonal variability
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南亚季风低压系统的四种区域变化及其热带季内变率的调节
作者：
Deoras A
印度次大陆每年夏季风季节（6月至9月）都会受到天气尺度气旋性涡旋的影响。这些被称为季风低压系统（LPS）的涡旋最常在孟加拉湾（BoB）的顶部和邻近的陆地地区发展，在印度上空向西北偏西方向传播，并沿其路径沿着大量降水（如Mooley，1973; Godbole，1977）。LPS在印度次大陆引发了几次灾难性的洪水，包括2018年的喀拉拉邦洪水（Hunt和Menon，2020）。以前的研究表明，平均寿命为3至5天的LPS负责印度夏季季风降雨量的一半左右（例如Yoon和Chen，2005; Hunt和弗莱彻，2019）。根据印度气象局的资料，1在陆地上以2 hPa的间隔具有两个闭合的等压线的系统，或在海上具有3分钟最大持续风速8.5-13.5 ms− 1的系统被称为季风低压，而比这更弱的系统被称为季风低压区。通常情况下，每年夏天形成约14个LPS，其中一半会增强为季风低压（Boos et al.，2015年）。LPS的频率和寿命在7月和8月都比6月和9月大（Krishnamurthy和Ajayamohan，2010）。
The Indian subcontinent is affected by synoptic-scale cyclonic vortices each summer monsoon season (June–September). These vortices, known as monsoon low-pressure systems (LPSs), most frequently develop over the head of the Bay of Bengal (BoB) and adjoining land area, propagate westnorthwestward over India, and produce abundant precipitation along their tracks (eg Mooley, 1973; Godbole, 1977). LPSs have triggered several catastrophic floods in the Indian subcontinent, including the 2018 Kerala floods (Hunt and Menon, 2020). Previous studies have suggested that LPSs, which have an average lifespan of 3 to 5 days, are responsible for around half of the summer monsoon rainfall over India (eg Yoon and Chen, 2005; Hunt and Fletcher, 2019). According to the India Meteorological Department, 1 systems featuring two closed isobars in surface pressure at 2 hPa intervals over land, or those featuring 3-minute maximum sustained surface wind speeds of 8.5–13.5 ms− 1 over sea are referred to as monsoon depressions, whereas systems weaker than this are referred to as monsoon low-pressure areas. Typically, around 14 LPSs form each summer and half of them intensify into monsoon depressions (Boos et al., 2015). Both the frequency and lifespan of LPSs are larger in July and August than in June and September (Krishnamurthy and Ajayamohan, 2010).