The monsoon low-level jet (MLLJ) originates at Mascarene high and after traveling thousands of kilometers enters India from the western boundary causing deep convection, cloudiness, and rainfall. Although its core lies at 850 hPa, it has a large vertical extent; therefore, different meteorological parameters at different levels have a large influence on the Indian summer monsoon rainfall. This study aims to examine the upper-air climatology of 9 stations on the west coast and central Peninsular India and to find out the effects of various parameters at different standard pressure levels on the Indian summer monsoon rainfall variability. We used the 34-yr (1971–2004) actual upper-air radiosonde/radio wind and standard synoptic surface observations data from these 9 stations and reported some new aspects of the MLLJ. The NCEP/NCAR and ECMWF reanalysis wind data have also been used to holistically study the features of MLLJ over sea and land areas. This study, as opposed to some recent studies, confirms the splitting of MLLJ into two branches, which can be seen on a few days during the monsoon season. Further analyses show that the change in geopotential height between 800 and 900 hPa has a strong bearing on the strength of MLLJ. The change in the upper-air pressure gradient force over the Indian landmass can cause a change in the wind speed of MLLJ during the monsoon season.

季风低空急流 (MLLJ) 起源于马斯克林高地，行进数千公里后从西部边界进入印度，造成深层对流、多云和降雨。其核心虽然位于850 hPa，但垂直范围较大；因此，不同层次的不同气象参数对印度夏季风降水影响较大。本研究旨在检查西海岸和印度半岛中部 9 个站点的高空气候学，并找出不同标准压力水平下各种参数对印度夏季季风降雨变化的影响。我们使用了来自这 9 个台站的 34 年（1971-2004 年）实际高空无线电探空仪/无线电风和标准天气表面观测数据，并报告了 MLLJ 的一些新方面。NCEP/NCAR 和 ECMWF 再分析风数据也被用于全面研究 MLLJ 在海洋和陆地区域的特征。与最近的一些研究相反，这项研究证实了 MLLJ 分裂成两个分支，这可以在季风季节的几天内看到。进一步分析表明，位势高度在800~900 hPa之间的变化对MLLJ的强度有很强的影响。印度大陆上空高空气压梯度力的变化会导致季风季节MLLJ的风速发生变化。进一步分析表明，位势高度在800~900 hPa之间的变化对MLLJ的强度有很强的影响。印度大陆上空高空气压梯度力的变化会导致季风季节MLLJ的风速发生变化。进一步分析表明，位势高度在800~900 hPa之间的变化对MLLJ的强度有很强的影响。印度大陆上空高空气压梯度力的变化会导致季风季节MLLJ的风速发生变化。