The impact of land-sea thermal contrast on the South Asian summer monsoon (SASM) was investigated by calculating the atmospheric heat sources (AHS) and baroclinic component with ERA5 data for the period 1979–2019. Using diagnostic and statistical methods, it was found that the thermal contrast between the Tibetan Plateau (TP) and the tropical Indian Ocean (TIO) affects the South Asian monsoon circulation through the meridional temperature gradient in the upper troposphere. The seasonal changes of the AHS of the TP and TIO are reversed. In summer, the TP is the strongest at the same latitude whereas the TIO is the weakest, and the thermal contrast is the most obvious. The heat sources of the TP and TIO are located on the north and south side of the strong baroclinic area of the SASM region, respectively, and both of which are dominated by deep convective heating in the upper troposphere. The TP-TIO regional meridional thermal contrast index (QI) based on the AHS, and the SASM index (MI) based on baroclinicity were found to be strongly positively correlated. In years of abnormally high QI, the thermal contrast between the TP and TIO is strong in summer, which warms the upper troposphere over Eurasia and cools it over the TIO. The stronger temperature gradient enhances the baroclinicity in the troposphere, which results in a strengthening of the low-level westerly airflow and the upper-level easterly airflow. The anomalous winds strengthen the South Asian high (SAH), with the warmer center in the upper troposphere, and the enhanced Walker circulation over the equatorial Indian Ocean. Finally, the anomalous circulation leads to much more precipitation over the SASM region. The influence of abnormally low QI is almost the opposite.

通过使用ERA5数据计算1979-2019年期间的大气热源（AHS）和斜压分量，研究了陆海热反差对南亚夏季风（SASM）的影响。使用诊断和统计方法，发现青藏高原（TP）与热带印度洋（TIO）之间的热反差通过对流层上层的子午温度梯度影响南亚季风环流。TP和TIO的AHS的季节性变化是相反的。在夏季，相同纬度下的TP最强，而TIO最弱，并且热对比度最明显。TP和TIO的热源分别位于SASM地区强斜压区的北侧和南侧，两者都以对流层高层的对流加热为主导。TP-TIO区域子午热对比指数（发现基于AHS的QI）和基于斜压度的SASM指数（MI）呈强正相关。在QI异常高的年份中，夏季TP和TIO之间的热反差很强，这使欧亚大陆上的对流层温暖并在TIO上使之冷却。较强的温度梯度会增强对流层中的斜压度，从而增强低层西风气流和上层东风气流的强度。异常风增强了南亚高压（SAH），对流层上层的中心变暖，赤​​道印度洋上空的沃克环流增强。最后，异常环流导致SASM地区更多的降水。影响力异常偏低QI几乎相反。