Correlation Between the Arabian Sea Surface Temperature and the Onset Period of South Asian Summer Monsoon with Trend Analysis on the Intensity

The long-term trend of the Arabian Sea surface temperature (ASST) during the formation of the South Asian summer monsoon (SASM) is discussed in this manuscript. From April to June, ASST changed from a meridional gradual distribution to a spatially uniform distribution and then to a zonal gradual distribution. The South Asian summer monsoon intensity (SASMI) and South Asian summer monsoon direction (SASMD) indicate that the variation of the ASST is highly related to the formation of the SASM during the summer monsoon period and can contribute to the spread of the SASM from the Southwest Arabian Sea throughout all of South Asia. Results of the correlation between the ASST and SASMI for the same month and its adjacent months were the same, and the areas of the positive correlation between the ASST and SASMI significantly increased from May-June as compared to April-May. The maximum correlation coefficient was 0.86. The results of the ASST and SASMD for the same month and its adjacent months were substantially different. However, the ASST and SASMD for May and April also showed a high positive correlation with a maximum correlation coefficient of 0.61 in the southwestern Arabian Sea. Existence of the ASST had a spatially consistent and significant upward trend with a mean increase of 0.6 degrees C during the summer monsoon period from 1980 to 2020 (between April and September), whereas the SASMI had a strengthening trend along the western and southwestern regions of the Arabian Sea and the southeastern region of the Arabian Peninsula. Meanwhile, the rest of the study regions showed a declining trend. Overall, the entire study region showed a slight downward trend, and the average value decreased by 0.02ms(-1).