Formation and maintenance of monsoon inversion over the Arabian Sea

Monsoon Inversion (MI) plays a key role and is one of the semi-permanent features of Asian Summer Monsoon. MI is defined as a sustained temperature inversion (TI) that is observed in the lower troposphere, during summer monsoon (June to September) over the Western AS (WAS) with its peak between July and August. A comprehensive analysis of formation, evolution, and dissipation of MI is made using long-term observations from satellites and ERA-5 reanalysis of 15 years (2008-2022). The climatological day-to-day and monthly variations of MI over the Arabian Sea are studied. The occurrence of inversion (TI) during pre-monsoon, i.e., during April and May, is at a lower altitude and is strengthened by subsidence. The MI is found to occur strongly over the WAS, while it is seen occasionally with lesser strength over the Eastern Arabian Sea (EAS) during July-August. The advection is nearly five times stronger than subsidence. The reasons for the existence and strength of MI are investigated using the data of dust from the CALIPSO. There is a similar to 15% difference in the occurrence of dust over WAS compared to EAS. Also, MI occurrence has shown significant differences in temperature profiles during dust and non-dust cases. The analysis of MI reveals that strong MI is due to more advection of warm dry and dust laden air from desert regions (west, north and northwest directions). The present study has significance to the understanding of interannual monsoon variability.