Interactions Between Mesoscale Eddies and Synoptic Oscillations in the Bay of Bengal During the Strong Monsoon of 2019

Abstract

AbstractThe 2019 southwest monsoon season is the first strong monsoon in the last 25 years and occurred concurrently with a strong positive Indian Ocean Dipole (pIOD). Given these unique circumstances, we examine the mesoscale eddy field in the Bay of Bengal (BoB) during 2019 and the interactions between these eddies and 3–7‐day synoptic oscillations and tropical systems, which contribute to monsoon rainfall and modulate the active (wet) and break (dry) phases of the Indian monsoon. We find that there is a drastic difference in eddy characteristics between the western (80–90°E) and eastern (90–100°E) BoB, where eddies in the eastern BoB are dominated by coastal Kelvin wave (CKW) dynamics and topographical influences, and the eddies in the western BoB are more heavily modulated by East India Coastal Current dynamics. We further find that the pIOD increased the overall sea level in the BoB and modified CKW propagation in the BoB such that all eddy types had more positive sea level anomalies. We find that cyclonic eddies vary coherently with both upper ocean heat content and 3–7‐day bandpass filtered precipitation and that both the number of cyclonic eddies and eddy amplitude increase in coherence with precipitation and ocean heat content following the passage of a tropical system. These results suggest a strong relationship between cyclonic eddies and 3–7‐day atmospheric variability.