Offshore Migration of Summer Monsoon Low-Level Jet on a Diurnal Scale

Abstract

This study investigates the diurnal migration of the low-level jet (LLJ) over the Bay of Bengal in the summer monsoon, which remains understudied despite the well-documented diurnal offshore propagation of rainfall worldwide. The southwesterly LLJ exhibits maximum strength during the night and morning. The LLJ undergoes a substantial eastward migration of approximately 600 km from the eastern offshore of India at midnight to the center of the Bay of Bengal by afternoon. A linear land-sea breeze model is effective in capturing the diurnal migration with similar speed and phase. Including background wind offshore extends the migration, rather than confining it to the coast. This migration is driven by inertia-gravity waves arising from the diurnal land-sea thermal contrast and is influenced by the westerly upstream wind from the Indian subcontinent. Our results have important implications for understanding diurnal monsoon circulations and their associated precipitation.