Paradigms for the Origin of the Monsoon Onset Vortex

In certain years, during the onset of the Indian Summer Monson, a synoptic scale vortex, known as the Monsoon onset vortex (MOV) forms in the Arabian Sea within the seasonal northward propagating region of precipitating convection. Many MOVs intensify into tropical cyclones and significantly impact the onset and advance of the Monsoon. Using reanalysis data from 1982-2022, we find two pathways for MOV formation – a) vertical alignment of a low-level and mid-level vortex and b) top-down development of a mid-level vortex. Our results indicate that most MOVs have formed by the former mechanism. The dynamics governing the MOV formation, and its observed structure is further elucidated through diagnostics based on potential vorticity and moist static energy budgets in this ongoing work.