Barotropic or Baroclinic: The Hybrid Genesis of Indian Summer Monsoon Low-Pressure Systems

Synoptic-scale vortices play a central role in regulating atmospheric energy and the hydrological cycle, but the dynamical identity of Indian Summer Monsoon Low-Pressure Systems (ISM-LPSs), critical for delivering 60−80% of India's seasonal rainfall, remains fundamentally unresolved. This persistent failure stems from reductive attempts to interpret these crucial systems within a binary tropical or baroclinic framework, which is inadequate for the unique monsoon environment. To address this gap, we present a systematic, comparative dynamical analysis of the large-scale environment (LSE) and storm-centered structure of synoptic vortices across the Northern Hemisphere. Using high-resolution reanalysis, we reveal that ISM-LPSs are associated with strong large-scale ascent forcing despite negligible near-surface baroclinicity, a unique combination that distinguishes them sharply from both canonical tropical and mid-latitude cyclones. Storm-centred composite analyses further reveal vertically coherent circulations that lack the pronounced frontal asymmetry characteristic of baroclinic systems. Together, these results indicate that ISM-LPSs occupy a distinct dynamical regime defined by monsoon-specific large-scale conditions, exhibiting systematic similarities to and departures from canonical tropical and baroclinic storms. By moving beyond dualistic classification, this study provides a clearer dynamical context for interpreting ISM-LPS genesis and evolution, with implications for their representation in weather and climate models.