A Vorticity-Based Climatology of Mesocyclogenesis Hotspots in the Southern Ross Sea

Polar lows (PLs) are intense small-scale cyclones whose detection remains challenging, limiting our understanding of their climatology. This study addresses this gap by developing an objective tracking algorithm to create a 35-year (1990-2024) climatology of potential PLs for the Southern Ross Sea using high resolution ERA5 reanalysis.

The method employs a multi-scale filtering approach to identify the key dynamical drivers and characteristic signatures of mesocyclogenesis. Potential systems are first detected using a primary dynamical criterion, defined by a significant maximum in 850-hPa relative vorticity, typically associated with an upper-level trough. Candidates are then filtered using a deep static instability criterion representing the thermodynamic contribution. The final selection retains features that exhibit canonical mesoscale characteristics of mesocyclones, including a compact vortex size, a short lifetime, strong surface winds, and a distinct negative mean sea level pressure (MSLP) anomaly. The results reveal that the primary regions for potential PL formation are concentrated along the Transantarctic Mountain coastline, with key hotspots near Terra Nova Bay, the Byrd Glacier and Siple Coast. The seasonal cycle is dominated by peaks in the transitional months of March and October, which represent the highest frequency of polar low candidates annually. A secondary, less pronounced peak in activity is observed during the mid-winter months of June and July. On an interannual scale, the climatology reveals a significant negative trend in summer PLs from 2008 to 2018. This decreasing trend is strongly correlated with a concurrent decline in regional atmospheric static instability, suggesting that a stabilization of the lower troposphere is a key driver of potential decline in PL number occurrence in the Ross Sea region. A key limitation of this vorticity-based approach is the potential for false positives, particularly the detection of shear-induced vorticity features that lack a coherent surface circulation.  This work creates the comprehensive, long-term, and objective climatology of mesocyclogenesis for the Ross Sea Region. This foundational dataset enables a quantitative analysis of the key drivers of mesocyclogenesis in the region. It provides a crucial benchmark for systematically investigating the interaction between large-scale atmospheric patterns, katabatic wind surges, sea ice extent, and topography in forcing high-latitude PLs activity, and for assessing how these relationships may shift under future climate change.