Intensification of Arabian Sea cyclone genesis potential and its association with Warm Arctic Cold Eurasia pattern

Abstract

The present study examines the drivers of the observed increasing trend in the Genesis Potential Index (GPI) of the post-monsoon season (October-November-December) tropical cyclones in the Arabian Sea (AS) during the period, 1998–2021. The increase in atmospheric moisture loading, ocean heat content in the upper 300 m (OHC300) and reduction in vertical wind shear are the major factors which caused the intensification in cyclone GPI in the recent decades. The increase in atmospheric moisture loading and OHC300 are consistent with the overall observed ocean warming trend of the region. However, the reduction in vertical wind shear has resulted from an anomalous large-scale upper atmospheric anticyclonic circulation over central India. Further investigation shows a concurrent transition of the Warm Arctic Cold Eurasia (WACE) pattern to its positive phase which strengthened and shifted the Subtropical Jet (STJ) poleward. This resulted in the anticyclonic circulation anomaly and altered the upper tropospheric zonal winds over the AS cyclone genesis region, weakening the vertical wind shear. The study demonstrates a possible physical mechanism through which remote forcing due to changes in the northern high-latitude climate can influence the AS cyclone genesis.