Role of Convective and Circulation features on Multi Scales in Modulating Tracks of Tropical Cyclones Formed Over the Bay of Bengal

Abstract

Large-scale background environment, which can regulate Tropical cyclones (TCs) movement, is modulated by the atmospheric anomalies prevailing on quasi-biweekly (10-20 days;QBWO), intra-seasonal (20-90 days;ISO) and inter-annual (≥91 days) scales. In this regard, many studies noticed the influence of multi-scale atmospheric variability on TCs formation over the North Indian Ocean, including the Arabian Sea and the Bay of Bengal (BoB). However, their influence on the TCs movement needs to be better understood. The current study presents the role of atmospheric variations that prevailed on the various scales, as mentioned above, in determining the movement of TCs formed over the BoB region. Based on the IMD TCs best-track data available from 1982-2020 and global ERA5 reanalysis dataset consisting of single-and multi-level variables, composites of various diagnostic parameters related to the convection and circulation are examined. The identified features from the composite analysis indicated that the atmospheric anomalies on QBWO and ISO scales, in combination with mean climatology, predominantly determine tracks of TCs formed during the pre-monsoon season (March-April-May). In contrast, the mean climatology mean environment (CLM) seems responsible for the observed TCs tracks during the post-monsoon season (October-November-December). More importantly, TCs track-wise diagnosis reveals that QBWO and ISO-induced anomalies jointly providea guiding effect for TCs moving in northward, north-eastward, and north-westward directions and TCs taking re-curvature. Meanwhile, CLM mainly drives the westward-moving TCs. However, examined anomalies on the inter-annual scale do not exhibit any significant physical linkages with the TCs movement. Further, a case study analysis by performing a set of experiments using the Weather Research and Forecasting (WRF-ARW) model initialized with unfiltered and scale-filtered fields also substantiates our previousfindings. The findings may provide better insights into an improved understanding of TCs movement over the BoB region and help in undergoing research on TCs track prediction at sub-seasonal scales.