Evaluation of multi-level upper ocean heat content and its relationship with intensity and translation speed of tropical cyclones in the North Indian Ocean.

This study evaluated the changes in cyclone track parameters, which include the maximum sustained wind speed (Vmax) and translation speed (Vt) during 2010–2019. It established the Vt and Vmax connection with the oceanic heat content for the upper 50-m, 100-m, and 150-m layers (UOHC50, UOHC100, and UOHC150) for cyclones that formed over the North Indian Ocean (NIO) basin. The study considered a total of 20 cyclone cases (10 each) for the Arabian Sea (AS) and Bay of Bengal (BoB) utilizing the India Meteorological Department (IMD) best-track data to establish a quantitative relationship connecting the UOHC with Vmax and Vt. The correlation of Vt is slightly positive with UOHC50 for NIO and moderately positive (+0.253) for the BoB; however, a proper correlation is lacking for AS region. Also, an inter-comparison was performed for UOHC50, UOHC100, and UOHC150 with Vmax. Maximum correlation of Vmax is obtained with UOHC100 for AS and UOHC50 for the BoB. Analysis was also performed with cyclone cases individually for the two periods 2010–2015 and 2016–2019. Results signify a phase reversal (positive to negative) for (Vmax-UOHC) correlation values from upper 50 to 100 m for BoB cyclones Phailin (2013) and Hudhud (2014). A similar negative (−0.182) to positive (+0.602) shift is observed for the recent BoB cyclone Fani (2019). The parameter Vmax for recent storms showed significant correlation with oceanic warming at 150 m depth for Titli (2018) (−0.869) and Fani (2019) (+0.735). Relationship between UOHC50 and Vt for AS cyclones is evident compared to BoB cyclones. Both the AS and BoB pre-monsoon cyclones viz; Sagar (2018), Vayu (2019), and Fani (2019) showed negative (Vt –UOHC50) correlation in spite of the overall positive correlation noticed for other cases. The above three pre-monsoon cyclones showed high (Vmax –UOHC) correlation values. Recent accelerated warming for the AS basin can further accelerate Vt over this region, with a higher probability of more rapidly intensifying storms. The proximal factors have collinearity in enhancing the coastal vulnerability over this region. [ABSTRACT FROM AUTHOR]