Modified tropical cyclone genesis potential index over the Bay of Bengal during southwest and post-monsoon seasons

In the present study, an attempt has been made to develop a modified genesis potential index (GPI) by considering the atmospheric parameters of relative humidity (RH), thermal instability (TI), relative vorticity (RV), vertical wind shear (WS) and the ocean parameters of sea surface height (SSH) and upper ocean heat content (UOHC). The new genesis potential index (GPI) is a modified version of the currently used GPI by the India Meteorological Department (IMD), New Delhi for the North Indian Ocean which does not consider the ocean parameters. The main objective of the present study is to examine and improve our earlier GPI (Suneeta and Sadhuram 2018), during southwest monsoon (June–September) and post-monsoon (October–December) seasons for the period 1995–2018, over Bay of Bengal. In addition to UOHC and atmospheric parameters, we have introduced a new term, sea surface height (SSH) to compute the new GPI. Correlations have been computed between GPI and TNDC (total number of depressions, cyclones and severe cyclones) during both the seasons. This new index displayed very high correlation coefficient (CC) r = 0.85 (significant at a level greater than 99%) with the TNDC for the post-monsoon season. But it showed low correlation during SW monsoon season in which the GPI (Kotal et al. 2009) (which considers only atmospheric parameters) showed a correlation of 0.5 which is significant at 95% level. From this, it is inferred that the atmospheric parameters are important during southwest monsoon, while both atmospheric and ocean parameters (UOHC and SSH) appear to be playing important role during post-monsoon season. In this paper, the SSH has been included or the first time in the GPI which showed better performance during post-monsoon season.