Changes in tropical cyclone activity in north Indian Ocean during satellite era (1981-2014)

Recent findings have raised the debate on increase in tropical cyclone activity (TCA) in major tropical ocean basins like North Atlantic and western North Pacific. To address the similar evidence in North Indian Ocean (NIO) basins, an attempt has been made in the present study to investigate TCA in NIO basins in the context of warmer climate during the satellite era (1981-2014). The most suitable cyclone energy metric called accumulated cyclone energy (ACE) is estimated for this purpose. A statistical change-point analysis is conducted to detect the shift in ACE during the study period. Environmental factors influencing TCA are investigated to infer possible causes in the observed variability. The results indicate the increasing trend in ACE in NIO during satellite era with statistical significance of 95%. The frequency and duration of intense cyclones (wind speed >64knots) show notable increase in recent years. However, a decreasing trend is observed in total frequency. The change-point analysis of ACE in NIO reveals objectively that the shift occurs in 1997, with 20.8 ACE during 1981-1996 and 41.4 ACE during 1997-2014. The analysis reveals that increase in number and duration of very severe cyclonic storm (VSCS) (wind speed >64knots) in the recent epoch (1997-2014) is the major cause for the observed twofold increase in ACE. Also, the mean genesis location of intense BoB cyclones exposes a longitudinal eastwards shift of 2.3 degrees in the recent epoch, which could have aided the longevity of intense cyclones. Analysis of sea surface temperature (SST), upper ocean heat content (UOHC) and genesis potential index (GPI) climatology shows a positive agreement to the observed shift in genesis. The analysis of seven environmental factors shows substantial agreement with the increase and variability of ACE. Predominantly, atmospheric water vapour and SST show better correlation (.72 and .66) with ACE in NIO.