The role of ENSO and MJO on rapid intensification of tropical cyclones in the Bay of Bengal during October–December
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- Girishkumar, M.S., Suprit, K., Vishnu, S. et al. Theor Appl Climatol (2015) 120: 797. doi:10.1007/s00704-014-1214-z
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The influence of El Niño/Southern Oscillation (ENSO) and Madden–Julian Oscillation (MJO) and their combined effect on the rapid intensification (RI) of tropical cyclones (TCs) in the Bay of Bengal (BoB) during the primary cyclone season (October–December) is investigated. An empirical index, called genesis potential index (GPI), is used to quantify the relative importance of four environmental parameters responsible for the modulation of TCs characteristics. The analysis shows that TC frequency and RI of TC’s is higher in La Niña than El Niño regime during the primary TC season in the BoB. The combined effect of enhancement (reduction) in mid-tropospheric humidity (primary factor) and relative vorticity (secondary factor) played a major role in the enhancement (reduction) of the TC activity under La Niña (El Niño) regime. In addition, when the MJO is active over the BoB (phases 3–4; characterized by enhanced convective activity in the BoB) under La Niña regime, environmental conditions were more conducive for enhancement of TC activity and RI of TCs compared to corresponding MJO phase under El Niño regime. Increase in mid-tropospheric humidity and reduction in vertical wind shear were identified as the primary and secondary factors enhancing the likelihood of RI of TCs in the BoB during phases 3–4 of MJO under La Niña regime. Further, the role of accumulated tropical cyclone heat potential (ATCHP) on the RI of TC during primary TC season is also investigated. Our analysis demonstrates that ATCHP is large for TCs which undergo RI compared to TCs not undergoing RI.