Influence of MJO on cyclone activity in the north Indian Ocean and Western North Pacific

Abstract

We investigate the changes in cyclogenesis and tropical cyclone (TC) activity by the warped life cycle of MJO triggered by the two-fold expansion of the warm pool that occurred during the period of the past 40 years (1979-2019). To study the impact of MJO on TC genesis and activity, we have used the genesis potential index (GPI), accumulated cyclonic energy (ACE) and frequency of cyclones in the active, moderately active and non-active periods of MJO in the North Indian Ocean (NIO) and Western North Pacific (WNP). We find an inverse characteristic of anomalies of relative humidity, vertical wind shear, absolute vorticity, potential intensity, GPI and sea surface temperature over the tropical region between active and non-active years of MJO (1979-2019). High TC activity is experienced during the moderately active years of MJO over the Bay of Bengal (BoB) and WNP. The impact of MJO on TC activity over WNP from October to December (OND) is not particularly dominant during the active years. The genesis of TCs over the Arabian Sea (AS) have also increased during the active years of MJO; indicating that the impact of MJO is increasing over AS. In addition, stalling of eastward propagation of MJO is noticed over the Maritime Continent (MC) during the active and moderately active MJO years. After phase 5, a strong decline in the trend of the phase duration over WNP is noticed, which can be attributed to the reduced TC genesis and activity over WNP during the MJO active years. Reduced MJO activity during OND over WNP, along with lower absolute vorticity and vertical velocity, resulted in lower TC activity and genesis. Our analysis reveals the basin dependency of TC activity and genesis over AS, BoB and WNP due to the stalled propagation of MJO over MC by the extended Indo-Pacific warm pool driven by anthropogenic activities.