Tropical Cyclone Interactions with Madden-Julian Oscillation Convection in the Indian Ocean

The Madden-Julian Oscillation (MJO) can create favorable conditions for tropical cyclone (TC) genesis in the Indian Ocean, but past work has not thoroughly investigated how TCs after genesis may influence MJO convection development and therefore the MJO lifecycle. This work utilizes long-term composite analysis to broadly establish the relationship between TCs and each MJO phase over the Indian basin, and then seeks to isolate direct impacts of TCs on MJO convection coverage and intensity. We first examine TC interactions with MJO convection through compositing daily-mean ERA5 reanalysis products from 1998-2018 for TC and non-TC periods per MJO phase, excluding 3 days before and after best-track TC lifespans to reduce contamination of non-TC periods. Preliminary analysis suggests that TC periods are associated with anomalously weaker equatorial easterly winds and drier conditions during convectively-active MJO phases over the Indian Ocean, with a corresponding anomalous decrease in MJO rainfall observed by the TRMM satellite. While these findings allude to suppression of MJO convection during TC periods, we will isolate possible direct TC impacts by developing metrics for (1) a TCs range of influence, (2) the likelihood of interaction with MJO convection, and (3) the strength of TC-MJO convection interactions. Since a TCs influence likely extends beyond the 34-kt wind radii provided by best-track, we will determine an outer wind radius by integrating a radial wind model outward from each 34-kt wind radii measurement. With the MJO convection boundary found using a large-scale precipitation dataset, we will quantify the degree of overlap between TC outer wind radius and the MJO convection and then the size of the overlapping area if one exists. For time periods when TCs and MJO convection overlap, we will compare convection coverage and intensity observed by TRMM between MJO convection sectors with and without TC overlap. The strength of the TC-MJO convection interaction will finally be quantified by the amount of difference in each convection characteristic between these sectors. With climatological statistics on the likelihood and strength of TC-MJO interactions, future MJO prediction and Maritime Continent rainfall forecasts could be adjusted according to the presence or absence of Indian Ocean TCs.