Tropical Cyclone Interactions with the Madden–Julian Oscillation in the Indian Ocean

Tropical cyclones (TCs) have been thoroughly studied in relation to their environment in the Atlantic and Pacific Oceans, but there is a limited understanding of these TC-environment interactions in the Indian Ocean. Specifically, the feedback between TCs after genesis and the convectively-active phase of the Madden-Julian Oscillation (MJO) has not been examined in the Indian basin. Previous work by the authors has indicated that changes in MJO convection depth, coverage, and frequency are linked with westerly dry air advection during 1 MJO active phase. A TC was also present in the Arabian Sea during this period which possibly contributed to the advection strength. Feedback of TCs onto the MJO could therefore affect the preferred development regions of synoptic-scale MJO convection, the strength of anomalous low-level westerly winds associated with the MJO structure (i.e. westerly wind burst; WWB), and ultimately the eastward propagation of the MJO active phase.

The impacts of TCs on the MJO are first investigated using satellite observations of MJO active phase convection, reanalysis products for analyzing the Indian Ocean environment, and best-track datasets of Indian Ocean TCs from 2000-2013. Initial observational comparisons between periods with and without the presence of TCs in the basin have shown statistically significant increases in MJO and WWB strength along with decreases in low-level equatorial moisture when TCs are present. Future satellite and Hovmöller analysis will similarly compare MJO convection and propagation over periods with and without TCs. Beyond observations, insight into TC-MJO interactions will be accomplished through examination of high-resolution simulations of MJO events during the DYNAMO field campaign. Trajectory analysis within these simulations will diagnose dry air origins, while moisture and momentum fluxes into the MJO convection regions will be used to link TC impacts on the synoptic-scale convective envelope.