The interannual relationship between MJO activity and tropical cyclone genesis in the Indian Ocean

Abstract

The present study investigated the relationship between the interannual variations of Madden-Julian Oscillation (MJO) and tropical cyclone genesis (TCG) over the Indian Ocean during the October-November-December season by conducting statistical analyses with the use of 33-year reanalysis data. Through dividing the 33-year period into the active year and the non-active year of MJO, we identified the characteristics of TCG in the active and the non-active year. Environmental conditions for TCG under the influence of the MJO activity were diagnosed by an empirical index, Genesis Potential Index (GPI). It was shown that TCG events over the Indian Ocean in the active year are significantly increased when the convectively active phase of MJO develops over the Indian Ocean and the Maritime Continent. GPI in the active (non-active) year showed positive (negative) anomaly over almost the whole Indian Ocean. In addition, TCG is enhanced (suppressed) in the area of positive (negative) GPI anomaly. Diagnosing the factors constituting GPI showed that relative humidity and vertical velocity have more pronounced contributions than the other factors of GPI. The present analyses demonstrate that the activity of MJO has an influence on the inter-annual relationship of TCG through the modulation of environmental conditions.