Modulation of Tropical Cyclone Genesis by Madden–Julian Oscillation in the Southern Hemisphere

Abstract

AbstractThis chapter advances intelligent methodologies to study the modulation of cyclone genesis. Tropical cyclones (TCs) are hazardous weather elements with detrimental impacts on populations, wildlife, ecosystems, infrastructure, and the economy of developed as well as developing nations. Understanding the climatological behavior of TCs in relation to onsets, origin, and causal factors conductive to cyclogenesis can aid in the risk-management of cyclone vulnerability. This chapter studies the observed modulation of TC genesis in two study regions, namely the South Indian Ocean (SIO: 0–30° S, 30° E–130° E) and the South Pacific Ocean (SPO: 0–30° S, 130° E–130° W) was examined for the period 1980–2012. We define regional Madden–Julian Oscillation (MJO) indices based on the convective anomalies of large OLR variability centers, which exhibit a stronger modulation of the TC genesis than previously identified. Overall, an increase in the number of TC formations was recorded for the enhanced convective phase of the MJO compared to the dry phase. The modulation of TC genesis by MJO appeared to be pronounced with a ratio of 2:1 to the east of 70° E (for the SIO) and 7:1 to the west of 170° W (for the SPO). Stronger modulation in the latter region is attributable to (1) MJO-induced wind field impacts that were notably larger than the background mean flow, (2) TC genesis locations being consistent with MJO action centers, i.e., the TCs occur over the region of the MJO-induced low-level circulation with enhanced convection, and (3) TC genesis occurs in the South Pacific Convergence Zone (SPCZ), a region where MJO has a strong modulating effect. An analysis of large-scale dynamic and thermodynamic conditions demonstrated that low-level relative vorticity was strongly related to TC genesis modulation in both the SIO and SPO regions. However, the MJO appears to show little effect on TC genesis in the western SIO due to the existence of climatological conditions less conducive to TC formation throughout the cyclonic season. Finally, the chapter ascertains that TCs are generally produced further from the equatorial region in the southwest Indian zone where the MJO signal appears to be very weak.