Seasonality of Relationship between Tropical Cyclone Frequency over the Southern Hemisphere and Tropical Climate Modes

Abstract

In this study, the author examined the tropical cyclone (TC) activity over the southern hemisphere (SH) and its relationship with tropical climate modes, such as the El Niño–Southern Oscillation (ENSO), during the austral summer (December–January–February; DJF) and fall (March–April–May; MAM). The correlation analysis between the TC activity and the global sea surface temperature (SST) suggested that an increased TC activity over the southwestern and southeastern Indian Ocean (SWIO and SEIO) was associated with a La Niña-like SST pattern, while an increased TC activity over the southwestern Pacific (SWP) was associated with an El Niño-like SST pattern. The atmospheric conditions accompanying the TC increase over the SWIO/SEIO indicated that a La Niña induces tropospheric cooling over the tropics with cyclonic circulation anomalies over the TC genesis region. Both the SST anomalies and the cyclonic circulation anomalies were significantly correlated with TC genesis parameters, suggesting that they contributed to TC genesis. To investigate the SST precursors, a lead-lag correlation analysis was performed. For the TC variations over the SEIO, an SST pattern that resembled the Pacific Meridional Mode (PMM) was statistically significant at a two-season lead. However, such a TC-ENSO relationship is seasonally dependent, with different patterns during DJF and MAM. These results suggest that the Matsuno-Gill response to ENSO is an important factor in TC activity but that this influence is seasonally modulated over the SH.