13.3
Tropical cyclones in the Southern Hemisphere: influence of the El Niño-Southern Oscillation phenomenon.
Yuriy A. Kuleshov, National Climate Centre, Bureau of Meteorology, Melbourne, Victoria, Australia
Spatial profiles of tropical cyclone track densities and temporal (or seasonal) profiles of tropical cyclone daily frequencies for the Southern Hemisphere and two sub-regions – the South Indian Ocean (west of 135ºE) and the western South Pacific Ocean (east of 135ºE) - have been analyzed. Average profiles have also been constructed for El Niño, La Niña and neutral years. The average annual number of tropical cyclones in the Southern Hemisphere is around 27; on average 16 tropical cyclones occur in the South Indian Ocean and 11 tropical cyclones occur in the South Pacific Ocean. The tropical cyclone season usually extends from November to April but occasionally early and late season cyclones occur. The tropical cyclone season reaches its greatest intensity during January, February and March with the average daily frequency between 1 and 2 cyclones. There is no apparent trend in occurrences of tropical cyclones in the Southern Hemisphere during the last three decades.
Tropical cyclone behavior in the South Pacific and the South Indian Oceans is influenced by the phases of the El Niño – Southern Oscillation phenomenon. Tropical cyclone activity in the South Pacific east of 165ºW is higher during El Niño years than in La Niña and neutral years. Tropical cyclones increase in number between 70ºE and 165ºW during La Niña years in comparison with El Niño and neutral years. The maximum tropical cyclone frequency in the Southern Hemisphere during La Niña years occurs at the end of January, during El Niño years - at the end of February / beginning of March. The daily frequency of tropical cyclones, averaged across the season, is 30% higher in the South Indian Ocean than in the South Pacific. The tropical cyclone season for the South Indian Ocean starts a month earlier in La Niña and neutral years than in El Niño years. It is the opposite in the South Pacific Ocean: the tropical cyclone season starts a month earlier in El Niño years than in La Niña and neutral years.
Session 13, Tropical-extratropical interactions and teleconnections over the Southern Hemisphere II
Thursday, 27 March 2003, 9:00 AM-11:30 AM
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