Extended Abstract (188K)13.6
Southern Hemisphere atmospheric low frequency variability in a climate AGCM simulation
Iracema F. A. Cavalcanti, Centro de Previsao de Tempo e Estudos Climaticos, Cachoeira Paulista, São Paulo, Brazil; and C. C. Castro
Observed atmospheric patterns of low frequency variability have been identified in the Southern Hemisphere, as the Pacific South America, wavenumber three, blocking and persistent anomalies. As these structures have influence over the continents of the SH, it is important to know if GCMs can represent low frequency variability patterns and how are these influences. Previous analysis using results of a climate AGCM simulation indicated the ability of the CPTEC/COLA AGCM to represent the PSA pattern in the SH winter season and high frequency wavetrains over middle latitudes of the SH and over South America. In the present study, a climate simulation using a higher resolution AGCM than that used before, is analysed to study atmospheric low frequency variability in the Southern Hemisphere, in the summer. Daily results of nine integrations with the AGCM CPTEC/COLA are analysed in the period of 1982/1983 to 1990/1991. OLR, meridional wind component and streamfunction are filtered to select the frequency between 30 and 90 days. Correlation and EOF analyses, considering several regions, as well as analyses of convective areas over South America and Indonesia are performed to compare with observations. When the South America area is considered, the model results show two opposite centers of OLR over the continent, similar to the seasaw pattern found in observations. These are related to the South Atlantic Convergence Zone convection and its influence on areas to the south. When the meridional wind is analysed considering the Pacific and South America areas, a pattern of alternating centers is seen over South America and, over the Pacific Ocean, the PSA pattern depicting the tropics/extratropics teleconnection mode is well represented. Other areas, as Australia and Indian Ocean are also analysed and an opposite relation between Australia and New Zealand area is found. Considering South America, South Atlantic and austral Africa areas, two centers of opposite sign over the brazilian coast are the dominant pattern. Larger anomaly alternating centers are also seen over middle latitudes from the western South Atlantic to the Indian Ocean, and directed to the South Indian Convergence Zone, over southeastern Africa. When the whole SH is considered, the wavetrain over the Pacific and South America is still the dominant pattern. An intraseasonal oscillation is noticed over Indonesia area and also over tropical South America in the OLR filtered model data. The behaviour of convective activity over Indonesia and its influence on teleconnection patterns will also be discussed.
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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