83rd Annual

Thursday, 13 February 2003
Antarctic oscillation variations and teleconnections with convective activity in the South Atlantic Convergence Zone
Leila M. V. Carvalho, University of Sao Paulo, Sao Paulo, Brazil; and C. Jones and T. Ambrizzi
Convective activity in the tropical South America during the wet season exhibits a wide range of space and time scales variability. Previous works have shown evidence that, on intraseasonal time-scales (10-90 days), propagating mid-latitude wave trains modulate the intensity and extent to the Atlantic Ocean of the South Atlantic Convergence Zone (SACZ). The same phenomenon has been linked to intraseasonal variations in low-level (10-90 days) wind regimes over tropical South America and extreme precipitation in southeastern Brazil.

The present study investigates the relationships between variations in the Antarctic Oscillation (AAO), storm tracks, and teleconnections with the convective activity in the SACZ during the austral summer. Daily AAO index (AOI) is obtained by applying EOF analysis to 700hPa geopotential height from 1979-2000. Spectral analysis of the AOI, geopotential height (700hPa) and winds (700hPa and 200hPa) over the storm track are then performed to identify intraseasonal variations in the AAO regime. Intraseasonal variations in daily Antarctic sea ice area are also examined to identify linkages with AAO and, therefore, with the storm track.

Another index obtained from Outgoing long-wave radiation (OLR) data and factor analysis is used to identify periods of intense/weak and continental/oceanic SACZ. Composites of 200hPa geopotential height (over the tropics, mid and high latitudes) and OLR (over the tropics) anomalies are performed during extreme phases of the AAO. Statistical analysis is used to identify the role of AAO and storm tracks in modulating intraseasonal variations in the SACZ convective activity.

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