Extended Abstract (44K)16.9
Extratropical cyclone and anticyclone tracks and trends for the Southern Hemisphere: possible ENSO related impacts and climate changes
Alexandre Bernardes Pezza, University of Sao Paulo, Sao Paulo, Brazil; and T. Ambrizzi
The Southern Hemisphere (SH) total amount of cyclone and anticyclone tracks (every 12 hours) and trends were analyzed for the 1973 –1996 period using sea level pressure from the National Centers for Environmental Prediction (NCEP) Reanalysis. Composites for seven El Niño (EN) and La Niña (LN) years were constructed in order to analyze the association between the hemispheric cyclone and anticyclone propagation and the phase of the El Niño – Southern Oscillation phenomenon (ENSO).
A climatology of the cyclonic and anticyclonic paths all over the hemisphere was determined, emphasizing the regions frequently crossed by high and low pressure centers (most of the transient area), and the regions crossed by cyclones or anticyclones alone. The total hemispheric number of cyclone and anticyclone tracks during the austral winter was also analyzed, and an overall decline was observed, particularly at the end of the 1970s. This result is in agreement with previous ones from the literature. However, it was found that the trends could strongly depend on the pressure selection used. Further studies using different methodologies and other data sets are needed in order to verify if the observed trends are a consequence of real climate changes or just an artifice of different techniques.
The ENSO composites indicated a higher anticyclone concentration near the Subtropical South Atlantic High during EN years, while in the Subtropical South Pacific High it occurs during LN years. On the other hand, the cyclone tracks showed a higher variability, with an excess of lows over the subtropical Pacific, west of South America and southern Argentina during EN years and a more pronounced activity over the subtropical Atlantic and southeastern Australia during LN years.
Session 16, Interdecadal and Longer Term Climate Variability II
Friday, 28 March 2003, 8:30 AM-11:45 AM
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