Extended Abstract (2.7M)P2.23
Temperature extremes variability in the south of South America in relation to Atlantic SST and the Southern Annular Mode
Mariana Barrucand, CONICET/Departamento de Ciencias de la Atmósfera y los Océanos (FCEN-UBA), Buenos Aires, Argentina; and M. Rusticucci and W. Vargas
This study analyses common variability modes between frequency of temperature extremes in the south of South America (Argentina), Atlantic sea surface temperatures (SST) and The Southern Annular Mode (SAM). The frequency of temperature extreme events (both cold and warm) are analyzed by 4 indices that take into account the percentage of days per month with extreme temperatures lower (higher) than the 10 (90) percentile, calculated following the ETCCDMI guidelines. Five reference stations were selected through a cluster method. They represent different regions of Argentina. A previous work showed high correlations between extreme temperatures and South Atlantic sea surface temperatures, specially at coastal areas. Based on these result, three Atlantic Ocean “boxes” were considered, centered at 30ºS-48ºW (SST30), 36ºS-50ºW (SST36) and 46ºS-62ºW (SST46). Seasonal average temperatures at the different boxes were obtained from the NCEP/NCAR datasets. A cross-wavelet analysis was performed between extreme temperature and SST indices. During spring, a noticeable 8-year signal was observed with the frequency of cold events (TN10), SST30 and SST36 series at the stations located in the north and center of the country. The series are in anti-phase: the temperature increase in the ocean regions is associated with a decrease in the cold events, This characteristic shows an 8-year wave modulation. However, there is no such a relation in the late 80's, which could imply a change in the relations within the system. The 8-year wave modulation does not appear in the southern station, except for a signal in the cross-wavelet with SST30 –in phase– that appears after 1990. Considering that the signal especially appears in the frequency of cold events, the potential source of variability would be associated with processes coming from the south, not only affecting high latitude regions but also modulating the frequency of the extremes at different latitudes. Within this context, the SAM index was analyzed It is observed a clear 8-year wave signal common to TN10, SST30 and SST36 indices. The relation observed between the SAM and the index of frequencies of cold events TN10 is in anti-phase, a characteristic physically consistent if it is considered that, for the positive (negative) SAM index, there is higher (lower) relative pressure over the south of South America. This would be associated with a lower (higher) passage of cyclones and a lower (higher) number of cold events. The fact that the 8-year wave signal has been found in different variables coming from different sources of information, makes this a significant signal, which should not be overlooked in further climate modeling studies.
Poster Session 2, General Climate Studies: Poster Session
Monday, 21 January 2008, 2:30 PM-4:00 PM, Exhibit Hall B
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