Intraseasonal variability in subtropical South America as depicted by precipitation data.

GONZALEZ, PAULA; VERA, CAROLINA; LIEBMANN, BRANT; KILADIS, GEORGE

CLIMATE DYNAMICS

Springer-Verlag

Lugar: Berlin, Alemania; Año: 2008 vol. 30 p. 727 - 744

0930-7575

Abstract Daily precipitation data from three stations inDaily precipitation data from three stations in 11 subtropical Argentina are used to describe intraseasonalsubtropical Argentina are used to describe intraseasonal 12 variability (20–90 days), during the austral summer. Thisvariability (20–90 days), during the austral summer. This 13 variability is compared locally and regionally with thatvariability is compared locally and regionally with that 14 present in outgoing longwave radiation (OLR) data, in orderpresent in outgoing longwave radiation (OLR) data, in order 15 to evaluate the performance of this variable as a proxy forto evaluate the performance of this variable as a proxy for 16 convection in the region. The influence of the intraseasonalconvection in the region. The influence of the intraseasonal 17 activity of the South American Seesaw (SASS) leadingactivity of the South American Seesaw (SASS) leading 18 convection pattern on precipitation is also explored. Resultsconvection pattern on precipitation is also explored. Results 19 show that intraseasonal variability explains a significantshow that intraseasonal variability explains a significant 20 portion of summer precipitation variance, with a clearportion of summer precipitation variance, with a clear 21 maximum in the vicinity of the SASS subtropical center.maximum in the vicinity of the SASS subtropical center. 22 Correlation analysis reveals that OLR can explain only aCorrelation analysis reveals that OLR can explain only a 23 small portion of daily precipitation variability, implyingsmall portion of daily precipitation variability, implying 24 that it does not constitute a proper proxy for precipitation onthat it does not constitute a proper proxy for precipitation on 25 daily timescales. On intraseasonal timescales, though, OLRdaily timescales. On intraseasonal timescales, though, OLR 26 is able to reproduce the main features of precipitationis able to reproduce the main features of precipitation 27 variability. The dynamical conditions that promote thevariability. The dynamical conditions that promote the 28 development of intraseasonal variability in the region aredevelopment of intraseasonal variability in the region are 29 further analyzed for selected summers. Seasons associatedfurther analyzed for selected summers. Seasons associated 30 with a strong intraseasonal signal in precipitation variabilitywith a strong intraseasonal signal in precipitation variability 31 show distinctive wet/dry intraseasonal periods in daily rawshow distinctive wet/dry intraseasonal periods in daily raw data, and are associated with a well defined SASS-like 33 spatial pattern of convection. During these summers, strongspatial pattern of convection. During these summers, strong 34 large-scale forcing (such as warm El Nin˜o/Southernlarge-scale forcing (such as warm El Nin˜o/Southern 35 Oscillation (ENSO) events and/or tropical intraseasonalOscillation (ENSO) events and/or tropical intraseasonal 36 convective activity), and Rossby-wave-like circulationconvective activity), and Rossby-wave-like circulation 37 anomalies extending across the Pacific Ocean, are alsoanomalies extending across the Pacific Ocean, are also 38 observed.observed.