Interannual Rainfall Variability over the South American Altiplano
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2001-06-15Metadata
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Garreaud Salazar, René
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Interannual Rainfall Variability over the South American Altiplano
Abstract
Altiplano, a semiarid, high-level plateau entrenched in the central Andes. On the interannual timescale, Altiplano
rainfall exhibits pronounced fluctuations between drought and very wet conditions, with subsequent impacts on
agriculture and hydrology. In this work, the large-scale patterns of convective cloudiness and circulation associated
with interannual variability of the summer rainfall over this region are investigated using a regression
analysis between relevant atmospheric fields (NCEP–NCAR reanalysis, outgoing longwave radiation) and an
index of convection over the Altiplano.
It is found that the seasonal-mean, large-scale zonal flow over the central Andes is directly related with the
number of days with easterly flow within the season, that, in turn, favor the occurrence of summertime deep
convection on the Altiplano by transporting moist air from the interior of the continent. Consequently, interannual
variability of the seasonal-mean zonal wind explains nearly half of the variance of summertime convection over
the Altiplano through an easterly/wet–westerly/dry pattern. The circulation anomalies are in geostrophic balance
with changes in the meridional baroclinicity at the southern border of the tropical belt. Thus, a previously
documented relationship between El Nin˜o–Southern Oscillation (ENSO) phenomenon and interannual rainfall
variability over the Altiplano is explained by the generalized warming (cooling) of the tropical troposphere
during the negative (positive) phase of ENSO and the associated strengthening (weakening) of the westerlies
over the central Andes.
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URI: https://repositorio.uchile.cl/handle/2250/125988
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JOURNAL OF CLIMATE. 15 JUNE 2001
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