Alternating Wet and Dry Conditions over South America during Summer

Abstract Time series of outgoing longwave radiation (OLR) fields and various gridded reanalysis products are used to identify and describe periods with abundant and deficient rainfall over South America during summer. Empirical orthogonal function analyses of OLR anomalies filtered to retain variations longer than 10 days reveal a meridional seesaw of dry and wet conditions over tropical and subtropical South America. It appears that intensification of the South Atlantic convergence zone (SACZ) is associated with rainfall deficits over the subtropical plains of South America. In contrast, when the SACZ weakens, precipitation over these plains is abundant. These results are in agreement with those of Kousky and Casarin. This seesaw pattern appears to be a regional component of a larger-scale system, possibly related to the 30–60-day oscillation in the Tropics, with the southward extension and strengthening of the SACZ found with enhanced tropical convection over the central and eastern Pacific and dry cond...

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