Principal modes of outgoing longwave radiation and 250-mb circulation for the South American sector

Abstract

The first and second interannual modes contain many atmospheric features related to extremes in the Southern Oscillation. These include 1) variations in the pattern of tropical convection, and 2) changes in the intensity of upper-tropospheric zonal flow in the equatorial band and in the subtropics. The first intraseasonal mode has its greatest loadings in the Tropics and is most active during the southern summer season. For positive (negative) amplitudes of this mode, anomalous upper-tropospheric westerly (easterly) flow dominates the Tropics throughout the region, and positive (negative) OLR anomalies are observed over northeastern South America and over the eastern equatorial Pacific. These features are associated with the 30-60 day (Madden-Julian) oscillation. -from Authors