Observations of the 30–60 Day Oscillation in Zonal Mean Atmospheric Angular Momentum and High Cloud Cover

Abstract

Data on zonally averaged atmospheric angular momentum and high cloud cover percent are analyzed for the periods April?October 1979 and November 1982?October 1983. The dominant periodicity in both momentum and cloud datasets was the so called ?30?60 day atmospheric oscillation? in tropical and subtropical belts. In lag correlations between high cloud belts, both the periodicity and a latitudinally varying correlation structure were evident. In the 1979 period (Northern Hemisphere summer) the cloud-cloud correlations had nodes near 17°S, 5°N, 24°N and 36°N, i.e., anomalously high/low zonal mean convection between 5 and 24°N coincided with anomalously low/high zonal mean convection between 17°S and 5°N, and between 24 and 36°N. In April?October 1983, a similar periodicity and phase structure were present, but not as well defined. The principal node in the northern Hemisphere summer, near 5°N, appears to lie between the belt of maximum cloud cover for the period (which is between 5 and 9°N) and the equator. In an analysis of the period November 1982?April 1983 (Southern Hemisphere summer), the principal node was located in the Southern Hemisphere. Lag correlations between high cloud belts and momentum belts showed strong correlations with the 30?60 day oscillation present. Anomalously high/low zonal mean high cloudiness in the tropics is accompanied by anomalously high/low zonal mean momentum in the tropics, with the latter anomalies subsequently propagating into midlatitudes.