Zonally symmetric and asymmetric features of the tropospheric Madden‐Julian oscillation

Abstract

The evolving intraseasonal (IS) modes of the zonally symmetric (ZS) part (the latitudinal profile) of the 200‐hPa stream function have been determined by performing extended empirical orthogonal function (EEOF) analyses for the northern hemisphere (NH) summer and winter. In each analysis the first EEOF mode describes an oscillation with a period of about 50 days. The prominent feature of the upper tropospheric stream function latitudinal profiles, for both seasons, is the propagation of the largest loadings in both hemispheres from near the equator toward higher latitudes. This propagation is more evident during the NH winter and throughout the year in the southern hemisphere (SH). In the NH the poleward propagation of the loadings is more conspicuous within the equator and the 30°N latitudinal band. The associated patterns for the zonally asymmetric (ZA) part of the sea level pressure and the 850‐ and 200‐hPa zonal winds have also been determined. These patterns feature, in general, the largest correlations in the tropics and a large‐scale zonal wavenumber one structure propagating continuously eastward around the globe with a 50‐day period. The ZA patterns for certain variables show strong seasonal dependence. The 850‐hPa ZA zonal wind patterns feature the largest correlations approximately along the climatological position of the Intertropical Convergence Zone, whereas the largest correlations for the upper level ZA zonal wind patterns are found near the equator, mainly in the winter hemisphere.