Organization of convection within the Madden-Julian oscillation

Harry H. Hendon
Program in Atmospheric and Oceanic Sciences and Cooperative Institute for Research in Environmental Sciences
University of Colorado, Boulder

Brant Liebmann
Cooperative Institute fir Research in Environmental Sciences
University of Colorado, Boulder

Abstract

Convection associated with the Madden-Julian oscillation (MJO) is organized over a broad range of time and space scales within a large-scale envelope of activity. The large-scale envelpoe of convection is characterized as an eastward propagating disturbance, predominantly of zonal wavenumber 2, which os confined over the warmest waters of the Indian and western Pacific oceans. Large-scale convection is shifted toward the disturbance's temperature anomaly. which appears to result from frictional effects in the boundary layer. Synoptic and mesoscale convection activity is enhanced within the wet phase of the large-scale envelope. The increase at synoptic scales occurs uniformly over all scales, but little difference in the character of the variability is observed between dry and wet phases. The enhanced mesoscale activity within the wet phase exhibits a marked tenency to be organized into westward propagating clusters with periods near 2 days and half wavelengths of about 1000km. The role of these modes for the evolution of the MJO is discussed.