Abstract
Numerous studies have devoted to energetic balance diagnosis of the synoptic scale disturbance (SSD) in the northern summer monsoon region, but few work has concentrated on that during boreal winter. This study investigated the energetics of the SSD associated with the eastward propagating Madden–Julian oscillation (MJO) convection south of the equator during boreal winter. The eddy kinetic energy is enhanced within and to the west of the MJO convection and is weakened to the east of it. This is related to the barotropic energy conversion (CK) in lower and middle troposphere and conversion of eddy available potential energy (CA) in upper troposphere. CK arises from interactions between SSD and MJO/lower-frequency flows. The SSD in the vicinity of the MJO is characterized by a wavelike pattern, with northwest to southeast tilt of elongated extrema of vorticity anomalies. The MJO flow in lower troposphere is characterized by zonal convergence at the convection center and cyclonic (anticyclonic) circulation to the east (west). The lower-frequency background flow is cyclonically sheared in the southern Indian Ocean. More (less) CA to the west (east) is due to more (less) generated eddy available potential energy from diabatic effects. The SSD contribute to the MJO eastward propagation through inducing a zonal asymmetry in nonlinear moisture advective tendency. This accounts for 30% of the observed asymmetric intraseasonal moisture tendency.
Published Version
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