Space-Time Structure of Diabatic Heating in Monsoon Intraseasonal Oscillation

The space-time structure of the leading monsoon intraseasonal oscillation (MISO) in three-dimensional diabatic heating is studied. Using the ERA-Interim data of the European Centre for Medium-Range Weather Forecasts, the diabatic heating data were constructed by the residual method of the thermodynamic equation. The MISO was extracted by applying multichannel singular spectrum analysis on the daily anomalies of three-dimensional diabatic heating over the South Asian monsoon region for the period 1979-2011. The diabatic heating MISO has a period of 45 days, and exhibits eastward propagation in the equatorial Indian and Pacific Oceans and northward propagation over the entire monsoon region. The horizontal structure shows a long tilted band of heating anomalies propagating northeastward. The period, horizontal pattern, and propagation properties of the diabatic heating MISO are similar to those found in precipitation, outgoing long wave radiation, and circulation in earlier studies. The vertical structure of the diabatic heating MISO indicates deep columns, with maximum values at about 450 hPa, propagating northeastward. The vertical structure of the heating anomalies has good correspondence with that of the moisture anomalies but with a phase difference. The moisture anomalies lead the heating anomalies and may provide a preconditioning process for the propagation mechanism. The temperature anomalies also show oscillatory behavior corresponding to the diabatic heating MISO but the phase difference between the two varies from region to region.