Moist Static Energy Budget Analysis of Quasi 2-Day Oscillation Using Satellite and Reanalysis Data

Abstract:

Quasi 2-day oscillation is a convectively coupled equatorial wave with the period of about 2 days. Previous observational studies have shown that its dry dynamics is presumably explained by n=1 westward inertia gravity wave (WIG1), while detailed mechanisms involved in the moist processes for the quasi 2-day wave is less understood. This study is aimed to reveal the mechanism by analyzing the moist static energy (MSE) budget and gross moist stability (GMS) based on satellite and reanalysis data. Since WIG fluctuates in a time scale from a few hours to one day, it is difficult to track WIG variability by a coarse temporal sampling of these data sets. In this study, the difficulty is overcome by compositing reanalysis data with respect to the convective peaks in band-pass filtered OLR data. By this technique, we can achieve a high temporal resolution in a statistical sense to show the rapid variation of convection and environmental fields associated with WIG. It is found that positive zonal advection increases between the lower and middle tropospheres mainly owing to background easterly preceding deep convection. An MSE impost due to the zonal advection is speculated to raise an unstable area with a low GMS on the west of the precipitation active area and originates new convection. On the east of precipitation active area, it is suggested that a stable area with a high GMS arises. Meanwhile, both meridional and vertical advection terms are less important for regulating thermodynamic stability. This could provide a possible scenario about why inertia gravity wave prefers to move westward rather than eastward.