Role of the equatorial Kelvin wave in stratosphere-troposphere exchange in a general circulation model

Large-scale disturbances which cause the variations of ozone and water around the equatorial tropopause axe investigated with a general circulation model incorporating a simplified ozone photochemistry, realistic topography, and seasonal cycle of the sea surface temperature. Eastward moving large-scale equatorial gravity waves are found to be dominant to modulate the minor constituents' distribution around the equatorial tropopause. A case over the Indian Ocean in the northern summer was investigated in detail. The disturbance had the characteristics of the equatorial Kelvin wave at the tropopause level, coupled with organized active convections in the troposphere. Associated with the downward displacement (and suppressed-convection) phase of this system, dry, ozone-rich stratospheric air moved downward into the upper troposphere. At the opposite phase, physical and dynamical processes above the organized active convections prevented the lower stratosphere from accumulating excess water. Thus the dryness around the equatorial tropopause is maintained during the passage of such a system. Analysis of 4-year integration data reveals that such disturbances axe especially active over the Indian Ocean during the northern summer through autumn. This is probably related to the development of the summer monsoon circulation over south Asia. This model has also simulated the zonal wave one structure of tropical tropospheric ozone and suggested the important contribution of convective transport to the structure.