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

Large-scale disturbances which cause the variations of ozone and water arou nd the equatorial tropopause axe investigated with a general circulation mo del incorporating a simplified ozone photochemistry, realistic topography, and seasonal cycle of the sea surface temperature. Eastward moving large-sc ale equatorial gravity waves are found to be dominant to modulate the minor constituents' distribution around the equatorial tropopause. A case over t he Indian Ocean in the northern summer was investigated in detail. The dist urbance had the characteristics of the equatorial Kelvin wave at the tropop ause level, coupled with organized active convections in the troposphere. A ssociated with the downward displacement (and suppressed-convection) phase of this system, dry, ozone-rich stratospheric air moved downward into the u pper troposphere. At the opposite phase, physical and dynamical processes a bove the organized active convections prevented the lower stratosphere from accumulating excess water. Thus the dryness around the equatorial tropopau se is maintained during the passage of such a system. Analysis of 4-year in tegration data reveals that such disturbances axe especially active over th e Indian Ocean during the northern summer through autumn. This is probably related to the development of the summer monsoon circulation over south Asi a. This model has also simulated the zonal wave one structure of tropical t ropospheric ozone and suggested the important contribution of convective tr ansport to the structure.