Abstract
Abstract
Material tracers such as ozone and water vapor concentration as observed by balloon measurements often show a marked vertical fluctuation. Previous studies examined the formation mechanism of such a “layered structure” mainly by using a correlation analysis between O_3 and potential temperature (θ) as obtained by balloon measurements: if the correlation is high, the vertical wind fluctuation associated with gravity waves is a key. The present study has found a case where this analysis alone cannot specify the formation mechanism. We thus for the first time adopt a backward trajectory analysis for identifying the formation mechanism. It is clearly shown that this structure was primarily formed by the quasi-horizontal mixing of distinct air masses: an O_3-poor/"H2O" -rich tropical air mass and an O_3-rich/"H2O" -poor subtropical air mass. The observed high correlation between O_3 and θ likely results from weak upward and downward motions of these air masses associated with the Hadley circulation rather than vertical wind fluctuations. It is suggested that conventional correlation methods may overestimate the contribution of gravity waves.