This study involves the direct diagnosis of two-way stratosphere-troposphere exchange. The method introduced by Wei is applied to the GEOS-1 assimilated data set. This method, in principle, allows both upward and downward components of the cross-tropopause mass flux to be separately determined. Downward control methods only constrain the net mass flux, which is in general inadequate to determine fluxes of chemical species. In some respects, particularly regarding the net (i.e. temporal and/or spatially averaged) mass flux, the results complement other studies using the same method and different data sets, helping to illustrate which results may be robust and which may be more data set dependent. However, sensitivity tests and theoretical considerations indicate that the instantaneous two-way exchange may be significantly exaggerated by the Wei method, due to its being rather sensitive to the noise that is invariantly present in observed or assimilated data sets. The method becomes better conditioned as the results are more heavily averaged, but this also reduces the method's ability to diagnose two-way exchange. Since we expect that model simulations are generally less noisy than observed or assimilated data sets, our analysis appears to explain the fairly large discrepancies between the two way fluxes obtained in studies using models and assimilated data sets
Symposium on Interdisciplinary Issues in Atmospheric Chemistry