Transport Circulation Deduced from SAMS Trace Species Data

Abstract

Three years of zonally averaged N2O and CH4 data from the SAMS instrument on Nimbus 7 are utilized to investigate the annual and semiannual cycles in long-lived tracer mixing ratios. The annual and semiannual variations are shown to be approximately antisymmetric and symmetric about the equator, respectively. Using the first three components of the annual cycle to estimate the time tendency, the tracer continuity equation is solved diagnostically to obtain the effective transport velocity (i.e., the meridional circulation that can produce the observed seasonal variations in the tracer fields). The resulting circulation is qualitatively in agreement with the diabatic circulations computed by other workers. The present calculations, however, exhibit a stronger equinoctial subsidence in the equatorial upper stratosphere than deduced in other studies as required to produce a ?double peak? tracer structure that has the amplitude and vertical extent that is observed.