ZONAL ASYMMETRIES IN SAMS STRATOSPHERIC METHANE AND NITROUS OXIDE


J. R. Ziemke and J. L. Stanford, Department of Physics and Astronomy, Iowa State University, Ames, IA 50011


Quart. J. Roy. Meteor. Soc., London, 121, 911-925 (1994).


Abstract

Stratospheric And Mesospheric Sounder (SAMS) CH4 and N2O constituent measurements were taken a decade prior to the Upper Atmosphere Research Satellite (UARS) observations and are generally of lesser quality. However, SAMS data are important due to the limited lifetime of UARS and because they provide unique, historical data series for these gases involved in greenhouse and ozone-depletion effects. While most prior SAMS analyses focused on zonal means, the present paper assesses the strengths and weaknesses of analyzing zonally asymmetric perturbations in SAMS. It is shown that wave 1 perturbations can be successfully investigated, provided sufficient care is taken and aliasing considered.

At the lowest SAMS level, 20 hPa (approx 28 km altitude) zonal wave 1 CH4 and N2O data reveal similar features in latitudes 45 deg N--65 deg N during stratospheric warming events and breakup of the polar vortex. Large wave 1 anomalies in the upper stratosphere (2 and 0.6 hPa) were found to be out of phase with the corresponding anomalies at 20 hPa. In one episode in early 1981 (during stratospheric sudden warming) southward winds over North America transported low mixing ratio from polar latitudes, while northward winds over Siberia transported high mixing from subtropical latitudes. The effect produced strong wave 1 amplitudes in both CH4 and N2O mixing ratios.

Cross-correlations between wave 1 CH4 and N2O are large and positive in middle and high latitudes (consistent with ideal tracer behaviour for both constituent gases) but weak over the tropics. The cause of the latter remains an open issue.