EQUATORIAL KELVIN WAVE VARIABILITY DURING 1992 AND 1993

Temperature and ozone data from the Microwave Limb Sounder (MLS) instr ument on UARS are used to analyze the variability of Kelvin wave activ ity during the first two years of the UARS mission. The analysis is ca rried out using the asynoptic mapping technique. Time frequency plots for zonal wavenumbers 1 and 2, at two heights representing the middle stratosphere and the stratopause, respectively, are used to analyze th e temporal variability of the waves, and its possible relationship to the equatorial quasi-biennial oscillation (QBO) and semiannual oscilla tion(SAO), Kelvin wave activity reaches a maximum during the solstice seasons and almost disappears during the equinoxes, in agreement with previous studies. Eastward propagating variance is estimated for wave periods from 4 to 20 days, at all UARS pressure surfaces currently ava ilable for MLS. The semiannual modulation of variance is observed to e xtend down to the lower limits of the height ranges of the temperature and ozone retrievals. Furthermore, a superposed QBO modulation is det ected up to the stratopause. Comparison between the variance in eastwa rd propagating waves and the mean zonal wind shows a possible particip ation of kelvin waves in the forcing of the QBO. At the stratopause th e role of Kelvin waves in forcing the SAO appears to be limited, in ag reement with previous results. Between the 21-hPa and 4.6-hPa surfaces there appears to be a transition zone where there is no clear relatio nship between Kelvin wave activity and mean zonal flow acceleration.