EQUATORIAL KELVIN WAVES - A UARS MLS VIEW

Data from the Microwave Limb Sounder instrument on the Upper Atmospher e Research Satellite are used to compare two periods of Kelvin wave ac tivity during different stages of the equatorial quasi-biennial oscill ation. The analysis is carried out using an asynoptic mapping techniqu e. A wide bandpass filter is used to isolate the frequency bands where Kelvin waves have been identified in previous studies. Time-height an d time-latitude plots of the bandpassed data are used to identify Kelv in wave activity in the temperature and ozone fields. Frequency spectr a of temperature and ozone amplitudes are constructed to further analy ze the latitudinal and meridional distribution of Kelvin wave activity in zonal wavenumbers 1 and 2. The characteristics identified in these plots agree well with theoretical predictions and previous observatio ns of middle atmosphere Kelvin waves. The time-height and time-latitud e plots support the existence of Kelvin waves in discrete frequency ba nds; the slow, fast, and ultrafast Kelvin modes are all identified in the data. The characteristics of these modes do not vary much despite different mean flow conditions in the two periods examined. For the Ke lvin wave-induced perturbations in ozone, the change from a transport- dominated regime below 10 hPa to a photochemically controlled regime a bove 10 hPa is clearly apparent in the height dependence of the phase difference between temperature and ozone. The ratios of the ozone pert urbation amplitude to the temperature perturbation amplitude for the v arious observed Kelvin wave modes are in agreement with model estimate s and LIMS (Limb Infrared Monitor of the Stratosphere) observations in the lower half of the region sampled but appear to be too large in th e upper stratosphere and lower mesosphere.