Stratospheric Kelvin Wave Activity as a Function of Equivalent Depth in AIRS and Reanalysis Datasets

Stratospheric equatorial Kelvin waves provide a necessary source of momentum to the Quasi-Biennial Oscillation (QBO). In turn, due to distributions of zonal winds and static stability, different modes of variability including the QBO, zonal mean perturbations, the seasonal cycle, and El Nino-Southern Oscillation (ENSO) influence the activity of the Kelvin waves. While previous literature has observed connections to these modes of variability, we further analyze the relationships of temporal to zonal scales for the waves considering spatial, seasonal, and interannual variability. Kelvin wave activity is identified locally in space and time using a time-longitude partial Morlet wavelet analysis with temperature from the Atmospheric Infrared Sounder (AIRS), the Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2), and the fifth generation of the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA-5) for comparison, then analyzed as a function of equivalent depth. Results show that, in the mean, AIRS is shifted to higher equivalent depths as compared to MERRA-2 and ERA-5, possibly due to differences in the vertical resolutions of the AIRS dataset. Kelvin wave activity near the peak equivalent depths is increased over Africa, the Indian Ocean, and the Maritime Continent with a westward tilt with increasing equivalent depth; during the solstice seasons, but over a larger range of equivalent depths for boreal winter; and for QBO easterlies. El Nino shifts Kelvin wave activity to higher equivalent depths.