Stratospheric Kelvin Wave Activity as a Function of Equivalent Depth in AIRS...

Gahtan, J., and B. Tian (2022), Stratospheric Kelvin Wave Activity as a Function of Equivalent Depth in AIRS and Reanalysis Datasets, J. Geophys. Res., 127, e2021JD035572, doi:10.1029/2021jd035572.

Stratospheric equatorial Kelvin waves provide a necessary source of momentum to the QuasiBiennial 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 Niño-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 Niño shifts Kelvin wave activity to higher equivalent depths. Plain Language Summary Stratospheric Kelvin waves move eastward and are trapped along the equator, moving through the level of the atmosphere above where weather occurs, the stratosphere. They help force winds in the tropical stratosphere to switch between coming from the east to coming from the west in a cycle of about 28 months. Kelvin wave activity changes based on the strength and direction of the winds. Our goal is to understand how differences in natural variability affect the vertical depth and relationship between the size and timing of the Kelvin waves. The waves are identified in three different datasets: a satellite and two models that input observations. Kelvin waves measured in the satellite versus reanalysis datasets have different sizes and timings, likely due to varying distances between vertical measurements. Kelvin wave activity is stronger over Africa, the Indian Ocean, and the islands near Indonesia; during summer and winter; and when winds in the stratosphere come from the east. El Niño changes the preferred size and way the Kelvin waves move.

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Modeling Analysis and Prediction Program (MAP)
Energy & Water Cycle Program (EWCP)
Climate Variability and Change Program
Atmospheric Dynamics and Precipitation Program (ADP)
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