Global wave activity from upper stratosphere to lower thermosphere: A new turbopause concept

Global temperature measurements are available from CRISTA (CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere) and from SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) up to 110 km . Standard deviation from zonal mean temperature is used as a wave activity indicator (proxy). Altitude/latitude plots of these standard deviations σ or variances σ 2 show a structure that is dependent on the season. There is also substantial zonal asymmetry. Vertical cuts through the σ -field show a remarkable transition between 90 and 100 km : linear fit curves above 100 km have a gradient similar to the amplitude increase of freely (upward) propagating waves. The corresponding gradients below 90 km are much flatter and thus indicate considerable wave damping. The intersection of the two fit curves is dubbed the “wave-turbopause” here, and is believed to be near the turbulent or transport turbopause. This wave-turbopause is found in the vicinity of 90 – 95 km for CRISTA-1, CRISTA-2, and SABER. It is compared to the corresponding cold point mesopause and to the isolines of estimated potential vorticities to show similarities with the tropopause. The height of the wave-turbopause depends on latitude. It also has considerable seasonal variation, which is very different at high and low latitudes.