Determination of the Wave Turbopause Using a Numerical Differentiation Method

This paper proposes a new algorithm to determine the wave turbopause based on numerical differentiation using temperature data collected from the Sounding of the Atmosphere using Broadband Emission Radiometry onboard the Thermosphere Ionosphere Mesosphere Energetics Dynamics satellite. The vertical gradient profile of the temperature standard deviation, which serves as a proxy of wave activity, is obtained based on Tikhonov regularization. In the vicinity of the altitude of wave turbopause, wave damping is much reduced, and upward wave propagation occurs with little damping effect. The corresponding vertical gradient profile should reach a maximum with values that are no longer negative. Thus, we determine the wave turbopause as the unique maximum that is the first after the last change in the derivative value from negative to positive. The wave turbopause altitudes determined by this new method agree well with those of previous studies, especially regarding the behavior of the monthly variation. The error of the wave turbopause altitude derived from this new method is 1.9 km, which is much improved from the error of 3.3 km estimated by the previous method. Additionally, latitudinal variations of the wave turbopause altitude for different seasons and their monthly variations for 0 degrees, 30 degrees N, and 70 degrees N latitudes during 2016-2018 are presented. Similar to the mesopause, the wave turbopause also exhibits a two-level structure with a summer minimum at high latitudes.