ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-27-2937-2009 Overturning instability in the mesosphere and lower thermosphere: analysis of instability conditions in lidar data Hurd L. 1 Larsen M. F. 1 Liu A. Z. 2 Department of Physics and Astronomy, Clemson University, Clemson, SC, USA Department of Electrical and Computer Engineering, University of Illinois, Urbana, IL, USA 24 07 2009 27 7 2937 2945 Copyright: © 2009 L. Hurd et al. 2009 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/27/2937/2009/angeo-27-2937-2009.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/27/2937/2009/angeo-27-2937-2009.pdf

Resonant sodium lidar measurements from the transition region between the mesosphere and lower thermosphere have revealed frequently-occurring overturning events characterized by vertical scales of ~3–6 km and timescales of several hours. Larsen et al. (2004) proposed that a convective roll instability, similar to that found in the planetary boundary layer, is the likely mechanism responsible for the events. This type of instability requires an inflection point in the background winds near the center of the vortex roll with a low static stability region capped by an inversion. The earlier paper argued that the conditions required to support the instability are common in the altitude range where the features are found. In this paper, we use data from the University of Illinois sodium lidar that was located at the Starfire Optical Range near Albuquerque, New Mexico, and from the Maui/MALT Lidar Facility in Hawaii and present several cases that are used to examine the behavior of the inflection point in detail as a function of time during the evolution of the overturning event. In addition, we examine the background static stability conditions using the temperature data from the lidar.

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