Mesospheric inversions and their relationship to planetary wave structure

Abstract

Mesospheric inversions are studied in vertical soundings from the French lidar at Observatoire de Haute-Provence and in synoptic global structure that was observed simultaneously by the UARS satellite. The latter provides the instantaneous three-dimensional (3-D) structure of the circulation that accompanies mesospheric inversions. A numerical simulation with a 3-D primitive equation model is then shown to reproduce major features of the observed behavior. Both reveal an extensive pattern of inverted thermal structure. The behavior is closely related to planetary waves, which, in the model, experience strong absorption in the upper mesosphere and lower thermosphere. Inverted thermal structure mirrors the synoptic pattern of potential vorticity, which marks the polar night vortex. Both are strongly distorted during stratospheric warmings, when inverted thermal structure at midlatitudes is favored. The region of negative lapse rate coincides with those altitudes where planetary wave temperature undergoes an abrupt phase shift. Wave temperature is then driven out of phase with wave geopotential. This alters the vertical structure of planetary waves, from westward tilt and upward amplification below the inversion to nearly barotropic structure and upward decay above the inversion. Accompanying the upward decay of planetary waves above the inversion is a decay of flow distortion, as the disturbed vortex is gradually restored toward polar symmetry.