The effect of breaking gravity waves on the dynamics and chemical composition of the mesosphere and lower thermosphere

Abstract

The influence of breaking gravity waves on the dynamics and chemical composition of the 60‐ to 110‐km region has been investigated with a two‐dimensional dynamical/chemical model that includes a parameterization of gravity wave drag and diffusion. The momentum deposited by breaking waves at mesospheric altitudes reverses the zonal winds, drives a strong mean meridional circulation, and produces a very cold summer and warm winter mesopause, in general agreement with observations. The seasonal variations of the computed eddy diffusion coefficient are consistent with the behavior of mesospheric turbulence inferred from MST radar echoes. In particular, it is found that eddy diffusion is strong in summer and winter but much weaker at the equinoxes and that this seasonal behavior has important consequences for the distribution of chemical species. Comparison between computed atomic oxygen and ozone, and the abundances of these constituents inferred from the 557.7‐nm and 1.27‐μm airglow emissions, reveals excellent agreement. The consistency between model results and these diverse types of observations lends strong support to the hypothesis that gravity waves play a very important role in determining the zonally averaged structure of the mesosphere and lower thermosphere.

Seasonal variations of the nighttime O(1S) and OH airglow emission rates at mid‐to‐high latitudes in the context of the large‐scale circulation

“…[6] Some previous model studies have proposed that the semi-annual variation of atomic oxygen and oxygen airglow is due to seasonal changes in eddy diffusion (i.e., turbulent mixing) caused by gravity wave dissipation [e.g., Garcia and Solomon, 1985]. However, those authors assumed that higher eddy diffusivity produces reduced airglow emission (by downward mixing out of the airglow region) which is opposite to what is currently believed.…”

“…Atomic oxygen is produced through the photo-dissociation of molecular oxygen in the thermosphere, and its global distribution in the MLT region is mainly controlled by dynamical transport processes [e.g., Garcia and Solomon, 1985;Brasseur and Solomon, 1986]. The two emissions provide valuable information on dynamical variations of atomic oxygen concentration at two different altitude levels [e.g., Takahashi et al, 1995;Shepherd et al, 1995Shepherd et al, , 2005Taylor et al, 1995;McLandress et al, 1996;Yee et al, 1997;Scheer et al, 2005].…”

First results from mesospheric airglow observations at 7.5º S.

“…Cogger et al (1981) studied seasonal variation using satellite data and concluded that the amplitude of the semi-annual oscillation of OI5577 rises towards higher latitude. Garcia & Solomon (1985) predicted that the amplitude decreases towards the equatorial region. Takahashi et al (1995) observed strong seasonal variation of OI5577, OH(9,4) and TOH(9,4) from 4 0 S and from 23 0 S. They concluded that the semi-annual oscillations in 23 0 S are smaller than 4 0 S.…”

Global ozone monitoring by occultation of stars: an overview of GOMOS measurements on ENVISAT

“…27) ozone exhibits a bi-annual oscillation (Kyrölä et al, 2010b), with maxima at equinoxes and minima at solstices. This behavior has been explained by Garcia and Solomon (1985) by invoking the effect of enhancement of gravity waves breaking at both solstices. They transport more H 2 O from below, a source of H, OH and HO 2 radicals that initiate a catalytic cycle of ozone destruction in this region.…”