Reply on RC3

Abstract

The increase in amplitudes of upward propagating gravity waves (GWs) with height due to decreasing density is usually described by exponential growth; however, recent measurements detected a much stronger increase in gravity wave potential energy density (GWPED) during daylight than night-time (increase by a factor of about 4 to 8 between middle stratosphere and upper mesosphere), which is not well understood up to now. This paper suggests that ozone-gravity wave interaction in the upper stratosphere/lower mesosphere is largely responsible for this phenomenon. The coupling between ozone-photochemistry and temperature is particularly strong in the upper stratosphere where the time-mean ozone mixing ratio is decreasing with height; therefore, an initial uplift of an air parcel must lead to a local increase in ozone and in the heating rate compared to the environment, and, hence, to an amplification of the initial uplift. Standard solutions of upward propagating GWs with linear ozone-temperature coupling are formulated suggesting local amplitude amplifications during daylight of 5 to 15 % for low-frequency GWs (periods ≥4 hours), as a function of the intrinsic frequency which decreases if ozone-temperature coupling is included. Subsequently, for horizontal wavelengths larger than 500 km and vertical wavelengths smaller than 5 km, the cumulative amplification during the upward level-by-level propagation leads to much stronger amplitudes in the GW perturbations (factor of about 1.5 to 3) and in the GWPED (factor of about 3 to 9) at upper mesospheric altitudes. The results open a new viewpoint for improving general circulation models with resolved or parameterized GWs.