Wave mixing effects on minor chemical constituents in the MLT region: Results from a global CTM driven by high-resolution dynamics

Abstract

[1] The dynamical fields of a high-resolution mechanistic general circulation model (GCM) with resolved gravity waves (GWs) are used to drive a chemistry-transport model (CTM) of the mesosphere-lower thermosphere (MLT). Both models have been used in previous studies and are coupled in off-line mode in order to study the explicit effects of GWs on the transport and photochemistry of minor constituents of the MLT. This is done on the basis of a sensitivity experiment. In our control simulation the CTM is driven with the full dynamical fields from an annual cycle simulated with the GCM, where mid-frequency GWs down to horizontal wavelengths of 350 km are resolved and their wave-mean flow interaction is self-consistently induced by an advanced turbulence model. A perturbation simulation with the CTM is defined by eliminating all meso-scale variations with horizontal wavelengths shorter than 1000 km from the dynamical fields by means of spectral filtering before running the CTM. The response of the CTM to GWs perturbations reveals strong effects on the trace-gas concentrations. In particular, minor chemical constituents with large photochemical life-time are strongly affected by vertical wave mixing, while constituents with short life-time reflect the dependence of their reaction rates on meso-scale temperature perturbations and on the changed distributions of long-lived constituents. The mean model response is strongest around the mesopause. We present detailed discussions of the simulated gravity-wave mixing effects on the photochemistry and highlight the consequences for our understanding of the general circulation of the MLT.