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.Citation: Grygalashvyly, M., E. Becker, and G. R. Sonnemann (2011), Wave mixing effects on minor chemical constituents in the MLT region: Results from a global CTM driven by high-resolution dynamics,

Atmospheric gravity wave effects on polar mesospheric clouds: A comparison of numerical simulations from CARMA 2D with AIM observations

“…In the opposite phase of the wave, the pump transports water (and particles) downward, causing a negative growth rate and lower brightness. Such effects of AGW on trace gas transport have been investigated on global scales recently by Grygalashvyly et al [2011]. While AGWs with short horizontal wavelengths and short period induce higher vertical velocities than large period large horizontal wavelength AGWs, they do not last long enough for this process to significantly change PMC brightness.…”

Hydroxyl layer: Mean state and trends at midlatitudes

“…Atomic oxygen in the mesopause region is a photochemically long-lived constituent, and it has a strong vertical gradient. Thus, its distribution, as well as its long term behavior, is determined by the vertical component of general mean circulation, by tides [e.g., Smith et al, 2010], by gravity waves [Grygalashvyly et al, 2011, and [Hoffmann et al, 2011;Grygalashvyly et al, 2012]. Thus, we can suppose the long-term effect of GWs, mediated by atomic oxygen, on the excited hydroxyl layer.…”

Several notes on the OH* layer

“…The alternative point of view is that the semi-annual variation of OH * at low latitudes is related to seasonal variability of GWs and changes in turbulent diffusion due to GW dissipation (Garcia and Solomon, 1985). In view of new knowledge on GW mixing (Grygalashvyly et al, 2011(Grygalashvyly et al, , 2012, it can be stated that the semi-annual variation of OH * is related to down-gradient fluxes of atomic oxygen by GW mixing. All three potentially responsible processes are connected to the downward flux of atomic oxygen, which, according to Eqs.…”