Modeling the Observable Signatures and Effects of Short Period Gravity Waves at Large Amplitudes

Abstract:

Analyses of ground-based airglow data suggest that gravity waves at relatively small scales and short intrinsic periods may carry significant momentum through the mesosphere and lower thermosphere (MLT) [e.g., Fritts et al., JGR, 119(24), 2014; Fritts et al, BAMS, 10.1175/BAMS-D-14-00269, 2015.]. The quantification of wave momentum fluxes, and thus wave amplitudes, by airglow measurements is complicated by assumptions regarding chemical processes and initial states [e.g., Liu and Swenson, JGR, 108(D4), 2003] and by assumptions of wave propagation characteristics [e.g., Fritts, JGR, 105(D17), 2000]. Recent studies leveraging short-wave infrared hydroxyl (OH) imagers, such as the Utah State University (USU) Advanced Mesospheric Temperature Mapper (AMTM), suggest that airglow temperature measurements provide a promising capability to improve estimates of momentum fluxes [e.g., Fritts et al., 2014]. Nevertheless, integrated OH intensity and temperature signatures depend on multiple layered species [e.g., Snively et al., JGR 2010] that may be significantly and nonlinearly perturbed by strong or breaking gravity waves.

To elucidate gravity wave propagation, effects, and the observable airglow responses, we use a nonlinear, compressible atmospheric dynamics model in both two and three dimensions, coupled with a photochemical model [e.g., Adler-Golden, JGR, 102(A9), 1997; Snively, GRL, 40(17), 2013, and references therein]. In particular, we consider specific case studies where species layers become dramatically distorted by the evolving gravity waves. First, we assess the range of validity of momentum flux estimates, derived from integrated airglow intensity and temperature measurements, for waves at short periods and large amplitudes. Second, we estimate the impacts of the modeled large-amplitude waves at altitudes above in the lower thermosphere. Guidance towards the quantitative interpretations of airglow data is provided. Results also strongly suggest that waves with large amplitudes in the OH layer may have significant impacts in the lower thermosphere when their vertical propagation is unimpeded.