The interaction between gravity waves and solar tides in a linear tidal model with a 4‐D ray‐tracing gravity‐wave parameterization

• Published in: Journal of geophysical research. Space physics 2016-09, Vol.121 (9), p.8936-8950
• Main Authors: Ribstein, B., Achatz, U.
• Format: Article
• Language: English
• Subjects: Atmosphere; Atmospheric dynamics; Atmospheric models; Buoyancy; Buoyancy flux; Climate models; Climatology; Diurnal variations; Dynamics; Gravitational waves; gravity wave; Gravity waves; Heating; Internal waves; Mathematical models; mesosphere‐lower thermosphere; Momentum; Parameterization; Parametrization; Primitive equations; Propagation; ray tracer; solar tide; Solar tides; Stratospheric heating; Tides; Wavelengths; Weather forecasting
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1002/2016JA022478

Gravity waves (GWs) play an important role in atmospheric dynamics. Due to their short wavelengths, they must be parameterized in current weather and forecast models, which cannot resolve them explicitly. We are here the first to report the possibility and the implication of having an online GW parameterization in a linear but global model that incorporates their horizontal propagation, the effects of transients and of horizontal background gradients on GW dynamics. The GW parameterization is based on a ray‐tracer model with a spectral formulation that is safe against numerical instabilities due to caustics. The global model integrates the linearized primitive equations to obtain solar tides (STs), with a seasonally dependent reference climatology, forced by a climatological daily cycle of the tropospheric and stratospheric heating, and the (instantaneous) GW momentum and buoyancy flux convergences resulting from the ray tracer. Under a more conventional “single‐column” approximation, where GWs only propagate vertically and do not respond to horizontal gradients of the resolved flow, GW impacts are shown to be significantly changed in comparison with “full” experiments, leading to significant differences in ST amplitudes and phases, pointing at a sensitive issue of GW parameterizations in general. In the full experiment, significant semidiurnal STs arise even if the tidal model is only forced by diurnal heating rates. This indicates that an important part of the tidal signal is forced directly by GWs via their momentum and buoyancy deposition. In general, the effect of horizontal GW propagation and the GW response to horizontal large‐scale flow gradients is rather observed in nonmigrating than in migrating tidal components. Key Points Middle atmosphere solar tides and internal gravity waves interaction is analyzed A 4‐D ray‐tracer model is directly coupled to a global atmosphere model An important part of the tidal signal is forced directly by gravity waves