Description

The GFS Unified GWP version 1 combines the GSL_drag_suite orographic gravity wave drag (OGW) scheme with the version 1 UGWP non-stationary gravity wave drag (NGW) scheme developed by Yudin et al. (2020)[140] and described in Toy et al. (2025)[128].

The NGW scheme represents the effects of non-stationary waves unresolved by the model dynamical cores. These waves, characterized by periods bounded by the Coriolis and Brunt-Väisälä frequencies and horizontal scales ranging from tens to several hundreds of kilometers, are generated by imbalances associated with convection, fronts, and jet dynamics in the troposphere and lower stratosphere (Fritts 1984 [35]; Alexander et al. 2010 [2]; Plougonven and Zhang 2014 [107]). As NGWs propagate upward through the atmosphere, their amplitudes increase approximately exponentially with decreasing air density. Eventually, the waves become unstable and undergo breaking or saturation. Large-amplitude gravity waves can induce convective and dynamical instabilities generating small-scale turbulence and leading to wave dissipation. In gravity-wave theory, this self-limiting process is commonly referred to as wave saturation (Lindzen 1981 [79]; Weinstock 1984 [131]; Fritts 1984 [35]). In this context, the terms “saturation” and "breaking" broadly denote processes that reduce wave amplitudes through instabilities and nonlinear interactions, thereby limiting their otherwise exponential growth with height. This differs from background dissipation mechanisms, such as molecular diffusion and radiative cooling, which act independently of GW amplitudes. The importance of NGW breaking and dissipation in driving the large-scale circulation, mixing, and tracer transport in the middle atmosphere has been recognized since the pioneering studies by Lindzen (1981) [79] and Holton (1983) [60]. Since then, numerous NGW parameterizations have been developed for weather and climate models. Comprehensive reviews can be found in Kim et al. 2003 [135], Alexander et al. 2010 [2], Geller et al. 2013 [41], and Garcia et al. 2017 [38]. These parameterizations differ in their treatment of wave generation, propagation, instability, breaking, and dissipation, as well as in their representation of GW sources (Garcia et al. 2007 [37]; Richter et al. 2010 [110]; Eckermann et al. 2009 [29]; Eckermann 2011 [30]; Lott et al. 2012 [84]).

Several studies have demonstrated the importance of NGW physics for improving model predictions in the stratosphere and upper atmosphere (Alexander et al. 2010 [2]; Geller et al. 2013). Within the UGWP framework, both subgrid-scale OGWs and NGWs are represented in a physically consistent and self-contained manner, enabling a unified treatment of unresolved gravity-wave effects in global forecasting systems.

Intraphysics Communication

Argument Table

General Algorithm

Unified Gravity Wave Physics General Algorithm