Description

The GFS Unified GWP version 1 combines the Orographic Drag Scheme with the version 1 UGWP non-stationary gravity wave drag (NGW) scheme of Yudin et al. (2020)[208].

The NGW physics scheme parameterizes the effects of non-stationary waves unresolved by dynamical cores. These non-stationary oscillations with periods bounded by Coriolis and Brunt-Väisälä frequencies and typical horizontal scales from tens to several hundreds of kilometers, are forced by the imbalance of convective and frontal/jet dynamics in the troposphere and lower stratosphere (Fritts 1984 [64]; Alexander et al. 2010 [2]; Plougonven and Zhang 2014 [166]). The NGWs propagate upwards and the amplitudes exponentially grow with altitude until instability and breaking of waves occur. Convective and dynamical instability induced by GWs with large amplitudes can trigger production of small-scale turbulence and self-destruction of waves. The latter process in the theory of atmospheric GWs is frequently referred as the wave saturation (Lindzen 1981 [122]; Weinstock 1984 [196]; Fritts 1984 [64]). Herein, “saturation” or "breaking" refers to any processes that act to reduce wave amplitudes due to instabilities and/or interactions arising from large-amplitude perturbations limiting the exponential growth of GWs with height. Background dissipation processes such as molecular diffusion and radiative cooling, in contrast, act independently of GW amplitudes. In the middle atmosphere, impacts of NGW saturation (or breaking) and dissipation on the large-scale circulation, mixing, and transport have been acknowledged in the physics of global weather and climate models after pioneering studies by Lindzen 1981 [122] and Holton 1983 [92]. Comprehensive reviews on the physics of NGWs and OGWs in climate and weather models have been discussed in Kim et al. 2003 [201], Alexander et al. 2010 [2], Geller et al. 2013 [70], and Garcia et al. 2017 [67]. They are formulated using different aspects of the nonlinear and linear propagation, instability, breaking and dissipation of waves along with different specifications of GW sources (Garcia et al. 2007 [66]; Richter et al 2010 [169]; Eckermann et al. 2009 [48]; Eckermann 2011 [49]; Lott et al. 2012 [128]).

Several studies have demonstrated the importance of NGW physics to improve model predictions in the stratosphere and upper atmosphere (Alexander et al. 2010 [2]; Geller et al. 2013). In order to describe the effects of unresolved GWs in global forecast models, the representation of subgrid OGWs and NGWs has been implemented in the self-consistent manner using the UGWP framework.

Intraphysics Communication

Argument Table

General Algorithm

Unified Gravity Wave Physics General Algorithm