Evidence for gravity wave drag in the boundary layer of a numerical forecast model: a comparison with observations

Abstract The impacts of enhanced lower-tropospheric gravity wave drag induced by subgrid-scale orography on short- and medium-range forecasts as well as seasonal simulations are examined. This study reports on the enhanced performance of the scheme proposed by Kim and Arakawa, which has been used in the National Centers for Environmental Prediction (NCEP) Global Spectral Model since 1997. The performance is evaluated against a traditional upper-level drag scheme that is also available in the model. The experiment results reveal that the Kim–Arakawa scheme improves the movement and intensity of an extratropical cyclone and a continental high pressure system that was accompanied by heavy snowfall over Korea on 14–15 February 2001. The monthly verification for medium-range forecasts in December 2006, which are initialized by the NCEP operational analysis, demonstrates overall improvements in the forecasts of large-scale fields in the Northern Hemisphere. Moderate improvements are also found in the seasonal simulation of December–February for the years 1996/97, 1997/98, and 1999/2000. This study concludes that the enhanced lower-level drag should be properly parameterized in global atmospheric models for numerical weather prediction and seasonal prediction.

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Gravity-Wave Drag in the Stable Boundary Layer Over Moderate Terrain

Boundary-Layer Meteorology ◽

10.1007/s10546-018-00422-3 ◽

2019 ◽

Vol 171 (2) ◽

pp. 175-189

Author(s):

A. Lapworth ◽

S. R. Osborne

Keyword(s):

Boundary Layer ◽

Gravity Wave ◽

Stable Boundary Layer ◽

Wave Drag ◽

Stable Boundary

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Self-Acceleration in the Parameterization of Orographic Gravity Wave Drag

Journal of the Atmospheric Sciences ◽

10.1175/2010jas3358.1 ◽

2010 ◽

Vol 67 (8) ◽

pp. 2537-2546 ◽

Cited By ~ 10

Author(s):

John F. Scinocca ◽

Bruce R. Sutherland

Keyword(s):

Gravity Wave ◽

Middle Atmosphere ◽

Wave Train ◽

Leading Edge ◽

Wave Theory ◽

Wave Drag ◽

Tuning Parameter ◽

Mean Flow ◽

Propagating Waves ◽

The Impact

Abstract A new effect related to the evaluation of momentum deposition in conventional parameterizations of orographic gravity wave drag (GWD) is considered. The effect takes the form of an adjustment to the basic-state wind about which steady-state wave solutions are constructed. The adjustment is conservative and follows from wave–mean flow theory associated with wave transience at the leading edge of the wave train, which sets up the steady solution assumed in such parameterizations. This has been referred to as “self-acceleration” and it is shown to induce a systematic lowering of the elevation of momentum deposition, which depends quadratically on the amplitude of the wave. An expression for the leading-order impact of self-acceleration is derived in terms of a reduction of the critical inverse Froude number Fc, which determines the onset of wave breaking for upwardly propagating waves in orographic GWD schemes. In such schemes Fc is a central tuning parameter and typical values are generally smaller than anticipated from conventional wave theory. Here it is suggested that self-acceleration may provide some of the explanation for why such small values of Fc are required. The impact of Fc on present-day climate is illustrated by simulations of the Canadian Middle Atmosphere Model.

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The southern stratospheric gravity wave hot spot: individual waves and their momentum fluxes measured by COSMIC GPS-RO

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-7797-2015 ◽

2015 ◽

Vol 15 (14) ◽

pp. 7797-7818 ◽

Cited By ~ 47

Author(s):

N. P. Hindley ◽

C. J. Wright ◽

N. D. Smith ◽

N. J. Mitchell

Keyword(s):

Southern Ocean ◽

Gravity Wave ◽

General Circulation ◽

Hot Spot ◽

Polar Vortex ◽

General Circulation Models ◽

Wave Drag ◽

Southern Andes ◽

Analysis Technique ◽

Modelling Studies

Abstract. Nearly all general circulation models significantly fail to reproduce the observed behaviour of the southern wintertime polar vortex. It has been suggested that these biases result from an underestimation of gravity wave drag on the atmosphere at latitudes near 60° S, especially around the "hot spot" of intense gravity wave fluxes above the mountainous Southern Andes and Antarctic peninsula. Here, we use Global Positioning System radio occultation (GPS-RO) data from the COSMIC satellite constellation to determine the properties of gravity waves in the hot spot and beyond. We show considerable southward propagation to latitudes near 60° S of waves apparently generated over the southern Andes. We propose that this propagation may account for much of the wave drag missing from the models. Furthermore, there is a long leeward region of increased gravity wave energy that sweeps eastwards from the mountains over the Southern Ocean. Despite its striking nature, the source of this region has historically proved difficult to determine. Our observations suggest that this region includes both waves generated locally and orographic waves advected downwind from the hot spot. We describe and use a new wavelet-based analysis technique for the quantitative identification of individual waves from COSMIC temperature profiles. This analysis reveals different geographical regimes of wave amplitude and short-timescale variability in the wave field over the Southern Ocean. Finally, we use the increased numbers of closely spaced pairs of profiles from the deployment phase of the COSMIC constellation in 2006 to make estimates of gravity wave horizontal wavelengths. We show that, given sufficient observations, GPS-RO can produce physically reasonable estimates of stratospheric gravity wave momentum flux in the hot spot that are consistent with measurements made by other techniques. We discuss our results in the context of previous satellite and modelling studies and explain how they advance our understanding of the nature and origins of waves in the southern stratosphere.

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Compensation between Resolved Wave Driving and Parameterized Orographic Gravity Wave Driving of the Brewer–Dobson Circulation and Its Response to Climate Change

Journal of Climate ◽

10.1175/jcli-d-13-00644.1 ◽

2014 ◽

Vol 27 (14) ◽

pp. 5601-5610 ◽

Cited By ~ 23

Author(s):

Michael Sigmond ◽

Theodore G. Shepherd

Keyword(s):

Climate Change ◽

Gravity Wave ◽

Northern Hemisphere ◽

Rossby Wave ◽

Climate Model ◽

Wave Drag ◽

High Latitudes ◽

Remarkable Degree ◽

The Impact

Abstract Following recent findings, the interaction between resolved (Rossby) wave drag and parameterized orographic gravity wave drag (OGWD) is investigated, in terms of their driving of the Brewer–Dobson circulation (BDC), in a comprehensive climate model. To this end, the parameter that effectively determines the strength of OGWD in present-day and doubled CO2 simulations is varied. The authors focus on the Northern Hemisphere during winter when the largest response of the BDC to climate change is predicted to occur. It is found that increases in OGWD are to a remarkable degree compensated by a reduction in midlatitude resolved wave drag, thereby reducing the impact of changes in OGWD on the BDC. This compensation is also found for the response to climate change: changes in the OGWD contribution to the BDC response to climate change are compensated by opposite changes in the resolved wave drag contribution to the BDC response to climate change, thereby reducing the impact of changes in OGWD on the BDC response to climate change. By contrast, compensation does not occur at northern high latitudes, where resolved wave driving and the associated downwelling increase with increasing OGWD, both for the present-day climate and the response to climate change. These findings raise confidence in the credibility of climate model projections of the strengthened BDC.

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The GCM Response to Current Parameterizations of Nonorographic Gravity Wave Drag

Journal of the Atmospheric Sciences ◽

10.1175/jas3483.1 ◽

2005 ◽

Vol 62 (7) ◽

pp. 2394-2413 ◽

Cited By ~ 61

Author(s):

Charles McLandress ◽

John F. Scinocca

Keyword(s):

Gravity Wave ◽

General Circulation ◽

Critical Level ◽

Climate Modeling ◽

Circulation Model ◽

Wave Drag ◽

Nonlinear Dissipation ◽

Additional Experiment ◽

Identical Response ◽

Dissipation Mechanism

Abstract A comparison is undertaken of the response of a general circulation model (GCM) to the nonorographic gravity wave drag parameterizations of Hines, Warner and McIntyre, and Alexander and Dunkerton. The analysis is restricted to a comparison of each parameterization’s nonlinear dissipation mechanism since, in principle, this is the only component that differs between the schemes. This is achieved by developing a new, more general parameterization that can represent each of these dissipation mechanisms, while keeping all other aspects of the problem identical. The GCM simulations reveal differences in the climatological response to the three dissipation mechanisms. These differences are documented for both tropopause and surface launch elevations of the parameterized waves. The simulations also reveal systematic differences in the height at which momentum is deposited. This behavior is investigated further in a set of experiments designed to reduce these systematic differences, while leaving the details of the dissipation mechanisms unaltered. These sensitivity experiments demonstrate that it is possible to obtain nearly identical responses from all three mechanisms, which indicates that the GCM response is largely insensitive to the precise details of the dissipation mechanisms. This finding is supported by an additional experiment in which the nonlinear dissipation mechanisms are turned off and critical-level filtering is left to act as the only source of dissipation. In this experiment, critical-level filtering effectively replaces the nonlinear dissipation mechanism, producing a nearly identical response. The results of this study suggest that climate modeling efforts would potentially benefit more from the refinement of other aspects of the parameterization problem, such as the properties of the launch spectrum, than they have benefited from the refinement of dissipation mechanisms.

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