Towards a transient gravity wave parametrization in atmospheric models

2021 ◽  
Author(s):  
Georg Sebastian Voelker ◽  
Gergely Bölöni ◽  
Young-Ha Kim ◽  
Ulrich Achatz
Keyword(s):  
Gravity Wave ◽  
Prediction Models ◽  
Weather Prediction ◽  
Potential Temperature ◽  
Internal Gravity Waves ◽  
Wave Drag ◽  
Mean Flow ◽  
Direct Wave ◽  
Flow Interactions ◽  
The Mean

<p>Subgrid-scale internal gravity waves (IGWs) are important distributors of energy in a stratified atmosphere. While they are mostly excited at lower altitudes their effects are most important between the upper troposphere to the mesopause (~85km). During propagation–both in the vertical and the horizontal–nonlinear IGWs can exert a wave drag on the mean winds, interact with the mean potential temperature, and mix atmospheric tracers such as aerosols or greenhouse gases.</p> <p>In state-of-the art weather prediction models IGWs are typically parametrized using the single-column and the steady-state assumptions. These parametrizations take into account dissipative effects of IGWs but neglect their horizontal propagation and all of their transient interaction mechanisms such as direct wave-mean-flow interactions. However, the latter have been shown to contribute to IGW dynamics in various idealized studies.</p> <p>Here we present advances of the use of the transient Multi Scale Gravity Wave Model (MS-GWaM) in the upper atmosphere model UA-ICON. Based on Lagrangian ray-tracing the parametrization includes various non-orographic wave sources, transient propagation in both the horizontal and vertical directions, direct wave-mean-flow interactions and wave breaking. The resulting setup satisfactorily reproduces the observed mean-wind and potential temperature climatology and already shows promising insights into the details of the role of IGWs in the atmosphere.</p>

Application of the IDEMIX Concept for Internal Gravity Waves in the Atmosphere

2020 ◽  
Vol 77 (10) ◽  
pp. 3601-3618
Author(s):  
B. Quinn ◽  
C. Eden ◽  
D. Olbers
Keyword(s):  
Energy Balance ◽  
Wave Field ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Middle Atmosphere ◽  
Internal Gravity Waves ◽  
Wave Drag ◽  
Mean Flow ◽  
The Mean

AbstractThe model Internal Wave Dissipation, Energy and Mixing (IDEMIX) presents a novel way of parameterizing internal gravity waves in the atmosphere. IDEMIX is based on the spectral energy balance of the wave field and has previously been successfully developed as a model for diapycnal diffusivity, induced by internal gravity wave breaking in oceans. Applied here for the first time to atmospheric gravity waves, integration of the energy balance equation for a continuous wave field of a given spectrum, results in prognostic equations for the energy density of eastward and westward gravity waves. It includes their interaction with the mean flow, allowing for an evolving and local description of momentum flux and gravity wave drag. A saturation mechanism maintains the wave field within convective stability limits, and a closure for critical-layer effects controls how much wave flux propagates from the troposphere into the middle atmosphere. Offline comparisons to a traditional parameterization reveal increases in the wave momentum flux in the middle atmosphere due to the mean-flow interaction, resulting in a greater gravity wave drag at lower altitudes. Preliminary validation against observational data show good agreement with momentum fluxes.

On strongly nonlinear gravity waves in a vertically sheared atmosphere

2021 ◽  
Author(s):  
Georg Sebastian Voelker ◽  
Mark Schlutow
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Internal Gravity Wave ◽  
Internal Gravity Waves ◽  
Wave Drag ◽  
Mean Flow ◽  
Flow Strength ◽  
Weakly Nonlinear ◽  
Strongly Nonlinear ◽  
The Mean

<p>Internal gravity waves are a well-known mechanism of energy redistribution in stratified fluids such as the atmosphere. They may propagate from their generation region, typically in the Troposphere, up to high altitudes. During their lifetime internal waves couple to the atmospheric background through various processes. Among the most important interactions are the exertion of wave drag on the horizontal mean-flow, the heat generation upon wave breaking, or the mixing of atmospheric tracers such as aerosols or greenhouse gases.</p><p>Many of the known internal gravity wave properties and interactions are covered by linear or weakly nonlinear theories. However, for the consideration of some of the crucial effects, like a reciprocal wave-mean-flow interaction including the exertion of wave drag on the mean-flow, strongly nonlinear systems are required. That is, there is no assumption on the wave amplitude relative to the mean-flow strength such that they may be of the same order.</p><p>Here, we exploit a strongly nonlinear Boussinesq theory to analyze the stability of a stationary internal gravity wave which is refracted at the vertical edge of a horizontal jet. Thereby we assume that the incident wave is horizontally periodic, non-hydrostatic, and vertically modulated. Performing a linear stability analysis in the vicinity of the jet edge we find necessary and sufficient criteria for instabilities to grow. In particular, the refracted wave becomes unstable if its incident amplitude is large enough and both mean-flow horizontal winds, below and above the edge of the jet, do not exceed particular upper bounds.</p>

Toward transient subgrid-scale gravity wave representation in atmospheric models. Part I: Propagation model including non-dissipative direct wave-mean-flow interactions

2021 ◽  
Author(s):  
Gergely Bölöni ◽  
Young-Ha Kim ◽  
Sebastian Borchert ◽  
Ulrich Achatz
Keyword(s):  
Steady State ◽  
Gravity Wave ◽  
Climate Model ◽  
Propagation Model ◽  
Small Scale ◽  
Mean Flow ◽  
Direct Wave ◽  
Steady State Assumption ◽  
Flow Interactions ◽  
State Assumption

AbstractCurrent gravity-wave (GW) parameterization (GWP) schemes are using the steady-state assumption, where an instantaneous balance between GWs and mean flow is postulated, thereby neglecting transient, non-dissipative direct interactions between the GW field and the resolved flow. These schemes rely exclusively on wave dissipation, by GW breaking or near critical layers, as a mechanism leading to forcing of the mean flow. In a transient GWP, without steady-state assumption, non-dissipative direct wave-mean-flow interactions are enabled as an additional mechanism. Idealized studies have shown that this is potentially important, so that the transient GWP Multi-Scale Gravity-Wave Model (MS-GWaM) has been implemented into a state-of-the-art weather and climate model. In this implementation, MS-GWaM leads to a zonal-mean circulation well in agreement with observations, and increases GW momentum-flux intermittency as compared to steady-state GWPs, bringing it into better agreement with super-pressure balloon observations. Transient effects taken into account by MS-GWaM are shown to make a difference even on monthly time-scales: in comparison with steady-state GWPs momentum fluxes in the lower stratosphere are increased and the amount of the missing drag at Southern Hemispheric high latitudes is decreased to a modest but non-negligible extent. An analysis of the contribution of different wavelengths to the GW signal in MS-GWaM suggests that small scale GWs play an important role down to horizontal and vertical wavelengths of 50km (or even smaller) and 200m respectively.

An overview of the past, present and future of gravity‐wave drag parametrization for numerical climate and weather prediction models

2003 ◽  
Vol 41 (1) ◽  
pp. 65-98 ◽  
Author(s):  
Survey Article ◽  
Young‐Joon Kim ◽  
Stephen D. Eckermann ◽  
Hye‐Yeong Chun
Keyword(s):  
Gravity Wave ◽  
Prediction Models ◽  
Weather Prediction ◽  
Wave Drag ◽  
The Past

Towards the implementation of a transient gravity wave drag parameterization in atmospheric models

2020 ◽  
Author(s):  
Gergely Bölöni ◽  
Young-Ha Kim ◽  
Sebastian Borchert ◽  
Ulrich Achatz
Keyword(s):  
Steady State ◽  
Gravity Wave ◽  
Wave Drag ◽  
Altitude Range ◽  
Mean Flow ◽  
Atmospheric Models ◽  
Parameterization Schemes ◽  
Steady State Assumption ◽  
Flow Interactions ◽  
State Assumption

<p>The aim of the presented work is to improve the parameterization of subgrid-scale gravity wave (GW) effects on the resolved flow in atmospheric models in a large altitude range from the upper troposphere to the mesopause (~85km). State of the art GW parameterization schemes are using the steady-state approximation for the wave field and therefore assume an instantaneous GW propagation neglecting direct interactions between the GW field and the resolved flow within the whole altitude range mentioned above. As such, these schemes rely on dissipative processes - GW breaking and critical layer filtering - as the only mechanism to accelerate/decelerate the resolved flow. In contrast to this, by dropping the steady-state assumption a contribution to the mean-flow forcing emerges in the form of direct GW-mean-flow interactions. Several idealized studies show that, besides dissipative effects, direct GW-mean-flow interactions contribute to GW dynamics in an important extent (Bölöni et al., 2016, J. Atmos. Sci.}, 73, 4833-4852, Wilhelm et al., 2018, J. Atmos. Sci., 75, 2257-2280, Wei et al., 2019, J. Atmos. Sci., 76, 2715-2738). This motivates the implementation of a transient GW model (MS-GWaM: Multi Scale Gravity Wave Model) to UA-ICON, the upper atmosphere version of ICON (Borchert et al., 2019, Geosci. Model Dev., 12, 3541-3569) which does not rely on the steady-state assumption and thus includes direct GW-mean-flow interactions. As a reference and a representative of currently available GW parameterization schemes a steady-state version of MS-GWaM (ST-MS-GWaM) has been implemented to UA-ICON as well, which shares the treatment of all possible components (wave sources and wave saturation scheme) with the transient MS-GWaM scheme and differs from it "only" in the treatment of propagation, i.e. excluding direct GW-mean-flow interactions and thus transience. Both MS-GWaM and ST-MS-GWaM reproduce the observed wind and temperature climatology (e.g. URAP data: Swinbank, R. and D. A. Ortland, 2003, J. Geophys. Res., 108, D19, 4615) reasonably well, but the transient propagation makes a robust difference in the circulation in perpetual runs. The transient propagation in MS-GWaM substantially contributes to an increase of the GW intermittency in the whole altitude range, giving a better comparison with super-pressure balloon observations (e.g. Hertzog et al., 2012, J. Atmos. Sci., 69, 3433-3448), whereas the lack of transience prevents any occurrence of higher GW momentum flux values than the launch magnitude itself. This is explained by the fact that the direct GW-mean-flow interactions involve a highly transient evolution of the wave action and the vertical group velocity, which often leads to increased pseudo-momentum fluxes as compared to the launch magnitude.</p>

Sensitivity of the middle and upper atmospheric dynamics to the modification of the gravity wave drag parameterization in ICON model

2021 ◽  
Author(s):  
Khalil Karami ◽  
Sebastian Borchert ◽  
Roland Eichinger ◽  
Christoph Jacobi ◽  
Ales Kuchar ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
General Circulation ◽  
Southern Oscillation ◽  
Weather Prediction ◽  
Polar Vortex ◽  
Circulation Model ◽  
Internal Variability ◽  
Wave Drag ◽  
Mean Flow

<p>The gravity waves play a crucial role in driving and shaping the middle atmospheric circulation. The Upper-Atmospheric extension of the ICOsahedral Non-hydrostatic (UA-ICON) general circulation model was recently developed with satisfying performances in both idealized test cases and climate simulations, however the sensitivity of the circulation to the parameterized orographic and non-orographic gravity wave drag remains largely unexplored. Using UA-ICON and ICON-NWP, the sensitivity of the dynamics and circulation to both orographic and non-orographic parameterized gravity waves effects are investigated. ICON-NWP stands for the numerical-weather prediction mode of the ICON model (see Zängl et al, 2015, QJRMetSoc), with a model top at about 80 km altitude. The UA-ICON mode differs from ICON-NWP in deep-atmosphere dynamics (instead of shallow-atmosphere dynamics) and upper-atmosphere physics parameterizations being switched on. In addition, the model top is at about 150 km.</p> <p>The sensitivity experiments involve employing repeated annual cycle sea surface temperatures, sea ice, and greenhouse gases under year 1988. This year is selected as both El-Nino southern oscillation and pacific decadal oscillation are in their neutral phase and no explosive volcano eruption has occurred and hence conditions in this year can serve as a useful proxy for the multi-year mean condition and an estimate of its internal variability. For both UA-ICON and ICON-NWP, we perform simulations where in the control (CTL) simulation both orographic and non-orographic gravity wave drags are switched on. The other two experiments are identical to the control simulation except that either orographic (OGWD-off) or b) non-orographic (NGWD-off) gravity wave drags are switched off. The analysis include comparisons between CTL and OGWD-off and NGWD-off simulations and include wave-mean flow interaction diagnostics (Eliassen-Palm flux and its divergence and refractive index of Rossby waves) and mass stream function of the Brewer-Dobson circulation. We also investigate the sudden stratospheric warming frequency and polar vortex morphology in order to understand whether a missing gravity wave forcing can further amplify or curtail the effects of future climate. We present our goal, method as well as first results and discuss possible further analysis. </p>

Self-Acceleration in the Parameterization of Orographic Gravity Wave Drag

2010 ◽  
Vol 67 (8) ◽  
pp. 2537-2546 ◽  
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.

Spurious Grid-Scale Precipitation in the North American Regional Reanalysis

2007 ◽  
Vol 135 (6) ◽  
pp. 2168-2184 ◽  
Author(s):  
Gregory L. West ◽  
W. James Steenburgh ◽  
William Y. Y. Cheng
Keyword(s):  
North American ◽  
Prediction Models ◽  
Weather Prediction ◽  
Regional Climate ◽  
Potential Temperature ◽  
Climate Data ◽  
The North ◽  
North American Regional Reanalysis ◽  
Upper Level ◽  
Regional Reanalysis

Abstract Spurious grid-scale precipitation (SGSP) occurs in many mesoscale numerical weather prediction models when the simulated atmosphere becomes convectively unstable and the convective parameterization fails to relieve the instability. Case studies presented in this paper illustrate that SGSP events are also found in the North American Regional Reanalysis (NARR) and are accompanied by excessive maxima in grid-scale precipitation, vertical velocity, moisture variables (e.g., relative humidity and precipitable water), mid- and upper-level equivalent potential temperature, and mid- and upper-level absolute vorticity. SGSP events in environments favorable for high-based convection can also feature low-level cold pools and sea level pressure maxima. Prior to 2003, retrospectively generated NARR analyses feature an average of approximately 370 SGSP events annually. Beginning in 2003, however, NARR analyses are generated in near–real time by the Regional Climate Data Assimilation System (R-CDAS), which is identical to the retrospective NARR analysis system except for the input precipitation and ice cover datasets. Analyses produced by the R-CDAS feature a substantially larger number of SGSP events with more than 4000 occurring in the original 2003 analyses. An oceanic precipitation data processing error, which resulted in a reprocessing of NARR analyses from 2003 to 2005, only partially explains this increase since the reprocessed analyses still produce approximately 2000 SGSP events annually. These results suggest that many NARR SGSP events are not produced by shortcomings in the underlying Eta Model, but by the specification of anomalous latent heating when there is a strong mismatch between modeled and assimilated precipitation. NARR users should ensure that they are using the reprocessed NARR analyses from 2003 to 2005 and consider the possible influence of SGSP on their findings, particularly after the transition to the R-CDAS.

Effects of Nonlinearity on Convectively Forced Internal Gravity Waves: Application to a Gravity Wave Drag Parameterization

2008 ◽  
Vol 65 (2) ◽  
pp. 557-575 ◽  
Author(s):  
Hye-Yeong Chun ◽  
Hyun-Joo Choi ◽  
In-Sun Song
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Lower Thermosphere ◽  
Internal Gravity Waves ◽  
Wave Drag ◽  
Scale Factor ◽  
Wide Range ◽  
Flux Spectrum ◽  
Diabatic Forcing

Abstract In the present study, the authors propose a way to include a nonlinear forcing effect on the momentum flux spectrum of convectively forced internal gravity waves using a nondimensional numerical model (NDM) in a two-dimensional framework. In NDM, the nonlinear forcing is represented by nonlinear advection terms multiplied by the nonlinearity factor (NF) of the thermally induced internal gravity waves for a given specified diabatic forcing. It was found that the magnitudes of the waves and resultant momentum flux above the specified forcing decrease with increasing NF due to cancellation between the two forcing mechanisms. Using the momentum flux spectrum obtained by the NDM simulations with various NFs, a scale factor for the momentum flux, normalized by the momentum flux induced by diabatic forcing alone, is formulated as a function of NF. Inclusion of the nonlinear forcing effect into current convective gravity wave drag (GWD) parameterizations, which consider diabatic forcing alone by multiplying the cloud-top momentum flux spectrum by the scale factor, is proposed. An updated convective GWD parameterization using the scale factor is implemented into the NCAR Whole Atmosphere Community Climate Model (WACCM). The 10-yr simulation results, compared with those by the original convective GWD parameterization considering diabatic forcing alone, showed that the magnitude of the zonal-mean cloud-top momentum flux is reduced for wide range of phase speed spectrum by about 10%, except in the middle latitude storm-track regions where the cloud-top momentum flux is amplified. The zonal drag forcing is determined largely by the wave propagation condition under the reduced magnitude of the cloud-top momentum flux, and its magnitude decreases in many regions, but there are several areas of increasing drag forcing, especially in the tropical upper mesosphere and lower thermosphere.

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