A new parameterization of gravity waves for atmospheric circulation models based on the radiative transfer equation

2020 ◽  
Author(s):  
Matthäus Mai ◽  
Erich Becker
Keyword(s):  
Radiative Transfer ◽  
Wave Field ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Transfer Equation ◽  
Middle Atmosphere ◽  
Radiative Transfer Equation ◽  
Dynamical Instability ◽  
Mean Flow ◽  
Wave Dissipation

<p>Gravity waves play an important role in the momentum and heat budgets of the middle atmosphere. Global circulation models used for long-term simulations need to parameterize the transport of wave momentum and energy from the lower to the middle atmosphere and the associated wave-mean flow interaction. This gravity wave-mean flow interaction is usually due to dynamical instability triggered by wave refraction and amplitude growth, giving rise to wave dissipation. In addition, gravity waves can interact with the mean flow through the passage of finite wave packets without dissipation. Conventional gravity wave parameterizations cannot describe this effect; nor can they account for wave sources being continuous in space and time, for the finite duration of vertical propagation, or wave acceleration induced by a temporally varying mean flow.<br>All these effects are accommodated when the wave field is described by the wave-energy density in wave number and physical space, and its evolution is computed by the radiative transfer equation for the wave field. A corresponding parameterization called IDEMIX has successfully been applied in ocean models. Here we present a corresponding parameterization for atmosphere models in single-column approximation. The new scheme is validated in off-line simulations. Results show that the evolution of wave packets forced in the troposphere and propagating upward into stratospheric and mesospheric jets is simulated consistently with theoretical expectations. This includes wave reflection and critical layers. Furthermore, an explicit diffusion scheme was added to account for wave dissipation due to dynamical instability.</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.

Multi-scale mountain waves observed with the ALIMA lidar during SOUTHTRAC-GW above the southern Andes

2021 ◽  
Author(s):  
Natalie Kaifler ◽  
Bernd Kaifler ◽  
Andreas Dörnbrack ◽  
Sonja Gisinger ◽  
Tyler Mixa ◽  
...  
Keyword(s):  
Wave Field ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Middle Atmosphere ◽  
Airborne Lidar ◽  
Horizontal Wind ◽  
Measured Temperature ◽  
Southern Andes ◽  
Mountain Waves

<p>During the SOUTHTRAC-GW (Southern hemisphere Transport, Dynamics and Chemistry – Gravity Waves) field campaign, gravity waves above the Southern Andes mountains, the Drake passage and the Antarctic Peninsula were probed with airborne instruments onboard the HALO research aircraft. The Airborne Lidar for Middle Atmosphere research (ALIMA) detected particularly strong mountain waves in excess of 25 K amplitude in cross-mountain legs above the Southern Andes of research flight ST08 on 12 September 2019. The mountain waves propagated well into the mesosphere up to 65 km altitude with possible generation of smaller-scale secondary waves during wave breaking above 65 km. A superposition of mountain waves with horizontal wavelengths in the range 15-200 km and vertical wavelengths 7-24 km dominated the wave field between 18 and 65 km altitude. Vertical wavelengths predicted by the hydrostatic equation and horizontal wind from the European Center for Medium-Range Weather Forecasts’ Integrated Forecasting System are in good agreement with observed vertical wavelengths. We apply wavelet analysis to the measured temperature field along the flight track in order to identify and separate dominant scales, and estimate their relative contributions to the total gravity wave momentum flux as well as the local and zonal-mean gravity wave drag. Furthermore, we compare our observations to results obtained by Fourier ray analysis of the terrain of the Southern Andes. The Fourier model allows the investigation of the 3d-wave field and trapped waves which are not well sampled by the ALIMA instrument because of the relative alignment between the wave fronts and the flight track. These sampling biases are quantified from virtual flights through the model domain at multiple angles and taken into account in the estimation of the total momentum flux derived from ALIMA observations. The combination of high-resolution observations and model data reveals the significance of this and similar mountain wave events in the Southern Andes region for the atmospheric dynamics at ~60° S.</p>

scholarly journals A Closure for Internal Wave–Mean Flow Interaction. Part I: Energy Conversion

2017 ◽  
Vol 47 (6) ◽  
pp. 1389-1401 ◽  
Author(s):  
Dirk Olbers ◽  
Carsten Eden
Keyword(s):  
Radiative Transfer ◽  
Internal Wave ◽  
Ocean Circulation ◽  
Transfer Equation ◽  
Radiative Transfer Equation ◽  
Exchange Energy ◽  
Mean Flow ◽  
Flow Interaction ◽  
The Mean ◽  
Internal Inertia

AbstractWhen internal (inertia-)gravity waves propagate in a vertically sheared geostrophic (eddying or mean) flow, they exchange energy with the flow. A novel concept parameterizing internal wave–mean flow interaction in ocean circulation models is demonstrated, based on the description of the entire wave field by the wave-energy density in physical and wavenumber space and its prognostic computation by the radiative transfer equation. The concept enables a simplification of the radiative transfer equation with a small number of reasonable assumptions and a derivation of simple but consistent parameterizations in terms of spectrally integrated energy compartments that are used as prognostic model variables. The effect of the waves on the mean flow in this paradigm is in accordance with the nonacceleration theorem: only in the presence of dissipation do waves globally exchange energy with the mean flow in the time mean. The exchange can have either direction. These basic features of wave–mean flow interaction are theoretically derived in a Wentzel–Kramers–Brillouin (WKB) approximation of the wave dynamics and confirmed in a suite of numerical experiments with unidirectional shear flow.

Sign in / Sign up

Export Citation Format

Share Document