scholarly journals Parameterization of momentum flux and energy flux associated with orographically excited internal gravity waves in a baroclinic background flow

MAUSAM ◽  
2021 ◽  
Vol 58 (4) ◽  
pp. 459-470
Author(s):  
SOMENATH DUTTA
Keyword(s):  
Energy Flux ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Internal Gravity Waves ◽  
Background Flow

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.

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.

scholarly journals Momentum Flux Spectrum of Convectively Forced Internal Gravity Waves and Its Application to Gravity Wave Drag Parameterization. Part I: Theory

2005 ◽  
Vol 62 (1) ◽  
pp. 107-124 ◽  
Author(s):  
In-Sun Song ◽  
Hye-Yeong Chun
Keyword(s):  
Gravity Waves ◽  
Momentum Flux ◽  
Three Dimensional ◽  
Internal Gravity Waves ◽  
Buoyancy Frequency ◽  
Spectral Structure ◽  
Two Dimensional ◽  
Resonance Factor ◽  
Flux Spectrum ◽  
Wave Momentum

Abstract The phase-speed spectrum of momentum flux by convectively forced internal gravity waves is analytically formulated in two- and three-dimensional frameworks. For this, a three-layer atmosphere that has a constant vertical wind shear in the lowest layer, a uniform wind above, and piecewise constant buoyancy frequency in a forcing region and above is considered. The wave momentum flux at cloud top is determined by the spectral combination of a wave-filtering and resonance factor and diabatic forcing. The wave-filtering and resonance factor that is determined by the basic-state wind and stability and the vertical configuration of forcing restricts the effectiveness of the forcing, and thus only a part of the forcing spectrum can be used for generating gravity waves that propagate above cumulus clouds. The spectral distribution of the wave momentum flux is largely determined by the wave-filtering and resonance factor, but the magnitude of the momentum flux varies significantly according to spatial and time scales and moving speed of the forcing. The wave momentum flux formulation in the two-dimensional framework is extended to the three-dimensional framework. The three-dimensional momentum flux formulation is similar to the two-dimensional one except that the wave propagation in various horizontal directions and the three-dimensionality of forcing are allowed. The wave momentum flux spectrum formulated in this study is validated using mesoscale numerical model results and can reproduce the overall spectral structure and magnitude of the wave momentum flux spectra induced by numerically simulated mesoscale convective systems reasonably well.

scholarly journals Synthetic observations of internal gravity waves in the solar atmosphere

2020 ◽  
Vol 633 ◽  
pp. A140
Author(s):  
G. Vigeesh ◽  
M. Roth
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Flux Density ◽  
Solar Atmosphere ◽  
Energy Flux ◽  
Gravity Waves ◽  
Internal Gravity Waves ◽  
Spectral Lines ◽  
Magnetic Flux Density ◽  
Phase Differences

Aims. We study the properties of internal gravity waves (IGWs) detected in synthetic observations that are obtained from realistic numerical simulation of the solar atmosphere. Methods. We used four different simulations of the solar magneto-convection performed using the CO5BOLD code. A magnetic-field-free model and three magnetic models were simulated. The latter three models start with an initial vertical, homogeneous field of 10, 50, and 100 G magnetic flux density, representing different regions of the quiet solar surface. We used the NICOLE code to compute synthetic spectral maps from all the simulated models for the two magnetically insensitive neutral iron lines Fe I λλ 5434 Å and 5576 Å. We carried out Fourier analyses of the intensity and Doppler velocities to derive the power, phase, and coherence in the kh − ω diagnostic diagram to study the properties of internal gravity waves. Results. We find the signatures of the internal gravity waves in the synthetic spectra to be consistent with observations of the real Sun. The effect of magnetic field on the wave spectra is not as clearly discernible in synthetic observations as in the case of numerical simulations. The phase differences obtained using the spectral lines are significantly different from the phase differences in the simulation. The phase coherency between two atmospheric layers in the gravity wave regime is height dependent and is seen to decrease with the travel distance between the observed layers. In the studied models, the lower atmosphere shows a phase coherency above the significance level for a height separation of ∼400 km, while in the chromospheric layers it reduces to ∼100–200 km depending on the average magnetic flux density. Conclusion. We conclude that the energy flux of IGWs determined from the phase difference analysis may be overestimated by an order of magnitude. Spectral lines that are weak and less temperature sensitive may be better suited to detecting internal waves and accurately determining their energy flux in the solar atmosphere.

scholarly journals Momentum Flux Spectrum of Convectively Forced Gravity Waves: Can Diabatic Forcing Be a Proxy for Convective Forcing?

2005 ◽  
Vol 62 (11) ◽  
pp. 4113-4120 ◽  
Author(s):  
Hye-Yeong Chun ◽  
In-Sun Song ◽  
Takeshi Horinouchi
Keyword(s):  
Gravity Waves ◽  
Momentum Flux ◽  
Internal Gravity Waves ◽  
Reference Level ◽  
Wave Source ◽  
Control Simulation ◽  
Cloud Microphysical Processes ◽  
Flux Spectrum ◽  
Microphysical Processes ◽  
Diabatic Forcing

Abstract The momentum flux of convectively forced internal gravity waves is calculated using explicitly resolved model-simulated gravity wave data. The momentum flux in a control simulation with nonlinearity and cloud microphysical processes is compared with that in quasi-linear dry simulations with either diabatic forcing or nonlinear forcing. It is found that the momentum flux induced by either of these two sources is significantly different from each other and also from the momentum flux in the control simulation. This is because the spectral distribution and magnitude of each wave source are significantly different and the cancellation of the momentum flux by cross-correlation terms between the two sources cannot be included in the momentum flux by a single source. This suggests that a parameterization of convectively forced gravity waves must take into account nonlinear forcing as well as diabatic forcing in order to qualitatively and quantitatively represent the reference-level momentum flux spectrum.

Studies of atmospheric internal gravity waves at Halley station, Antarctica, using radiosondes

1989 ◽  
Vol 1 (1) ◽  
pp. 65-75 ◽  
Author(s):  
S.D. Mobbs ◽  
J.M. Rees
Keyword(s):  
Gravity Waves ◽  
Momentum Flux ◽  
Lower Troposphere ◽  
Internal Gravity Wave ◽  
Internal Gravity Waves ◽  
Ice Shelf ◽  
High Resolution Data ◽  
Momentum Fluxes ◽  
The Mean ◽  
Wave Phenomena

Analysis of high-resolution data from slow-ascent radiosondes released at Halley station, Antarctica (75°38′S, 26°40′W), shows that internal gravity wave phenomena are frequently present in the lower troposphere. There is a strong tendency for these waves to induce a vertical transport of the SE-NW component of momentum, this being the component perpendicular to the alignment of regular ridges in the ice shelf on which the base is built and is independent of the mean wind direction. A method for estimating the variation of the momentum fluxes with height is described. Results show that momentum flux divergences equivalent to accelerations of about 10 ms−1 per day are common at Halley.

scholarly journals Resolving the horizontal direction of internal tide generation

2019 ◽  
Vol 864 ◽  
pp. 381-407 ◽  
Author(s):  
Friederike Pollmann ◽  
Jonas Nycander ◽  
Carsten Eden ◽  
Dirk Olbers
Keyword(s):  
Internal Wave ◽  
Energy Flux ◽  
Gravity Waves ◽  
Large Scale ◽  
Bottom Topography ◽  
Internal Gravity Waves ◽  
Global Ocean ◽  
Wide Field ◽  
Practical Advantage ◽  
Analytical Approaches

The mixing induced by breaking internal gravity waves is an important contributor to the ocean’s energy budget, shaping, inter alia, nutrient supply, water mass transformation and the large-scale overturning circulation. Much of the energy input into the internal wave field is supplied by the conversion of barotropic tides at rough bottom topography, which hence needs to be described realistically in internal gravity wave models and mixing parametrisations based thereon. A new semi-analytical method to describe this internal wave forcing, calculating not only the total conversion but also the direction of this energy flux, is presented. It is based on linear theory for variable stratification and finite depth, that is, it computes the energy flux into the different vertical modes for two-dimensional, subcritical, small-amplitude topography and small tidal excursion. A practical advantage over earlier semi-analytical approaches is that the new one gives a positive definite conversion field. Sensitivity studies using both idealised and realistic topography allow the identification of suitable numerical parameter settings and corroborate the accuracy of the method. This motivates the application to the global ocean in order to better account for the geographical distribution of diapycnal mixing induced by low-mode internal gravity waves, which can propagate over large distances before breaking. The first results highlight the significant differences of energy flux magnitudes with direction, confirming the relevance of this more detailed approach for energetically consistent mixing parametrisations in ocean models. The method used here should be applicable to any physical system that is described by the standard wave equation with a very wide field of sources.

Sign in / Sign up

Export Citation Format

Share Document