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.

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.

Characteristics and Momentum Flux Spectrum of Convectively Forced Internal Gravity Waves in Ensemble Numerical Simulations

2007 ◽  
Vol 64 (10) ◽  
pp. 3723-3734 ◽  
Author(s):  
Hyun-Joo Choi ◽  
Hye-Yeong Chun ◽  
In-Sun Song
Keyword(s):  
Numerical Simulations ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Tropical Ocean ◽  
Convective Storms ◽  
Control Simulation ◽  
Toga Coare ◽  
Flux Spectrum ◽  
Diabatic Forcing ◽  
Convective Gravity Waves

Abstract Characteristics of convectively forced gravity waves are investigated through ensemble numerical simulations for various ideal and real convective storms. For ideal storm cases, single-cell-, multicell-, and supercell-type storms are considered, and for real cases, convection events observed during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) and in Indonesia are used. For each storm case, wave perturbations and the momentum flux spectrum of convective gravity waves in a control simulation with nonlinearity and cloud microphysical processes are compared with those in quasi-linear dry simulations forced by either diabatic forcing or nonlinear forcing obtained from the control simulation. In any case, gravity waves in the control simulation cannot be represented well by wave perturbations induced by a single forcing. However, when both diabatic and nonlinear forcing terms are considered, the gravity waves and their momentum flux spectrum become comparable to those in the control simulation, because of cancellation between wave perturbations by two forcing terms. These results confirm that the two forcing mechanisms of convective gravity waves proposed by previous studies based on a single convective event can be applied generally to various types of convective storms. This suggests that nonlinear forcing, as well as diabatic forcing, should be considered appropriately in parameterizations of convectively forced gravity waves.

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.

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 Regional variations of mesospheric gravity-wave momentum flux over Antarctica

2006 ◽  
Vol 24 (1) ◽  
pp. 81-88 ◽  
Author(s):  
P. J. Espy ◽  
R. E. Hibbins ◽  
G. R. Swenson ◽  
J. Tang ◽  
M. J. Taylor ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Cross Correlation ◽  
Polar Vortex ◽  
Correlation Coefficients ◽  
Vertical Flux ◽  
Horizontal Wind ◽  
Wave Source ◽  
Horizontal Momentum

Abstract. Images of mesospheric airglow and radar-wind measurements have been combined to estimate the difference in the vertical flux of horizontal momentum carried by high-frequency gravity waves over two dissimilar Antarctic stations. Rothera (67° S, 68° W) is situated in the mountains of the Peninsula near the edge of the wintertime polar vortex. In contrast, Halley (76° S, 27° W), some 1658 km to the southeast, is located on an ice sheet at the edge of the Antarctic Plateau and deep within the polar vortex during winter. The cross-correlation coefficients between the vertical and horizontal wind perturbations were calculated from sodium (Na) airglow imager data collected during the austral winter seasons of 2002 and 2003 at Rothera for comparison with the 2000 and 2001 results from Halley reported previously (Espy et al., 2004). These cross-correlation coefficients were combined with wind-velocity variances from coincident radar measurements to estimate the daily averaged upper-limit of the vertical flux of horizontal momentum due to gravity waves near the peak emission altitude of the Na nightglow layer, 90km. The resulting momentum flux at both stations displayed a large day-to-day variability and showed a marked seasonal rotation from the northwest to the southwest throughout the winter. However, the magnitude of the flux at Rothera was about 4 times larger than that at Halley, suggesting that the differences in the gravity-wave source functions and filtering by the underlying winds at the two stations create significant regional differences in wave forcing on the scale of the station separation.

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.

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