scholarly journals Secondary waves generated by breaking of convective gravity waves in the mesosphere and their influence in the wave momentum flux

2008 ◽  
Vol 113 (D23) ◽  
Author(s):  
Hye-Yeong Chun ◽  
Young-Ha Kim
Keyword(s):  
Gravity Waves ◽  
Momentum Flux ◽  
Convective Gravity Waves ◽  
Wave Momentum

Characterization of Momentum Transport Associated with Organized Moist Convection and Gravity Waves

2010 ◽  
Vol 67 (10) ◽  
pp. 3208-3225 ◽  
Author(s):  
Todd P. Lane ◽  
Mitchell W. Moncrieff
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Tropical Convection ◽  
Momentum Transport ◽  
Moist Convection ◽  
Convective Systems ◽  
Convective Momentum Transport ◽  
Convective Organization ◽  
Wave Momentum

Abstract Tropical convection is inherently multiscalar, involving complex fields of clouds and various regimes of convective organization ranging from small disorganized cumulus up to large organized convective clusters. In addition to being a crucial component of the atmospheric water cycle and the global heat budget, tropical convection induces vertical fluxes of horizontal momentum. There are two main contributions to the momentum transport. The first resides entirely in the troposphere and is due to ascent, descent, and organized circulations associated with precipitating convective systems. The second resides in the troposphere, stratosphere, and farther aloft and is caused by vertically propagating gravity waves. Both the convective momentum transport and the gravity wave momentum flux must be parameterized in general circulation models; yet in existing parameterizations, these two processes are treated independently. This paper examines the relationship between the convective momentum transport and convectively generated gravity wave momentum flux by utilizing idealized simulations of multiscale tropical convection in different wind shear conditions. The simulations produce convective systems with a variety of regimes of convective organization and therefore different convective momentum transport properties and gravity wave spectra. A number of important connections are identified, including a consistency in the sign of the momentum transports in the lower troposphere and stratosphere that is linked to the generation of gravity waves by tilted convective structures. These results elucidate important relationships between the convective momentum transport and the gravity wave momentum flux that will be useful for interlinking their parameterization in the future.

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 Momentum Flux and Flux Divergence of Gravity Waves in Directional Shear Flows over Three-Dimensional Mountains

2012 ◽  
Vol 69 (12) ◽  
pp. 3733-3744 ◽  
Author(s):  
Xin Xu ◽  
Yuan Wang ◽  
Ming Xue
Keyword(s):  
Gravity Waves ◽  
Momentum Flux ◽  
Numerical Models ◽  
Surface Wind ◽  
Vertical Shear ◽  
Mean Flow ◽  
Turning Angle ◽  
Maximum Wind ◽  
Vertical Divergence ◽  
Wave Momentum

Abstract Linear mountain wave theory is used to derive the general formulas of the gravity wave momentum flux (WMF) and its vertical divergence that develop in directionally sheared flows with constant vertical shear. Height variations of the WMF and its vertical divergence are studied for a circular bell-shaped mountain. The results show that the magnitude of the WMF decreases with height owing to variable critical-level height for different wave components. This leads to continuous—rather than abrupt—absorption of surface-forced gravity waves, and the rate of absorption is largely determined by the maximum turning angle of the wind with height. For flows turning substantially with height, the wave momentum is primarily trapped in the lower atmosphere. Otherwise, it can be transported to the upper levels. The vertical divergence of WMF is oriented perpendicularly to the right (left) of the mean flow that veers (backs) with height except at the surface, where it vanishes. First, the magnitude of the WMF divergence increases with height until reaching its peak value. Then, it decreases toward zero above that height. The altitude of peak WMF divergence is proportional to the surface wind speed and inversely proportional to the vertical wind shear magnitude, increasing as the maximum wind turning angle increases. The magnitude of the peak WMF divergence also increases with the maximum wind turning angle, but it in general decreases as the ambient flow Richardson number increases. Implications of the findings for treating mountain gravity waves in numerical models are discussed.

scholarly journals Momentum Flux of Convective Gravity Waves Derived from an Offline Gravity Wave Parameterization. Part II: Impacts on the Quasi-Biennial Oscillation

2018 ◽  
Vol 75 (11) ◽  
pp. 3753-3775 ◽  
Author(s):  
Min-Jee Kang ◽  
Hye-Yeong Chun ◽  
Young-Ha Kim ◽  
Peter Preusse ◽  
Manfred Ern
Keyword(s):  
Shear Zone ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Large Scale ◽  
Reanalysis Data ◽  
Equatorial Region ◽  
Small Scale ◽  
Quasi Biennial Oscillation ◽  
Convective Gravity Waves ◽  
Biennial Oscillation

Abstract The characteristics of small-scale convective gravity waves (CGWs; horizontal wavelengths <100 km) and their contributions to the large-scale flow in the stratosphere, including the quasi-biennial oscillation (QBO), are investigated using an offline calculation of a source-dependent, physically based CGW parameterization with global reanalysis data from 1979 to 2010. The CGW momentum flux (CGWMF) and CGW drag (CGWD) are calculated from the cloud top (source level) to the upper stratosphere using a Lindzen-type wave propagation scheme. The 32-yr-mean CGWD exhibits large magnitudes in the tropical upper stratosphere and near the stratospheric polar night jet (~60°). The maximum positive drag is 0.1 (1.5) m s−1 day−1, and the maximum negative drag is −0.9 (−0.7) m s−1 day−1 in January (July) between 3 and 1 hPa. In the tropics, the momentum forcing by CGWs at 30 hPa associated with the QBO in the westerly shear zone is 3.5–6 m s−1 month−1, which is smaller than that by Kelvin waves, while that by CGWs in the easterly shear zone (3.1–6 m s−1 month−1) is greater than that by any other equatorial planetary waves or inertio-gravity waves (inertio-GWs). Composite analyses of the easterly QBO (EQBO) and westerly QBO (WQBO) phases reveal that the zonal CGWMF is concentrated near 10°N and that the negative (positive) CGWD extends latitudinally to ±20° (±10°) at 30 hPa. The strongest (weakest) negative CGWD is in March–May (September–November) during the EQBO, and the strongest (weakest) positive CGWD is in June–August (March–May) during the WQBO. The CGWMF and CGWD are generally stronger during El Niño than during La Niña in the equatorial region.

scholarly journals Vertical resolution dependence of gravity wave momentum flux simulated by an atmospheric general circulation model

2015 ◽  
Vol 8 (6) ◽  
pp. 1637-1644 ◽  
Author(s):  
S. Watanabe ◽  
K. Sato ◽  
Y. Kawatani ◽  
M. Takahashi
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
General Circulation ◽  
Horizontal Resolution ◽  
Sensitivity Test ◽  
Vertical Resolution ◽  
Time Step ◽  
Atmospheric General Circulation ◽  
Wave Momentum

Abstract. The dependence of the gravity wave spectra of energy and momentum flux on the horizontal resolution and time step of atmospheric general circulation models (AGCMs) has been thoroughly investigated in the past. In contrast, much less attention has been given to the dependence of these gravity wave parameters on models' vertical resolutions. The present study demonstrates the dependence of gravity wave momentum flux (GWMF) in the stratosphere and mesosphere on the model's vertical resolution, which is evaluated using an AGCM with a horizontal resolution of about 0.56°. We performed a series of sensitivity test simulations changing only the model's vertical resolution above a height of 8 km, and found a global reduction of GWMF with increasing vertical resolution. Inertial gravity waves with short vertical wavelengths simulated at higher vertical resolutions might play an important role in determining GWMF in the summertime stratosphere. The sensitivity test simulation also demonstrated the importance of the model's vertical resolution on representing realistic behaviors of gravity waves near their critical level.

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 Sensitivity of Gravity Wave Fluxes to Interannual Variations in Tropical Convection and Zonal Wind

2017 ◽  
Vol 74 (9) ◽  
pp. 2701-2716 ◽  
Author(s):  
M. Joan Alexander ◽  
David A. Ortland ◽  
Alison W. Grimsdell ◽  
Ji-Eun Kim
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Large Scale ◽  
Climate Models ◽  
Interannual Variations ◽  
Model Framework ◽  
Quasi Biennial Oscillation ◽  
Regional Variations ◽  
Wave Momentum

Abstract Using an idealized model framework with high-frequency tropical latent heating variability derived from global satellite observations of precipitation and clouds, the authors examine the properties and effects of gravity waves in the lower stratosphere, contrasting conditions in an El Niño year and a La Niña year. The model generates a broad spectrum of tropical waves including planetary-scale waves through mesoscale gravity waves. The authors compare modeled monthly mean regional variations in wind and temperature with reanalyses and validate the modeled gravity waves using satellite- and balloon-based estimates of gravity wave momentum flux. Some interesting changes in the gravity spectrum of momentum flux are found in the model, which are discussed in terms of the interannual variations in clouds, precipitation, and large-scale winds. While regional variations in clouds, precipitation, and winds are dramatic, the mean gravity wave zonal momentum fluxes entering the stratosphere differ by only 11%. The modeled intermittency in gravity wave momentum flux is shown to be very realistic compared to observations, and the largest-amplitude waves are related to significant gravity wave drag forces in the lowermost stratosphere. This strong intermittency is generally absent or weak in climate models because of deficiencies in parameterizations of gravity wave intermittency. These results suggest a way forward to improve model representations of the lowermost stratospheric quasi-biennial oscillation winds and teleconnections.

scholarly journals Momentum Flux of Convective Gravity Waves Derived from an Offline Gravity Wave Parameterization. Part I: Spatiotemporal Variations at Source Level

2017 ◽  
Vol 74 (10) ◽  
pp. 3167-3189 ◽  
Author(s):  
Min-Jee Kang ◽  
Hye-Yeong Chun ◽  
Young-Ha Kim
Keyword(s):  
Gravity Waves ◽  
Momentum Flux ◽  
Secondary Peak ◽  
Convective Heating ◽  
Spatiotemporal Variations ◽  
Primary Peak ◽  
Resonance Factor ◽  
Decadal Scale ◽  
Source Level ◽  
Convective Gravity Waves

Abstract Spatiotemporal variations in momentum flux spectra of convective gravity waves (CGWs) at the source level (cloud top), including nonlinear forcing effects, are examined based on calculations using an offline version of CGW parameterization and global reanalysis data for a period of 32 years (1979–2010). The cloud-top momentum flux (CTMF) is not solely proportional to the convective heating rate but is affected by the wave-filtering and resonance factor and background stability and temperature underlying the convection. Consequently, the primary peak of CTMF is in the winter hemisphere midlatitudes, associated with storm tracks, where a secondary peak of convective heating exists, whereas the secondary peak of CTMF appears in the summer hemisphere tropics and intertropical convergence zone (ITCZ), where the primary peak of convective heating exists. The magnitude of CTMF fluctuates largely with 1-yr and 1-day periods in major CTMF regions. At low latitudes and Pacific storm-track regions, a 6-month period is also significant, and the decadal cycle appears in the southern Andes. The equatorial eastern Pacific region exhibits a substantial interannual to decadal scale of variabilities. The correlation between convective heating and the CTMF is relatively lower in the equatorial region than in other regions. The CTMF in 10°N–10°S during the period of the pre-Concordiasi campaign approximately follows a lognormal distribution but with a slight underestimation in the tail of the probability density function. In Part II, the momentum flux and drag of CGW in the stratosphere will be examined.

scholarly journals Momentum flux estimates accompanying multiscale gravity waves over Mount Cook, New Zealand, on 13 July 2014 during the DEEPWAVE campaign

2015 ◽  
Vol 120 (18) ◽  
pp. 9323-9337 ◽  
Author(s):  
Katrina Bossert ◽  
David C. Fritts ◽  
Pierre‐Dominique Pautet ◽  
Bifford P. Williams ◽  
Michael J. Taylor ◽  
...  
Keyword(s):  
New Zealand ◽  
Gravity Waves ◽  
Momentum Flux
Sign in / Sign up

Export Citation Format

Share Document