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Hyeyeong Chun - One of the best experts on this subject based on the ideXlab platform.
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Momentum Flux of convective gravity waves derived from an offline gravity wave parameterization part i spatiotemporal variations at source level
Journal of the Atmospheric Sciences, 2017Co-Authors: Min Jee Kang, Hyeyeong Chun, Youngha KimAbstract:AbstractSpatiotemporal 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...
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Momentum Flux spectrum of convective gravity waves part i an update of a parameterization using mesoscale simulations
Journal of the Atmospheric Sciences, 2011Co-Authors: Hyunjoo Choi, Hyeyeong ChunAbstract:AbstractThe convective source and Momentum Flux spectra of a parameterization of convective gravity wave drag (GWDC) are validated in a three-dimensional spectral space using mesoscale numerical simulations for various ideal and real convective storms. From this, two important free parameters included in the GWDC parameterization—the moving speed of the convective source and the wave propagation direction—are determined. In the numerical simulations, the convective source spectrum shows nearly isotropic features in terms of magnitude, and its primary peak in any azimuthal direction occurs at a phase speed that equals the moving speed of the convective source in the same direction. It is found that the moving speed of the convective source is closely correlated with the basic-state wind averaged below 700 hPa (u700 and υ700). When the analytic convective source spectrum of the parameterization is calculated using the moving speed of the convective source as determined by u700 and υ700, its shape in all sto...
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Momentum Flux spectrum of convectively forced internal gravity waves and its application to gravity wave drag parameterization part ii impacts in a gcm waccm
Journal of the Atmospheric Sciences, 2007Co-Authors: Insun Song, Hyeyeong Chun, Rolando R Garcia, Byron A BovilleAbstract:Abstract Impacts of a spectral parameterization of gravity wave drag (GWD) induced by cumulus convection (GWDC) in the NCAR Whole Atmosphere Community Climate Model (WACCM1b) are investigated. In the spectral GWDC parameterization, reference wave Momentum Flux spectrum is launched at cloud top and analytically calculated based on the physical properties of convection and the large-scale flow. The cloud-top wave Momentum Flux is strong mainly in the Tropics and midlatitude storm-track regions, and exhibits anisotropy and spatiotemporal variability. The anisotropy and variability are determined by the distributions and variations of convective activities, the moving speed of convection, and horizontal wind and stability in convection regions. Zonal-mean zonal GWDC has a maximum of 13–27 (37–50) m s−1 day−1 in the mesosphere in January (July). Impacts of GWDC on zonal wind appear mainly in the low to midlatitudes of the upper stratosphere and mesosphere. In these regions, biases of zonal wind with respect to...
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Momentum Flux spectrum of convectively forced internal gravity waves and its application to gravity wave drag parameterization part i theory
Journal of the Atmospheric Sciences, 2005Co-Authors: Insun Song, Hyeyeong ChunAbstract: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...
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Momentum Flux by thermally induced internal gravity waves and its approximation for large scale models
Journal of the Atmospheric Sciences, 1998Co-Authors: Hyeyeong Chun, Jongjin BaikAbstract:Abstract Gravity wave Momentum Flux induced by thermal forcing representing latent heating due to cumulus convection is investigated analytically from a viewpoint of a subgrid-scale drag for the large-scale flow, and a possible way to parameterize the Momentum Flux in large-scale models is proposed. For the formulations of the Momentum Flux and its vertical derivative, two-dimensional, steady-state, linear perturbations induced by thermal forcing in a uniform basic-state wind are considered. The calculated Momentum Flux is zero below the forcing bottom, varies with height in the forcing region, and remains constant above the forcing top with the forcing top value. The sign of the Momentum Flux at the forcing top depends on the basic-state wind according to the wave energy–Momentum Flux relationship. Inside the forcing region, there exists a vertical convergence or divergence of the Momentum Flux that can influence the zonal mean flow tendency. The maximum magnitude of the zonal mean flow tendency contribu...
Joan M Alexander - One of the best experts on this subject based on the ideXlab platform.
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global and seasonal variations in three dimensional gravity wave Momentum Flux from satellite limb sounding temperatures
Geophysical Research Letters, 2015Co-Authors: Joan M AlexanderAbstract:Satellite limb-sounding methods provide the best global temperature data available for simultaneous measurement of gravity wave horizontal and vertical structures needed to estimate Momentum Flux and constrain wave effects on general circulation. Gravity waves vary in the three spatial dimensions and time, so the ideal measurement observes all three dimensions at high resolution nearly simultaneously. High Resolution Dynamics Limb Sounder (HIRDLS) measurements give near-simultaneous profiles in close proximity and at high vertical resolution, but these coincident profiles lie only along the plane of the measurement track. Here we combine HIRDLS and radio occultation data sets to obtain three-dimensional properties of gravity waves on a global scale as well as seasonal variations. The results show dramatic changes from previous estimates using either data set alone. Changes include much larger Momentum Fluxes and latitudinal variations in propagation direction that support an enhanced role for gravity wave forcing of middle atmosphere circulation.
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on the intermittency of gravity wave Momentum Flux in the stratosphere
Journal of the Atmospheric Sciences, 2012Co-Authors: Albert Hertzog, Joan M Alexander, Riwal PlougonvenAbstract:In this article, long-duration balloon and spaceborne observations, and mesoscale numerical simulations are used to study the intermittency of gravity waves in the lower stratosphere above Antarctica and the SouthernOcean;namely, thecharacteristics ofthegravitywaveMomentum-Fluxprobabilitydensityfunctions (pdfs)obtainedwith thesethreedatasetsaredescribed.Thepdfs consistentlyexhibitlongtailsassociatedwith the occurrence of rare and large-amplitude events. The pdf tails are even longer above mountains than above oceanic areas, which is in agreement with previous studies of gravity wave intermittency in this region. It is moreover found that these rare, large-amplitude events represent the main contribution to the total Momentum Flux during the winter regime of the stratospheric circulation. In contrast, the wave intermittency significantly decreases when stratospheric easterlies develop in late spring and summer. It is also shown that, except above mountainous areas in winter, the Momentum-Flux pdfs tend to behave like lognormal distributions. Monte Carlo simulations are undertaken to examine the role played by critical levels in influencing the shape of Momentum-Flux pdfs. In particular, the study finds that the lognormal shape may result from the propagation of a wave spectrum into a varying background wind field that generates the occurrence of frequent critical levels.
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on the intermittency of gravity wave Momentum Flux in the stratosphere
Journal of the Atmospheric Sciences, 2012Co-Authors: Albert Hertzog, Joan M Alexander, Riwal PlougonvenAbstract:AbstractIn this article, long-duration balloon and spaceborne observations, and mesoscale numerical simulations are used to study the intermittency of gravity waves in the lower stratosphere above Antarctica and the Southern Ocean; namely, the characteristics of the gravity wave Momentum-Flux probability density functions (pdfs) obtained with these three datasets are described. The pdfs consistently exhibit long tails associated with the occurrence of rare and large-amplitude events. The pdf tails are even longer above mountains than above oceanic areas, which is in agreement with previous studies of gravity wave intermittency in this region. It is moreover found that these rare, large-amplitude events represent the main contribution to the total Momentum Flux during the winter regime of the stratospheric circulation. In contrast, the wave intermittency significantly decreases when stratospheric easterlies develop in late spring and summer. It is also shown that, except above mountainous areas in winter, ...
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absolute values of gravity wave Momentum Flux derived from satellite data
Journal of Geophysical Research, 2004Co-Authors: Manfred Ern, Peter Preusse, Joan M Alexander, C D WarnerAbstract:[1] Temperature data obtained by the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) are analyzed for gravity waves (GWs). Amplitude, phase and vertical wavelength are determined from detrended temperature height profiles. The retrieved phases are utilized to estimate the horizontal wavelengths. At 25 km altitude an equatorial maximum of horizontal wavelength with a decrease toward mid and high latitudes is found. Simultaneous estimates of both horizontal and vertical wavelengths and temperature amplitudes allow the direct calculation of GW Momentum Flux (MF) from satellite observations for the first time. However, histograms of horizontal wavelength distributions indicate severe undersampling which prevents the retrieval of the propagation directions of the waves, and suggests our MF estimates may be too low, particularly at the high latitudes. Therefore an empirical aliasing correction has been applied. A world map of MF at 25 km altitude shows high variability and pronounced source regions and deviates in structure from a map of GW variances at the same altitude. Results from the Warner and McIntyre GW parameterization scheme (three-part model) show better agreement with CRISTA MF estimates than with CRISTA squared GW amplitudes. Best agreement is found for low model launch levels. Large error ranges of the estimated MF values obtained in this paper could be substantially reduced by improved horizontal sampling in future satellite missions.
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gravity wave Momentum Flux in the lower stratosphere over convection
Geophysical Research Letters, 1995Co-Authors: Joan M Alexander, Leonhard PfisterAbstract:This work describes a method for estimating vertical Fluxes of horizontal Momentum carried by short horizontal scale gravity waves (lambda(sub x) = 10-100 km) using aircraft measured winds in the lower stratosphere. We utilize in situ wind vector and pressure altitude measurements provided by the Meteorological Measurement System (MMS) on board the ER-2 aircraft to compute the Momentum Flux vectors at the flight level above deep convection during the tropical experiment of the Stratosphere Troposphere Exchange Project (STEP-Tropical). Data from Flight 9 are presented here for illustration. The vertical Flux of horizontal Momentum these observations points in opposite directions on either side of the location of a strong convective updraft in the cloud shield. This property of internal gravity waves propagating from a central source compares favorably with previously described model results.
John C Gille - One of the best experts on this subject based on the ideXlab platform.
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global observations of gravity wave intermittency and its impact on the observed Momentum Flux morphology
Journal of Geophysical Research, 2013Co-Authors: Corwin J Wright, John C Gille, Scott OspreyAbstract:[1] Three years of gravity wave observations from the High Resolution Dynamics Limb Sounder instrument on NASA's Aura satellite are examined. We produce estimates of the global distribution of gravity wave Momentum Flux as a function of individual observed wave packets. The observed distribution at the 25 km altitude level is dominated by the small proportion of wave packets with Momentum Fluxes greater than ∼0.5 mPa. Depending on latitude and season, these wave packets only comprise ∼7–25% of observations, but are shown to be almost entirely responsible for the morphology of the observed global Momentum Flux distribution. Large-amplitude wave packets are found to be more important over orographic regions than over flat ocean regions, and to be especially high in regions poleward of 40°S during austral winter. The Momentum Flux carried by the largest packets relative to the distribution mean is observed to decrease with height over orographic wave generation regions, but to increase with height at tropical latitudes; the mesospheric intermittency resulting is broadly equivalent in both cases. Consistent with previous studies, waves in the top 10% of the extratropical distribution are observed to carry Momentum Fluxes more than twice the mean and waves in the top 1% more than 10× the mean, and the Gini coefficient is found to characterize the observed distributions well. These results have significant implications for gravity wave modeling.
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implications for atmospheric dynamics derived from global observations of gravity wave Momentum Flux in stratosphere and mesosphere
Journal of Geophysical Research, 2011Co-Authors: Peter Preusse, John C Gille, Christopher L Hepplewhite, Martin G Mlynczak, J M Russell, Martin RieseAbstract:[1] In this work absolute values of gravity wave (GW) Momentum Flux are derived from global temperature measurements by the satellite instruments High Resolution Dynamics Limb Sounder (HIRDLS) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). Momentum Fluxes in the stratosphere are derived for both instruments and for SABER in the whole mesosphere. The large-scale atmospheric background state is removed by a two-dimensional Fourier decomposition in longitude and time, covering even planetary-scale waves with periods as short as 1–2 days. Therefore, it is possible to provide global distributions of GW Momentum Flux from observations for the first time in the mesosphere. Seasonal as well as longer-term variations of the global Momentum Flux distribution are discussed. GWs likely contribute significantly to the equatorward tilt of the polar night jet and to the poleward tilt of the summertime mesospheric jet. Our results suggest that GWs can undergo large latitudinal shifts while propagating upward. In particular, GWs generated by deep convection in the subtropical monsoon regions probably contribute significantly to the mesospheric summertime wind reversal at mid- and high latitudes. Variations in the GW longitudinal distribution caused by those convectively generated GWs are still observed in the mesosphere and could be important for the generation of the quasi two-day wave. Indications for quasi-biennial oscillation (QBO) induced variations of GW Momentum Flux are found in the subtropics. Also variations at time scales of about one 11-year solar cycle are observed and might indicate a negative correlation between solar Flux and GW Momentum Flux.
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global estimates of gravity wave Momentum Flux from high resolution dynamics limb sounder observations
Journal of Geophysical Research, 2008Co-Authors: M J Alexander, John C Gille, Charles Cavanaugh, M T Coffey, C Craig, T Eden, Gene Francis, C Halvorson, James W HanniganAbstract:analyzed to derive global properties of gravity waves. We describe a wavelet analysis technique that determines covarying wave temperature amplitude in adjacent temperature profile pairs, the wave vertical wavelength as a function of height, and the horizontal wave number along the line joining each profile pair. The analysis allows a local estimate of the magnitude of gravity wave Momentum Flux as a function of geographic location and height on a daily basis. We examine global distributions of these gravity wave properties in the monthly mean and on an individual day, and we also show sample instantaneous wave events observed by HIRDLS. The results are discussed in terms of previous satellite and radiosonde observational analyses and middle atmosphere general circulation model studies that parameterize gravity wave effects on the mean flow. The high vertical and horizontal resolution afforded by the HIRDLS measurements allows the analysis of a wider range of wave vertical and horizontal wavelengths than previous studies and begins to show individual wave events associated with mountains and convection in high detail. Mountain wave observations show clear propagation to altitudes in the mesosphere.
Steven A Hughes - One of the best experts on this subject based on the ideXlab platform.
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wave Momentum Flux parameter a descriptor for nearshore waves
Coastal Engineering, 2004Co-Authors: Steven A HughesAbstract:Abstract A new parameter representing the maximum depth-integrated wave Momentum Flux occurring over a wave length is proposed for characterizing the wave contribution to nearshore coastal processes on beaches and at coastal structures. This parameter has units of force per unit crest width, and it characterizes flow kinematics in nonbreaking waves at a given depth better than other wave parameters that do not distinguish increased wave nonlinearity. The wave Momentum Flux parameter can be defined and estimated for periodic and nonperiodic (transient) waves. Thus, it has potential application for correlating to processes responding to different types of waves. This paper derives the wave Momentum Flux parameter for linear, extended linear, and solitary waves; and it presents an empirical formula estimating the parameter for nonlinear steady waves of permanent form. Guidance is suggested for application to irregular waves. It is anticipated that the wave Momentum Flux parameter may prove useful for developing improved semiempirical formulas to describe nearshore processes and wave/structure interactions such as wave runup, overtopping, reflection, transmission, and armor stability. Surf zone processes where waves break as plunging or spilling breakers may not benefit from use of the wave Momentum Flux parameter because the breaking processes effectively negates the advantage of characterizing the wave nonlinearity.
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estimation of wave run up on smooth impermeable slopes using the wave Momentum Flux parameter
Coastal Engineering, 2004Co-Authors: Steven A HughesAbstract:This paper re-examines existing wave run-up data for regular, irregular and solitary waves on smooth, impermeable plane slopes. A simple physical argument is used to derive a new wave run-up equation in terms of a dimensionless wave parameter representing the maximum, depth-integrated Momentum Flux in a wave as it reaches the toe of the structure slope. This parameter is a physically relevant descriptor of wave forcing having units of force. The goal of the study was to provide an estimation technique that was as good as existing formulas for breaking wave run-up and better at estimating nonbreaking wave run-up. For irregular waves breaking on the slope, a single formula for the 2% run-up elevation proved sufficient for all slopes in the range 2/3≤tanα≤1/30. A slightly different formula is given for nonbreaking wave run-up. In addition, two new equations for breaking and nonbreaking solitary maximum wave run-up on smooth, impermeable plane slopes are presented in terms of the wave Momentum Flux parameter for solitary waves. This illustrates the utility of the wave Momentum Flux parameter for nonperiodic waves.
Tetsu Hara - One of the best experts on this subject based on the ideXlab platform.
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Momentum Flux budget across the air sea interface under uniform and tropical cyclone winds
Journal of Physical Oceanography, 2010Co-Authors: Yalin Fan, Isaac Ginis, Tetsu HaraAbstract:In coupled ocean‐atmosphere models, it is usually assumed that the Momentum Flux into ocean currents is equal to the Flux from air (wind stress). However, when the surface wave field grows (decays) in space or time, it gains (loses) Momentum and reduces (increases) the Momentum Flux into subsurface currents compared to the Flux from the wind. In particular, under tropical cyclone (TC) conditions the surface wave field is complex and fast varying in space and time and may significantly affect the Momentum Flux from wind into ocean. In this paper, numerical experiments are performed to investigate the Momentum Flux budget across the air‐sea interface under both uniform and idealized TC winds. The wave fields are simulated using the WAVEWATCH III model. The difference between the Momentum Flux from wind and the Flux into currents is estimated using an air‐sea Momentum Flux budget model. In many of the experiments, the Momentum Flux into currents is significantly reduced relative to the Flux from the wind. The percentage of this reduction depends on the choice of the drag coefficient parameterization and can be as large as 25%. For the TC cases, the reduction is mainly in the right-rear quadrant of the hurricane, and the percentage of the Flux reduction is insensitive to the changes of the storm size and the asymmetry in the wind field but varies with the TC translation speed and the storm intensity. The results of this study suggest that it is important to explicitly resolve the effect of surface waves for accurate estimations of the Momentum Flux into currents under TCs.
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a physics based parameterization of air sea Momentum Flux at high wind speeds and its impact on hurricane intensity predictions
Monthly Weather Review, 2007Co-Authors: Ilju Moon, Isaac Ginis, Tetsu Hara, Biju ThomasAbstract:Abstract A new bulk parameterization of the air–sea Momentum Flux at high wind speeds is proposed based on coupled wave–wind model simulations for 10 tropical cyclones that occurred in the Atlantic Ocean during 1998–2003. The new parameterization describes how the roughness length increases linearly with wind speed and the neutral drag coefficient tends to level off at high wind speeds. The proposed parameterization is then tested on real hurricanes using the operational Geophysical Fluid Dynamics Laboratory (GFDL) coupled hurricane–ocean prediction model. The impact of the new parameterization on the hurricane prediction is mainly found in increased maximum surface wind speeds, while it does not appreciably affect the hurricane central pressure prediction. This helps to improve the GFDL model–predicted wind–pressure relationship in strong hurricanes. Attempts are made to provide physical explanations as to why the reduced drag coefficient affects surface wind speeds but not the central pressure in hurric...
