scholarly journals Momentum and Energy Transport by Gravity Waves in Stochastically Driven Stratified Flows. Part II: Radiation of Gravity Waves from a Gaussian Jet

2008 ◽  
Vol 65 (7) ◽  
pp. 2308-2325 ◽  
Author(s):  
Nikolaos A. Bakas ◽  
Brian F. Farrell
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Energy Transport ◽  
Middle Atmosphere ◽  
Wave Spectrum ◽  
Flux Divergence ◽  
Stochastic Forcing ◽  
Forced Waves ◽  
Horizontal Wavelength ◽  
Wave Momentum

Abstract Interaction between the midlatitude jet and gravity waves is examined, focusing on the nonnormality of the underlying linear dynamics, which plays an essential role in processing the wave activity and selecting structures that dominate wave momentum and energy transport. When the interior of a typical midlatitude jet is stochastically forced, waves with short horizontal wavelength are trapped inside the jet and deposit momentum and energy at jet interior critical levels. Longer waves transport momentum and energy away from the jet, and the resulting momentum flux divergence produces a significant deceleration of the tropospheric and lower-stratospheric jet. This induced drag is found to depend on the shape of the jet and on the horizontal wavelength of the excited waves, reaching a maximum at wavelength λx = 20 km and leading to a deceleration O(1) m s−1 day−1 for a stochastic forcing rate of 0.1 W m−2 distributed over the height of the jet. This deceleration is robust to changes in static stability but is reduced when the stochastic forcing is correlated over too long a time. Implications of gravity wave absorption for middle-atmosphere circulation are discussed, focusing on differences implied for acceleration of the winter and summer midlatitude upper-stratospheric jets. The tropospheric flow is found not only to passively filter transiting waves, but also to amplify portions of the wave spectrum in conjunction with the distributed forcing, leading to enhanced gravity wave momentum and energy fluxes in agreement with observations linking middle-atmosphere enhanced variance with regions of high jet velocities.

scholarly journals Momentum and Energy Transport by Gravity Waves in Stochastically Driven Stratified Flows. Part I: Radiation of Gravity Waves from a Shear Layer

2007 ◽  
Vol 64 (5) ◽  
pp. 1509-1529 ◽  
Author(s):  
Nikolaos A. Bakas ◽  
Petros J. Ioannou
Keyword(s):  
Shear Flow ◽  
Shear Layer ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Wave Energy ◽  
Energy Transport ◽  
Wave Spectrum ◽  
Internal Gravity Waves ◽  
Wave Interference ◽  
Wide Range

Abstract In this paper, the emission of internal gravity waves from a local westerly shear layer is studied. Thermal and/or vorticity forcing of the shear layer with a wide range of frequencies and scales can lead to strong emission of gravity waves in the region exterior to the shear layer. The shear flow not only passively filters and refracts the emitted wave spectrum, but also actively participates in the gravity wave emission in conjunction with the distributed forcing. This interaction leads to enhanced radiated momentum fluxes but more importantly to enhanced gravity wave energy fluxes. This enhanced emission power can be traced to the nonnormal growth of the perturbations in the shear region, that is, to the transfer of the kinetic energy of the mean shear flow to the emitted gravity waves. The emitted wave energy flux increases with shear and can become as large as 30 times greater than the corresponding flux emitted in the absence of a localized shear region. Waves that have horizontal wavelengths larger than the depth of the shear layer radiate easterly momentum away, whereas the shorter waves are trapped in the shear region and deposit their momentum at their critical levels. The observed spectrum, as well as the physical mechanisms influencing the spectrum such as wave interference and Doppler shifting effects, is discussed. While for large Richardson numbers there is equipartition of momentum among a wide range of frequencies, most of the energy is found to be carried by waves having vertical wavelengths in a narrow band around the value of twice the depth of the region. It is shown that the waves that are emitted from the shear region have vertical wavelengths of the size of the shear region.

scholarly journals Consistent Scale Interaction of Gravity Waves in the Doppler Spread Parameterization

2009 ◽  
Vol 66 (5) ◽  
pp. 1434-1449 ◽  
Author(s):  
Erich Becker ◽  
Charles McLandress
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Wave Spectrum ◽  
Upper Atmosphere ◽  
Doppler Spread ◽  
Vertical Diffusion ◽  
Wave Damping ◽  
Scale Interaction

Abstract The standard Doppler spread parameterization of gravity waves, which was proposed by C.-O. Hines and has been applied in a number of middle atmosphere general circulation models, is extended by the inclusion of all effects associated with vertical diffusion. Here the Wentzel–Kramers–Brillouin (WKB) approximation is employed to calculate the vertical propagation of the wave spectrum in the presence of wave damping. According to the scale interaction between quasi-stationary turbulence and the larger nonturbulent flow, all vertical diffusion applied to the resolved flow should damp the parameterized gravity waves as well. Hence, the unobliterated part of the gravity wave spectrum is subject to diffusive damping by the following processes: 1) the background diffusion derived from the model’s boundary layer vertical diffusion scheme, which may extend into the middle atmosphere, 2) molecular diffusion, and 3) the turbulent diffusion resulting from the truncation of the gravity wave spectrum by Doppler spreading, which thus feeds back on the unobliterated gravity waves. The extended Doppler spread parameterization is examined using perpetual July simulations performed with a mechanistic general circulation model. For reasonable parameter settings, the convergence of the potential temperature flux cannot be neglected in the sensible heat budget, especially in the thermosphere. Less gravity wave flux enters the model thermosphere when vertical diffusion is included, thus avoiding the need for artificial means to control the parameterized gravity waves in the upper atmosphere. The zonal wind in the tropical middle and upper atmosphere is found to be especially sensitive to gravity wave damping by diffusion.

scholarly journals The nonlinear effects on the characteristics of gravity wave packets: dispersion and polarization relations

2000 ◽  
Vol 18 (10) ◽  
pp. 1316-1324 ◽  
Author(s):  
S.-D. Zhang ◽  
F. Yi ◽  
J.-F. Wang
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Middle Atmosphere ◽  
Wave Packets ◽  
Nonlinear Effects ◽  
Wave Theory ◽  
Nonlinear Propagation ◽  
Waves And Tides ◽  
Time Variations ◽  
Isothermal Atmosphere

Abstract. By analyzing the results of the numerical simulations of nonlinear propagation of three Gaussian gravity-wave packets in isothermal atmosphere individually, the nonlinear effects on the characteristics of gravity waves are studied quantitatively. The analyses show that during the nonlinear propagation of gravity wave packets the mean flows are accelerated and the vertical wavelengths show clear reduction due to nonlinearity. On the other hand, though nonlinear effects exist, the time variations of the frequencies of gravity wave packets are close to those derived from the dispersion relation and the amplitude and phase relations of wave-associated disturbance components are consistent with the predictions of the polarization relation of gravity waves. This indicates that the dispersion and polarization relations based on the linear gravity wave theory can be applied extensively in the nonlinear region.Key words: Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

scholarly journals Observation of Kelvin–Helmholtz instabilities and gravity waves in the summer mesopause above Andenes in Northern Norway

2018 ◽  
Vol 18 (9) ◽  
pp. 6721-6732 ◽  
Author(s):  
Gunter Stober ◽  
Svenja Sommer ◽  
Carsten Schult ◽  
Ralph Latteck ◽  
Jorge L. Chau
Keyword(s):  
Gravity Waves ◽  
Middle Atmosphere ◽  
Phase Speed ◽  
Velocity Measurements ◽  
Wind Variability ◽  
Short Period ◽  
Strong Shear ◽  
Summer Echoes ◽  
Period Wave ◽  
Horizontal Wavelength

Abstract. We present observations obtained with the Middle Atmosphere Alomar Radar System (MAARSY) to investigate short-period wave-like features using polar mesospheric summer echoes (PMSEs) as a tracer for the neutral dynamics. We conducted a multibeam experiment including 67 different beam directions during a 9-day campaign in June 2013. We identified two Kelvin–Helmholtz instability (KHI) events from the signal morphology of PMSE. The MAARSY observations are complemented by collocated meteor radar wind data to determine the mesoscale gravity wave activity and the vertical structure of the wind field above the PMSE. The KHIs occurred in a strong shear flow with Richardson numbers Ri < 0.25. In addition, we observed 15 wave-like events in our MAARSY multibeam observations applying a sophisticated decomposition of the radial velocity measurements using volume velocity processing. We retrieved the horizontal wavelength, intrinsic frequency, propagation direction, and phase speed from the horizontally resolved wind variability for 15 events. These events showed horizontal wavelengths between 20 and 40 km, vertical wavelengths between 5 and 10 km, and rather high intrinsic phase speeds between 45 and 85 m s−1 with intrinsic periods of 5–10 min.

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 Simulation of Inertia–Gravity Waves in a Poleward-Breaking Rossby Wave

2006 ◽  
Vol 63 (12) ◽  
pp. 3253-3276 ◽  
Author(s):  
Christoph Zülicke ◽  
Dieter Peters
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Rossby Wave ◽  
Rossby Waves ◽  
Mesoscale Model ◽  
Wave Packets ◽  
The Impact ◽  
Jet Streak ◽  
Horizontal Wavelength ◽  
Inertia Gravity Waves

Poleward-breaking Rossby waves often induce an upper-level jet streak over northern Europe. Dominant inertia–gravity wave packets are observed downstream of this jet. The physical processes of their generation and propagation, in such a configuration, are investigated with a mesoscale model. The study is focused on an observational campaign from 17 to 19 December 1999 over northern Germany. Different simulations with the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) have been performed. For a high-resolution process study, three domains were set up that encompass the evolution of Rossby waves and that of inertia–gravity waves. To minimize the impact of model damping, the horizontal and vertical resolution has been adjusted appropriately. With a novel statistical approach, the properties of inertia–gravity wave packets have been estimated. This method uses the horizontal divergence field and takes into account the spatial extension of a wave packet. It avoids the explicit treatment of the background field and works for arbitrary wavelength. Two classes of inertia–gravity waves were found: subsynoptic waves with a horizontal wavelength of about 500 km and mesoscale waves with a horizontal wavelength of about 200 km. The subsynoptic structures were also detected in radiosonde observations during this campaign. The similarity between simulated and observed wavelengths and amplitudes suggests that the simulations can be considered as near realistic. Spontaneous radiation from unbalanced flow is an important process of inertia–gravity wave generation. Synoptic-scale imbalances in the exit region of the upper-tropospheric jet streak were identified with the smoothed cross-stream Lagrangian Rossby number. In a number of simulations with different physics, it was found that the inertia–gravity wave activity was related to the tropospheric jet, orography, and moist convection. The upward propagation of inertia–gravity waves was favored during this event of a poleward-breaking Rossby wave. The presence of the polar vortex induced background winds exceeding the critical line. Consequently, the activity of inertia–gravity waves in the lower stratosphere increased by an order of magnitude during the case study. The successful simulation of the complex processes of generation and propagation showed the important role of poleward Rossby wave breaking for the appearance of inertia–gravity waves in the midlatitudes.

Sensitivity of middle atmosphere GW forcing to vertical model resolution

2020 ◽  
Author(s):  
Andrea Schneidereit ◽  
Hauke Schmidt ◽  
Claudia Stephan
Keyword(s):  
Zonal Wind ◽  
Middle Atmosphere ◽  
Wave Spectrum ◽  
Austral Summer ◽  
Vertical Gradient ◽  
Summer Season ◽  
Grid Spacing ◽  
Flux Divergence ◽  
The Mean ◽  
Horizontal Grid

&lt;p&gt;Several current general atmospheric circulation models provide sufficiently high resolutions to resolve important parts of the internal gravity wave spectrum allowing for numerical experiments without GW drag parameterizations. GWs start to be well resolved from horizontal wavelengths of about 7 times the horizontal grid spacing. How much does the resolved wave spectrum and its forcing on the mean circulation depend on the vertical resolution?&lt;/p&gt;&lt;p&gt;&amp;#8722;1,The middle atmosphere summer hemisphere provides a suitable background to investigate this question. The mean stratospheric and mesospheric circulation is characterised by prevailing easterlies which prevent planetary wave propagation upwards and represents a mean state driven by IGWs. The sensitivity of the forcing by IGWs is analysed on the basis of the Eliassen-Palm (EP) flux divergence, which describes the forcing on the circulation by resolved eddies.&lt;br&gt;Model simulations are performed using the upper atmosphere version of the ICON (ICOsahedral Nonhydrostatic) general circulation model, UA-ICON (Borchert et al. 2019, GMD). The simulations start in October and run for an extended austral summer season until March with a horizontal grid spacing of roughly 20 km. The top of the model atmosphere is located at 150 km. Three different model configurations are used with 90, 180, and 360 vertical model layers. The mean vertical grid spacing ranges from roughly 1300 m (90 layers) to 320 m (360 layers) at stratospheric levels, and from roughly 2300 m to 500 m at mesospheric levels. Gravity wave drag parameterizations (orographic and non-orographic) are turned off. The resolved forcing on the mean state due to the EP flux divergence is decomposed into contributions of different scales with respect to horizontal wave numbers. For contributions of IGWs wave numbers above 20 are considered.&lt;/p&gt;&lt;p&gt;The stratospheric and mesospheric easterlies appear stronger in the lower resolution from October to the end of the austral summer season. Westerlies occur above the mesopause. This strong vertical gradient in the zonal mean zonal wind amplifies in the lower resolution. At the beginning of the simulation period, differences between the mean states are weak, of the order of 5 ms&lt;sup&gt;&amp;#8722;1&lt;/sup&gt; , and strengthen during the summer season. The forcing due to internal GWs appears stronger in the lower resolution at higher altitudes and amplifies in the region of the strong vertical gradient of the zonal mean zonal wind. Furthermore, wave spectra are discussed. In accordance with previous studies, an increased vertical resolution results in a reduction of the IGW forcing close to strong zonal mean zonal wind gradients in the upper mesosphere/lower thermosphere.&lt;/p&gt;

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 Intercomparison of AIRS and HIRDLS stratospheric gravity wave observations

2018 ◽  
Vol 11 (1) ◽  
pp. 215-232 ◽  
Author(s):  
Catrin I. Meyer ◽  
Manfred Ern ◽  
Lars Hoffmann ◽  
Quang Thai Trinh ◽  
M. Joan Alexander
Keyword(s):  
High Resolution ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Wave Spectrum ◽  
Horizontal Resolution ◽  
Wave Activity ◽  
Large Variability ◽  
Wave Event ◽  
The Waves

Abstract. We investigate stratospheric gravity wave observations by the Atmospheric InfraRed Sounder (AIRS) aboard NASA's Aqua satellite and the High Resolution Dynamics Limb Sounder (HIRDLS) aboard NASA's Aura satellite. AIRS operational temperature retrievals are typically not used for studies of gravity waves, because their vertical and horizontal resolution is rather limited. This study uses data of a high-resolution retrieval which provides stratospheric temperature profiles for each individual satellite footprint. Therefore the horizontal sampling of the high-resolution retrieval is 9 times better than that of the operational retrieval. HIRDLS provides 2-D spectral information of observed gravity waves in terms of along-track and vertical wavelengths. AIRS as a nadir sounder is more sensitive to short-horizontal-wavelength gravity waves, and HIRDLS as a limb sounder is more sensitive to short-vertical-wavelength gravity waves. Therefore HIRDLS is ideally suited to complement AIRS observations. A calculated momentum flux factor indicates that the waves seen by AIRS contribute significantly to momentum flux, even if the AIRS temperature variance may be small compared to HIRDLS. The stratospheric wave structures observed by AIRS and HIRDLS often agree very well. Case studies of a mountain wave event and a non-orographic wave event demonstrate that the observed phase structures of AIRS and HIRDLS are also similar. AIRS has a coarser vertical resolution, which results in an attenuation of the amplitude and coarser vertical wavelengths than for HIRDLS. However, AIRS has a much higher horizontal resolution, and the propagation direction of the waves can be clearly identified in geographical maps. The horizontal orientation of the phase fronts can be deduced from AIRS 3-D temperature fields. This is a restricting factor for gravity wave analyses of limb measurements. Additionally, temperature variances with respect to stratospheric gravity wave activity are compared on a statistical basis. The complete HIRDLS measurement period from January 2005 to March 2008 is covered. The seasonal and latitudinal distributions of gravity wave activity as observed by AIRS and HIRDLS agree well. A strong annual cycle at mid- and high latitudes is found in time series of gravity wave variances at 42 km, which has its maxima during wintertime and its minima during summertime. The variability is largest during austral wintertime at 60∘ S. Variations in the zonal winds at 2.5 hPa are associated with large variability in gravity wave variances. Altogether, gravity wave variances of AIRS and HIRDLS are complementary to each other. Large parts of the gravity wave spectrum are covered by joint observations. This opens up fascinating vistas for future gravity wave research.

scholarly journals A New Method to Estimate Three-Dimensional Residual-Mean Circulation in the Middle Atmosphere and Its Application to Gravity Wave–Resolving General Circulation Model Data

2013 ◽  
Vol 70 (12) ◽  
pp. 3756-3779 ◽  
Author(s):  
Kaoru Sato ◽  
Takenari Kinoshita ◽  
Kota Okamoto
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
General Circulation ◽  
Three Dimensional ◽  
Circulation Model ◽  
Mean Flow ◽  
Flux Divergence ◽  
Mean Circulation ◽  
Residual Mean Circulation ◽  
Wave Induced

Abstract A new method is proposed to estimate three-dimensional (3D) material circulation driven by waves based on recently derived formulas by Kinoshita and Sato that are applicable to both Rossby waves and gravity waves. The residual-mean flow is divided into three, that is, balanced flow, unbalanced flow, and Stokes drift. The latter two are wave-induced components estimated from momentum flux divergence and heat flux divergence, respectively. The unbalanced mean flow is equivalent to the zonal-mean flow in the two-dimensional (2D) transformed Eulerian mean (TEM) system. Although these formulas were derived using the “time mean,” the underlying assumption is the separation of spatial or temporal scales between the mean and wave fields. Thus, the formulas can be used for both transient and stationary waves. Considering that the average is inherently needed to remove an oscillatory component of unaveraged quadratic functions, the 3D wave activity flux and wave-induced residual-mean flow are estimated by an extended Hilbert transform. In this case, the scale of mean flow corresponds to the whole scale of the wave packet. Using simulation data from a gravity wave–resolving general circulation model, the 3D structure of the residual-mean circulation in the stratosphere and mesosphere is examined for January and July. The zonal-mean field of the estimated 3D circulation is consistent with the 2D circulation in the TEM system. An important result is that the residual-mean circulation is not zonally uniform in both the stratosphere and mesosphere. This is likely caused by longitudinally dependent wave sources and propagation characteristics. The contribution of planetary waves and gravity waves to these residual-mean flows is discussed.

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