scholarly journals Verifications of the high-resolution numerical model and polarization relations of atmospheric acoustic-gravity waves

2015 ◽  
Vol 8 (6) ◽  
pp. 1831-1838 ◽  
Author(s):  
N. M. Gavrilov ◽  
S. P. Kshevetskii ◽  
A. V. Koval
Keyword(s):  
High Resolution ◽  
Numerical Model ◽  
Numerical Simulations ◽  
Gravity Waves ◽  
Numerical Models ◽  
Lower Boundary ◽  
Simulation Models ◽  
Free Atmosphere ◽  
Wave Source ◽  
Acoustic Gravity Waves

Abstract. Comparisons of amplitudes of wave variations of atmospheric characteristics obtained using direct numerical simulation models with polarization relations given by conventional theories of linear acoustic-gravity waves (AGWs) could be helpful for testing these numerical models. In this study, we performed high-resolution numerical simulations of nonlinear AGW propagation at altitudes 0–500 km from a plane wave forcing at the Earth's surface and compared them with analytical polarization relations of linear AGW theory. After some transition time te (increasing with altitude) subsequent to triggering the wave source, the initial wave pulse disappears and the main spectral components of the wave source dominate. The numbers of numerically simulated and analytical pairs of AGW parameters, which are equal with confidence of 95 %, are largest at altitudes 30–60 km at t > te. At low and high altitudes and at t < te, numbers of equal pairs are smaller, because of the influence of the lower boundary conditions, strong dissipation and AGW transience making substantial inclinations from conditions, assumed in conventional theories of linear nondissipative stationary AGWs in the free atmosphere. Reasonable agreements between simulated and analytical wave parameters satisfying the scope of the limitations of the AGW theory prove the adequacy of the used wave numerical model. Significant differences between numerical and analytical AGW parameters reveal circumstances when analytical theories give substantial errors and numerical simulations of wave fields are required. In addition, direct numerical AGW simulations may be useful tools for testing simplified parameterizations of wave effects in the atmosphere.

scholarly journals Verifications of the nonlinear numerical model and polarization relations of atmospheric acoustic-gravity waves

2014 ◽  
Vol 7 (6) ◽  
pp. 7805-7822 ◽  
Author(s):  
N. M. Gavrilov ◽  
S. P. Kshevetskii
Keyword(s):  
Numerical Model ◽  
Numerical Simulations ◽  
Gravity Waves ◽  
Numerical Models ◽  
Lower Boundary ◽  
Simulation Models ◽  
Free Atmosphere ◽  
Wave Source ◽  
Acoustic Gravity Waves ◽  
Nonlinear Numerical Model

Abstract. Comparisons of amplitudes of wave variations of atmospheric characteristics simulated using direct numerical simulation models with polarization relations given by conventional theories of linear acoustic-gravity waves (AGWs) could be helpful for testing these numerical models. In this study, we performed high-resolution numerical simulations of nonlinear AGW propagation at altitudes 0–500 km from a plane wave forcing at the Earth's surface and compared them with analytical polarization relations of linear AGW theory. After some transition time te (increasing with altitude) subsequent to triggering the wave source, initial wave pulse disappear and the main spectral components of the wave source dominate. The numbers of numerically simulated and analytical pairs of AGW parameters, which are equal with confidence 95%, are largest at altitudes 30–60 km at t > te. At low and high altitudes and at t < te numbers of equal pairs are smaller, because of influence of the lower boundary conditions, strong dissipation and AGW transience making substantial inclinations from conditions, assumed in conventional theories of linear nondissipative stationary AGWs in the free atmosphere. Reasonable agreements between simulated and analytical wave parameters satisfying the scope the limitations of the AGW theory proof adequacy of the used nonlinear numerical model. Significant differences between numerical and analytical AGW parameters reveal circumstances, when analytical theories give substantial errors and numerical simulations of wave fields are required. In addition, direct numerical AGW simulations may be useful tools for testing simplified parameterizations of wave effects in the atmosphere.

scholarly journals The South Georgia Wave Experiment: A Means for Improved Analysis of Gravity Waves and Low-Level Wind Impacts Generated from Mountainous Islands

2018 ◽  
Vol 99 (5) ◽  
pp. 1027-1040 ◽  
Author(s):  
D. R. Jackson ◽  
A. Gadian ◽  
N. P. Hindley ◽  
L. Hoffmann ◽  
J. Hughes ◽  
...  
Keyword(s):  
High Resolution ◽  
Gravity Waves ◽  
Numerical Models ◽  
Small Island ◽  
Small Scale ◽  
The South ◽  
South Georgia ◽  
Low Level ◽  
Wave Experiment ◽  
Realistic Representation

AbstractGravity waves (GWs) play an important role in many atmospheric processes. However, the observation-based understanding of GWs is limited, and representing them in numerical models is difficult. Recent studies show that small islands can be intense sources of GWs, with climatologically significant effects on the atmospheric circulation. South Georgia, in the South Atlantic, is a notable source of such “small island” waves. GWs are usually too small scale to be resolved by current models, so their effects are represented approximately using resolved model fields (parameterization). However, the small-island waves are not well represented by such parameterizations, and the explicit representation of GWs in very-high-resolution models is still in its infancy. Steep islands such as South Georgia are also known to generate low-level wakes, affecting the flow hundreds of kilometers downwind. These wakes are also poorly represented in models.We present results from the South Georgia Wave Experiment (SG-WEX) for 5 July 2015. Analysis of GWs from satellite observations is augmented by radiosonde observations made from South Georgia. Simulations were also made using high-resolution configurations of the Met Office Unified Model (UM). Comparison with observations indicates that the UM performs well for this case, with realistic representation of GW patterns and low-level wakes. Examination of a longer simulation period suggests that the wakes generally are well represented by the model. The realism of these simulations suggests they can be used to develop parameterizations for use at coarser model resolutions.

scholarly journals On the Spectra of Gravity Waves Generated by Two Typical Convective Systems

Atmosphere ◽  
2019 ◽  
Vol 10 (7) ◽  
pp. 405
Author(s):  
Yuan Wang ◽  
Lifeng Zhang ◽  
Jun Peng ◽  
Yun Zhang ◽  
Tongfeng Wei
Keyword(s):  
High Resolution ◽  
Tropical Cyclone ◽  
Gravity Waves ◽  
Spectral Characteristics ◽  
Wave Source ◽  
Convective Systems ◽  
Spectral Distributions ◽  
The Waves

Spectral characteristics of lower-stratospheric gravity waves generated in idealized mei-yu front and tropical cyclone (TC) are compared by performing high-resolution simulations. The results suggest that the systems which organize convection in different forms can generate waves with distinctly different presentation. The mei-yu front appears as a linear zonal wave source and gravity waves are dominated by cross-frontal (meridional) propagating components. The northward (southward) components have dominant meridional wavelengths of 125–333 km (>250 km), periods of 100–200 min (83–143 min), and phase speeds of 0–15 m s−1 (15–20 m s−1). The TC appears as a point wave source and gravity waves propagate equally in various horizontal directions. The waves exhibit greater power and broader spectral distributions compared with those in the mei-yu front, with dominant horizontal wavelengths longer than 62.5 km, periods of 33–600 min, and phase speeds slower than ~40 m s−1.

scholarly journals Collisional Ring Galaxies in Small Groups

2000 ◽  
Vol 174 ◽  
pp. 277-280
Author(s):  
C. Horellou
Keyword(s):  
High Resolution ◽  
Numerical Model ◽  
Numerical Simulations ◽  
Small Groups ◽  
Large Scale ◽  
Rotating Disk ◽  
Groups Of Galaxies ◽  
Ring Galaxies ◽  
History Of

AbstractThe probability of plunging orbits is enhanced in groups of galaxies and indeed, observations show that ring galaxies, which are believed to form when a galaxy passes through the center of a larger rotating disk, are often found in small groups. Numerical simulations combined with a knowledge of the large-scale H I distribution provide strong constraints on the dynamical history of these systems and on the identity of the intruder. Here we present a numerical model of the Cartwheel galaxy which supports the suggestion that the most distant companion is the intruder. We also present high-resolution H I observations of the more irregular system Arp 119 that reveal a possible connection to the most distant companion.

Numerical Modeling of Nonlinear Interactions of Spectral Components of Acoustic-Gravity Waves in the Middle and Upper Atmosphere

2020 ◽  
Author(s):  
Nikolai M. Gavrilov ◽  
Sergej P. Kshevetskii
Keyword(s):  
Gravity Waves ◽  
Upper Atmosphere ◽  
Jet Flows ◽  
Small Scale ◽  
Nonlinear Interactions ◽  
Mean Flow ◽  
Wave Source ◽  
Acoustic Gravity Waves ◽  
The Mean ◽  
Wave Modes

&lt;p&gt;Acoustic-gravity waves (AGWs) measuring at big heights may be generated in the troposphere and propagate upwards. A high-resolution three-dimensional numerical model was developed for simulating nonlinear AGWs propagating from the ground to the upper atmosphere. The model algorithms are based on the finite-difference analogues of the main conservation laws. This methodology let us obtaining the physically correct generalized wave solutions of the nonlinear equations. Horizontally moving sinusoidal structures of vertical velocity on the ground are used for the AGW excitation in the model. Numerical simulations were made in an atmospheric region having horizontal dimensions up to several thousand kilometers and the height extention up to 500 km. Vertical distributions of the mean temperature, density, molecular viscosity and thermal conductivity are specified using standard models of the atmosphere.&lt;/p&gt;&lt;p&gt;Simulations were made for different horizontal wavelengths, amplitudes and speeds of the wave sources at the ground. After &amp;#8220;switch on&amp;#8221; the tropospheric wave source, an initial AGW pulse very quickly (for several minutes) could propagate to heights up to 100 km and above. AGW amplitudes increase with height and waves may break down in the middle and upper atmosphere. Wave instability and dissipation may lead to formations of wave accelerations of the mean flow and to producing wave-induced jet flows in the middle and upper atmosphere. Nonlinear interactions may lead to instabilities of the initial wave and to the creation of smaller-scale perturbations. These perturbations may increase temperature and wind gradients and could enhance the wave energy dissipation.&lt;/p&gt;&lt;p&gt;In this study, the wave sources contain a superposition of two AGW modes with different periods, wavelengths and phase speeds. Longer-period AGW modes served as the background conditions for the shorter-period wave modes. Thus, the larger-scale AGWs can modulate amplitudes of small-scale waves. In particular, interactions of two wave modes could sharp vertical temperature gradients and make easier the wave breaking and generating&amp;#160; turbulence. On the other hand, small-wave wave modes might increase dissipation and modify the larger-scale modes.This study was partially supported by the Russian Basic Research Foundation (# 17-05-00458).&lt;/p&gt;

scholarly journals Propagation to the upper atmosphere of acoustic-gravity waves from atmospheric fronts in the Moscow region

2019 ◽  
Vol 37 (3) ◽  
pp. 447-454 ◽  
Author(s):  
Yuliya Kurdyaeva ◽  
Sergey Kulichkov ◽  
Sergey Kshevetskii ◽  
Olga Borchevkina ◽  
Elena Golikova
Keyword(s):  
Experimental Data ◽  
Gravity Waves ◽  
Pressure Fluctuations ◽  
Lower Boundary ◽  
Lower Troposphere ◽  
Upper Atmosphere ◽  
Moscow Region ◽  
Atmospheric Front ◽  
Lower Boundary Condition ◽  
Acoustic Gravity Waves

Abstract. The paper uses experimental data of pressure variations on the Earth's surface during the passage of an atmospheric front recorded by a network of four microbarographs in the Moscow region. Applying these experimental data, empirical approximations of atmospheric pressure field oscillations are suggested. The obtained approximating surface pressure functions are used as the lower boundary condition for simulating the vertical propagation of acoustic-gravity waves from a source in the lower troposphere. Estimates of the amplitude of temperature disturbances in the upper atmosphere caused by acoustic-gravity waves from a propagating atmospheric front are obtained. For the amplitude of wave temperature disturbances, values of about 200 K are obtained. The amplitude of temperature disturbances in the upper atmosphere caused by background pressure fluctuations on the Earth's surface is estimated at 4–5 K.

scholarly journals A Comparison between Gravity Wave Momentum Fluxes in Observations and Climate Models

2013 ◽  
Vol 26 (17) ◽  
pp. 6383-6405 ◽  
Author(s):  
Marvin A. Geller ◽  
M. Joan Alexander ◽  
Peter T. Love ◽  
Julio Bacmeister ◽  
Manfred Ern ◽  
...  
Keyword(s):  
High Resolution ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Climate Models ◽  
Radiosonde Data ◽  
Wave Source ◽  
Wide Range ◽  
Momentum Fluxes ◽  
High Resolution Models ◽  
Wave Momentum

Abstract For the first time, a formal comparison is made between gravity wave momentum fluxes in models and those derived from observations. Although gravity waves occur over a wide range of spatial and temporal scales, the focus of this paper is on scales that are being parameterized in present climate models, sub-1000-km scales. Only observational methods that permit derivation of gravity wave momentum fluxes over large geographical areas are discussed, and these are from satellite temperature measurements, constant-density long-duration balloons, and high-vertical-resolution radiosonde data. The models discussed include two high-resolution models in which gravity waves are explicitly modeled, Kanto and the Community Atmosphere Model, version 5 (CAM5), and three climate models containing gravity wave parameterizations, MAECHAM5, Hadley Centre Global Environmental Model 3 (HadGEM3), and the Goddard Institute for Space Studies (GISS) model. Measurements generally show similar flux magnitudes as in models, except that the fluxes derived from satellite measurements fall off more rapidly with height. This is likely due to limitations on the observable range of wavelengths, although other factors may contribute. When one accounts for this more rapid fall off, the geographical distribution of the fluxes from observations and models compare reasonably well, except for certain features that depend on the specification of the nonorographic gravity wave source functions in the climate models. For instance, both the observed fluxes and those in the high-resolution models are very small at summer high latitudes, but this is not the case for some of the climate models. This comparison between gravity wave fluxes from climate models, high-resolution models, and fluxes derived from observations indicates that such efforts offer a promising path toward improving specifications of gravity wave sources in climate models.

scholarly journals Testing the accuracy of high-resolution satellite-based and numerical model output precipitation products over Ethiopia

2021 ◽  
Author(s):  
Getachew Dubache ◽  
Birhanu Asmerom ◽  
Waheed Ullah ◽  
Bob Alex Ogwang ◽  
Farshad Amiraslani ◽  
...  
Keyword(s):  
High Resolution ◽  
Numerical Model ◽  
Numerical Models ◽  
Reanalysis Data ◽  
The Other ◽  
Model Output ◽  
Mean Square ◽  
Data Set ◽  
Index Of Agreement ◽  
Rainfall Estimates

AbstractThe indirect rainfall estimates by satellites and numerical models are the alternative options for the regions lacking enough and accurate ground observations. However, these indirect estimates often lack homogeneity and need to be evaluated before application. This study used gauge observations to test the accuracy of recently produced high-resolution satellite-based and numerical model output rainfall products over Ethiopia. Tropical Applications of Meteorology Using Satellite data and Ground-Based Observations (TAMSAT v3.1), Climate Hazard group Infrared Precipitation with Stations (CHIRPS v2.0), and the ERA5 reanalysis products were evaluated at monthly, seasonal, and annual temporal scales for the years 1992–2009. The satellite products showed nearly similar characteristics with much better accuracy than the model reanalysis output, which underestimated the rainfall amounts. Both satellite and reanalysis products captured the shapes of the rainfall at a monthly scale but less accurately at a seasonal scale. In general, the satellite-based products outperformed the reanalysis data set with a high correlation coefficient and index of agreement values, as well as low Root Mean Square Error and BIAS values. On the other hand, the reanalysis (ERA5) product showed a considerable underestimation in all sites. Therefore, satellite-based products are more reliable for researches in the region. However, the algorithms in both satellites need further calibration for a better estimation of seasonal rainfall amounts.

scholarly journals Vertical propagation acoustic-gravity waves from atmospheric fronts into the upper atmosphere

2019 ◽  
Vol 55 (4) ◽  
pp. 3-12
Author(s):  
Y. A. Kurdyaeva ◽  
S. N. Kulichkov ◽  
S. P. Kshevetskii ◽  
O. P. Borchevkina ◽  
E. V. Golikova
Keyword(s):  
Gravity Waves ◽  
Atmospheric Pressure ◽  
Lower Boundary ◽  
Lower Troposphere ◽  
Upper Atmosphere ◽  
Atmospheric Front ◽  
Lower Boundary Condition ◽  
Acoustic Gravity Waves ◽  
Temperature Disturbance ◽  
Atmospheric Fronts

Using experimental observations of atmospheric pressure variations on the Earth’s surface recorded with a network of 4 microbarographs located in the Moscow region during the passage of an atmospheric front, empirical approximations of oscillations of atmospheric pressure field were constructed. The obtained approximating functions were used as the lower boundary condition for the numerical simulation of acoustic-gravity wave propagation to the upper atmosphere from the source in the lower troposphere. Estimates of the amplitude of temperature disturbances in the upper atmosphere caused by iacoustic gravity waves from the atmospheric front are given. The obtained estimates for the temperature disturbance amplitude take values around 170 K. The amplitude of temperature disturbances in the upper atmosphere, caused by background variations of pressure on the Earth's surface, is estimated at 4-5 K.

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