scholarly journals Combination of Lidar and Model Data for Studying Deep Gravity Wave Propagation

2015 ◽  
Vol 144 (1) ◽  
pp. 77-98 ◽  
Author(s):  
Benedikt Ehard ◽  
Peggy Achtert ◽  
Andreas Dörnbrack ◽  
Sonja Gisinger ◽  
Jörg Gumbel ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Gravity Waves ◽  
Wave Breaking ◽  
High Temporal Resolution ◽  
Mountain Range ◽  
Mountain Waves ◽  
Induced Gravity ◽  
Vertically Propagating ◽  
Rayleigh Lidar ◽  
Lidar Observations

Abstract The paper presents a feasible method to complement ground-based middle atmospheric Rayleigh lidar temperature observations with numerical simulations in the lower stratosphere and troposphere to study gravity waves. Validated mesoscale numerical simulations are utilized to complement the temperature below 30-km altitude. For this purpose, high-temporal-resolution output of the numerical results was interpolated on the position of the lidar in the lee of the Scandinavian mountain range. Two wintertime cases of orographically induced gravity waves are analyzed. Wave parameters are derived using a wavelet analysis of the combined dataset throughout the entire altitude range from the troposphere to the mesosphere. Although similar in the tropospheric forcings, both cases differ in vertical propagation. The combined dataset reveals stratospheric wave breaking for one case, whereas the mountain waves in the other case could propagate up to about 40-km altitude. The lidar observations reveal an interaction of the vertically propagating gravity waves with the stratopause, leading to a stratopause descent in both cases.

scholarly journals Night-to-night changes in the characteristics of gravity waves at stratospheric and lower-mesospheric heights

1998 ◽  
Vol 16 (2) ◽  
pp. 229-237 ◽  
Author(s):  
A. J. McDonald ◽  
L. Thomas ◽  
D. P. Wareing
Keyword(s):  
Gravity Waves ◽  
Wave Activity ◽  
Mountain Waves ◽  
Long Period ◽  
Convective Instabilities ◽  
Radar Systems ◽  
Mst Radar ◽  
Vertical Propagation ◽  
Rayleigh Lidar ◽  
Lidar Observations

Abstract. Observations made with the co-located Rayleigh lidar and MST radar systems at Aberystwyth (52.4°N, 4.1°W) in Wales and radiosondes from Valentia (51.9°N, 10.2°W) in Eire are used to investigate the changes in the vertical propagation of gravity waves during periods of 4 days in June 1995 and February 1993. In each month, the lidar observations show that the wave activity in the upper stratosphere and lower mesosphere changes between two pairs of days. The radar and radiosonde measurements indicate that mountain waves make no contribution to the changes in intensity. Instead, the changes seem to arise largely from the presence or absence of long-period waves with vertical wavelengths near 8 and 10 km in June and February, respectively. The influence of such waves on the vertical wavenumber spectra is examined and related to the evidence for convective instabilities provided by the temperature profiles.Key words. Rayleigh lidar · MST radar systems · Radiosondes · Gravity waves

A study of the occurrence of dynamically unstable conditions in the middle atmosphere

1984 ◽  
Vol 62 (10) ◽  
pp. 963-967 ◽  
Author(s):  
Kevin Hamilton
Keyword(s):  
Gravity Waves ◽  
Wave Breaking ◽  
Middle Atmosphere ◽  
Internal Gravity Waves ◽  
Small Scale ◽  
Simple Analysis ◽  
Quantitative Estimates ◽  
Shear Instabilities ◽  
Vertically Propagating ◽  
The Tropics

There has recently been a great deal of interest in the possibility that vertically propagating internal gravity waves may be dissipated by small-scale convective or shear instabilities in the upper stratosphere and mesosphere. In the present study, a very simple analysis of about 3000 rocket soundings of temperature and wind at several stations between 8°N and 59°N was conducted in order to obtain quantitative estimates of the frequency of occurrence of dynamically unstable conditions as a function of height, latitude, and season. It was found that in about one-third of the profiles, the local Richardson number dropped below 0.25 at some level near the stratopause. From the results, it appears that gravity wave "breaking" generally occurs at considerably higher altitudes in the tropics than in midlatitudes. There is also a fairly clear indication of higher wave breaking levels in summer than in winter, at least at high latitudes.

Effects of Wave Streaming and Wave Variations on Nearshore Wave-Driven Circulation

2020 ◽  
Vol 50 (10) ◽  
pp. 3025-3041
Author(s):  
Peng Wang ◽  
James C. McWilliams ◽  
Yusuke Uchiyama ◽  
Mickaël D. Chekroun ◽  
Daling Li Yi
Keyword(s):  
Numerical Simulations ◽  
Gravity Waves ◽  
Wave Breaking ◽  
Surf Zone ◽  
Material Transport ◽  
Inner Shelf ◽  
Surface Gravity Waves ◽  
Wave Heights ◽  
Passive Tracers ◽  
Mean Current

AbstractWave streaming is a near-bottom mean current induced by the bottom drag on surface gravity waves. Wave variations include the variations in wave heights, periods, and directions. Here we use numerical simulations to study the effects of wave streaming and wave variations on the circulation that is driven by incident surface waves. Wave streaming induces an inner-shelf Lagrangian overturning circulation, which links the inner shelf with the surf zone. Wave variations cause alongshore-variable wave breaking that produces surf eddies; however, such eddies can be suppressed by wave streaming. Moreover, with passive tracers we show that wave streaming and wave variations together enhance the cross-shelf material transport.

scholarly journals Lidar Observations of Mountain Waves During Bora Episodes

2020 ◽  
Vol 237 ◽  
pp. 06007
Author(s):  
Longlong Wang ◽  
Marija Bervida ◽  
Samo Stanič ◽  
Klemen Bergant ◽  
William Eichinger ◽  
...  
Keyword(s):  
Numerical Models ◽  
Dimensional Structure ◽  
Mountain Range ◽  
Mountain Waves ◽  
Downslope Winds ◽  
Fixed Direction ◽  
Jump Phenomena ◽  
Scanning Lidar ◽  
Set Up ◽  
Lidar Observations

Airflows over mountain barriers in the Alpine region may give rise to strong, gusty downslope winds, called Bora. Oscillations, caused by the flow over an orographic barrier, lead to formation of mountain waves. These waves can only rarely be observed visually and can, in general, not be reliably reproduced by numerical models. Using aerosols as tracers for airmass motion, mountain waves were experimentally observed during Bora outbreak in the Vipava valley, Slovenia, on 24-25 January 2019 by two lidar systems: a vertical scanning lidar positioned just below the peak of the lee side of the mountain range and a fixed direction lidar at valley floor, which were set up to retrieve two-dimensional structure of the airflow over the orographic barrier into the valley. Based on the lidar data, we determined the thickness of airmass layer exhibiting downslope motion, observed hydraulic jump phenomena that gave rise to mountain waves and characterized their properties.

scholarly journals Five-Wave Resonances in Deep Water Gravity Waves: Integrability, Numerical Simulations and Experiments

Fluids ◽  
2021 ◽  
Vol 6 (6) ◽  
pp. 205
Author(s):  
Dan Lucas ◽  
Marc Perlin ◽  
Dian-Yong Liu ◽  
Shane Walsh ◽  
Rossen Ivanov ◽  
...  
Keyword(s):  
Normal Form ◽  
Numerical Simulations ◽  
Gravity Waves ◽  
Deep Water ◽  
Plane Waves ◽  
Surface Elevation ◽  
Wave Interactions ◽  
Frequency Space ◽  
Target Mode ◽  
The Hilbert Transform

In this work we consider the problem of finding the simplest arrangement of resonant deep-water gravity waves in one-dimensional propagation, from three perspectives: Theoretical, numerical and experimental. Theoretically this requires using a normal-form Hamiltonian that focuses on 5-wave resonances. The simplest arrangement is based on a triad of wavevectors K1+K2=K3 (satisfying specific ratios) along with their negatives, corresponding to a scenario of encountering wavepackets, amenable to experiments and numerical simulations. The normal-form equations for these encountering waves in resonance are shown to be non-integrable, but they admit an integrable reduction in a symmetric configuration. Numerical simulations of the governing equations in natural variables using pseudospectral methods require the inclusion of up to 6-wave interactions, which imposes a strong dealiasing cut-off in order to properly resolve the evolving waves. We study the resonance numerically by looking at a target mode in the base triad and showing that the energy transfer to this mode is more efficient when the system is close to satisfying the resonant conditions. We first look at encountering plane waves with base frequencies in the range 1.32–2.35 Hz and steepnesses below 0.1, and show that the time evolution of the target mode’s energy is dramatically changed at the resonance. We then look at a scenario that is closer to experiments: Encountering wavepackets in a 400-m long numerical tank, where the interaction time is reduced with respect to the plane-wave case but the resonance is still observed; by mimicking a probe measurement of surface elevation we obtain efficiencies of up to 10% in frequency space after including near-resonant contributions. Finally, we perform preliminary experiments of encountering wavepackets in a 35-m long tank, which seem to show that the resonance exists physically. The measured efficiencies via probe measurements of surface elevation are relatively small, indicating that a finer search is needed along with longer wave flumes with much larger amplitudes and lower frequency waves. A further analysis of phases generated from probe data via the analytic signal approach (using the Hilbert transform) shows a strong triad phase synchronisation at the resonance, thus providing independent experimental evidence of the resonance.

Sign in / Sign up

Export Citation Format

Share Document