scholarly journals Lidar Observations and Numerical Simulations of an Atmospheric Hydraulic Jump and Mountain Waves

2021 ◽  
Vol 126 (4) ◽  
Author(s):  
A. Peña ◽  
P. Santos
Keyword(s):  
Numerical Simulations ◽  
Hydraulic Jump ◽  
Mountain Waves ◽  
Lidar Observations

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 Multilevel Cloud Structures over Svalbard

2017 ◽  
Vol 145 (4) ◽  
pp. 1149-1159 ◽  
Author(s):  
Andreas Dörnbrack ◽  
Sonja Gisinger ◽  
Michael C. Pitts ◽  
Lamont R. Poole ◽  
Marion Maturilli
Keyword(s):  
Large Scale ◽  
Wave Structure ◽  
Horizontal Resolution ◽  
Temperature Fields ◽  
The Arctic ◽  
Mountain Waves ◽  
Air Masses ◽  
Flow Features ◽  
Stratospheric Clouds ◽  
Lidar Observations

Abstract The presented picture of the month is a superposition of spaceborne lidar observations and high-resolution temperature fields of the ECMWF Integrated Forecast System (IFS). It displays complex tropospheric and stratospheric clouds in the Arctic winter of 2015/16. Near the end of December 2015, the unusual northeastward propagation of warm and humid subtropical air masses as far north as 80°N lifted the tropopause by more than 3 km in 24 h and cooled the stratosphere on a large scale. A widespread formation of thick cirrus clouds near the tropopause and of synoptic-scale polar stratospheric clouds (PSCs) occurred as the temperature dropped below the thresholds for the existence of cloud particles. Additionally, mountain waves were excited by the strong flow at the western edge of the ridge across Svalbard, leading to the formation of mesoscale ice PSCs. The most recent IFS cycle using a horizontal resolution of 8 km globally reproduces the large-scale and mesoscale flow features and leads to a remarkable agreement with the wave structure revealed by the spaceborne observations.

scholarly journals Diurnal Variation of Downslope Winds in Owens Valley during the Sierra Rotor Experiment

2008 ◽  
Vol 136 (10) ◽  
pp. 3760-3780 ◽  
Author(s):  
Qingfang Jiang ◽  
James D. Doyle
Keyword(s):  
Diurnal Variation ◽  
Numerical Simulations ◽  
Western Slope ◽  
Owens Valley ◽  
Mountain Waves ◽  
Downslope Winds ◽  
Wind Event ◽  
Downslope Wind ◽  
Rotor Experiment ◽  
The Impact

The impact of diurnal forcing on a downslope wind event that occurred in Owens Valley in California during the Sierra Rotors Project (SRP) in the spring of 2004 has been examined based on observational analysis and diagnosis of numerical simulations. The observations indicate that while the upstream flow was characterized by persistent westerlies at and above the mountaintop level the cross-valley winds in Owens Valley exhibited strong diurnal variation. The numerical simulations using the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) capture many of the observed salient features and indicate that the in-valley flow evolved among three states during a diurnal cycle. Before sunrise, moderate downslope winds were confined to the western slope of Owens Valley (shallow penetration state). Surface heating after sunrise weakened the downslope winds and mountain waves and eventually led to the decoupling of the well-mixed valley air from the westerlies aloft around local noon (decoupled state). The westerlies plunged into the valley in the afternoon and propagated across the valley floor (in-valley westerly state). After sunset, the westerlies within the valley retreated toward the western slope, where the downslope winds persisted throughout the night.

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

scholarly journals Assessing the Impact of the Tropopause on Mountain Waves and Orographic Precipitation Using Linear Theory and Numerical Simulations

2015 ◽  
Vol 72 (2) ◽  
pp. 803-820 ◽  
Author(s):  
Nicholas Siler ◽  
Dale Durran
Keyword(s):  
Numerical Simulations ◽  
Linear Theory ◽  
Three Dimensional ◽  
Orographic Precipitation ◽  
Two Dimensional ◽  
Tropopause Height ◽  
Atmospheric Conditions ◽  
Mountain Waves ◽  
Wave Induced ◽  
The Impact

Abstract The partial reflection of mountain waves at the tropopause has been studied extensively for its contribution to downslope windstorms, but its impact on orographic precipitation has not been addressed. Here linear theory and numerical simulations are used to investigate how the tropopause affects the vertical structure of mountain waves and, in turn, orographic precipitation. Relative to the no-tropopause case, wave-induced ascent above the windward slope of a two-dimensional ridge is found to be enhanced or diminished depending on the ratio of the tropopause height to the vertical wavelength of the mountain waves—defined here as the “nondimensional tropopause height” . In idealized simulations of flow over both two-dimensional and three-dimensional ridges, variations in are found to modulate the precipitation rate by roughly a factor of 2 under typical atmospheric conditions. The sensitivity of precipitation to is related primarily to the depth of windward ascent but also to the location and strength of leeside descent, with significant impacts on the distribution of precipitation across the range (i.e., the rain-shadow effect). Using a modified version of Smith and Barstad’s orographic precipitation model, variations in are found to produce significant rain-shadow variability in the Washington Cascades, perhaps explaining some of the variability in rain-shadow strength observed among Cascade storms.

The Effect of Initial Momentum Flux on the Circular Hydraulic Jump

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
K. P. Vishwanath ◽  
Ratul Dasgupta ◽  
Rama Govindarajan ◽  
K. R. Sreenivas
Keyword(s):  
Numerical Simulations ◽  
Hydraulic Jump ◽  
Momentum Flux ◽  
Fluid Viscosity ◽  
Hydraulic Jumps ◽  
Initial Momentum ◽  
Flow Parameters ◽  
Controlling Parameter ◽  
Study Results ◽  
Wide Range

Earlier studies on the circular hydraulic jump have shown that the radial position of the hydraulic jump depends on the flow rate, gravity, and fluid viscosity. In this study, results from numerical simulations and experiments on circular hydraulic jumps are presented and through analysis, it is shown that the momentum flux is an additional controlling parameter in determining the jump location. Apart from the jump location, the variation of the film thickness with flow parameters is also obtained from experiments and numerical simulations. By including the dependence of the momentum flux and dissipation in the film along with other controlling parameters, the data on jump radius obtained from experiments and simulation (including the present study) covering a wide range of parameters reported in the literature can be collapsed on to a single curve.

scholarly journals Investigation of a mesospheric bore event over northern China

2013 ◽  
Vol 31 (3) ◽  
pp. 409-418 ◽  
Author(s):  
Q. Li ◽  
J. Xu ◽  
J. Yue ◽  
X. Liu ◽  
W. Yuan ◽  
...  
Keyword(s):  
Phase Velocity ◽  
Hydraulic Jump ◽  
Northern China ◽  
Temperature Data ◽  
Meteor Radar ◽  
Downward Displacement ◽  
Density Perturbations ◽  
Wind Measurements ◽  
Lidar Observations ◽  
Horizontal Wavelength

Abstract. A mesospheric bore event was observed using an OH all-sky airglow imager (ASAI) at Xinglong (40.2° N, 117.4° E), in northern China, on the night of 8–9 January 2011. Simultaneous observations by a Doppler meteor radar, a broadband sodium lidar, and TIMED/SABER OH intensity and temperature measurements are used to investigate the characteristics and environment of the bore propagation and the possible relations with the Na density perturbations. The bore propagated from northeast to southwest and divided the sky into bright and dark halves. The calculations show that the bore has an average phase velocity of 68 m s−1. The crests following the bore have a horizontal wavelength of ~ 22 km. These parameters are consistent with the hydraulic jump theory proposed by Dewan and Picard, as well as the previous bore reports. Simultaneous wind measurements from the Doppler meteor radar at Shisanling (40.3° N, 116.2° E) and temperature data from SABER on board the TIMED satellite are used to characterize the propagating environment of the bore. The result shows that a thermal-Doppler duct exists near the OH layer that supports the horizontal propagation of the bore. Simultaneous Na lidar observations at Yanqing (40.4° N, 116.0° E) suggest that there is a downward displacement of Na density during the passage of the mesospheric bore event.

scholarly journals Numerical Simulations of the Flow Field of a Submerged Hydraulic Jump over Triangular Macroroughnesses

Water ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 674
Author(s):  
Amir Ghaderi ◽  
Mehdi Dasineh ◽  
Francesco Aristodemo ◽  
Costanza Aricò
Keyword(s):  
Energy Loss ◽  
Numerical Simulations ◽  
Hydraulic Jump ◽  
Sudden Change ◽  
Air Entrainment ◽  
Streamwise Velocity ◽  
Flow Patterns ◽  
Mean Velocity ◽  
Rough Beds ◽  
Submerged Hydraulic Jump

The submerged hydraulic jump is a sudden change from the supercritical to subcritical flow, specified by strong turbulence, air entrainment and energy loss. Despite recent studies, hydraulic jump characteristics in smooth and rough beds, the turbulence, the mean velocity and the flow patterns in the cavity region of a submerged hydraulic jump in the rough beds, especially in the case of triangular macroroughnesses, are not completely understood. The objective of this paper was to numerically investigate via the FLOW-3D model the effects of triangular macroroughnesses on the characteristics of submerged jump, including the longitudinal profile of streamlines, flow patterns in the cavity region, horizontal velocity profiles, streamwise velocity distribution, thickness of the inner layer, bed shear stress coefficient, Turbulent Kinetic Energy (TKE) and energy loss, in different macroroughness arrangements and various inlet Froude numbers (1.7 < Fr1 < 9.3). To verify the accuracy and reliability of the present numerical simulations, literature experimental data were considered.

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