Examination of Gravity Waves Associated with the 13 March 2003 Bow Echo

2013 ◽  
Vol 141 (11) ◽  
pp. 3735-3756 ◽  
Author(s):  
Rebecca D. Adams-Selin ◽  
Richard H. Johnson
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Vertical Motion ◽  
Cold Pool ◽  
Positive Pressure ◽  
Vertical Mode ◽  
Low Level ◽  
Oklahoma Mesonet ◽  
Bow Echo ◽  
Pressure Surge

Abstract Numerical simulations of the 13 March 2003 bow echo over Oklahoma are used to evaluate bow echo development and its relationship with gravity wave generation. Multiple fast-moving (with speeds of 30–35 m s−1) gravity waves are generated in association with fluctuations in the first vertical mode of heating in the convective line. The surface impacts of four such waves are observed in Oklahoma Mesonet data during this case. Observations of surface pressure surges ahead of convective lines prior to the bowing process are reproduced; a slower gravity wave produced in the simulation is responsible for a prebowing pressure surge. This slower gravity wave, moving at approximately 11 m s−1, is generated by an increase in low-level microphysical cooling associated with an increase in rear-to-front flow and low-level downdrafts shortly before bowing. The wave moves ahead of the convective line and is manifested at the surface by a positive pressure surge. The pattern of low-level vertical motion associated with this wave, in conjunction with higher-frequency gravity waves generated by multicellularity of the convective line, increases the immediate presystem CAPE by approximately 250 J kg−1 just ahead of the bowing segment of the convective line. Increased presystem CAPE aids convective updraft strength in that segment despite amplified updraft tilt due to a stronger cold pool and surface-based rear-to-front flow, compared to updraft strength in other, nonbowing segments of the convective line.

Mesoscale Surface Pressure and Temperature Features Associated with Bow Echoes

2010 ◽  
Vol 138 (1) ◽  
pp. 212-227 ◽  
Author(s):  
Rebecca D. Adams-Selin ◽  
Richard H. Johnson
Keyword(s):  
Gravity Wave ◽  
Surface Pressure ◽  
Temperature Drop ◽  
Gravity Current ◽  
Pressure Rise ◽  
Surface Pattern ◽  
Cold Pool ◽  
Surface Features ◽  
Oklahoma Mesonet ◽  
Reflectivity Data

Abstract This study examines observed mesoscale surface pressure, temperature, and wind features of bow echoes. Bow-echo events in the area of the Oklahoma Mesonet are selected for study to take advantage of high-resolution surface data. Thirty-six cases are identified using 2-km-resolution radar reflectivity data over a 4-yr period (2002–05); their surface features are interrogated using the mesonet data. Distinct surface features usually associated with squall lines, the mesohigh and cold pool, are found to also accompany bow echoes. A common surface pattern preceding bowing is identified. Prior to new bowing development, the mesohigh surges ahead of the convective line while the cold pool remains centered behind it. Surface winds shift to a ground-relative outflow pattern upon arrival of the mesohigh surge. Approximately 30 min later, a new bowing segment forms with its apex slightly to the left (with respect to the direction of system motion) of the mesohigh surge. The cold pool follows the convective line as it bows. This process is termed the “pressure surge–new bowing” cycle, and a conceptual model is presented. In one representative case, the surface signature of a gravity wave, identified through spatial and temporal filtering, is tracked. It is presumed to be generated by deep heating within the convective line. The wave moved at nearly 35 m s−1 and has heretofore been undetected in mesoanalysis studies. Two other distinct features, a sharp pressure rise and temperature drop, were also observed at all mesonet stations affected by the system. Possible explanations for these features in terms of a gravity current, gravity wave, or atmospheric bore are explored.

scholarly journals Gravity Wave Excitation during the Coastal Transition of an Extreme Katabatic Flow in Antarctica

2020 ◽  
Vol 77 (4) ◽  
pp. 1295-1312 ◽  
Author(s):  
Étienne Vignon ◽  
Ghislain Picard ◽  
Claudio Durán-Alarcón ◽  
Simon P. Alexander ◽  
Hubert Gallée ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Wave Train ◽  
Katabatic Wind ◽  
Blowing Snow ◽  
Katabatic Flow ◽  
Low Level ◽  
Strong Control

Abstract The offshore extent of Antarctic katabatic winds exerts a strong control on the production of sea ice and the formation of polynyas. In this study, we make use of a combination of ground-based remotely sensed and meteorological measurements at Dumont d’Urville (DDU) station, satellite images, and simulations with the Weather Research and Forecasting Model to analyze a major katabatic wind event in Adélie Land. Once well developed over the slope of the ice sheet, the katabatic flow experiences an abrupt transition near the coastal edge consisting of a sharp increase in the boundary layer depth, a sudden decrease in wind speed, and a decrease in Froude number from 3.5 to 0.3. This so-called katabatic jump manifests as a turbulent “wall” of blowing snow in which updrafts exceed 5 m s−1. The wall reaches heights of 1000 m and its horizontal extent along the coast is more than 400 km. By destabilizing the boundary layer downstream, the jump favors the trapping of a gravity wave train—with a horizontal wavelength of 10.5 km—that develops in a few hours. The trapped gravity waves exert a drag that considerably slows down the low-level outflow. Moreover, atmospheric rotors form below the first wave crests. The wind speed record measured at DDU in 2017 (58.5 m s−1) is due to the vertical advection of momentum by a rotor. A statistical analysis of observations at DDU reveals that katabatic jumps and low-level trapped gravity waves occur frequently over coastal Adélie Land. It emphasizes the important role of such phenomena in the coastal Antarctic dynamics.

How white is the sky? 

2021 ◽  
Author(s):  
Nedjeljka Žagar ◽  
Žiga Zaplotnik ◽  
Valentino Neduhal
Keyword(s):  
Kinetic Energy ◽  
Gravity Wave ◽  
Power Law ◽  
Gravity Waves ◽  
Global Analysis ◽  
Vertical Motion ◽  
Energy Spectra ◽  
Horizontal Wind ◽  
Unified Framework ◽  
Inertia Gravity Waves

<p>The energy spectrum of atmospheric horizontal motions has been extensively studied in observations and numerical simulations. Its canonical shape includes a transition from the -3 power law at synoptic scale to -5/3 power law at mesoscale. The transition is taking place at scales around 500 km that can be seen as the scale where energy associated with quasi-linear inertia-gravity waves exceeds the balanced (or Rossby wave) energy. In contrast to the horizontal spectrum, the spectrum of kinetic energy of vertical motions is poorly known since the vertical motion is not an observed quantity of the global observing system and vertical kinetic energy spectra from non-hydrostatic models are difficult to validate.</p> <p>Traditionally, vertical velocities associated with the Rossby and gravity waves have been treated separately using the quasi-geostrophic omega equations and polarization relations for the stratified Boussinesq fluid in the (x,z) plane, respectively. In the tropics, the Rossby and gravity  wave regimes are difficult to separate and their frequency gap, present in the extra-tropics, is filled with the Kelvin and mixed Rossby-gravity waves. A separate treatment of the Rossby and gravity wave regimes makes it challenging to quantify energies of their vertical motions and vertical momentum fluxes. A unified treatment and wave interactions is performed by high-resolution non-hydrostatic models but their understanding requires the toolkit of theory. </p> <p>This contribution presents a unified framework for the derivation of vertical velocities of the Rossby and inertia-gravity waves and associated kinetic energy spectra. Expressions for the Rossby and gravity wave vertical velocities are derived using the normal-mode framework in the hydrostatic atmosphere that can be considered applicable up to the scale around 10 km. The derivation involves the analytical evaluation of divergence of the horizontal wind associated with the Rossby and inertia-gravity eigensolutions of the linearized primitive equations. The new framework is applied to the global analysis data of the ECMWF system. Results confirm that the tropical vertical kinetic energy spectra associated with inertia-gravity waves are on average indeed white. Deviations from the white spectrum are discussed for latitude and altitude bands.</p>

Nocturnal Low-Level Jet in a Mountain Basin Complex. Part I: Evolution and Effects on Local Flows

2004 ◽  
Vol 43 (10) ◽  
pp. 1348-1365 ◽  
Author(s):  
Robert M. Banta ◽  
Lisa S. Darby ◽  
Jerome D. Fast ◽  
James O. Pinto ◽  
C. David Whiteman ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Salt Lake ◽  
Great Salt Lake ◽  
Vertical Motion ◽  
Cold Pool ◽  
Lake Basin ◽  
The South ◽  
Low Level ◽  
Low Level Jet ◽  
Convergence Zones

Abstract A Doppler lidar deployed to the center of the Great Salt Lake (GSL) basin during the Vertical Transport and Mixing (VTMX) field campaign in October 2000 found a diurnal cycle of the along-basin winds with northerly up-basin flow during the day and a southerly down-basin low-level jet at night. The emphasis of VTMX was on stable atmospheric processes in the cold-air pool that formed in the basin at night. During the night the jet was fully formed as it entered the GSL basin from the south. Thus, it was a feature of the complex string of basins draining toward the Great Salt Lake, which included at least the Utah Lake basin to the south. The timing of the evening reversal to down-basin flow was sensitive to the larger-scale north–south pressure gradient imposed on the basin complex. On nights when the pressure gradient was not too strong, local drainage flow (slope flows and canyon outflow) was well developed along the Wasatch Range to the east and coexisted with the basin jet. The coexistence of these two types of flow generated localized regions of convergence and divergence, in which regions of vertical motion and transport were focused. Mesoscale numerical simulations captured these features and indicated that updrafts on the order of 5 cm s−1 could persist in these localized convergence zones, contributing to vertical displacement of air masses within the basin cold pool.

Bow Echo Mesovortices. Part I: Processes That Influence Their Damaging Potential

2009 ◽  
Vol 137 (5) ◽  
pp. 1497-1513 ◽  
Author(s):  
Nolan T. Atkins ◽  
Michael St. Laurent
Keyword(s):  
Cold Pool ◽  
Horizontal Shear ◽  
Saint Louis ◽  
Low Level ◽  
Wind Speeds ◽  
Cold Pools ◽  
Bow Echo ◽  
Mesoscale Convective ◽  
The Impact ◽  
Relative Wind

Abstract This two-part study examines the damaging potential and genesis of low-level, meso-γ-scale mesovortices formed within bow echoes. This was accomplished by analyzing quasi-idealized simulations of the 10 June 2003 Saint Louis bow echo event observed during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX). This bow echo produced both damaging and nondamaging mesovortices. A series of sensitivity simulations were performed to assess the impact of low- and midlevel shear, cold-pool strength, and Coriolis forcing on mesovortex strength. By analyzing the amount of circulation, maximum vertical vorticity, and number of mesovortices produced at the lowest grid level, it was observed that more numerous and stronger mesovortices were formed when the low-level environmental shear nearly balanced the horizontal shear produced by the cold pool. As the magnitude of deeper layer shear increased, the number and strength of mesovortices increased. Larger Coriolis forcing and stronger cold pools also produced stronger mesovortices. Variability of ground-relative wind speeds produced by mesovortices was noted in many of the experiments. It was observed that the strongest ground-relative wind speeds were produced by mesovortices that formed near the descending rear-inflow jet (RIJ). The strongest surface winds were located on the southern periphery of the mesovortex and were created by the superposition of the RIJ and mesovortex flows. Mesovortices formed prior to RIJ genesis or north and south of the RIJ core produced weaker ground-relative wind speeds. The forecast implications of these results are discussed. The genesis of the mesovortices is discussed in Part II.

The 8 May 2009 Superderecho: Analysis of a Real-Time Explicit Convective Forecast

2013 ◽  
Vol 28 (3) ◽  
pp. 863-892 ◽  
Author(s):  
Morris L. Weisman ◽  
Clark Evans ◽  
Lance Bosart
Keyword(s):  
Wind Shear ◽  
Convective Available Potential Energy ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Cold Pool ◽  
Low Level ◽  
Warm Core ◽  
Bow Echo ◽  
Low Level Jet ◽  
Baroclinic Zone

Abstract Herein, an analysis of a 3-km explicit convective simulation of an unusually intense bow echo and associated mesoscale vortex that were responsible for producing an extensive swath of high winds across Kansas, southern Missouri, and southern Illinois on 8 May 2009 is presented. The simulation was able to reproduce many of the key attributes of the observed system, including an intense [~100 kt (51.4 m s−1) at 850 hPa], 10-km-deep, 100-km-wide warm-core mesovortex and associated surface mesolow associated with a tropical storm–like reflectivity eye. A detailed analysis suggests that the simulated convection develops north of a weak east–west lower-tropospheric baroclinic zone, at the nose of an intensifying low-level jet. The system organizes into a north–south-oriented bow echo as it moves eastward along the preexisting baroclinic zone in an environment of large convective available potential energy (CAPE) and strong tropospheric vertical wind shear. Once the system moves east of the low-level jet and into an environment of weaker CAPE and weaker vertical wind shear, it begins an occlusion-like phase, producing a pronounced comma-shaped reflectivity echo with an intense warm-core mesovortex at the head of the comma. During this phase, a deep strip of cyclonic vertical vorticity located on the backside of the bow echo consolidates into a single vortex core. A notable weakening of the low-level convectively generated cold pool also occurs during this phase, perhaps drawing parallels to theories of tropical cyclogenesis wherein cold convective downdrafts must be substantially mitigated for subsequent system intensification.

scholarly journals Gravity wave excitation during the coastal transition of an extreme katabatic flow in Antarctica

2020 ◽  
Author(s):  
Étienne Vignon ◽  
Ghislain Picard ◽  
Claudio Durán-Alarcón ◽  
Simon P. Alexander ◽  
Hubert Gallée ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Wave Train ◽  
Katabatic Wind ◽  
Blowing Snow ◽  
Katabatic Flow ◽  
Low Level ◽  
Strong Control

<p>The offshore extent of Antarctic katabatic winds exert a strong control on sea ice production and the formation of polynyas. In this study, we combine ground-based remotely-sensed and meteorological measurements at Dumont d’Urville (DDU) station, satellite images and simulations with the WRF model to analyze a major katabatic wind event in Adélie Land. Once developed over the slope of the ice sheet, the katabatic flow experiences an abrupt transition near the coastal edge. The transition consists in a sharp increase in the boundary layer depth, a sudden decrease in wind speed and a decrease in Froude number from 3.5 to 0.3. This so-called ‘katabatic jump’ visually manifests as a turbulent ‘wall’ of blowing snow in which updrafts exceed 5 m s −1 . The wall reaches heights of 1000 m and its horizontal extent along the coast is more than 400 km. By destabilizing the boundary-layer downstream, the jump favors the trapping of a gravity wave train  with an horizontal wavelength of 10.5 km. The trapped gravity waves exert a drag that significantly slows down the low-level outflow. Moreover, atmospheric rotors form below the first wave crests. The wind speed record measured at DDU in 2017 (58.5 m s −1 ) is due to the vertical advection of momentum by a rotor. A statistical analysis of observations at DDU reveals that katabatic jumps and low-level trapped gravity waves occur frequently over coastal Adélie Land. It emphasizes the important role of such phenomena in the coastal Antarctic dynamics.</p>

Mesoscale Processes Contributing to Extreme Rainfall in a Midlatitude Warm-Season Flash Flood

2008 ◽  
Vol 136 (10) ◽  
pp. 3964-3986 ◽  
Author(s):  
Russ S. Schumacher ◽  
Richard H. Johnson
Keyword(s):  
Gravity Wave ◽  
Flash Flood ◽  
Warm Season ◽  
Mesoscale Convective System ◽  
Extreme Rainfall ◽  
Cold Pool ◽  
Convective System ◽  
Low Level ◽  
Mesoscale Convective ◽  
Moist Environment

Observations and numerical simulations are used to investigate the atmospheric processes that led to extreme rainfall and resultant destructive flash flooding in eastern Missouri on 6–7 May 2000. In this event, a quasi-stationary mesoscale convective system (MCS) developed near a preexisting mesoscale convective vortex (MCV) in a very moist environment that included a strong low-level jet (LLJ). This nocturnal MCS produced in excess of 300 mm of rain in a small area to the southwest of St. Louis, Missouri. Operational model forecasts and simulations using a convective parameterization scheme failed to produce the observed rainfall totals for this event. However, convection-permitting simulations using the Weather Research and Forecasting Model were successful in reproducing the quasi-stationary organization and evolution of this MCS. In both observations and simulations, scattered elevated convective cells were repeatedly initiated 50–75 km upstream before merging into the mature MCS and contributing to the heavy rainfall. Lifting provided by the interaction between the LLJ and the MCV assisted in initiating and maintaining the convection. Simulations indicate that the MCS was long lived despite the lack of a convectively generated cold pool at the surface. Instead, a nearly stationary low-level gravity wave helped to organize the convection into a quasi-linear system that was conducive to extreme local rainfall amounts. Idealized simulations of convection in a similar environment show that such a low-level gravity wave is a response to diabatic heating and that the vertical wind profile featuring a strong reversal of the wind shear with height is responsible for keeping the wave nearly stationary. In addition, the convective system acted to reintensify the midlevel MCV and also caused a distinct surface low pressure center to develop in both the observed and simulated system.

scholarly journals Influence of the cloud-level neutral layer on the vertical propagation of topographically generated gravity waves on Venus

2019 ◽  
Vol 71 (1) ◽  
Author(s):  
Takeru Yamada ◽  
Takeshi Imamura ◽  
Tetsuya Fukuhara ◽  
Makoto Taguchi
Keyword(s):  
Layer Thickness ◽  
Gravity Wave ◽  
Local Time ◽  
Gravity Waves ◽  
Analytical Approach ◽  
Wave Activity ◽  
Neutral Layer ◽  
Low Latitudes ◽  
Vertical Propagation ◽  
The Waves

AbstractThe reason for stationary gravity waves at Venus’ cloud top to appear mostly at low latitudes in the afternoon is not understood. Since a neutral layer exists in the lower part of the cloud layer, the waves should be affected by the neutral layer before reaching the cloud top. To what extent gravity waves can propagate vertically through the neutral layer has been unclear. To examine the possibility that the variation of the neutral layer thickness is responsible for the dependence of the gravity wave activity on the latitude and the local time, we investigated the sensitivity of the vertical propagation of gravity waves on the neutral layer thickness using a numerical model. The results showed that stationary gravity waves with zonal wavelengths longer than 1000 km can propagate to the cloud-top level without notable attenuation in the neutral layer with realistic thicknesses of 5–15 km. This suggests that the observed latitudinal and local time variation of the gravity wave activity should be attributed to processes below the cloud. An analytical approach also showed that gravity waves with horizontal wavelengths shorter than tens of kilometers would be strongly attenuated in the neutral layer; such waves should originate in the altitude region above the neutral layer.

scholarly journals Influence of the Upstream Terrain on the Formation of a Cold Frontal Snowband in Northeast China

2021 ◽  
Author(s):  
Na Li ◽  
Baofeng Jiao ◽  
Lingkun Ran ◽  
Zongting Gao ◽  
Shouting Gao
Keyword(s):  
Gravity Waves ◽  
Northeast China ◽  
Large Scale ◽  
Control Experiment ◽  
Vertical Motion ◽  
Near Surface ◽  
Inertial Instability ◽  
Two Factors ◽  
Negative Effect ◽  
Conditional Instability

AbstractWe investigated the influence of upstream terrain on the formation of a cold frontal snowband in Northeast China. We conducted numerical sensitivity experiments that gradually removed the upstream terrain and compared the results with a control experiment. Our results indicate a clear negative effect of upstream terrain on the formation of snowbands, especially over large-scale terrain. By thoroughly examining the ingredients necessary for snowfall (instability, lifting and moisture), we found that the release of mid-level conditional instability, followed by the release of low-level or near surface instabilities (inertial instability, conditional instability or conditional symmetrical instability), contributed to formation of the snowband in both experiments. The lifting required for the release of these instabilities was mainly a result of frontogenetic forcing and upper gravity waves. However, the snowband in the control experiment developed later and was weaker than that in the experiment without upstream terrain. Two factors contributed to this negative topographic effect: (1) the mountain gravity waves over the upstream terrain, which perturbed the frontogenetic circulation by rapidly changing the vertical motion and therefore did not favor the release of instabilities in the absence of persistent ascending motion; and (2) the decrease in the supply of moisture as a result of blocking of the upstream terrain, which changed both the moisture and instability structures leeward of the mountains. A conceptual model is presented that shows the effects of the instabilities and lifting on the development of cold frontal snowbands in downstream mountains.

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