scholarly journals Analysis of Gravity Waves Generated at the Top of a Drainage Flow

2010 ◽  
Vol 67 (12) ◽  
pp. 3949-3966 ◽  
Author(s):  
Samuel Viana ◽  
Enric Terradellas ◽  
Carlos Yagüe
Keyword(s):  
Boundary Layer ◽  
Gravity Waves ◽  
Sonic Anemometer ◽  
Internal Gravity Waves ◽  
Common Source ◽  
Flux Divergence ◽  
Near Surface ◽  
Key Factor ◽  
Stable Atmospheric Boundary Layer ◽  
Drainage Current

Abstract Drainage or katabatic flows are common mesoscale circulations established as a result of differential radiative cooling of near-surface air masses in sloping terrain. The initial irruption of these flows, with sudden shifts in wind speed and direction, may result in vertical displacements of air parcels from their equilibrium position, which prove to be a common source of internal gravity waves. This paper illustrates this mechanism and describes the main features of the oscillations following the study of observational data gathered throughout one night during the Stable Atmospheric Boundary Layer Experiment in Spain 2006 (SABLES2006) field campaign. Pressure differences, measured by microbarometers set at different levels of a tower, help to interpret the evolution of other atmospheric variables, provide a detailed picture of the irruption of a drainage current, and reveal the formation of gravity waves at its top. The main parameters of the waves are derived from wavelet cross correlation of pressure time series, recorded by a surface array of microbarometers. The analysis yields, among other parameters, the horizontal component of the phase and group velocities of the gravity waves, which compare well with the velocity of irruption of the drainage current. Wavelet and other multiresolution techniques are also applied to sonic anemometer records to study the interaction between turbulence and larger-scale motions. The analysis shows evidence of heat flux divergence induced by the gravity waves, which may constitute a key factor for the vertical thermal profile in the nocturnal boundary layer (NBL) in situations of weak turbulence and important wave activity.

scholarly journals Photometric detection of internal gravity waves in upper main-sequence stars

2020 ◽  
Vol 640 ◽  
pp. A36 ◽  
Author(s):  
D. M. Bowman ◽  
S. Burssens ◽  
S. Simón-Díaz ◽  
P. V. F. Edelmann ◽  
T. M. Rogers ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Massive Stars ◽  
Pressure Fluctuations ◽  
Tangential Velocity ◽  
Chemical Species ◽  
Internal Gravity Waves ◽  
Spectral Lines ◽  
Photometric Variability ◽  
Near Surface ◽  
Photometric Detection

Context. Massive stars are predicted to excite internal gravity waves (IGWs) by turbulent core convection and from turbulent pressure fluctuations in their near-surface layers. These IGWs are extremely efficient at transporting angular momentum and chemical species within stellar interiors, but they remain largely unconstrained observationally. Aims. We aim to characterise the photometric detection of IGWs across a large number of O and early-B stars in the Hertzsprung–Russell diagram, and explain the ubiquitous detection of stochastic variability in the photospheres of massive stars. Methods. We combined high-precision time-series photometry from the NASA Transiting Exoplanet Survey Satellite with high-resolution ground-based spectroscopy of 70 stars with spectral types O and B to probe the relationship between the photometric signatures of IGWs and parameters such as spectroscopic mass, luminosity, and macroturbulence. Results. A relationship is found between the location of a star in the spectroscopic Hertzsprung–Russell diagram and the amplitudes and frequencies of stochastic photometric variability in the light curves of massive stars. Furthermore, the properties of the stochastic variability are statistically correlated with macroturbulent velocity broadening in the spectral lines of massive stars. Conclusions. The common ensemble morphology for the stochastic low-frequency variability detected in space photometry and its relationship to macroturbulence is strong evidence for IGWs in massive stars, since these types of waves are unique in providing the dominant tangential velocity field required to explain the observed spectroscopy.

The Effect of Internal Gravity Waves on Fluctuations in Meteorological Parameters of the Atmospheric Boundary Layer

2018 ◽  
Vol 54 (2) ◽  
pp. 173-181 ◽  
Author(s):  
D. V. Zaitseva ◽  
M. A. Kallistratova ◽  
V. S. Lyulyukin ◽  
R. D. Kouznetsov ◽  
D. D. Kuznetsov
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Gravity Waves ◽  
Meteorological Parameters ◽  
Internal Gravity Waves

Instability of a stratified boundary layer and its coupling with internal gravity waves. Part 2. Coupling with internal gravity waves via topography

2008 ◽  
Vol 595 ◽  
pp. 409-433 ◽  
Author(s):  
XUESONG WU ◽  
JING ZHANG
Keyword(s):  
Boundary Layer ◽  
Gravity Waves ◽  
Internal Gravity Waves ◽  
Shear Instability ◽  
Acoustic Analogy ◽  
Physical Processes ◽  
Reflected Waves ◽  
Instability Modes ◽  
Viscous Shear ◽  
Incident Waves

The aim of this paper is to show that the viscous shear instability identified in Part 1 is intrinsically coupled with internal gravity waves when a localized surface topography is present within a boundary layer. The coupling involves two aspects: receptivity and radiation. The former refers to excitation of shear instability modes by gravity waves, and the latter to emission of gravity waves by instability modes. Both physical processes are studied using triple-deck theory. In particular, the radiated gravity waves are found to produce a leading-order back action on the source, and this feedback effect, completely ignored in the acoustic analogy type of approach, is naturally taken into account by the triple-deck formalism. A by-product is that for certain incident angles, gravity waves are over-reflected by the boundary layer, i.e. the reflected waves are stronger than the incident waves.

Observational analysis of thermally-driven topographic flows and their turbulence-waves interaction

2020 ◽  
Author(s):  
Carlos Yagüe ◽  
Carlos Román-Cascón ◽  
Marie Lothon ◽  
Fabienne Lohou ◽  
Jon Ander Arrillaga ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Gravity Waves ◽  
Sonic Anemometer ◽  
Extended Period ◽  
Chem Phys ◽  
Small Scale ◽  
Mixing Ratios ◽  
Synoptic Conditions ◽  
Thermally Driven

<p>Thermally-driven flows (TDFs) are mesoscale circulations driven by horizontal thermal contrasts in scales ranging from 1 and 100-200 km. The presence of mountains can generate a kind of these TDFs called thermally-driven topographic flows, with a typical daily cycle which is observed when weak synoptic conditions are present. These flows impact the turbulence features in the Atmospheric Boundary Layer (ABL), as well as different scalars (temperature, CO<sub>2</sub>, water vapor, pollutants, etc.). Moreover, these circulations, which can be of different scales (from small-scale shallow drainage flows to for example the larger Mountain – Plain flows) can generate gravity waves (GWs) along the transition to the stable boundary layer (SBL) and during the night. In this work, 88 days belonging to an extended period of the BLLAST field campaign<sup>[1]</sup> have been analysed. The corresponding nocturnal TDFs have been detected through a systematic and objective algorithm which considers both synoptic and local meteorological conditions. The main objectives of the study are: to characterize the TDFs at CRA (which is placed on a plateau near the Pyrenees in France); to evaluate the performance of the objective algorithm<sup>[2]</sup> in obtaining the events of interest; to establish different categories of TDFs and search for driving mechanisms (local, synoptic,..); and finally to explore the connections between TDFs and the generation of Gravity Waves (GWs), often observed in the nocturnal SBL<sup>[3]</sup>. Their interaction with turbulence is also analysed using different multiscale techniques, such as wavelets applied to pressure measurements obtained from high accurate microbarometers, and MultiResolution Flux Decomposition –MRFD- applied to sonic anemometer data. The contribution of different scales to turbulent parameters will be deeply evaluated and related to the arrival of TDFs and to the presence of GWs.</p><p> </p><p>[1] Lothon, M., Lohou, F. et al (2014): The BLLAST field experiment: Boundary-Layer Late Afternoon and Sunset Turbulence. <em>Atmos. Chem. Phys.</em>, <strong>14,</strong> 10931-10960.</p><p> [2] Román-Cascón, C., Yagüe, C., Arrillaga, J.A., Lothon, M., Pardyjak, E,R., Lohou, F., Inclán, R.M., Sastre, M., Maqueda, G., Derrien, S., Meyerfeld, Y., Hang, C., Campargue-Rodríguez, P. & Turki, I. (2019): Comparing mountain breezes and their impacts on CO2 mixing ratios at three contrasting areas. <em>Atmos. Res.</em>, <strong>221,</strong> 111-126.</p><p>[3] Sun, J., Nappo, C.J., Mahrt, L., Belusic, D., Grisogono, B., Stauffer, D.R., Pulido, M., Staquet, C., Jiang, Q., Pouquet, A., Yagüe, C. Galperin, B., Smith, R.B., Finnigan, J.J., Mayor, S.D., Svensson, G., Grachev, A.A. & Neff., W.D.: (2015): Review of wave-turbulence interactions in the stable atmospheric boundary layer, <em>Rev. Geophys.</em>, <strong>53,</strong> 956–993.</p>

Anisotropy in internal gravity waves in conditions of a stable nocturnal boundary layer

2009 ◽  
Vol 18 (3) ◽  
pp. 331-337 ◽  
Author(s):  
Anke Kniffka ◽  
Astrid Ziemann ◽  
Igor Chunchuzov ◽  
Sergei Kulichkov ◽  
Vitali Perepelkin
Keyword(s):  
Boundary Layer ◽  
Gravity Waves ◽  
Internal Gravity Waves ◽  
Nocturnal Boundary Layer

scholarly journals The Influence of Slopes of Isolated Three-Dimensional Valleys on Near-Surface Turbulence

2021 ◽  
Author(s):  
Sylvio Freitas ◽  
Frank Harms ◽  
Bernd Leitl
Keyword(s):  
Boundary Layer ◽  
Longitudinal Velocity ◽  
Three Dimensional ◽  
Boundary Layer Flows ◽  
Homogeneous Surface ◽  
Near Surface ◽  
Surface Turbulence ◽  
Stable Atmospheric Boundary Layer ◽  
Recirculation Zones ◽  
Layer Flow

AbstractMotivated by a limited understanding of how valleys affect near-surface turbulence, characterizations of neutrally stable atmospheric-boundary-layer flows over isolated valleys are presented. In particular, the influence of the slopes of the three-dimensional ridges that form the idealized valleys are investigated. Flows over three distinct symmetric valley geometries were modelled in a large boundary-layer wind tunnel. For each valley geometry, the high-resolution measurements from the crests of each of the ridges and the midpoint between them are compared with an undisturbed moderately rough classed boundary-layer flow over flat terrain with homogeneous surface roughness. Flow separation originates above the crests of the first ridges of all geometries and generates recirculation zones. These are characterized by slope-dependent increases in three-dimensional near-surface turbulence when compared with the attached flows further upstream. The recirculation zones longitudinally extend to roughly half the valley width. Above the crests of the second ridges, the longitudinal velocity component decreases and turbulence intensity increases when compared with the flows above the crests of the first ridges. Results also exhibit significant increases of turbulence above the inner-valley regions of all geometries.

Near-Surface Vertical Flux Divergence in the Stable Boundary Layer

2018 ◽  
Vol 169 (3) ◽  
pp. 373-393 ◽  
Author(s):  
L. Mahrt ◽  
Christoph K. Thomas ◽  
Andrey A. Grachev ◽  
P. Ola G. Persson
Keyword(s):  
Boundary Layer ◽  
Stable Boundary Layer ◽  
Vertical Flux ◽  
Flux Divergence ◽  
Near Surface ◽  
Stable Boundary

scholarly journals An Observational Study of Convection Initiation on 12 June 2002 during IHOP_2002

2008 ◽  
Vol 136 (7) ◽  
pp. 2283-2304 ◽  
Author(s):  
Tammy M. Weckwerth ◽  
Hanne V. Murphey ◽  
Cyrille Flamant ◽  
Janine Goldstein ◽  
Crystalyne R. Pettet
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Gravity Waves ◽  
Doppler Radar ◽  
Internal Gravity Waves ◽  
Moist Convection ◽  
Outflow Boundary ◽  
Convection Initiation ◽  
Convective Rolls

Abstract The International H2O Project (IHOP_2002) was designed to sample the three-dimensional time-varying moisture field to better understand convective processes. Numerous research and operational water vapor measuring systems and retrievals, via in situ and remote sensing techniques, were operated in the U.S. Southern Great Plains from 13 May to 25 June 2002. This was done in combination with more traditional observations of wind and temperature. Convection initiation (CI) sampling strategies were designed to optimally employ the array of ground-based and airborne sensors to observe the processes leading to the development of deep, moist convection. This case study examines several clear-air features and their impact on CI on 12 June 2002. The supercells that developed produced damaging winds and hail. The clear-air, preconvective features included (i) a mesoscale low pressure region, (ii) a dryline, (iii) an old outflow boundary, (iv) the intersection of (ii) and (iii), (v) internal gravity waves, and (vi) horizontal convective rolls. A unique combination of instruments was positioned to sample the preconvective environment on 12 June 2002. The Lidar pour l’Etude des Interactions Aérosols Nuages Dynamique Rayonnement et du Cycle de l’Eau (LEANDRE II) water vapor differential absorption lidar (DIAL), the airborne Electra Doppler Radar (ELDORA), and the Navy Research Laboratory (NRL) P3 aircraft in situ measurements provided information on the moisture and vertical velocity distribution within the boundary layer. Radiosondes, dropsondes, wind profilers, and an Atmospheric Emitted Radiance Interferometer (AERI) provided temperature, moisture, and wind profiling information. Although other ground-based sensors (i.e., S-band dual-polarization Doppler radar, Mobile Integrated Profiling System) were 50–150 km west of the CI area, they were useful for illustrating the boundary layer kinematics and reflectivity fields. Results suggest that the mesolow and mesoscale boundaries, respectively, acted to enhance the low-level moisture advection and convergence in the CI region. While internal gravity waves were present and appeared to modulate water vapor along the old outflow boundary, they did not play an obvious role in CI in this case. Horizontal convective rolls were observed beneath the new storms that initiated and may have helped to focus the CI in this case.

Spontaneous inertia–gravity wave emission in the differentially heated rotating annulus experiment

2018 ◽  
Vol 838 ◽  
pp. 5-41 ◽  
Author(s):  
Steffen Hien ◽  
Joran Rolland ◽  
Sebastian Borchert ◽  
Lena Schoon ◽  
Christoph Zülicke ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Numerical Simulations ◽  
Gravity Waves ◽  
Internal Flow ◽  
Wave Structure ◽  
Key Factor ◽  
Side Walls ◽  
Wave Emission ◽  
Balanced Flow ◽  
Set Up

The source mechanism of inertia–gravity waves (IGWs) observed in numerical simulations of the differentially heated rotating annulus experiment is investigated. The focus is on the wave generation from the balanced part of the flow, a process presumably contributing significantly to the atmospheric IGW field. Direct numerical simulations are performed for an atmosphere-like configuration of the annulus and possible regions of IGW activity are characterised by a Hilbert-transform algorithm. In addition, the flow is separated into a balanced and unbalanced part, assuming the limit of a small Rossby number, and the forcing of IGWs by the balanced part of the flow is derived rigorously. Tangent-linear simulations are then used to identify the part of the IGW signal that is rather due to radiation by the internal balanced flow than to boundary-layer instabilities at the side walls. An idealised fluid set-up without rigid horizontal boundaries is considered as well, to investigate the effect of the identified balanced forcing unmasked by boundary-layer effects. The direct simulations of the realistic and idealised fluid set-ups show a clear baroclinic-wave structure exhibiting a jet–front system similar to its atmospheric counterparts, superimposed by four distinct IGW packets. The subsequent tangent-linear analysis indicates that three wave packets are radiated from the internal flow and a fourth one is probably caused by boundary-layer instabilities. The forcing by the balanced part of the flow is found to play a significant role in the generation of IGWs, so it supplements boundary-layer instabilities as a key factor in the IGW emission in the differentially heated rotating annulus.

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