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Journal ArticleDOI

Dissipative Waves Excited by Gravity-Wave Encounters with the Stably Stratified Planetary Boundary Layer

01 Oct 1986-Journal of the Atmospheric Sciences (American Meteorological Society)-Vol. 43, Iss: 19, pp 2048-2060
TL;DR: In this paper, the authors suggest that the strata of strong echo returns frequently revealed by remote-sensor records of the stably stratified planetary bound layer (PBL) represent the wavefronts of dissipative waves (viscous and thermal-conduction waves) excited by gravity-wave encounters with the PBL and the earth's surface.
Abstract: We suggest that the strata of strong echo returns frequently revealed by remote-sensor records of the stably stratified planetary bound layer (PBL) represent the wavefronts of dissipative waves (viscous and thermal-conduction waves) excited by gravity-wave encounters with the PBL and the earth's surface. The viscous waves appear to be more strongly forced and should therefore dominate the observations. This simple picture accounts for the following observed properties of the strata: 1) their nearly ubiquitous presence within the stably stratified PBL, 2) their nearly horizontal orientation, 3) the small spacing (some tens of meters, typically) separating the strata, 4) variability in that spacing in both height and time, and 5) the high shears and temperature gradients associated with the strata. Preliminary calculations of the energy fluxes and stresses associated with the wave motions, also presented here, suggest strongly that such waves are not mere curiosities of the PBL but reveal important...
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Journal ArticleDOI
TL;DR: The main source of turbulence may not be at the surface, but rather may result from shear above the surface inversion, sometimes preventing the formation of an inertial subrange as discussed by the authors.
Abstract: Atmospheric boundary layers with weak stratification are relatively well described by similarity theory and numerical models for stationary horizontally homogeneous conditions. With common strong stratification, similarity theory becomes unreliable. The turbulence structure and interactions with the mean flow and small-scale nonturbulent motions assume a variety of scenarios. The turbulence is intermittent and may no longer fully satisfy the usual conditions for the definition of turbulence. Nonturbulent motions include wave-like motions and solitary modes, two-dimensional vortical modes, microfronts, intermittent drainage flows, and a host of more complex structures. The main source of turbulence may not be at the surface, but rather may result from shear above the surface inversion. The turbulence is typically not in equilibrium with the nonturbulent motions, sometimes preventing the formation of an inertial subrange. New observational and analysis techniques are expected to advance our understanding of...

369 citations

Book ChapterDOI
01 Jan 1989
TL;DR: In this article, the authors argue that the diel schedule and altitude of bird migration have evolved in response to predictable variations in the structure of the atmosphere during its daily cycle and that the daily timing of migration is related to dietary habits or mode of migratory flight.
Abstract: Why do some birds migrate during daytime and others at night? Why do some fly at high altitudes and others at lower altitudes? Whereas no comprehensive explanation of the diel schedule and altitude of migration has been proposed, several hypotheses have been advanced to explain nocturnal migration. These hypotheses focus on the need to forage during daylight (Brewster, 1886; Palmgren, 1949; Dorst, 1962), on predator avoidance (Lincoln, 1952), and on avoidance of atmospheric turbulence (Nisbet, 1955; Raynor, 1956; Bellrose, 1967). In addition, some authorities have suggested that the daily timing of migration is related to dietary habits or mode of migratory flight (Dorst, 1962; Baker, 1978). We argue that the diel schedule and altitude of bird migration have evolved in response to predictable variations in the structure of the atmosphere during its daily cycle.

185 citations

Journal ArticleDOI
TL;DR: In this article, a helicopter-borne in situ turbulence measurement system HELIPOD was used to observe in situ coexisting atmospheric temperature and humidity sheets with thicknesses down to a few decimeters and with temperature gradients of up to 17G, where G denotes the adiabatic lapse rate.
Abstract: In recent years, temperature ‘‘sheets’’ with thicknesses on the order of 1 m have been observed with highresolution radiosondes throughout the stably stratified atmosphere, suggesting that they give rise to a major part of the well-known near-zenith aspect sensitivity of VHF radar echo intensities. It has been presumed but as yet not directly observed that these temperature sheets are accompanied by humidity sheets. In this paper, observations using the new helicopter-borne in situ turbulence measurement system HELIPOD are presented and discussed. For the first time it has been possible to observe in situ coexisting atmospheric temperature and humidity sheets with thicknesses down to a few decimeters and with temperature gradients of up to 17G, where G denotes the adiabatic lapse rate. Moreover, the first directly observed tropospheric temperature, humidity, and wind velocity profiles of a turbulent layer with a thickness of less than 10 m confined between two submeter sheets are presented. Simple theoretical reasoning leads to a lower limit for the sheet thicknesses: regardless of whether they are the remnants of Kelvin‐Helmholtz instability or attributed to viscosity/thermal-conduction waves, it should amount (apart from a numerical factor) to the square root of the product of molecular kinematic viscosity and a timescale that characterizes the age of a laminar sheet, the lifetime of a Kelvin‐Helmholtz billow, or the period of a primary gravity wave.

107 citations


Cites background from "Dissipative Waves Excited by Gravit..."

  • ...Those waves are modes of gravity waves with short vertical wavelengths, being strongly damped by the molecular viscosity (Hocking et al. 1991) or by an eddy viscosity (Hooke and Jones 1986)....

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  • ...Other researchers suggest the alternative explanation that ‘‘dissipative waves,’’ ‘‘viscosity waves,’’ or ‘‘thermal conduction waves’’ (Pitteway and Hines 1963; Hooke and Jones 1986; Hocking et al. 1991) could play an important role in the formation of sheets....

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Journal ArticleDOI
TL;DR: In this paper, physical mechanisms responsible for non-local features of the long-lived SBL turbulence are identified as: radiation of internal waves from the SBL upper boundary to the free atmosphere, and the internal-wave transport of the squared fluctuations of velocity and potential temperature.
Abstract: Until recently the concern of the traditional theory of the atmospheric stable boundary layer (SBL) was, almost without exception, the nocturnal SBL developing after sunset on the background of a neutral or slightly stable residual layer In the nocturnal SBLs the nature of turbulence is basically local Its lower portion is well described by the classical Monin–Obukhov surface-layer similarity theory Things are different in long-lived SBLs situated immediately below the stably stratified free flow Here, the surface-layer turbulence is affected by the free-flow Brunt–Vaisala frequency, N The surface layer represents approximately one-tenth of the SBL, so that it is separated from the free atmosphere by the upper nine-tenths of the SBL comprising hundreds of metres Traditional concepts fail to explain such distant links Zilitinkevich and Calanca extended the traditional Monin–Obukhov similarity theory by including N in the surface-layer scaling, and provided experimental evidence in support of this extension In the present paper, physical mechanisms responsible for non-local features of the long-lived SBL turbulence are identified as: radiation of internal waves from the SBL upper boundary to the free atmosphere, and the internal-wave transport of the squared fluctuations of velocity and potential temperature The third-order wave-induced fluxes are included in an advanced turbulence-closure model to correct the wind and temperature profiles in the surface layer The model explains why developed turbulence in the surface layer can exist at much larger Richardson numbers than the classical theory predicts Results from the new model are in good agreement with the extended similarity theory and experimental data Copyright © 2002 Royal Meteorological Society

81 citations

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed the stability and turbulence parameters in the free troposphere and the boundary layer of an aircraft at 20-Hz resolution with a total of over 300 km in vertical airspace sampled.
Abstract: [1] Velocity, temperature, and specific humidity data collected by aircraft at 20-Hz resolution are analyzed for stability and turbulence parameters. Over 100 vertical profiles (mostly over the ocean) with a total of over 300 km in vertical airspace sampled are used. The compiled statistics show that anisotropy in the velocity fluctuations prevail down to the smallest spatial separations measured. A partitioning of convective versus dynamical instability indicates that in the free troposphere, the ratio of shear-produced turbulence to convectively produced turbulence increases from roughly 2:1 for weak turbulence (ϵ 10−4 m2 s−3). For the boundary layer, this ratio is close to 1:1 for weak turbulence and roughly 2:1 for strong turbulence. There is also a correlation between the strength of the vertical shear in horizontal winds and the turbulence intensity. In the free troposphere the turbulence intensity is independent of the degree of static stability, whereas in the boundary layer the turbulence intensity increases with a fall in static stability. Vertical humidity gradients correlate with static stability for strong humidity gradients, which supports the basic notion that stable layers impede vertical mixing of trace gases and aerosols. Vertical shear correlates with vertical humidity gradient, so it appears that the effect of differential advection creating tracer gradients dominates the effect of differential advection destroying tracer gradients through shear-induced turbulence.

73 citations


Cites background from "Dissipative Waves Excited by Gravit..."

  • ...0148-0227/03/2002JD002820$09.00 GTE 5 - 1 not turbulence, as the creator of temperature sheets [Hooke and Jones, 1986; Hocking et al., 1991]....

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  • ...not turbulence, as the creator of temperature sheets [Hooke and Jones, 1986; Hocking et al., 1991]....

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