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J. M. Wilczak E. E. Gossard W. D. Neff W. L. Eberhard 《Boundary-Layer Meteorology》1996,78(3-4):321-349
The role of ground-based remote sensors in boundary-layer research is reviewed, emphasizing the contributions of radars, sodars, and lidars. The review begins with a brief comparison of the state of remote sensors in boundary-layer research 25 years ago with its present-day status. Next, a summary of the current capabilities of remote sensors for boundary-layer studies demonstrates that for boundary-layer depth and for profiles of many mean quantities, remote sensors offer some of the most accurate measurements available. Similar accuracies are in general not found for most turbulence parameters. Important contributions of remote sensors to our understanding of the structure and dynamics of various boundary-layer phenomena or processes are then discussed, including the sea breeze, convergence boundaries, dispersion, and boundary-layer cloud systems. The review concludes with a discussion of the likely future role of remote sensors in boundary-layer research. 相似文献
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The kinematic structure of the convective boundary layer, observed by a dual-Doppler radar system, is compared with the structure predicted by simple shear models. We first consider the models to be inviscid, then add viscous effects. Model 1 assumes a linear ambient wind profile from the surface through the boundary layer, and a constant wind above. The shear layer is assumed to be statically neutral, but static stability is permitted in the region above the shear. Model 2 has a hyperbolic tangent ambient wind profile.After considering the inviscid models, some of the effects of viscosity are incorporated into the models in a crude way, and the results are compared.We conclude that although the presence of shear is important, the kinematic structure is relatively independent of the details of the wind and temperature profiles. Viscosity has important effects, especially near the critical level where the disturbance velocity is equal to the wind speed. The patterns predicted by both models agree very well with the dual-Doppler radar observations when viscosity is included. 相似文献
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An FM/CW radar sounding system designed and built by one of us (Richter, 1969) reveals atmospheric wave structure in unparalleled detail.The most outstanding features evident in the record are; internal gravity waves; features resembling Kelvin/Helmholtz instability structures; and multiple layering, often with lamina only a few meters thick.This paper shows a variety of atmospheric structural patterns and compares them with several hypothetical models of internal waves to obtain more insight into the atmospheric processes at work. Special attention is given to the distribution of the Richardson number in trapped and untrapped gravity waves. It is proposed that the multiple layers result from untrapped internal gravity waves whose propagation vector is directed nearly vertically within very stable height regions. It is argued that the layers are caused by dynamic instability resulting from reduction in the Richardson number due to wave induced shear and to some background wind shear when the amplitude-to-wavelength ratio grows during propagation into thermally stable height regions of the atmosphere. 相似文献
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Observations of a single boundary-layer event — the generation of an atmospheric gravity wave by an unstable shear flow at Haswell, Colorado on November 12, 1971 — are briefly described and discussed. The observations were made using: (a) an acoustic echo sounder, (b) anemometers mounted at two fixed levels on a 150-m tower, (c) an anemometer and a thermometer mounted on a movable carriage on the tower, and (d) a microbarograph array, including one microbarograph mounted atop the tower. The wave phase velocity (–3.5–4.0 m s–1) was found to equal the wind velocity in the middle of the shear flow, as assumed by other authors. The wave-associated vertical fluxes of momentum and energy measured just above the wave critical layer were estimated to be –5 dyn cm–2 and –800 erg cm–2 s–1, respectively. These are large values. The annual average vertical flux of momentum at temperate and high latitudes is –0.25 dyn cm–2, while the average kinetic energy dissipation rate in a unit column of atmosphere is –5 × 103 erg cm–2 s–1. If the region of wave generation was itself propagating horizontally, its propagation velocity was large compared with the horizontal phase speed of the small-scale waves generated. Wave generation appeared to occur over an area large compared with the size of the microbarograph array (i.e., 2 km). 相似文献
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