Wintertime stratification on Oregon’s continental shelf often produces a near-bottom layer of densefluid that acts as an internal waveguide on which nonlinear internal waves propagate. Shipboard profiling and bottom lander observations capture disturbances that exhibit properties of internal solitary waves, bores and gravity currents. Wave-like pulses are highly turbulent (instantaneous bed stresses are 1 N m 2 ), resuspending bottom sediments into the water column and raising them 30 + m above the seafloor. The waves’ cross-shelf transport of fluid counters the time-averaged Ekman transport in the bottom boundary layer. In the nonlinear internal waves we have observed, the kinetic energy is roughly equal to the available potential energy and is O(0.1) MJ per m of coastline. The energy transported by these waves includes a nonlinear advection term huEi that is negligible in linear internal waves. Unlike linear internal waves, the pressure-velocity energy flux hupi includes important contributions from nonhydrostatic effects and surface displacement. It is found that, statistically, huEi ’ 2hupi. Vertical profiles indicate that up(z) is more important in transporting energy near the seafloor while uE(z) dominates farther from the bottom. With the wave speed, c, estimated from weakly nonlinear wave theory it is verified experimentally that the total energy transported by the waves, hupi + huEi ’ chEi. The high but intermittent energyflux by the waves is, in an averaged sense, O(100) W per m of coastline. This is similar to independent estimates of the shoreward energy flux in the semidiurnal internal tide at the shelfbreak.

/pdf/energy-transport-by-nonlinear-internal-waves-50m8lkpo9y.pdf

Energy Transport by Nonlinear Internal Waves

Some potential sources of low-level wind shear in and around airports and their likely effects are probed and analyzed. Wind shear over flat terrain with near-homogeneous surface properties (roughness, specific heat), the turning layer, shear flows over inhomogeneous terrain (airport + urban areas), thunderstorms, turbulent flowfields over bluff bodies (individual buildings), and recirculating wake flow downstream of three-dimensional block bodies are among the topics covered. Overshoot or undershoot of runways, and induced moments (pitch, roll, yaw) in takeoff and landing, and other potential hazards traceable to wind shear patterns at low heights are discussed, with emphasis on mean flow or steady-state wind shear (time-averaged, say 2-min averaged, wind fields). Wind tunnel studies and V/STOL operations are included in the study.

Sources of low-level wind shear around airports

Acoustic sounder observations of thunderstorm density currents reveal a complicated but ordered internal structure. Fast-response anemometers on a 150-m tower reveal a succession of internal shear layers which occur following the leading portion or nose of the current. The measured wind shear revealed by the anemometers is found to be a function of the temperature differential between the ambient air and the interior of the gust, measured near the surface. An heuristic model is developed to explain this observation.

Wind shear observations in thunderstorm density currents

We give a detailed review of developments in atmospheric acoustics of the last decade. These developments include new ways to use refractive effects, studies of phase and amplitude fluctuations during propagation of sound along a path, nonlinear effects near high-powered acoustic antennas, problems related to noise, insights into large-scale atmospheric processes gained from infrasound, applications dependent on the Doppler frequency shift, and hybrid devices using both acoustic and electromagnetic waves. The introduction of the echosonde approximately 10 years ago results in the considerable emphasis given to advances in active acoustic remote sensing of atmospheric structure.

Advances in atmospheric acoustics

A comparison is made between acoustic radar echoes and conventional meteorological data obtained from the WKY tower, for the purpose of better understanding the relationships between acoustic radar echoes and boundary layer processes. Two thunderstorm outflow cases are presented and compared to both acoustic radar data and Charba's gust front model. The acoustic radar echoes reveal the boundary between warm and cold air and other areas of mixing and strong thermal gradient quite well. The thunderstorm outflow of 27 June 1972 is found to compare with in most respects to Charba's gust front model. The major difference is the complete separation of the head from the main body of cold air, probably caused by erosion of the area behind the head by mixing with the ambient air. Two cases of nocturnal inversions caused by advection of warmer air aloft are presented. It is found that areas of turbulent mixing or strong thermal gradient can be identified quite easily in the acoustic radar record.

/pdf/acoustic-radar-investigations-of-boundary-layer-phenomena-2wm02jghlr.pdf

Acoustic radar investigations of boundary layer phenomena

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Acoustic radar investigations of boundary layer phenomena