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H. Dean Parry, Melvin J. Sanders Jr., and Hans P. Jensen

Abstract

A monostatic acoustic sounding system and its capabilities in providing information about the temperature structure of the lower atmosphere are described. By means of the sounder record the meteorologist can 1) detect stable atmospheric strata including inversion layers, 2) determine the height of base and top of such strata, 3) detect convections, 4) determine height of base and top of convections, 5) determine time rate of change of all heights because the record is continuous and in real time, and 6) infer the form of the temperature profile. Numerous examples of applications of the sounder information to actual weather situations are discussed.

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Fabrice Ardhuin, T. H. C. Herbers, Kristen P. Watts, Gerbrant Ph van Vledder, R. Jensen, and Hans C. Graber

Abstract

Wind-sea generation was observed during two experiments off the coast of North Carolina. One event with offshore winds of 9–11 m s−1 directed 20° from shore normal was observed with eight directional stations recording simultaneously and spanning a fetch from 4 to 83 km. An opposing swell of 1-m height and 10-s period was also present. The wind-sea part of the wave spectrum conforms to established growth curves for significant wave height and peak period, except at inner-shelf stations where a large alongshore wind-sea component was observed. At these short fetches, the mean wave direction θm was observed to change abruptly across the wind-sea spectral peak, from alongshore at lower frequencies to downwind at higher frequencies. Waves from another event with offshore winds of 6–14 m s−1 directed 20°–30° from shore normal were observed with two instrument arrays. A significant amount of low-frequency wave energy was observed to propagate alongshore from the region where the wind was strongest. These measurements are used to assess the performance of some widely used parameterizations in wave models. The modeled transition of θm across the wind-sea spectrum is smoother than that in the observations and is reproduced very differently by different parameterizations, giving insights into the appropriate level of dissipation. Calculations with the full Boltzmann integral of quartet wave–wave interactions reveal that the discrete interaction approximation parameterization for these interactions is reasonably accurate at the peak of the wind sea but overpredicts the directional spread at high frequencies. This error is well compensated by parameterizations of the wind input source term that have a narrow directional distribution. Observations also highlight deficiencies in some parameterizations of wave dissipation processes in mixed swell–wind-sea conditions.

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