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Sven-Erik Gryning

The atmospheric dispersion process and the modifications in the wind field across the 20-km-wide Øresund strait between Denmark and Sweden were studied in this project. The meteorological observational network extended over an 80-km-wide cross section through the Øresund. The dispersion process was investigated by carrying out SF6 tracer experiments, and the air trajectories were determined by tetroon flights. Emphasis was placed on the periods when the water surface was colder than the surrounding land, which in the experimental period typically occurred during daytime. Although the measuring program was intensified during the day, when tracer releases were carried out, a fairly large proportion of the meteorological measurements were carried out on a regular day-and-night basis throughout the whole experimental period. This yielded data for a large variety of meteorological situations. All data from the experiment will be made available for general use.

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Sven-Erik Gryning and Erik Lyck

Abstract

Atmospheric dispersion experiments were carried out in the Copenhagen area under neutral and unstable conditions. The tracer sulphurhexafluoride was released without buoyancy from a tower at a height of 115 m and then collected at ground-level positions in up to three crosswind series of tracer sampling units, positioned 2–6 km from the point of release. The site was mainly residential having a roughness length of 0.6 m. The meteorological measurements performed during the experiments included the three-dimensional wind velocity fluctuations at the height of release.

Dispersion parameters estimated from the measured tracer concentrations were compared with dispersion parameters calculated by various standard methods. These included methods based on the measured wind variances at the experiments and methods based on a stability classification of the atmospheric conditions. The wind variance-based methods are seen to be better than the stability-based methods in predicting the variation of σy. In addition to being a function of downwind distance, the normalized lateral spread estimated from the measurements was found also to vary as a function of the wind speed as already demonstrated by Doran and others for low-level sources. The centerline ground-level concentrations were calculated by use of σy and σz derived according to the aforementioned methods and assuming the ordinary Gaussian concentration profile. These were compared with the corresponding measured concentrations; in this case also, the wind variance-based methods were seen to be better. In some of the experiments, the assumed Gaussian tracer concentration profile in the vertical direction was found to be inconsistent with the measured crosswind-integrated tracer concentrations.

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Frank Beyrich and Sven-Erik Gryning

Abstract

This paper describes several methods for estimating the depth of the entrainment zone (Δh) at the top of the daytime convective boundary layer (CBL) from sodar data. Both averaged profiles of sound backscatter intensity and high-resolution time series of instantaneous CBL height values derived from the single-pulse intensity profiles are considered. Those methods that are based on the analysis of detrended time series of single-pulse sodar data give Δh values that are well correlated and quite consistent with each other. The frequency distribution of instantaneous CBL height variations around the mean value is shown to be nearly Gaussian. The estimated values of the normalized entrainment zone depth are plotted versus an entrainment Richardson number, resulting in a good ordering of the data and agreement with the parameterization proposed in a study by Gryning and Batchvarova. The analysis also suggests some dependence of this relationship on the stage of the CBL evolution;that is, there appears to exist different entrainment regimes and hysteresis effects in the daytime evolution of the entrainment zone.

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Sven-Erik Gryning and Dennis W. Thomson

Abstract

For an ongoing elevated-source, urban-scale tracer experiment, an instrument system to measure the three-dimensional wind velocity and the turbulent sensible heat flux was developed. The wind velocity was measured with a combination of cup anemometer, propeller (vertical) and vane sensor. The temperature fluctuations were derived using a uniquely referenced thermocouple pair. The temperature sensor is described in detail. The wind sensors have already been described elsewhere.

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J. C. Doran and Sven-Erik Gryning

Abstract

Wind and temperature data obtained on 5 June 1984 during the Øresund experiment are analyzed. The day was characterized by moderately strong winds blowing from a heated land area over a colder water surface and then over a second heated land area. To aid our interpretation of the data, the Colorado State University Hydrodynamic Mesoscale Model was used to simulate conditions on that day. The near-surface winds were found to accelerate over the water near the upwind coast, subsequently decelerated as the water fetch increased and accelerated once again as the second land surface was encountered. At higher levels, the winds accelerated over the water and decelerated over land. Good agreement was found between observations and the simulation. The more complicated behavior of the lower level wind fields is caused by a combination of roughness length changes and the development of a shallow stable layer over the water that inhibits vertical momentum transfer.

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Alfredo Peña, Sven-Erik Gryning, Jakob Mann, and Charlotte B. Hasager

Abstract

The wind speed profile for the neutral boundary layer is derived for a number of mixing-length parameterizations, which account for the height of the boundary layer. The wind speed profiles show good agreement with the reanalysis of the Leipzig wind profile (950 m high) and with combined cup–sonic anemometer and lidar measurements (300 m high) performed over flat and homogeneous terrain at Høvsøre, Denmark. In the surface layer, the mixing-length parameterizations agree well with the traditional surface-layer theory, but the wind speed profile is underestimated when the surface-layer scaling is extended to the entire boundary layer, demonstrating the importance of the boundary layer height as a scaling parameter. The turbulence measurements, performed up to 160-m height only at the Høvsøre site, provide the opportunity to derive the spectral-length scales from two spectral models. Good agreement is found between the behaviors of the mixing- and spectral-length scales.

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Alberto Troccoli, Pierre Audinet, Paolo Bonelli, Mohammed S. Boulahya, Carlo Buontempo, Peter Coppin, Laurent Dubus, John A. Dutton, Jane Ebinger, David Griggs, Sven-Erik Gryning, Don Gunasekera, Mike Harrison, Sue Ellen Haupt, Trevor Lee, Pascal Mailier, Pierre-Philippe Mathieu, Roberto Schaeffer, Marion Schroedter-Homscheidt, Rong Zhu, and John Zillman
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