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| 2. |
- Högström, Ulf, et al.
(författare)
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The atmospheric boundary layer during swell – a field study and interpretation of the turbulent kinetic energy budget for high wave ages
- 2009
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Ingår i: Journal of the Atmospheric Sciences. - 0022-4928 .- 1520-0469. ; 66:9, s. 2764-2779
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Tidskriftsartikel (refereegranskat)abstract
- Analysis of the turbulent kinetic energy (TKE) budget for five slightly unstable cases with swell has been performed based on measurements of mechanical production, buoyancy production, turbulent transport, and dissipation at five levels over the sea, from 2.5 to 26 m. The time rate of change and advection of TKE were found to be small, so the TKE residual is interpreted as an estimate of the pressure transport term (T-p). In two cases with high wave age, the T-p term is a gain at all heights. For three cases with smaller wave age, T-p is a loss in the TKE budget below 5-10 m and a gain for greater heights, where the decrease is exponential, thus showing the combined effects of swell waves and a range of waves traveling slower than the wind. The TKE budget for a case with growing sea but similar wind speed and stability as some of the swell cases has T-p close to zero at all heights. It is shown that the observed characteristic wind profile with either a low-level maximum in the 5-10-m range or a distinct "knee'' at that height is an effect of the T-p term.
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| 3. |
- Sahlée, Erik, et al.
(författare)
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Measurements of the damping of temperature fluctuations in a tube
- 2009
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Ingår i: Boundary-layer Meteorology. - : Springer Science and Business Media LLC. - 0006-8314 .- 1573-1472. ; 132:2, s. 339-348
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Tidskriftsartikel (refereegranskat)abstract
- Using field measurements we evaluate a previously deduced semi-empirical model for the dampening of temperature fluctuations in a circular tube. The measurements show that the model is a reasonably good approximation, and the previous recommendation of using a tube length of the order of 1,000 times the inner diameter of the tube to remove most of the temperature fluctuations seems to hold. Part of the difference between the empirical results and the model is possibly due to deviations from the idealized conditions assumed in the model such as no inclusion of the influence from the ambient atmospheric stability. Limitations of the measurements are also likely to affect the evaluation.
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| 4. |
- Smedman, Ann-Sofi, et al.
(författare)
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Observational study of the marine atmospheric boundary layer characteristics during swell
- 2009
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Ingår i: Journal of the Atmospheric Sciences. - 0022-4928 .- 1520-0469. ; 66:9, s. 2747-2763
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Tidskriftsartikel (refereegranskat)abstract
- By combining simultaneous data from an instrumented Air-Sea Interaction Spar (ASIS) buoy and a 30-m tower, profiles of wind and turbulence characteristics have been obtained at several heights from about 1 to 30 m above the water surface during swell conditions. Five cases formed as averages over time periods ranging from 2.5 to 9.5 h, representing quasi-steady conditions, have been selected. They represent a range of typical wave age and include wind-following swell cases and cross-swell cases. For relatively large wave age, the wind profile exhibits a well-defined maximum in the height range 5-10 m; for more modest wave age, this maximum turns into a sharp "knee'' in the wind profile. Below the maximum ( or knee), the wind increases rapidly with height; above that point the wind is very nearly constant up to the highest measuring level on the tower, 30 m. Analysis of balloon data from one day with swell indicates that the layer with constant wind in fact extends to the top of the boundary layer, in this case similar to 200 m. Analysis of the complete swell dataset from the 45 days of the 2003 Baltic Swell experiment shows that the results concerning wind profile shape obtained from the selected cases are generally valid in this experiment. Analysis of the nondimensional wind profile phi(m) shows that Monin-Obukhov scaling is not valid during swell. Wind and turbulence characteristics are found not to vary to a significant degree with the wind/swell angle within the range of angles encountered, +/- 90 degrees.
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