Monday 16 September, 2002
529 Walker Building
10:00 - 11:00 AM
refreshments at 9:45AM

THE MARINE ATMOSPHERIC BOUNDARY LAYER - NEW FINDINGS FROM THE ÖSTERGARNSHOM STATION IN THE BALTIC SEA

ANN-SOFI SMEDMAN
with
ULF HÖGSTRÖM
Uppsala University, Department of Earth Sciences, Meteorology, Villavägen 16,
S-752 36 Uppsala, Sweden

From studies at the air-sea interaction site Östergarnsholm, a coherent picture of how waves interact with the atmosphere is now beginning to emerge. It is clear that the surface of the ocean behaves similar to that of a solid surface with regard to the turbulence structure in the surface layer only for conditions of pure wind sea, i.e. during the phase when waves are in the process of being built up by increasing wind. At that stage of wave development, the dominant waves are short and move slowly relative to the wind. Then the drag coefficient CDN is a function only of the wave age, expressed as (where is friction velocity and is the phase velocity of the dominant waves). The relation obtained by us is identical to the corresponding expression obtained from several recent ocean experiments, Drennan et al. (2000). As soon as the wave field develops behind the 'pure wind sea' stage towards conditions where relatively long waves start to gain importance, inter-actions caused by these longer waves are felt in the atmosphere at our lowest turbulence measuring height, 10m. For example it is demonstrated that the logarithmic wind law is not valid in near-neutral conditions except when pure wind sea conditions prevail and, further that for mixed seas and swell conditions, CDN is a function not only of the wave age parameter but also of a second wave parameter , which is a measure of the proportion of energy of relatively long waves to short waves.

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