The atmospheric boundary layer during swell: A field study and interpretation of the turbulent kinetic energy budget for high wave ages

U. Högström, A. Smedman, E. Sahleé, W. M. Drennan, K. K. Kahma, H. Pettersson, F. Zhang

Research output: Contribution to journalArticlepeer-review

49 Scopus citations

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 (Tp). In two cases with high wave age, the Tp term is a gain at all heights. For three cases with smaller wave age, Tp 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 Tp 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 Tp term.

Original languageEnglish (US)
Pages (from-to)2764-2779
Number of pages16
JournalJournal of the Atmospheric Sciences
Volume66
Issue number9
DOIs
StatePublished - Sep 2009

ASJC Scopus subject areas

  • Atmospheric Science

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