Stability effects on heat and moisture fluxes at sea

W.A. Oost, C.M.J. Jacobs, C. Van Oort

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

During the 1996 ASGAMAGE experiment we measured wind speed, air temperature T(a), water temperature T(s), humidity and the momentum, heat and moisture fluxes at a research platform off the Dutch coast. For each quantity we used several (sets of) instruments simultaneously. This allowed us to make an extensive assessment of the quality of the measurements and to find optimal values for the various quantities for each run. From these values we calculated C(H) and C(E), the Stanton and Dalton numbers, and reduced them to 10-m height and neutral conditions. For this reduction we made a separate analysis for the effect of inclusion or non-inclusion of the assumption that the roughness length for heat or moisture is the same for the neutral and non-neutral cases. Differences in the reduced data due to this assumption turned out to be well within the measurement error. For C(H) we distinguished three separate groups of data: stable (A), unstable with θ(a) < θ(s) (B) and unstable with θ(a) > θ(s) (C), with θ indicating the potential temperature. The stable data separate into two groups, depending on water temperature and/or the wave field. The data of group B showed a relation with wave age. The data of group C consistently gave negative values for C(H), a result that might indicate conversion of latent heat into sensible heat through condensation of water vapour just above the water surface. An attempt to re-analyse the data in terms of density fluxes, combining the effects of heat and moisture, still gave negative transfer coefficients for group C. For the moisture flux we found the more conventional result of a separation in stable and unstable values; these categories showed a clear difference, but no trends with, for example, wind speed. We conclude that standard Monin-Obukhov similarity theory cannot explain our data.
Original languageEnglish
Pages (from-to)271-302
JournalBoundary-layer Meteorology
Volume95
Issue number2
DOIs
Publication statusPublished - 2000
Externally publishedYes

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