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The diurnal mixed layer 1
Author(s) -
Imberger J.
Publication year - 1985
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1985.30.4.0737
Subject(s) - mixed layer , convective mixing , atmospheric sciences , environmental science , morning , convection , surface layer , diurnal temperature variation , wind speed , wind stress , meteorology , climatology , layer (electronics) , geology , materials science , physics , astronomy , composite material
Fine‐scale measurements and temperature gradient microstructure data are used to describe the diurnal energetics of the mixed layer in the Wellington Reservoir in Western Australia. The data covered a morning period of solar heating, a period of severe wind mixing induced by an afternoon sea breeze, and a period of pure penetrative convection extending through most of the night. The Wedderburn number (W) ranged from a value of 0.02 at the start of the heating phase to a value of about 10 at the end of the convective period. During the intermediate strong wind period the value of W remained about 0.1; the surface wind stress induced a strong tilt of the isotherms at the base of the mixed layer. The other main parameter, the ratio of the Monin‐Obukhov length to the depth of the mixed layer, ranged from about 5.0 during the morning down to 0.005 at the end of the convective period. The full range of mixed‐layer deepening processes could thus be analyzed. A simple one‐dimensional integral mixed‐layer model was applied to assess the importance of the temporal terms in diurnal simulations and to verify the values of the energy conversion efficiencies used in such models. Overall, the model performed extremely well; however, the results showed the need to develop parameterizations for the energetics of billowing induced by large shears across the base of the mixed layer and for the mixing accompanying upwelling.