Turbulent Entrainment at a Buoyancy Interface Due to Convective Turbulence

Abstract

Penetrative convection is of considerable importance in geophysical problems. For example, in the upper layers of the ocean, convective cooling of the surface aids wind-mixing in the erosion of the seasonal thermocline during the winter. On a shorter time scale, nocturnal surface cooling in bodies of water such as the oceans, lakes and fjords helps to mix the heat gained during the day over a large depth. In the lower atmosphere, the rise of nocturnal inversions during the day due to convective heat flux from the ground governs the near-surface conditions and dispersal of pollutants. The process is also important to nocturnal and winter-cooling of fjords, growth of ice in cold saline bodies of water such as arctic fjords and the arctic sea and even in spring- heating of ice-covered fresh-water lakes (Farmer 1975). Its importance to the growth of ice In arctic fjords, where salt extrusion by growing ice initiates and maintains convection In the water column, which in turn controls the rate of ice-growth has been emphasized by Gade et al (1974) and Perkin and Lewis (1978), while the role of similar processes in subpolar oceans on climate has been discussed by Stewart (1978). Many attempts have been made to gain a better understanding of the entrainment processes due to convection, both from laboratory simulations (Deardorff et al 1969, Heidt 1977, and Willis and Deardorff 1974 and 1979) and field observations of various pehnomena involving them (Farmer 1975, Cade et al 1974, Kloppel et al 1978, and Readings et al 1973).