Abstract
This paper describes a theoretical and experimental study of penetrative convection within an initially thermally stably stratified fluid heated from below. Emphasis is placed on the experimental investigation of the growth of the mixed layer and the entrainment at its boundary. Both processes play an important role in density-induced geophysical phenomena such as the lifting of an inversion layer during the morning and the deepening of a thermocline in a lake during the fall.
Many laboratory experiments with water as the experimental fluid were performed, in which the convection process was generated and visualised. The height of the mixed layer, heat transfer across the bottom interface and temperature profiles were measured as functions of time.
Theoretically-based analytical equations are given, which predict the thickness and temperature of the mixed layer. The equations involve one empirical factor characterising the entrainment rate at the interface between the mixed and the upper stable layer.
The experimental results confirm the theoretical equations and show that the empirical factor is a constant. From this, an entrainment rate is calculated which agrees well with values presented in the meteorological literature.
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Work performed at Sonderforschungsbereich 80, University of Karlsruhe.
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Heidt, F.D. The growth of the mixed layer in a stratified fluid due to penetrative convection. Boundary-Layer Meteorol 12, 439–461 (1977). https://doi.org/10.1007/BF00123192
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DOI: https://doi.org/10.1007/BF00123192