Thermal compression waves. II: Mass adjustment and vertical transfer of total energy

A fully compressible model is used to simulate the mass adjustment that occurs in response to a prescribed heat source. Results illustrate the role that thermal compression waves have in this process. The vertical mass transport associated with compression waves decreases rapidly with height. Most of the mass transport occurs in the horizontal, with the vertical structure of the disturbance similar to that of a Lamb wave. The vertical transfer of total energy in a thermally driven mixed layer is also examined. It is shown that the upward transport of total energy is accomplished by a compression effect rather than by the exchange of warm and cold air by buoyant thermals. Model results are analysed to determine budgets of total energy, mass and entropy. It is demonstrated that buoyant thermals are predominantly responsible for a transfer of entropy, rather than total energy. In the light of these results the notion of ‘heat transport’ in a fluid is discussed.