Monday, 30 July 2001
On the concept of relative buoyancy
The traditional development of the theory of buoyancy is reviewed, noting the assumptions and approximations that are associated with this derivation. Since this view of buoyancy involves a linearization of the rhs of the vertical momentum equation about a hydrostatic base state, it is specification of the base state that becomes an issue of concern. As knowledge of the immediate environment of convective storms increases, it is becoming increasingly difficult to know what sort of base state is appropriate, especially in diagnosis of observations. Since many numerical simulation models associated with deep convection also employ the traditional formulation of buoyancy, its impact on the simulations is reviewed and, unless the effects of the vertical perturbation pressure gradients are ignored, it is shown the simulations are not actually dependent on the base state. However, the use of the traditional formulation might lead to erroneous interpretations of the model results. Using the classical concept of buoyancy (as a perturbation from a hydrostatic base state) to explain the physics of deep convection may have been useful in the past, but it is suggested that this explanation may no longer be as valuable as it has been.