Monday 13 Mar 2017: Parameterizing large-scale circulations based on the weak temperature gradient approximation
Prof Bob Plant - University of Reading
The thermodynamic budget within the tropics is a balance between cooling of the atmosphere due to radiation, warming due to convection, and either warming or cooling associated with large-scale circulations. Two-way interactions of convective activity with the radiation and the large-scale circulation dictate how that balance is achieved. GCMs attempt to simulate these interactions, but have longstanding problems with representing the convective activity. In contrast, large-eddy modelling can simulate convection well, but the large-scale circulation is typically prescribed, tightly constraining the simulations and essentially supplying much of the answer from the outset. Approaches such as the weak temperature gradient have been advocated over recent years in order to allow a dynamical coupling between directly-simulated convection and a non-trivial large-scale circulation. In this talk I will describe some extensions of the usual weak temperature gradient approach, in particular allowing the system to be treated as either thermodynamically open or closed. A two-column approach allows new configurations to be developed which may provide much more meaningful tests of GCM convective parameterizations. However, some cautionary notes will also be given about the use of weak-temperature gradient couplings, not least in its treatment of boundary-layer circulations.