TRR 181 Seminar "What is the best choice of prognostic variables for a global atmospheric dynamical core?" by Max Balsmeier (IAP)

The TRR 181 seminar is held byMax Balsmeier (IAP) on September 3, 11am.

What is the best choice of prognostic variables for a global atmospheric dynamical core?

Abstract

The formulation of a global atmospheric dynamical core which is consistent in terms of mass, energy and entropy is a challenging task even in a dry setup. While C-grid models make it straightforward to achieve global mass conservation, energy conversions can be mimicked by a model if Poisson brackets are employed when deriving the spatial discretization, which reflects in global total energy conservation apart from minor truncation errors arising by explicit time stepping. The properties of the global entropy budget of a dry model atmosphere, on the other hand, is particularly challenging because local entropy changes need to be diagnosed in terms of the other prognostic variables, with the possibility of truncation errors projecting onto the validity of the Second Law of Thermodynamics. Two competing theoretical approaches are presented to tackle this problem, each one having the ability to conserve both energy and mass when discretized properly, however, they differ in their formulation of entropy transport. The approaches are derived as two special cases of a more general dry thermodynamic formulation making use of the new concept of a  semi-prognostic variable. They are compared in their numerical implementations in two competing GCMs.