Convection in Lorenz's global energy cycle with the ECMWF model.

TitleConvection in Lorenz's global energy cycle with the ECMWF model.
Publication TypeMiscellaneous
Year of Publication2007
AuthorsSteinheimer, M, Hantel, M, Bechtold, P
Secondary TitleTechnical Memorandum

Lorenz's global energy cycle includes the conversion rate C between available potential and kinetic energy. In traditional estimates of C only gridscale processes were evaluated; sub-gridscale processes were lumped into dissipation. It is argued that this is inadequate; organized sub-gridscale heat fluxes like deep convection cannot be treated as molecular. Here both Cgrid and Csub are evaluated from the ECMWF Integrated Forecast System (IFS), for a one year forecast in climate mode. The sub-gridscale fluxes are obtained from the model parametrization and the results tested for consistency; the largest contribution comes from the convection scheme. The integrand of Csub, the familiar buoyancy is locally much smaller than its gridscale counterpart. However, the buoyancy flux is upward throughout, and thus representative for, the global atmosphere. The global annual means are Cgrid =(3.4±0.1)W/m2 and Csub=(1.7±0.1)W/m2. Further, the gridscale generation rate of available potential energy is evaluated independently and found to be Ggrid =(3.0±0.2)W/m2. These results suggest that (i) the sub-gridscale processes contribute signficantly to the Lorenz energy cycle, and (ii) the cycle, represented by the total dissipation of D=(5.1±0.2)W/m2, is more intense than all earlier gridscale estimates have indicated.