Implementing convection into Lorenz’s global cycle. Part II. A new estimate of the conversion rate into kinetic energy

Abstract

The global conversion rates into available potential and kinetic energy (Lorenz’s quantities Gand C) have been traditionally evaluated on the gridscale (G^grid, C^grid≈+2.5±0.4 W/m²).Convective phenomena acting on the sub-gridscale ( like, e.g., thunderstorms) have been treatedas molecular. In Part I of this study it has been outlined how Lorenz’s energy cycle may beextended to include sub-gridscale processes. For this purpose new fluxes, particularly the globalmean conversion rate into kinetic energy on the sub-gridscale (C^sub), have been defined.Evaluating them is the purpose of the present Part II. C^sub is closely related to the buoyancyproduction term of turbulence kinetic energy which can be expressed through the vertical subgridscalefluxes of moisture and heat. A thermodynamic diagnostic model (DIAMOD) thatestimates these fluxes indirectly from gridscale analyses is applied. In this way the conversionrate has been calculated for three months using global reanalysis data from ECMWF and from NCEP/NCAR. The errors of our results are caused by the analysis data used, by the specificationof the ratio between moisture and heat fluxes (the main closure assumption in DIAMOD)and by uncertainties in the radiative heating field; they are given here at the 95% level.We find C^sub=+2.2±1.7W/m². The new complete conversion rate C=C^grid+C^sub is+4.7±2.0W/m². This figure is the main result of this study, presented here for the first time:Lorenz’s energy cycle, if extended to the sub-gridscale, is about twice as intense as in thetraditional approximations. In contrast to C^sub the sub-gridscale generation rate G^sub and therefore the complete G cannot be evaluated. All one can do is to improve the estimate of G^grid by improving the estimates of the net heating. For Ggrid we find the new value of +3.1±0.5W/m².