Convection in PLDCAP part II: DIAMOD - A standard for diagnosing convective quantities

For the purpose of specifying the strength of atmospheric convection we rev iew how correlation fluxes and phase transition terms are generated from fi rst principles, i.e., from a thermodynamic set of equations. They may be us ed either for a forecast (prognostic mode) or for an analysis (diagnostic m ode). We identify the total convective heat flux c as key parameter for qua ntifying convection. Other convective quantities can be derived from c. In the prognostic mode the convective quantities are parameterized. In the dia gnostic mode they are indirectly inferred. Here we concentrate on the diagn ostic mode. We review how c can be estimated from the routinely analyzed gr idscale budget of moist enthalpy by solving a first-order linear differenti al equation, referred to as convection equation. A novel aspect of the pres ent standard of the convection equation is that the ice phase has now been included. The pertinent algorithm runs under the acronym DIAMOD (diagnostic model). The difference to a LAM is that DIAMOD takes the gridscale tendenc y as observed input while in a LAM it is output. We demonstrate the use of c (and of the net condensation rate CON) through an observation simulation experiment. Gridscale budget data from a forecast run with the Deutschland-Modell are taken as perfect input for DIAMOD; we study the corresponding output for several approximations of the convection quation. The vertical profiles of c (and to a lesser extent those of CON) are relatively robust and precise (error margins of a few percent) while th e accuracy of the other convective quantities is inferior. Conclusion is th at parameterization schemes of different LAMs can be compared with each oth er as well as validated in terms of c and CON. Application of this techniqu e has been demonstrated in Part I of this study.