VALIDATION OF PARAMETERIZED CONVECTIVE FLUXES WITH DIAMOD

A diagnostic model (DIAMOD) for the atmosphere over Europe is in use a t the University of Vienna. Central parameters in each diagnostic colu mn (horizontal resolution 100 km, time resolution 12 hours) are the ve rtical moisture plus heat flux (the total convective heat flux h) and the vertical rain flux (r); both are functions of pressure. In this st udy DIAMOD is applied to validate the output of a forecast model for t he simulation of acid deposition (EURAD) which is in use at the Univer sity of Cologne. The basic equations of both DIAMOD and EURAD models a re summarized with emphasis on the sub-gridscale hydrologic components . First, the nontrivial problem of validating model output versus obse rvations is discussed. Two different validation techniques based upon the budget equations are identified. The fully prognostic technique co mpares the forecast of EURAD for the total verification period with th e corresponding DIAMOD output. The semiprognostic validation technique involves only one-time-step tendencies. Neither yields an exact corre spondence between EURAD and DIAMOD; however, the semiprognostic techni que comes somewhat closer to the ideal of an objective validation The quantities investigated are: The fields, the time tendencies and the f luxes h and r. Second, EURAD is validated versus DIAMOD with both tech niques for the EUMAC Joint Wet Case (the Chernobyl episode) in April 1 986; the output fields include selected profiles of h(p) and r(p) over France (a moist night situation) and over Greece (a dry day situation ). The comparison demonstrates for both that the EURAD forecasts are a cceptable for the r-fluxes but are relatively poor for the h-fluxes. R easons for the differences are discussed.