A thermodynamic diagnostic model for the atmosphere. Part I: Analysis of the August 1991 rain episode in Austria

Abstract

A diagnostic model (acronym DIAMOD) for the free atmosphere is described. Core of DIAMOD is a module which calculates complete thermodynamic budgets of latent and sensible heat, including objective imbalance estimates. Input data are the uninitialized ECMWF analyses and the objectively analysed SYNOP precipitation field; these are specified on the gridscale (horizontal/vertical/time boxes of dimensions 100 km/100 hPal 12 h). Main output quantities are vertical profiles of the sub-gridscale fluxes of rain and of moisture and heat (q'ω', T'ω'); their divergences represent important components of the thermodynamic budgets. DIAMOD is applied to the intense Central European rain episode of August 1991 with maximum over northern Austria. The three sub-gridscale fluxes are the main diagnostic parameters considered, together with the analysed gridscale quantities. The column over Salzburg is discussed in detail. All sub-gridscale fluxes peak on 1 August 1991 with the rain flux exceeding 1600 W/m2. The Salzburg column is unique in that all gridscale components (tendency, horizontal and vertical moisture flux convergence) plus the sub-gridscale moisture flux convergence have the same sign which maximizes the rain flux. It is demonstrated that, with DIAMOD, one can diagnostically distinguish between large-scale rain, convective rain and convection without rain. The rms-imbalance of all boxes over Europe is of the order of 50 W/m2. The theoretical background of DIAMOD will be discussed in Part II of this paper.

Keywords

• precipitation field
• free atmosphere
• moisture
• thermodynamic
• austria
• niederschlagsfeld
• freie atmosphäre
• feuchtigkeit
• thermodynamisch
• österreich
• diamod
• synop