EFFECTS of TIME SCHEMES on THE CONVECTION PROCESSES IN NCEP ETA MODEL

Abstract

It was not until 1904 that Vilhelm Bjerknes - in a remarkable manifisto and testament of deterministic faith - stated the central problem of NWP. This was the first explicit, coherent recognition that the future state of the atmosphere is, in principle, completely determined by its detailed initial state and known boundary conditions, together with Newton's equations of motion, the Boyle-Charles-Dalton equation of state, the equation of mass continuity, and the thermodynamic energy equation. Namely the problem of prognosis as nothing less than ihe integration of the equations of motion of the atmosphere, but it remained for Richardson[33] to suggest the practical means for the solution of this problem [18]. He proposed to integrate the equations of motion numerically and showed exactly how this might be done. Charney, R. Fj0rtoft, and J. von Neuman[9] computed a historic first one­ day weather forecast using a barotropic (one-layer) filtered model. The work took place in 1948-9. They used one of the first electronic computers ENIAC (the Electronic Integrator and Computer), housed at the Aberdeen Proving Grounds of the US Army in Maryland. The results of the first forecasts were quite encouraging, we repreduce here the abstract of the paper. A method is given for the numerical solution of the barotropic vorticity equation over a limited area of the earth's surface. The lack of a natural boundary calls for an investigation of the appropriate boundary conditions. These are determined by a heuristic argument and are shown to be sufficient in a a special case. Approximate conditions necessary to insuTe the mathe­ matical stab'il'ity of the dijj"eTence equat'ion ar-e derived. The res-ults of a seTies of four 24-hour forecasts computed from actual data at 500mb level are pre­ sented, together with an interpretation and analysis. An attempt is made to determine the causes of the forecast errors. These are ascribed partly to the use of too large a space increment and partly to the effects of baToclinic­ ity. The role of the later is investigated in some detail by means of a simple