Conservation of Mass in Three Dimensions in Global Analyses

Abstract

Abstract For a number of reasons, conservation of mass in the global analyses on pressure coordinates is violated, yet this constraint is required for budget studies of all kinds. The imbalances arise from postprocessing the variables onto pressure surfaces, problems of dealing with the lower boundary and substituting an artificial atmosphere below ground, and diurnal pressure tendencies associated with the semidiurnal tide and the timing and distribution of observations. Methods are described and illustrated for May 1988 for adjusting the monthly mean global European Centre for Medium-Range Weather Forecasts analyses in three dimensions on pressure surfaces so that the mass balance is achieved, but the problems are present in analyses on constant pressure surfaces from all centers. First, a correction is needed for the global mean vertical motion. Second, it is shown that a local adjustment to the horizontal divergent velocity field is needed for regions that are below ground on constant pressure surface...