Convective activity quantified by sub-gridscale fluxes

Abstract

A dynamic quantity to measure the actual strength of convection is the sub-gridscale transport of equivalent temperature v≡ T+ c −1 p Lq; we refer to the corresponding correlation θ′ω′ with ω≡ dp dt as the convective flux. Vertical profiles of the convective flux within atmospheric columns are computed with a diagnostic model (DIAMOD) from the observed gridscale budgets by using analysed fields of ECMWF. Their high quality makes DIAMOD sufficiently accurate despite the strong internal compensation in the gridscale budget terms. Boundary value for the vertical integration is the latent plus sensible heat flux across the Earth's surface. We show that the maximum convective flux in a column is proportional to the mean vertical slope of the gridscale budget averaged over the troposphere. Results for 144 columns (100km/12h each) over Europe for a case of deep convection south of the Alps in September 1995 (the South Ticino case) are presented. There is areal precipitation of up to 45 mm/12 h. The areal convective flux exceeds 1 000 W/m 2 around 600 hPa in some columns. Maxima of precipitation and convective flux do not exactly coincide. This is not inconsistent with the notion that the convective flux (estimated with DIAMOD or an equivalent approach) is the proper dynamic measure to quantify the convective process.