Basic differences between continental and oceanic deep convection

Abstract

The space and time scales of tropical deep convection are estimated through analysis of satellite cloud observations. Three-hourly fields of Global Cloud Imagery (GCI) data from 1983 to 1992, with high horizontal resolution, are analyzed. A local characterization of space-time scales is accomplished through local decorrelation as well as probabilistic approaches. The results indicate systematically shorter scales of convection over the continents in both space (150-200 km vs. 200-300 km) and time (3-5 hours vs. 6-8 hours). Consistent with other studies, the diurnal variation of the convection is also found to be strikingly different over the continents and oceans. Additionally, the diurnal amplitude over land is shown to be comparable to the time-mean convection, raising the possibility of significant aliasing across time scales.

It is argued that General Circulation Models (GCMs) must represent these basic differences between continental and oceanic deep convection if they are to generate realistic simulations of the mean tropical climate and variability on all scales.

The local characterization of tropical convection decsribed here also provides a straightforward method for convective cumulus diagnostics in GCMs. As an example, a detailed examination of space-time characteristics of convective heating in the NCAR CCM3 is discussed.