Prediction of the diurnal change of precipitation using a multi model superensemble and TRMM data sets

Abstract

This is the first of a two part paper on diurnal change of precipitation and clouds. These studies exploit the data sets from the TRMM, DMSP satellites and the ISCCP data sets. This paper looks at TRMM 3B42 data sets and the precipitation from a suite of global coupled atmosphere ocean models to examine the phase and amplitude of the diurnal mode. The emphasis of the paper is on the diurnal change of precipitation over land and ocean areas of the tropics and subtropics. Our approach to the analysis of data sets follows a recent study of Song and Smith (J. Climate, 2006). We consider several versions of the FSU coupled global models that utilize different versions of radiative transfer and cloud radiation. With this suite of models we carry out 360 five-day forecasts. We examine the errors in phase and amplitudes of these member models, their ensemble mean and of the superensemble. This study utilizes 3 hourly TRMM and model based data sets between 40oS and 40oN. Observations show rapid changes of phase over land and over ocean. The modelling of such such changes is challenging. Diurnal changes are sensitive to all aspects of physical parameterizations in models. The superensemble based forecasts capture many of these changes very well.