89th American Meteorological Society Annual Meeting

Monday, 12 January 2009: 4:15 PM
Assessing the diurnal cycle of precipitation in a prototype multi-scale climate model
Room 129A (Phoenix Convention Center)
Michael S. Pritchard, SIO/Univ. Of California, La Jolla, CA; and R. C. J. Somerville and J. O. Roads
The Center for Multi-Scale Modeling of Atmospheric Processes (CMMAP; www.cmmap.org) employs a new approach to climate modeling whereby a nested cloud system resolving subdomain handles the subgrid fluxes and boundary layer processes in each grid column that are ordinarily relegated to the domain of cumulus pramaterization. This approach effectively relaxes the rigid dependence of simulated precipitation on instantaneous measures of large-scale instability that is characteristic of cloud parameterizations.

One promising result in the Multi-scale Modeling Framework (MMF) is a global improvement in the timing of peak precipitation over the continents, which is suggestive of improved moist dynamics at diurnal timescales. We explore the realism of the MMF simulated diurnal cycle of precipitation in detail, by comparing a comprehensive suite of diurnal cycle diagnostics - ranging from harmonic and empirical orthogonal function decomposition to local metrics of the broadness of the maximum precipitation in the mean summer day - to rainfall retrievals from the Tropical Rainfall Measuring Mission (TRMM) and to a control simulation that employs conventional cloud and boundary layer parameterizations. Our emphasis is on understanding the subset of physical processes resolved by the nested cloud model in the MMF that are implicated in improved diurnal rainfall variability in several regions of the globe.

Supplementary URL: