HR: 1330h
AN: U52A-0024    [PDF]
TI: Instantaneous Rain Rates in Satellite Observations and a General Circulation Model
AU: * Wilcox, E M
EM: ewilcox@princeton.edu
AF: Princeton University, NOAA Geophysical Fluid Dynamics Laboratory, P.O. Box 308, Princeton, NJ 08542-0308
AB: The frequency distribution of instantaneous rain rates is explored as a diagnostic tool for assessing the representation of precipitation in global atmospheric general circulation models (GCMs). A growing number of predictions are now being made about future changes in the frequency of extreme precipitation events in response to anthropogenic greenhouse gas loading. However, it is not yet clear that modern GCMs represent the process of precipitation sufficiently to capture present-day or future variability of precipitation on short time scales. This study is a first step toward making such an assessment. Observations of instantaneous rain rate from TRMM and SSM/I polar-orbiting satellites are averaged over model grid cells with horizontal spacing of approximately 200km, which is consistent with global scale atmospheric simulations used for climate change prediction. The grid cells are grouped by geographic region (such as tropical, extratropical, land and ocean) and sufficient satellite overpasses are collected to construct distribution functions for each region of the frequency of occurrence of rain rates ranging from less than 0.1 mm/hr to greater than 10 mm/hr. The observed frequency distributions are compared with output from a coincident simulation of the GFDL atmospheric general circulation model. Corresponding simulated frequency distribution functions are constructed from snapshots of rain rate from individual time steps of the model, which are sufficiently sampled to capture the full diurnal variability of precipitation. Excessive drizzle associated with difficulty parameterizing cumulus convection is commonly observed in modern GCMs. The extent of this problem is examined quantitatively in this study and the sensitivity of such problems to the formulation of cumulus convection is discussed.
DE: 1610 Atmosphere (0315, 0325)
DE: 1640 Remote sensing
DE: 1833 Hydroclimatology
DE: 3354 Precipitation (1854)
DE: 3367 Theoretical modeling
SC: U
MN: 2003 Fall Meeting