HR: 1330h
AN: A43A-02    [Abstracts]
TI: The Sensitivity of Simulations of the North American Monsoon to Convective Parameterization in CCM3
AU: * Collier, J C
EM: craigc@fiji.ucsd.edu
AU: Zhang, G J
EM: zhang@fiji.ucsd.edu
AB: Two nine-year runs of the NCAR Community Climate Model (Ver. 3) are compared in their simulations of the North American summer monsoon. The two simulations differ by their closures of the parameterization for deep convection: for the control run, closure is based on CAPE, while for the experimental run, it is based on the large-scale forcing of temperature and humidity. The sensitivity to the choice of closure in simulating the North American monsoon is measured. Model validation relies on hourly precipitation rates from surface gauges over the U.S., those derived from the combination of microwave and radar measurements from NASA's TRMM (Tropical Rainfall Measuring Mission) satellite over Mexico, and tropospheric horizontal wind, specific humidity, and CAPE values from NCEP-NCAR reanalysis. Results show that the experimental run improves the timing of monsoon onset and peak in the regions of core monsoon influence considered here, though it increases a negative bias in the peak monsoon intensity in at least one region. While deficiencies in the concentration of upper-tropospheric specific humidity are reduced by the experimental run, the upper and lower-tropospheric simulated horizontal circulations are largely insensitive to the change in the convective scheme and, aside from some biases in the simulation of the U.S. Great Plains low-level jet, agree well with the reanalysis-based circulation. Sensitivity of the diurnal cycle of precipitation to the convective scheme closure is highly geographically-dependent. The experimental run greatly improves the diurnal cycle of precipitation over the U.S. Great Plains and Upper Midwest, but in the monsoon region, the quality of the simulation over northern Mexico is degraded. The same degradation is seen in the southeastern and northeastern U.S. In these latter regions, the diurnal cycles of precipitation are better simulated when they are more in phase with the diurnal cycles of CAPE.
DE: 3314 Convective processes
DE: 3354 Precipitation (1854)
SC: Atmospheric Sciences [A]
MN: 2005 Joint Assembly