HR: 10:20h
AN: H22A-01    [Abstracts]
TI: Impacts of Mixed Physics on Ensemble Spread in Warm-Season Rainfall Forecasts
AU: * Gallus, W A
EM: wgallus@iastate.edu
AF: Dept. of Geological and Atmospheric Sciences, 3025 Agronomy Building, Iowa State University, Ames, IA 50011 United States
AU: Jankov, I
EM: ijankov@iastate.edu
AF: Dept. of Geological and Atmospheric Sciences, 3025 Agronomy Building, Iowa State University, Ames, IA 50011 United States
AB: A series of tests have been performed using both the Eta and WRF (Weather Research and Forecasting) models over several different domains in the central United States to better understand the role of mixed physics in generating spread in ensemble forecasts of warm season convective systems. In tests with a 10 km grid spacing version of the Eta model, it was found that the choice of convective parameterization exerted a much stronger impact on the resulting rainfall forecast than a wide range of mesoscale initial perturbations. A four member ensemble consisting of two Eta members, each with a different convective scheme, and two WRF members, also with different convective schemes, was found to be as skillful as an 18 member ensemble using the Eta model alone with most members having different initial conditions. Of particular interest, spread was greater among the two Eta members or two WRF members using different convective schemes than it was between the two different models using the same convective scheme. Additional tests were performed using an 18 member mixed-physics ensemble of 12 km grid spacing WRF simulations run over the International H2O Project domain. In this ensemble, three different convective treatments were used, two different planetary boundary layer schemes, and three different microphysical schemes. Again, the convective treatment had the biggest impact on the forecasts when evaluated subjectively and using spread ratio and correlation coefficient, although a factor separation analysis showed the microphysical scheme choice to exert a big influence on total domain rain volume. Other tests over a larger domain were performed at the WRF Developmental Test Center using 8 and 10 km grid spacing versions of the WRF model with different physics, initial conditions and dynamic cores. These tests suggest that initial conditions play a prominent role in only the first 6-12 hours of the forecast, with the dynamic core choice having its biggest impact after 12 hours, and physical scheme choice having a strong influence throughout the 48 hour simulations.
DE: 1854 Precipitation (3354)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting