HR: 10:45h
AN: A42A-02    [Abstracts]
TI: An efficient mixed-phase cloud and precipitation scheme for use in Operational NWP Models
AU: * Ferrier, B S
EM: Brad.Ferrier@noaa.gov
AF: NOAA/NWS/NCEP/EMC W/NP2, 5200 Auth Rd., Rm. 207, Camp Springs, MD 20746 United States
AU: * Ferrier, B S
EM: Brad.Ferrier@noaa.gov
AF: SAIC/GSO, 4600 Powder Mill Rd., Suite 400, Beltsville, MD 20705-2675 United States
AB: An efficient cloud microphysical parameterization that includes mixed-phase processes has been running in the operational Eta model at the National Centers for Environmental Prediction (NCEP) since November 2001. This scheme is also being run in the Non-hydrostatic Mesoscale Model version of the Weather Research and Forecasting (WRF-NMM) model as part of NCEP's production suite. It is intended to contain some of the functionality of more sophisticated microphysics packages used in cloud-resolving models and high resolution mesoscale models (e.g., Rutledge and Hobbs, 1983, 1984; Lin et al., 1983; Reisner et al., 1998), while remaining computationally efficient for use within operations. Within the microphysics subroutines, the prognostic variables are mixing ratios of water vapor, (nonprecipitating) cloud water, rain, and ice. The ice is a composite category composed of small, nonprecipitating ice crystals ("cloud ice") and precipitating ice particles ("precipitation ice"). Exponential size distributions are assumed for rain and precipitation ice, however, their intercepts and slopes are variable unlike in many of the other, more sophisticated schemes. Throughout the rest of the forecast model code outside of the microphysics routines, the prognostic variables are specific humidity and total condensate. Within the microphysics driver after the microphysical calculations, the updated cloud water, rain, and ice mixing ratios are summed to give the total condensate. Local arrays in the microphysics driver store the fractional contributions of each hydrometeor class to the total condensate. These arrays are then used to extract the mixing ratios of cloud water, rain, and ice from the condensate upon entry into the microphysics driver at the next physics time step. This approach assumes that changes due to advection in the relative composition of cloud water, rain, and ice from the previous time step are small within each grid column. Although some errors are bound to occur with this approach, advecting only a single variable saves considerable computing time. Different closures are assumed in this scheme compared to other bulk parameterizations, most notably in the size distributions of precipitation ice particles. These approaches, together with some methods of optimization, will be summarized at the meeting. Supercooled mixed-phase conditions are considered in the scheme, and it includes such microphysical processes as cloud water condensation and evaporation, deposition and sublimation of ice, conversion of cloud water to rain, riming of cloud water and accretion of rain onto ice, melting of ice, freezing of rain, and ice nucleation. In addition, more sophisticated physics are considered, such as shedding of rain from melting ice particles accreting cloud droplets, condensation of cloud water onto melting ice (instantly shed to form rain), and evaporation of liquid water from melting ice. Work will soon be underway to incorporate partial cloudiness effects into the scheme following the work of Sundqvist et al. (1989), which can be important in better representing cloud-radiation interactions.
DE: 3314 Convective processes
DE: 3329 Mesoscale meteorology
DE: 3337 Numerical modeling and data assimilation
DE: 3354 Precipitation (1854)
DE: 3364 Synoptic-scale meteorology
SC: Atmospheric Sciences [A]
MN: 2005 Joint Assembly