The 32-km EDAS/Eta parallel system is being used to test 1) changes to the Eta land-surface physics, 2) modified Eta radiation physics, 3) adjustment of biases in the multi-sensor precipitation analyses using daily gauge data, and 4) use of GOES-12 radiances in the Eta 3DVAR analysis
LAND-SURFACE PHYSICS CHANGES
A number of changes have been made to the Noah land-surface model (LSM) used in the operational mesoscale Eta model, from the previous version (2.3.2) to the current version (2.7). These involve changes to Noah LSM physics, model formulation parameters, and some additional numerical refinements. The surface albedo now includes a diurnal dependence on the solar zenith angle, appropriately yielding less incoming energy at the surface during earlier morning and later afternoon. Also, removing the vegetation greenness factor from the snow albedo formulation leads to an increase in albedo under snow-covered conditions. The Eta model cloud microphysics now passes the fraction of frozen precipitation to the Noah LSM, eliminating the crude determination of frozen precipitation by the Noah LSM based on lowest (atmospheric) model level air temperature. Separate snow sublimation and non-snow-covered evaporation is now considered for patchy snow cover conditions when snowpack is shallow, reducing snow sublimation and snowpack depletion. Changes to parameters in the patchy snow cover formulation decrease the snow depth for 100 percent snow cover. A reduction in vegetation-dependent soil moisture threshold values will increase transpiration. The depth at which the lower boundary condition on soil temperature is applied is increased from 3 meters to 8 meters. The thermal heat capacity of mineral soil has been changed to a more standard value. A change to the coefficient in the thermal-roughness length calculation will decrease the surface skin-atmosphere temperature gradient. The sea-ice albedo is changed from 0.60 to 0.65. Including a diagnostic soil heat flux calculation at the end of the Noah LSM code leads to better closure of the surface energy budget.
Reduced parameter CZIL from 0.2 to 0.1. This change will reduce aerodyamnic resistance (i.e. surface turbulent exchange coefficients are too low during mid-day)
PRECIP ASSIMILATION CHANGES
Details on the precipitation analysis adjustment can be found at http://www.emc.ncep.noaa.gov/mmb/ylin/pcpinflat12/.
1. Uses the solar radiation parameterization developed by Chou (1990, 1992, 1999, and later updates), which was implemented in the GFS model and described in NCEP Office Note 441 by Hou, Moorthi, and Campana. The following COMET web pages provide further descriptions of the clear-sky radiative transfer and the shortwave radiation processes. (Note that the 5th bullet on the shortwave radiation processes should read "Calculated over each of the eight UV and visible absorption bands for O3".) Scattering and absorption are calculated for eight UV (ultraviolet)/visible and for three NIR (near infrared) spectral bands. For purposes of computational efficiency in shorter-range forecasts, absorption of solar radiation by oxygen and carbon dioxide are omitted without significant loss of accuracy. Optical properties are calculated to be internally consistent with the microphysical characteristics of cloud droplets, rain, cloud ice, and snow assumed in the grid-scale microphysical scheme., while the optical properties of convection are parameterized as described in the recent Eta implementation.
2. Key tunable parameters in the grid-scale microphysics (T_ICE, RHgrd) are specified in GSMCONST and passed to other routines for internal consistency throughout the code.
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