The 32-km EDAS/Eta parallel system is being used to test 1) modifications to the solar radiation scheme, 2) changes to the BMJ convective parameterization, and 3) adjustment of biases in the multi-sensor precipitation analyses using daily gauge data.
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.
CONVECTIVE PARAMETERIZATION CHANGES
The forecast precipitation from a modified BMJ scheme becomes much more focused with greater temporal and spatial structure when convection is considered only when limiting the amount of lifting of (dry) air parcels from their source level to their condensation level to no more than 25 mb, and further lifting the amount of lifting to their level of free convection to no more than 50 mb. Two additional changes were needed in order to prevent the occurrence of spurious grid-scale precipitation maxima. The first includes adding the effects of ice, primarily through increased diabatic heating an lower ice saturation mixing ratios, in determining the cloud updraft parcel characteristics, as well as in the enthalpy conservation and entropy evaluations. Promising results were achieved when adjusting profiles towards a reference state saturated with respect to water (T>=0C) and ice (T<0C). The second change involves including the effects of grid-scale ascent in calculating the departure of the reference profiles from saturation, following eq. (10) of Betts (1986).
PRECIP ASSIMILATION CHANGES
Details on the precipitation analysis adjustment can be found at http://www.emc.ncep.noaa.gov/mmb/ylin/pcpinflat12/.
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