0e98bac1__change_package_microphysics____What
[When] 2004/11/05/12 [Who] Ferrier [What] 
Decreased the assumed number concentration of cloud droplets from 200 to 100 /cm**3, which reduces the threshold cloud water mixing ratio for autoconversion to rain from 0.838 to 0.419 g/m**3. Also decreased the maximum number concentration of precipitation ice particles from 20 to 10 per liter. Both changes are intended to lower the amount of suspended condensate in the atmosphere, which should help reduce the cool bias that has developed below clouds in the parallel. Fixed a minor bug in ADJPPT1 that limits the amount of cloud water from exceeding the autoconversion threshold A new cloud cover scheme is introduced in order to increase the presence of forecast partial cloudiness. Two adjustable parameters in the scheme have been tuned to match the AFWA total cloud cover product. The first parameter (STSDM) is the assumed standard deviation of total grid-scale relative humidity in the grid box, and it is set to 2%. The second parameter (RHsat) is the total relative humidity associated with an assumed cloud fraction of 50%, and it is set to the average of the threshold relative humidity for the onset of grid-scale condensation (RHgrd) and a value of 100% (i.e., 98.3% for the 32-km runs). In calculating longwave emissivities in cloudy layers, the optical depths for cloud water are obtained using the downwelling longwave (LW) relationships of Smith and Shi (1992). This change has resulted in nearly a factor of two increase in the LW absorption coefficient for cloud water. The LW absorption coefficient for ice remains the same as what's currently running in the operational Eta In calculating solar absorption, the optical depths for cloud water and for ice (cloud ice and snow) are obtained using the relationships described by eqs. (5.2), (5.3), and Table 9 from Hou et al. (2002), assuming a constant effective radius of 10 microns for cloud water and 75 microns for ice. For cloud water optical depths, equal weighting is assumed for absorption of UV-VIS and near IR radiation. The net effect of this change is to double the solar absorption from liquid water clouds and halve the absorption from ice clouds. In the operational radiation, a minimum optical depth is assumed for grid-scale liquid water clouds consistent with a minimum mixing ratio of 0.1 g/kg. This lower limit has been removed.
Mesoscale Parallel Experiment Change Log for " Eta-12 with winter 2005 Eta change package microphysics "