Mesoscale Parallel Experiment Change Log

Experiment Name:  Eta-32 with winter 2005 Eta change package, experimental changes to GFS radiation and/or cloud microphysics

When Who What
2004/11/05/00 Ferrier
  • 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
  • 2004/11/04/12 Ferrier
  • 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).
  • 2004/11/02/00 Ferrier
  • Changes intended for the 10/30 change but were left out: reduce longwave emmissivity for ice, and removed a slight, accidential increase in the solar absorption of ice.
  • 2004/10/30/00 Ferrier
  • Changed the LW absorption coefficient for ice to be the same as what's currently used in the operational Eta
  • 2004/10/27/00 Ferrier
  • In calculating longwave emissivities in cloudy layers, the optical depths for cloud water and for ice (cloud ice and snow) are obtained using the downwelling longwave relationships of Smith and Shi (1992).
  • 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.
  • 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.
  • With respect to the EtaW, the biggest impact of these changes is to increase the optical depths for ice clouds by a factor of 5 when calculating (longwave) cloud emissivities. The net effect of all of the other changes are minor (i.e., less than 2.5%).
  • 2004/10/11/12 Ferrier
  • The ice absorption coefficient was modified to be one half of the value that's currently used in operations rather than 1/15 the value in the previous change
  • 2004/10/08/00 Ferrier
  • Reverted back to the operational code, except with the modified precipitation assimilation.
  • Doubled the absorption coefficient for cloud water based on values used in the GFS radiation. This change is intended to increase solar absorption of radiation by liquid water clouds at lower levels.
  • Decreased the absorption coefficient for ice by more than an order of magnitude to be more consistent with values used in the GFS radiation for an effective radius of 500 microns. This change is intended to reduce the upper-level warm bias believed to be caused by too much absorption of solar radiation by ice. reduction in solar radiation passing through clouds at low sun angles.
  • 2004/09/30/00 Ferrier
  • Set RHsat in RADTN to RHgrd (0.967 for 32-km runs). This change is intended to increase the amount of grid-scale cloudiness based on the latest comparisons against the AFWA total product.
  • Set STSD in RADTN to .02 rather than .01, which assumes a standard deviation of total grid-scale relative humidity of 2%
  • Multiply the cloud optical depths by a factor of 0.5+max(0., min(0.5, cosz(i) ) ), which reduces the cloud optical depths by at most a factor of two starting at zenith angles larger than 60 deg. This change is intended to cut down on the large reduction in solar radiation passing through clouds at low sun angles.
  • 2004/09/28/00 Ferrier
  • Set RHsat in RADTN to RHgrd+STSD (=0.967+.01=0.977) rather than to 0.98
  • 2004/09/25/00 Ferrier
  • Assumed standard deviation of total relative humidity of 1% is assumed rather than 2%, based on tuning experiments with AFWA total cloud product.
  • T_ICE=-10C rather than -25C, leading to less supercooled liquid water
  • XNCW=50.e6 (50 /cm**3) will lead to larger cloud droplets and easier formation of rain
  • FLARGE=0.5 rather than 0.1 or 0.2 will reduce the number of small ice crystals and reduce the solar absorption by ice
  • 2004/09/24/12 Ferrier
  • The assumed standard deviation of total relative humidity in the grid box and the threshold relative humidity for the onset of grid-scale condensation have been tuned to match the AFWA total cloud product, but using the modifications to radiation that are currently running in the EtaL.
  • Cycled EDAS started from ETAL parallel as of 9/24/04
  • Page Last Modified: September 24, 2004