Mesoscale Parallel Experiment Log

Experiment Name
NAM and DGEX with modified operational radiation physics, modified cloud cover parameterization, modified precipitation assimilation, modified PBL physics, modified land- surface physics with hi-res soil/veg type specifications, and NEXRAD level 2.5 radial wind data, and 2dvar assimilation of surface temperature data
Parallel Slot
NAMX, DGEXX
Control Slot
Operational NAM-12
Start date of parallel experiment
12Z 2004/11/01 for NAMX, 00Z 2005/01/01 for DGEXX
End date of parallel experiment
00Z 2005/05/03

CHANGES

RADIATION AND CLOUD CHANGES

1. Modified version of operational Lacis-Hansen scheme with modified water & ice absorption coefficients that are more consistent with those in the GFS radiation scheme

2. 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.

3. 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, and this change has been found to have the biggest impact.

PRECIPITATION ASSIMILATION CHANGES

The precipitation assimilation algorthim in the EDAS has been modified to be less aggressive by eliminating the addition /creation of latent heat and moisture fields. Details can be found at http://www.emc.ncep.noaa.gov/mmb/ylin/newpptasm/

LAND-SURFACE PHYSICS CHANGES

A number of changes have been made to the Noah land-surface model (LSM) used in the operational NAM 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. Also, removing the vegetation greenness factor from the snow albedo formulation leads to an increase in albedo under snow-covered conditions. The NAM 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)

Parameter SMHIGH_DATA reduced from 6.0 to 3.0; this will raise the value of the reference soil moisture value below which vegetation becomes stressed (SMCREF), which (at first order) should reduce the transpiration (surface moisture flux).

Minimum stomatal conductance increased from 40s/m to 70s/m for cropland, pasture, and grassland vegetation types in order to decrease surface evaporation.

The hi-res soil and vegetation type classifications:

  • CLASS USGS-WRF VEGETATION/SURFACE TYPE
    1. Urban and Built-Up Land
    2. Dryland Cropland and Pasture
    3. Irrigated Cropland and Pasture
    4. Mixed Dryland/Irrigated Cropland and Pasture
    5. Cropland/Grassland Mosaic
    6. Cropland/Woodland Mosaic
    7. Grassland
    8. Shrubland
    9. Mixed Shrubland/Grassland
    10. Savanna
    11. Deciduous Broadleaf Forest
    12. Deciduous Needleleaf Forest
    13. Evergreen Broadleaf Forest
    14. Evergreen Needleleaf Forest
    15. Mixed Forest
    16. Water Bodies
    17. Herbaceous Wetland
    18. Wooded Wetland
    19. Barren or Sparsely Vegetated
    20. Herbaceous Tundra
    21. Wooded Tundra
    22. Mixed Tundra
    23. Bare Ground Tundra
    24. Snow or Ice
    25. Playa
    26. Lava
    27. White Sand
  • SOIL TYPE CLASS
    1. SAND
    2. LOAMY SAND
    3. SANDY LOAM
    4. SILT LOAM
    5. SILT
    6. LOAM
    7. SANDY CLAY LOAM
    8. SILTY CLAY LOAM
    9. CLAY LOAM
    10. SANDY CLAY
    11. SILTY CLAY
    12. CLAY
    13. ORGANIC MATERIAL
    14. WATER
    15. BEDROCK
    16. OTHER(land-ice)
    17. PLAYA
    18. LAVA
    19. WHITE SAND
  • ANALYSIS CHANGES

    The NAM 3DVAR code has been modified to use the NEXRAD Level 2.5 radial wind data, and a 2dvar module is now run to analyze surface temperature data

    Experiment changes log
    Background links
    Evaluation of parallel results
    Daily forecast maps (NAMX)
    Daily forecast maps (Alaska DGEX)
    Daily forecast maps (CONUS DGEX)
    Daily forecast stats
    NAMX Verification of precipitation and against rawinsondes / surface data (3/21/05-4/24/05)
    NAMX Verification of precipitation and against rawinsondes / surface data (12/14/04-3/20/05)
    DGEX Verification against rawinsondes / surface data (3/21/05-4/24/05)
    DGEX Verification against rawinsondes / surface data (1/1/05-3/20/05)
    Retrospective NAMX Verification of precipitation and against rawinsondes / surface data (7/17/04-8/31/04)
    Conclusion

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