1. Please write down the name (and abbreviation) of your snow model or land-surface model with snow component?

No name really; it is a simple self-developed snow component added on
to RAMS.

2. Name and address of model developer;

     Brent M. Lofgren
     NOAA/Great Lakes Environmental Research Laboratory
     2205 Commonwealth Blvd.
     Ann Arbor, MI 48105-1593
e-mail: lofgren@glerl.noaa.gov
phone:  (313) 741-2383
fax:    (313) 741-2055

3. Name and address of model user;


4. Please indicate whether your model is developed for application

   in understanding snow processes,      
   in a runoff forecasting model,       X
   in a weather forecasting model,       
   in a global climate model (GCM),     
   or other (please specify)?           X       
   (I am trying to develop a regional climate
    model with a strong hydrological component including snow.)

5. The first year when the model was used;


6. One paragraph description of your model (e.g. abstract from report or paper);

Snow input is prognosticated by the atmospheric component (RAMS) of my regional model, which is called the Coupled Hydrosphere-Atmosphere Research Model (CHARM). CHARM is built around RAMS; the default configuration of RAMS has thermal storage and diffusion among 11 soil layers, but has no snowmelt scheme. I consider the snow to be part of the top soil layer for purposes of thermal capacity. Other than that, my added snowmelt scheme is essentially borrowed from the GFDL GCM. Snow is specified to have higher albedo than ground. The snow is allowed to get colder than the freezing point if conditions dictate that, but never warmer. If the freezing point is reached and there is an additional positive input of energy (imbalance among net radiative flux, sensible heat flux, latent heat flux, and soil heat flux), there is snowmelt equal to that energy input divide by the latent heat of fusion. Also, sublimation is prescribed when the water vapor mixing ratio corresponding to the vapor pressure of the snow exceeds the mixing ratio of the overlying air; a bulk aerodynamic formulation is used to calculate the sublimation rate.

7. Please specify any known application range or restrictions;

This is a highly simplified model, but is believed to be approximately applicable to most situations.

8. What are the development data needs;

None. No tuning is done.

9. What are the operational data needs?

None. Note that it is mainly intended for use in a regional *climate* model.

10. Please indicate with an "x" for those meteorological variables used to DRIVE your snow model?

   precipitation                   : X (snow only; rain does not affect melting)
   air temperature                 : X
   wind speed                      : X
   wind direction                  : 
   humidity                        : X
   downwelling shortwave radiation : X
   downwelling longwave  radiation : X
   cloud cover                     : (indirectly, as it affects radiation)
   surface pressure                : (only VERY weakly)

11. List the state variables (e.g., snow temperature, snow water equivalent, etc) your snow model uses?

Snow temperature and snow water equivalent are the only state variables.

12. List the measurable/adjustable parameters (e.g., snow surface aerodynamic roughness, maximum albedo at visible wavelength, etc, excluding initial conditions) your snow model uses?

I am not entirely clear on what this question is asking. Aerodynamic roughness is taken as being equal to that of the underlying vegetation. Surface albedo is not separated by bands, but is dependent on snow water equivalent and snow temperature.

13. What are the output data?

Snow water equivalent, snow temperature (output as top soil layer temperature), snowmelt, sublimation, snowfall.

14. What computer language does your model use?


15. How many subroutines (or functions) does your snow model have?

Most code contained within two subroutines, but interspersed with code for soil temperature determination and soil hydrology.

16. Number of lines of the snow code?

Approximately 30 dedicated to snow.

17. What is the recommended hardware?

RISC-based workstation. I use an HP 735 and will soon acquire an HP C180.

18. How does your model determine the form of precipitation (i.e., snowfall and rainfall)? Please give the formulation.

RAMS microphysical cloud model is used for this determination. See RAMS documentation.

19. Is your snow model one dimensional or multi-dimensional? Please specify.

I guess you would say that it is 1-D, as it is taken to represent a point on each 40 km x 40 km cell of the model grid.

20. If one dimensional, how many layers are there in your snow model? Please specify layering structure.

One layer.

21. What is your snow model time step?

90 seconds, dictated by atmospheric component of the model.

22. Does your model snow albedo allow its

    spectral differences    (visible vs. near-IR)?  
    directional differences (direct  vs. diffuse)? 

23. Is your model snow albedo a function of

      snow age                 
      grain size                  
      solar zenith angle        
      snow depth?          X            
Surface albedo of the ground-snow system is considered
dependent on snow water equivalent.  At zero SWE, the
albedo of the underlying ground is used; at SWE of 2 cm
or more, the snow's albedo is used; transition between
these two values has the ground albedo weighted at
(2 cm - SWE)^2/(2 cm)^2 and snow albedo weighted at one
minus the previous expression.

24. Does your snow model explicitly treat liquid water retention and percolation within the snowpack?


25. Does your snow model account for changes in the hydraulic and thermal properties of snow due to meltwater refreezing?


26. Is snow density in your snow model changing with time or fixed?

No explicit specification of density is made.

27. Is heat capacity and conductivity in your snow model changing with time or fixed?

Fixed heat capacity; conductivity not specified, but implied to be infinite.

28. Does your snow model simulate vapor transfer in the snowpack?


29. Does your snow model account for the heat transfer between the bottom of the snowpack and the underlying soil?

Snowpack and immediately underlying soil are considered to be a single heat reservoir.

30. In snow energy balance, does your model consider heat convected by rain or falling snow?


31. Does your snow model include snow drifting and redistribution by wind (or avalanche)? If so, how?


32. How is areal snow distribution treated?

It is considered uniform for each 40 km x 40 km cell.

33. Does your snow model account for sub-grid (or sub-watershed) effects of topography? If so, how is temperature distributed?

        how is precipitation (spatial, elevation and corrections) distributed?
        how is solar radiation distributed?
        how is wind distributed?
        how are other meteorological variables distributed?


34. Does your snow model consider snow-vegetation interaction?


35. Does the snow-vegetation interaction account for

 different vegetation types     (grass vs. forest),            
 different vegetation heights   (short vs. tall),            
 different vegetation densities (small vs. large LAI),      
 different vegetation coverages (sparse vs. dense vegetation)? 

36. Are snow interception, drip and melt on canopy surface allowed in your model?


37. How is the upper limit of the canopy interception determined?


38. In the presence of vegetation, how is snow surface albedo altered?

See 23. Canopy height does not affect albedo.

39. In the presence of vegetation, how is snow surface roughness altered?

Surface roughness is always assumed to be that due to vegetation.

40. In the presence of forest, does your snow model allow spatial variability of snow depth and water equivalent on forest floor?


41(a). How does your model deliver snowmelt to the soil system (e.g. affecting soil moisture)?

(b). Once snowmelt is generated, how does your model relate it to runoff?

I have two competing models of soil moisture, but both have runoff proportional to moisture storage in an upper soil zone.

42. How is frozen soil treated in your model?

It is considered to have no effect on water percolation.

43. Has your snow model been tested with the field data?


If so, what data? (areas)

what are their temporal and spatial scales?

44. Has your snow model been used together with remote sensing data as input?


If so, how?

45. If your snow model is coupled with a numerical weather forecasting model or climate model, has the model snow product been compared with satellite data? If so, what satellite data were used?


46. Please list any other previous applications.

47. Please specify verification criteria, if any?

48. What are the model fitting procedures, if any?

49. What are future plans for using/improving the model?

50. Please provide references relevant to the model description and use.

-- Last updated Fri Oct 8 12:47:54 MST 1999 by Zong-Liang Yang.
For questions and comments, please contact Zong-Liang Yang