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

The "Mosaic" land surface model

2. Name and address of model developer;

         Randal Koster
         Code 974, NASA/GSFC
         Greenbelt, MD 20771

3. Name and address of model user;

         Randal Koster
         Code 974, NASA/GSFC
         Greenbelt, MD 20771

4. Please indicate whether your model is developed for application

   in understanding snow processes,   
   in a runoff forecasting model,	 
   in a weather forecasting model,   
   in a global climate model (GCM),     X    
   or other (please specify)?            

5. The first year when the model was used;


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

Treatment of snow in the Mosaic LSM satisfies all water and energy balance constraints. Precipitation is deposited as snow when the surface air temperature lies below 0C. Snow depth is a prognostic variable; deposited snow remains on the surface until it sublimates or melts away. The energy required for sublimation or melting can be extracted from the net radiation or deep soil. The land surface remains at OC while the snow melts. The fractional areal coverage of snow is parameterized.

7. Please specify any known application range or restrictions;

We apply the model in a GCM with a grid resolution of 4 degrees X 5 degrees. The "restrictions" are the usual general ones regarding the adequacy of any simple parameterization applied to such a large spatial scale.

8. What are the development data needs;

9. What are the operational data needs?

The snow component requires atmospheric forcing data from the GCM (Radiation, precipitation, etc. -- see next = question.)

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

   precipitation                   : X
   air temperature                 : X
   wind speed                      : X
   wind direction                  :   
   humidity                        : X
   downwelling shortwave radiation : X 
   downwelling longwave  radiation : X
   cloud cover                     : 
   surface pressure                : X 

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

      snow temperature
      snow water equivalent

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?

           -- Snow albedo at visible and near-infrared wavelengths
           -- Fractional coverage parameter
           -- Latent heats of melting, sublimation

13. What are the output data?

           -- Current snow water equivalent
           -- Current snow temperature
           -- Snowmelt
           -- Sublimation / condensation onto snow

14. What computer language does your model use?


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

The snow component of the Mosaic LSM is not a separate subroutine. There are specific lines regarding snow in several of the LSM subroutines.

16. Number of lines of the snow code?

17. What is the recommended hardware?

The model has run on many different systems.

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

If the surface air temperature is at 0 degrees (or near 0 degrees, depending on the application), the precipitation is assumed to be snowfall.

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

The snow model is essentially one-dimensional, but the effects of the fractional coverage of snow on albedo and evaporation from the surface element are explicitly parameterized.

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

The snow component uses only one layer.

21. What is your snow model time step?

Between 5 and 20 minutes, depending on the application.

22. Does your model snow albedo allow its

    spectral differences    (visible vs. near-IR)? 
    directional differences (direct  vs. diffuse)? 
      Yes (though we don't take advantage of this yet -- diffuse
           and direct albedos are set to the same values).

23. Is your model snow albedo a function of

      snow age                   
      grain size                  
      solar zenith angle        
      snow depth?              X

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?


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


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?

Not explicitly.

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?

Using a BATS-type formulation, i.e., fractional coverage = snow/(snow+S0), where S0 is a vegetation-specific parameter.

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?

Convective storms cover a small (0.2) fraction of the surface element, whereas large scale storms cover the entire element.

how is solar radiation distributed?

Uniformly (for downwelling solar radiation; variations in surface albedo in the surface element do lead to spatial variations in net radiation)

how is wind distributed?


how are other meteorological variables distributed?


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

Only in the sense that the assumed fractional areal coverage is related to vegetation type (see below).

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?

It is proportional to LAI.

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

See answer to #32 above.

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

The vegetation type controls the surface roughness.

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

Yes, to the extent discussed above.

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

The snowmelt is added to any rain that falls concurrently, and the total liquid is deposited on the canopy leaves and soil surface. A portion of the applied liquid (related to the degree of saturation in the topmost soil layer) runs off the surface, and the rest infiltrates.

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

See #41a above.

42. How is frozen soil treated in your model?

When the ground is below 0C, transport of moisture between soil layers is prohibited.

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?

Yes, an older version of the model (one that didn't allow parallel evaporation from the snow-covered and snow-free fractions of the surface element) was tested against SMMR data (and against the U.S. Air Forces's global snow depth climatology). For details, see Jim Foster et al.'s paper "Snow Cover and Snow Mass Intercomparisons of General Circulation Models and Remotely Sensed Data Sets" (J. Climate, 9, 409-426, 1996).

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?

Add snow age to albedo formulation; account better for saturation over ice surfaces; possibly include separate surface temperature for snow fraction. Also, through our ongoing collaboration with Marc Stieglitz of Lamont, we may be incorporating aspects of his more detailed snow model into our own.

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

Koster, R. and M. Suarez, "Energy and Water Balance Calculations in the Mosaic LSM", NASA Tech. Memo. 104606, Vol. 9, 1996.

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