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

GFDL GCM Snow Model

2. Name and address of model developer;

                      S. Manabe and Ronald Stouffer
                      Room 244 GFDL Princeton, NJ USA 08542
                      Internet : rjs@gfdl.gov
                      FAX : 609 987 5063
                      PHONE 609 452 6576

3. Name and address of model user;

GFDL Climate Group

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,      X
   in a global climate model (GCM),     X
   or other (please specify)?           X      

5. The first year when the model was used;


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

We have many versions of the model in use although most will use the snow model descibed below. I could believe that a few people have tested various changes to the snow code and that I do not know about the tests.

The "snow model" used by our climate model is very simple and it is mainly diagnostic. That is to say, snow is not a predicted variable. We just keep track of snow depth from various budget computations (snow melt + snow fall etc). Snow depth also effects the surface albedo. We use a square root function for this computation. The presence of snow also effects the surface fluxes which are computed using bulk drag formula.

The hydrology/heat budget follows Manabe (1969) [Climate and the ocean circulation I. The atmospheric circulation and the hydrology of the Earth's surface, Mon. Wea. Rev., 97, 739-774]. The surface albedo calculation was changed in the 1980's to be what is described below. To solve for the sfc temp (TSTAR), we do a sfc heat budget. If TSTAR is greater than freezing (0 C) and there is snow on the ground, TSTAR is set to freezing and the heat is used to melt snow...snowmelt. The water then runs into the soil moisture bucket.

-- by Ron Stouffer [edited by Zong-Liang Yang]

7. Please specify any known application range or restrictions;

8. What are the development data needs;

9. What are the operational data needs?

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 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?

13. What are the output data?

snow water equivalent

14. What computer language does your model use?

Fortran 77

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

16. Number of lines of the snow code?

17. What is the recommended hardware?

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

By the temperature just above the surface. Above freezing => rain below => snowfall.

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


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?

Same as the GCM

22. Does your model snow albedo allow its

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

23. Is your model snow albedo a function of

      snow age                 
      grain size                  
      solar zenith angle      
      snow depth?          X

The details are as follows.

We prescribe a bare soil albedo. For thick snow (> 2.0 cm of water equil.), 
the albedo is set to 60%. For thin snow, we use the following formula:
    albedo = bare soil alb + sqrt(snwdpt/2)*(deep snow alb - bare soil alb)

The above albedos are also a function of the sfc temp. Below -10 C, they are 
the above. Warmer than that, the albedo is lower. I have included our code below...

Our sfc albedo code:
cc   zin=1 for land pts
cc we set the bare soil albs negative to indicate glacier pts.
cc  lousy code....ralb=abs(alb)
cc   ts   =TSTAR           
cc   tcrit=-10 C 
cc   tfra =0 C
cc   snwdpt units are water equil.

ca(nc) the sfc albedo

c determine surface albedo for land grid points (including glaciers)
c =================================================
      if (zin(ipt) .eq. 1.0) then
c albedo determination for unglaciated points (albedo > 0.0)
        if (alb(ipt,jrow) .ge. 0.0) then
            abase = ralb(ipt)
c compute albedo for thick snow based on surface temperature
            if (abs(ts(ipt,jrow)) .le. tcrit) then
                asnow = 0.60
              elseif (abs(ts(ipt,jrow)) .eq. tfra) then
                asnow = 0.45
                asnow = ((tfra-abs(ts(ipt,jrow)))*0.60 +
     $            (abs(ts(ipt,jrow))-tcrit)*0.45) / (tfra-tcrit)
c albedo determination for glaciated points (albedo < 0.0)
          elseif (alb(ipt,jrow) .lt. 0.0) then
c compute base albedo of glacier based on surface temperature
            if (abs(ts(ipt,jrow)) .le. tcrit) then
                abase = 0.65
              elseif (abs(ts(ipt,jrow)) .eq. tfra) then
                abase = 0.55
                abase = ((tfra-abs(ts(ipt,jrow)))*0.65 +
     $            (abs(ts(ipt,jrow))-tcrit)*0.55) / (tfra-tcrit)
c compute albedo for thick snow based on surface temperature
            if (abs(ts(ipt,jrow)) .le. tcrit) then
                asnow = 0.80
              elseif (abs(ts(ipt,jrow)) .eq. tfra) then
                asnow = 0.65
                asnow = ((tfra-abs(ts(ipt,jrow)))*0.80 +
     $            (abs(ts(ipt,jrow))-tcrit)*0.65) / (tfra-tcrit)
c assign final albedo based on snow depth
        if (snwdpt(ipt,jrow) .le. 0.0) then
            ca(nc) = abase
          elseif (snwdpt(ipt,jrow) .ge. 2.0) then
            ca(nc) = asnow
            ca(nc) = abase + sqrt(snwdpt(ipt,jrow)/2.0)*(asnow-abase)

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?

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?

0 (no snow) or 1 (snow)

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?

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

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)?

The melt water runs into the soil moisture bucket

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

Through the soil moisture "bucket" model of Manabe (1969)

42. How is frozen soil treated in your model?


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.

Numerous GCM co2 doubling and other studies.

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?

Not that I know of...there are a number of people working on the code, although I do not know of any which are working with the snow code. Also, there is a major effort to make a single source for all GFDL codes. When this is successful, I will have many more options available to me...I assume some would include various snow codes.

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

Manabe (1969): Climate and the ocean circulation I. The atmospheric circulation and the hydrology of the Earth's surface, Mon. Wea. Rev., 97, 739-774.

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