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

Snow model contained in land-surface scheme of Hadley Centre / UKMO GCM

2. Name and address of model developer;

   Ongoing development :

   Richard Essery                Model originally developed by
   Hadley Centre                 R. Smith, D. Gregory, W. Ingram
   London Road
   Bracknell, RG12 2SZ

3. Name and address of model user;

as above

4. Please indicate whether your model is developed for application

   in understanding snow processes,   
   in a runoff forecasting model,	 
   in a weather forecasting model,      X
   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);

Net radiation at the land surface is partitioned into sensible, latent, ground and snowmelt heat fluxes. Ground heat fluxes and surface temperatures are calculated using a soil model with four layers extending to about 2 m below the surface. Insulation of the ground by a snowpack, assumed to have a constant density, is represented by reducing the thermal conductivity of the surface layer when there is lying snow; the conductivities of the snowpack and the surface soil layer are combined in series. Model vegetation cover is derived from the Wilson and Henderson-Sellers (1985) land cover classification. A snow-free roughness length, a snow-free albedo and a cold deep-snow albedo are specified for each vegetation type. Surface roughness lengths and albedos are interpolated between snow-free and deep-snow values, according to snow depth. The albedo is decreased as a simple representation of aging when the surface temperature exceeds -2C. After the surface temperature reaches 0C, subsequent net energy input to the snowpack is used to melt snow, and the resulting melt water is passed to the hydrology routine, which calculates infiltration and run-off. A single unfrozen soil moisture store is used, but a multi-layer hydrology scheme which represents freezing and thawing of the soil has been developed.

7. Please specify any known application range or restrictions;

8. What are the development data needs;

9. What are the operational data needs?

No snow data assimilated at present

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?

Temperature of combined snow / surface soil layer

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-free albedo
   Deep-snow albedo
   Snow-free roughness length
   Deep-snow roughness length
   Snow density
   Snow thermal conductivity

13. What are the output data?

    Surface and soil temperatures
    Surface fluxes of heat, moisture and momentum
    Net radiation

14. What computer language does your model use?


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

Land-surface scheme has 20 subroutines

16. Number of lines of the snow code?

Land-surface scheme has c5000 lines

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.

Snowfall and rainfall have to be specified separately

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.

4 soil layers. Snowpack is included in surface soil layer.

21. What is your snow model time step?

30 minutes in climate GCM

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

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?

Not represented

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?

Snow modifies albedo and roughness of vegetation

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?

For snow albedo As, vegetation albedo Av and SWE S, albedo is A = Av + (As - Av)[1 - exp(-0.2S)]

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

Z0 = max ( Z0v - 4E-4S, 5E-4 )

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?

Snowmelt in excess of maximum soil infiltration rate is runoff

42. How is frozen soil treated in your model?

Current model does not represen soil freezing, new version does.

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


If so, what data? (areas)

Meteorological, snow depth and flux data from sites in Greenland, Saskatchewan and French Alps

what are their temporal and spatial scales?

All 1 hour point measurements over weeks to months

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?

    Introduce or improve representations of
    Soil freezing
    Heterogeneous snow cover
    Sublimation from blowing snow
    Spectral snow albedo / aging
    Snow / vegetation interactions

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

Essery, 1998: Snow modelling in the Hadley Centre GCM, Physics and Chemistry of the Earth, 23 (5/6), 655-660.

Essery. Boreal forests and snow in climate models. Submitted to Hydrological Processes.

Essery (1997). Seasonal snow cover in the Hadley Centre GCM. Ann. Glaciol., 25, in press.

Essery (1997). Modelling fluxes over heterogeneous snow cover. Ann. Glaciol., 25, in press.

Foster et al. (1996). Snow cover and snow mass intercomparisions of general circulation models and remotely sensed datasets. J. Climate, 9, 409-426.

Foster et al. (1996). Snow mass intercomparison in the boreal forest from general circulation models and remotely sensed datasets. Polar Record, 32, 199-208.

Foster et al. (1995). Snow cover and snow mass estimates from remote sensing, climatology and the United Kingdom Meteorological Office general circulation model. Proc. ESA/NASA Passive Microwave Workshop, St. Lary, France.

Foster et al. (1994). Intercomparison of snow cover and snow mass in North America from general circulation models and remote sensing. Proc. Sixth Conf. on Climate Variations, Nashville, TN, Amer. Meteor. Soc., 207-211.

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