Geoscience Reference
In-Depth Information
(e.g., boreal forest or tundra). Each grid cell can have numerous tiles, for which the
energy balance is calculated separately.
Canadian Land Surface Scheme (CLASS):
This model (Verseghy,
1991
;
Verseghy, McFarlane, and Lazar,
1993
) was specifically designed with cold land
processes in mind and was among the first to incorporate a separate snow layer.
CLASS was the focus of extensive activity by the Canadian Mackenzie GEWEX
study group, which has targeted more realistic treatments of soil, land cover, hydro-
logic routing, and sublimation.
ECMWF:
This tiled land surface scheme, first described by P. Viterbo and A.
Beljaars (
1995
), is designed for operational use within the ECMWF weather fore-
cast model. It includes up to six land surface tiles (bare ground, low vegetation, high
vegetation, intercepted water, shaded snow, and exposed snow). Recent advances
include a new soil hydrology and snow scheme. Vegetation seasonality is described
by the leaf area index (LAI) from climatological data.
Model intercomparison projects (MIPs) can provide valuable insight into the rel-
ative performance and behavior of different models. The Project for Intercomparison
of Land Surface Parameterization Schemes (PILPS 2e), within the GEWEX Global
Land-Surface/Atmosphere System Study (Bowling et al.,
2003
) was a MIP aimed
at evaluating the performance of uncoupled (“stand alone”) LSMs in northern high
latitudes. The project was motivated by the need to improve high-latitude land sur-
face representations within NWP models and GCMs.
PILPS 2e compared simulations of land-surface processes from twenty-one
models run for the Torne-Kalix (58,000 km
2
) catchment in northern Scandinavia
(
Figure 9.5
). The location was selected because reasonably detailed and high quality
surface observations for a twenty-year period (1979-1998) were available. Identical
atmospheric forcing data from these surface observations (precipitation, air temper-
ature, specific humidity, wind speed, downward shortwave, and longwave radiation)
were provided to each modeling group. Land cover classifications, leaf area index,
and soil characteristics were also provided.
Among the problems identified under PILPS activities especially critical to model
performance in the Arctic are: (1) treatment of snowpack redistribution attributed to
wind, and the accompanying issue of parameterization of sublimation; (2) snowfall
interception by tree canopies and the fate of this intercepted snow in boreal forests;
(3) the effects of lakes and wetlands on the timing of runoff, its availability for evap-
oration, and the regional energy balance; and (4) soil freezing and permafrost.
For example, J. Pomeroy, D. Gray, and P. Landine (
1993
) and Pomeroy and R.
Essery (
1999
) demonstrated that incorporation of blowing snow physics is nec-
essary to simulate adequately sublimation losses in prairie snow environments.
Similar issues exist in Arctic environments. Other and arguably more first-order
problems identified by Slater et al. (
2001
) as part of the precursor PILPS 2d effort
include: (1) difficulties in adequately modeling the albedo and fractional coverage
of snow, and associated effects on ablation; (2) the wide variety of model struc-
tures and resulting impacts on surface energy budget treatments; (3) the tendency
for “colder” models to create a stability-induced cutoff of turbulent heat fluxes,
