HR: 0830h
AN: C41B-0960    [PDF]
TI: Intercomparison of two models to simulate snowcover dynamics beneath forest canopies
AU: * Link, T E
EM: tlink@uidaho.edu
AF: University of Idaho, Dept. of Forest Resources 6th and Line Street, Moscow, ID 83844-1133 United States
AU: Tribbeck, M J
EM: mjt@cpom.ucl.ac.uk
AF: Centre for Polar Observation and Modeling, University College London Gower Street, London, WC1E 6BT United Kingdom
AU: Marks, D
EM: dmarks@nwrc.ars.usda.gov
AF: Northwest Watershed Research Center, USDA - ARS 800 Park Blvd., Ste. 105, Boise, ID 83712 United States
AU: Winstral, A
EM: awinstra@nwrc.ars.usda.gov
AF: Northwest Watershed Research Center, USDA - ARS 800 Park Blvd., Ste. 105, Boise, ID 83712 United States
AB: Numerical simulation of snowcover dynamics in mountain environments is complicated by the fact that forest canopies strongly affect the snow surface energy balance relative to open sites. A number of methods to simulate the affect of forest canopies on the snow surface microclimate have recently been developed and successfully applied across a range of canopy structures. A detailed comparison of two techniques to simulate snowcover processes beneath forest canopies is presented. One method uses empirically-derived canopy adjustment algorithms based on Beers Law to drive the 2-layer mass- and energy-balance model SNOBAL. The second model (SNOWCAN) contains a physically-based optical and thermal canopy radiation model that was recently coupled to a snow energy budget model based on the SNTHERM code. The two models were tested across a range of forest structures including deciduous, mixed deciduous-conifer, sparse conifer and dense conifer canopies. Both models accurately simulated the development and ablation of the seasonal snowcovers, however differences in the components of the energy balance were observed in all of the canopies. Simulated sub-canopy radiation components were relatively similar (within ~10%) in the leafless deciduous canopy, but diverged strongly in canopies with higher leaf area indices. Simulated sub-canopy direct solar radiation was larger at high sun angles in the SNOBAL simulations relative to the SNOWCAN simulations. Maximum direct solar radiation differences between the two models approached a factor of 3 during clear, midday, late-season periods in the dense conifer canopies. In contrast, simulated sub-canopy thermal radiation was lower in the SNOBAL simulations relative to the SNOWCAN simulations. Maximum differences between the two models were approximately 10% during clear periods, and negligible during cloudy periods. Simulated sub-canopy diffuse solar radiation differences were generally within 2% for all canopy structures during all times of the year. During the ablation phase, the net snowcover radiation was generally higher, and turbulent fluxes were generally lower in the SNOBAL simulations relative to the SNOWCAN results. The results of this investigation indicate that differences in canopy parameterizations can lead to very similar estimated sub-canopy radiation due to counteracting differences in solar and thermal streams. Additional long-term sub-canopy radiation data are needed to improve simple empirical and physically-based canopy radiation models for spatially-distributed snowcover simulations in mountain environments containing a range of vegetation structures.
DE: 1863 Snow and ice (1827)
DE: 1878 Water/energy interactions
DE: 3322 Land/atmosphere interactions
SC: Cryosphere [C]
MN: 2003 Fall Meeting