HR: 0800h
AN: C31A-0298 INVITED     [Abstracts]
TI: Variability of the Below Canopy Thermal Structure over Snow
AU: * Hardy, J P
EM: Janet.P.Hardy@erdc.usace.army.mil
AF: Engineering Research and Development Center - Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, NH 03755-1290
AU: Marks, D
EM: danny@nwrc.ars.usda.gov
AF: USDA Agricultural Research Service, Northwest Watershed Research Center 800 Park Blvd., Suite 105, Boise, ID 83712-7716
AU: Link, T E
EM: tlink@uidaho.edu
AF: University of Idaho, Department of Forest Resources PO Box 441133, Moscow, ID 83844-1133
AU: Koenig, G
EM: George.G.Koenig@erdc.usace.army.mil
AF: Engineering Research and Development Center - Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, NH 03755-1290
AB: Due to the complexity of energy exchange in forested environments, existing canopy models have difficulty capturing the impact of canopy elements on thermal signatures. Prior research suggests that below canopy solar and thermal fluxes, and forest snow pack variability, is controlled by canopy type and structure. Considerable research has been conducted on the interactions of solar radiation (visible through the near infrared) with canopy elements. This degree of research has not been conducted for the interaction of longwave infrared radiation with canopy elements and the underlying surface. The thermal contribution from the different tree elements varies spatially and temporally due to differential effects of point sources (i.e. the sun) and extended sources (terrain, sky, canopy, and canopy gaps). The objectives of this work are to document the complexity and variability of the thermal signature within a forest canopy, and to make simple calculations to asses the thermal impact of the canopy elements on the energy balance incident on the snow surface. Measurements of the thermal environment beneath forest canopies were made in April 2004 at the Reynolds Creek Experimental Watershed in Idaho as part of a larger effort to characterize the sub-canopy energetics at the snow surface in a sub-watershed complicated by forest cover and variable terrain. We made measurements of the thermal environment using a Flir System ThermaCAM S60 infrared camera (spectral range, 7.5 to 13$\mu$m; thermal sensitivity, $0.08\deg$C). Our measurements captured the spatial and temporal variability of thermal radiation in both conifer and deciduous stands. We used the infrared camera to obtain images of the trees from all cardinal orientations over a 24-hour period, as well as images of forest litter on the snow surface. Surface temperatures of deciduous tree trunks ranged from 2 to $25\deg$C depending on orientation and time of day. Conifer stem temperatures were measured $20\deg$C higher than the surrounding air temperature. The temperature of a single fir cone on the snow surface was measured at $13\deg$C; while small, thin fir needles on the snow surface reached $2\deg$C. A dead tree limb on the snow surface reached an extreme temperature of $37\deg$C. Simple calculations show the contribution of these tree elements and forest litter to the energy balance at the snow surface.
DE: 3359 Radiative processes
DE: 1863 Snow and ice (1827)
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting