| Summary: | The landscape of the boreal forest in north-central Canada is characterised by mosaics of broad-leaved deciduous trees (aspen, Populus; birch, Betula), evergreen conifers (black spruce, Picea mariana; jack pine, Pinus banksiana; and larch, Larix), fens and lakes. The forest has been cited as the possible location of a global carbon sink, and its likely response in the event of global climate change remains unclear. To improve our current understanding of the links between the boreal forest ecosystem and the lower atmosphere, the Boreal Ecosystem-Atmosphere Study (BOREAS) was executed in a series of field experiments in 1994 and 1996. This thesis documents the efforts made to characterise and map temporal and spatial distributions of the fluxes of heat, water vapour and CO2 over two 16 km x 16 km heterogeneous sites at the BOREAS study sites. === Most of the data in this thesis were obtained from the airborne observations by the Canadian Twin Otter Aircraft, operated by the Institute for Aerospace Research of the Canadian National Research Council, at the BOREAS Northern Study Area (NSA), and Southern Study Area (SSA). The research aircraft was flown at a fixed altitude of about 30 m agl. The data acquired in 1994 were primarily used to develop an objective deterending scheme in eddy-correlation flux estimates, that took into consideration the physical nature of turbulent transport during convective daytime conditions, and to map the spatial distribution of sensible heat, latent heat and CO2 fluxes over three intensive field campaigns. Maps of spatial patterns of the surface characteristics, such as the surface temperature excess over air temperature (Ts-T a) and Greenness index (GI), were also constructed. The mapping procedure involved generation of an array of grid points by block averaging the parameter of interests along the flight lines, spaced 2 km apart, over 2 km windows, with 1 km overlap between adjacent windows. The (Ts-Ta) maps showed, not surprisingly, that surface temperatures were relatively cooler over the mature forests than over the disturbed, regenerating and burn areas. However, they also showed a decoupling between sensible heat flux and T s-Ta not seen in less complex terrain. By contrast, close correspondence was observed between maps of CO2 flux and greenness, suggesting that the potential to infer CO2 exchange from remote sensing observations of the surface is higher than that for energy exchange. (Abstract shortened by UMI.)
|
|---|
