Use of satellite data to estimate regional surface energy budget and analysis of lake cover impact over Northern Canada.

摘要

Lakes occupy roughly 30% of Canada's northern landscape. They can have important impacts on the climate, and climate modification will affect lake thermal properties. Study of a lake most generally begins with heat budget at its surface. Accurate partitioning of the available energy at the surface into sensible and latent heat flux is crucial to the understanding of interactions between climate processes on a regional scale.;The results from this study present a picture of the daily, monthly and seasonally sensible energy over summer period at the land-air interface versus the Fraction of Water Surface (FWS). We compare our results with the NARR model's flux in addition to few in situ measurements.;Four sites covering different land cover types across Canada were investigated during the 1998 and 2000 summers (June to September): Northern Quebec (tundra), Northwest Territories (Great Slave Lake, or GSL, and Mackenzie River Basin), Manitoba (wetlands) and Labrador (taiga).;The results show that the satellite-derived sensible flux is close to the NARR flux estimate when the fraction of water surface is small (no lakes) and over large open water areas (Mackenzie Great Slave Lake), but differs when the FWS increases within the pixel. This means that regional climate models should take into account lake cover fraction. We infer that effects of the lake-size are closely related to surrounding environmental conditions. The results of the comparison with in situ measurements for Great Slave Lake (1998) and the Wetland site are encouraging.;In this study, sensible heat flux and the Bowen ratio for the summer period are retrieved using reanalysis and remote sensing data. The methodology is based on the use of microwave data for retrieving land surface temperature (SSM/I) with the method of Fily et al. (2003) and Mialon et al. (2007). The land cover characterization is derived from remotely sensed optical data (SPOT VGT sensor). Some meteorological parameters used for retrieving flux are derived from the North American Regional Reanalysis (NARR) database.;For the Mackenzie River Basin site, the results of the Bowen ratio show that there is an increase of sensible heat partition during the second half of the summer in comparison with the first half, meaning that there is more water stress over the second half of the summer than the first. But for the Wetland site, there is no clear pattern, and in comparison with GSL, temporal variation is less significant. Comparisons between different sites indicate minimum year to year energy variation for the Wetland area.;Keywords: Regional climate model, Passive microwave SSM/I, Sensible heat flux, Bowen ratio, Fraction of Water Surface, Normalized Surface Temperature, Bulk resistance.