Progress in understanding of land surface/atmosphere exchanges at high latitudes

Abstract

This paper summarises some of the key results from two European field programmes, WINTEX and LAPP, undertaken in the Boreal/Arctic regions in 1996–98. Both programmes have illustrated the very important role that snow plays within these areas, not only in the determination of energy, water and carbon fluxes in the winter, but also in controlling the length of the summer active season, and hence the overall carbon budget. These studies make a considerable advance in our knowledge of the fluxes from snow-covered landscape and the interactions between snow and vegetation. Also some of the first measurements of greenhouse gas fluxes (carbon dioxide and methane) are reported for the European arctic and sub-arctic. The measurements show a considerable variability across the arctic, with very high instantaneous values from sub-arctic birch and fen areas and extremely low fluxes reported from the polar desert in the high arctic. The overall annual budgets are everywhere limited by the very short active season in these regions. The heat flux over a high latitude boreal forest during late winter was found to be high. At low solar angles the forest shades most of the snow surface, therefore an important part of the radiation never reaches the snow surface but is absorbed by the forest. This indicates that in areas with sparse vegetation and low solar angles, absorption of direct solar radiation is due to an apparent vegetation cover, which is much greater than the actual one.