Analysis of flux maps versus surface characteristics from Twin Otter grid flights in BOREAS 1994

Abstract

In BOREAS 1994 the Canadian Twin Otter research aircraft was flown at a fixed altitude of about 30 m above ground level (agl) over two 16×16 km heterogeneous grid sites, in an attempt to document the spatial distributions of fluxes of sensible heat, latent heat, and CO 2 over typical boreal systems and to relate them to spatial distributions of surface characteristics. The acquired data were used to construct maps of surface temperature excess over air temperature ( T s ‐ T a ) and greenness index (GI) as well as flux maps of sensible heat, latent heat, and CO 2 . Fluxes were estimated by the eddy correlation method and the scalar and vertical wind variables detrended by a method that takes into account the physical nature of transport during convective daytime conditions. The ( T s ‐ T a ) maps showed that surface temperatures were relatively cooler over the forests than over the disturbed, regenerating, and burn areas. However, their juxtaposition with sensible heat flux maps showed highest heat flux predominantly over the forest areas. Close correspondence was observed between maps of CO 2 flux and greenness. Quantitative comparison of the flux maps for the three intensive field campaigns (IFCs) showed that the CO 2 flux was the most conservative of the three fluxes, while latent heat flux showed the highest variations. Areas with persistent patterns of flux distribution across the IFCs were also identified.