Increased heat fluxes near a forest edge |
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| Authors: | W Klaassen P B van Breugel E J Moors J P Nieveen |
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| Institution: | (1) Department of Marine Biology, University of Groningen, Haren (Gr.), The Netherlands, NL;(2) Air Research Laboratory (LLO), RIVM, Bilthoven, The Netherlands, NL;(3) Alterra (SC-DLO), AC Wageningen, The Netherlands, NL;(4) Meteorology and Air Quality Group, Wageningen Agricultural University, The Netherlands, NL |
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| Abstract: | Summary ?Observations of sensible and latent heat flux above forest downwind of a forest edge show these fluxes to be larger than
the available energy over the forest. The enhancement averages to 56 W m−2, or 16% of the net radiation, at fetches less than 400 m, equivalent to fetch to height ratios less than 15. The enhancement
of turbulent energy fluxes is explained by advection and increases with the difference in temperature and humidity of the
air over the upwind area as compared to the forest. The relatively high temperature and humidity of the upwind air are not
caused by high surface heat fluxes, but are explained by the relatively low aerodynamic roughness of the upwind surface. Although
the heat fluxes over forest are enhanced, the momentum fluxes are almost adjusted to the underlying forest. The different
behaviour of heat and momentum fluxes is explained by absorption of momentum by pressure gradients near the forest edge. It
is concluded that fetch requirements to obtain accurate surface fluxes from atmospheric observations need to be more stringent
for scalar fluxes as compared to momentum fluxes.
Received November 23, 2001; accepted May 13, 2002 |
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