The impact of fog on the energy budget of a subtropical cypress forest in Taiwan

Beiderwieden E, Klemm O, Hsia Y-J

Abstract

Results of energy balance measurements during an 11-d period under clear weather, and a 5-dperiod under foggy conditions are presented. The single most important factor discriminating the 2 periods was the intensity of solar radiation. With fog, a reduction in the incoming shortwave radiationof up to 95% was found. Using the eddy covariance method, turbulent fluxes of CO2, latentheat (E), and sensible heat (H), were measured. The energy balance (EB) was positive (26 W m-2)under clear conditions, resulting in a gain of energy for the ecosystem. In contrast, during the presenceof fog, EB was negative (-15 W m-2) indicating a loss of energy. In both situations, the EB wasnot completely closed. Possible reasons for this finding are discussed. The ratio of available energyand the sum of turbulent fluxes in E, H and soil heat flux (S) during the clear and foggy periodswere examined for daytime and nighttime conditions. The CO2 flux exhibited a diurnal cycle withnegative fluxes in the daytime associated with CO2 uptake by vegetation. The average CO2 fluxesof -7.8 μmol m-2 s-1 during clear conditions and -3.2 μmol m-2 s-1 during foggy conditions indicatethat the ecosystem benefits from clear weather conditions.