UU* filtering of nighttime net ecosystem CO2 exchange flux over forest canopy under strong wind in wintertime
The mechanism of the negative nighttime net CO2 flux in wintertime and reasonable treatment with it is of great importance in evaluating the carbon metabolism of boreal forest.Results, based on the data obtained with open-path eddy covariance system and CO2 profile measurement system from Nov. 2002 to Apr. 2003 and that obtained with five sonic anemometers in Nov. 1999, show that (1) the negative net ecosystem CO2 exchange flux (NEE) always appeared under conditions of strong wind; (2) the pressure fluctuation and horizontal advection flow are dominantly responsible for the negative NEE. Operable upper bound u* filtering method (UU* filtering) was introduced since the difficulties in real-time measuring of pressure fluctuation and horizontal advection fluxes under conditions of strong wind. Nighttime upper u* threshold for the broad-leaved Korean pine mixed forest of the Changbai Mountains is 0.4 ms-1 and can be applied to the daytime filtering; and (3) the UU* filtering corrected the nighttime ‘problem’ of negative NEE under strong wind and made the estimates more ecologically reasonable.
作 者： Zhang Junhui HAN Shijie SUN Xiaomin TANG Fengde 作者单位： Zhang Junhui,HAN Shijie(Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China)SUN Xiaomin(Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China)
TANG Fengde(Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China;Department of Environment and Life Sciences, Liaoning University, Shenyang 110036, China)
刊 名： 中国科学D辑（英文版） SCI 英文刊名： SCIENCE IN CHINA (EARTH SCIENCES) 年，卷(期)： 2005 48(z1) 分类号： P4 关键词： night in wintertime negative NEE eddy-covariance pressure fluctuation UU* filtering