The impact of logging on the surrounding flow in a managed forest
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The influence of a freshly logged area in a managed pine forest on the flow field is investigated by comparing sodar wind profile data over the forest canopy with the synoptic wind field extracted from North American Regional Reanalysis, National Centers for Environmental Prediction. As a consequence of the pressure gradient arising from the sharp temperature difference between the clearcut and the surrounding uncut forests, the local wind direction over the forest measured with the sodar departs dramatically from the prevailing synoptic wind direction when the latter is transverse to the clearcut-sodar direction. Sodar measurements also indicate systematic strong updrafts during daytime followed by nighttime downdrafts with wind coming from the logged area. This suggests the presence of horizontal advection carrying daytime warm air (or nighttime cool air) from the clearcut to the forested area. This paper also examines the influence of wind velocity, clearcut fetch, and solar radiation on locally generated circulations and advection. The presence of local circulations arising from contrasting neighboring surface characteristics well outside the footprint is of particular relevance for atmospheric flux sites where robust surface–atmosphere exchange values are sought. This study highlights the high level of circumspection required at the time of identifying locations for flux sites. It also suggests vigilant monitoring of the surrounding landscape during eddy–flux measurements particularly in actively managed landscapes.
KeywordsWind Speed Wind Direction Pressure Gradient Force Horizontal Pressure Gradient Sodar Measurement
The authors wish to thank the US Dept. of Energy, Terrestrial Carbon Processes Program for the funding of the present research. We wish to thank sincerely N. Pingintha, D. Durden, and L. Pires for their comments and discussions. We wish to thank M. Binford for providing the remote sensing map as part of this project and to T. Prabha for loaning us the executable program of the Meteo-Science sodar. We also wish to acknowledge the staff from the University of Florida for their help during the field experiments. Thanks also are given to the Donaldson family for providing the study area. This manuscript is based on work done by H. Gholz while serving at the National Science Foundation (NSF). The views expressed in this paper do not necessarily reflect those of the National Science Foundation or the United States Government.
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