Influence of clearcut in a managed pine plantation on flow circulation

The influence of a recent clearcut on the flow field in the forest flux site downwind is investigated by comparing sodar data collected over the forest canopy against the synoptic wind field extracted from National Center for Environmental Prediction (NCEP) North American Regional Reanalysis (NARR) data. The clearcut was at least 500 m away from flux/sodar site, and extended about 300 – 500 m and about 1200 – 1800 m in the northwest and in the southwest of the flux/sodar site, respectively. The results show that the local wind direction over the forest canopy departs dramatically from the synoptic wind direction. This shift in mean flow direction arises from temperature differences between the clearcut and the forest. Furthermore, the flow downwind of the clearcut is characterized by the presence of strong updrafts in daytime conditions with the reverse in nocturnal conditions. This suggests that caution be exerted when tower flux measurements are made at a single point. Results from the present study highlights the importance of ensuring that surface temperature differential resulting from adjoining contrasting surfaces are minimal, even though these inhomogeneities may be hundreds of meters away from the flux tower and thus well outside the tower footprint, if one is to measure fluxes which are representative of the region near the flux tower.