Nocturnal CO_2 exchange over a tall forest canopy associated with intermittent low-level jet activity

摘要

Nocturnal eddy-covariance carbon dioxide fluxes have uncertainties arising from non-stationary atmospheric processes. Low-level jets (LLJ) are one of the prominent nocturnal boundary-layer phenomena observed over non-mountainous terrain, and are capable of generating shear and turbulence close to the ground. The influence of intermittent LLJ activity on nocturnal carbon dioxide exchange measurements is investigated using wind profile observations and eddy-covariance flux measurements over a tall forest canopy. Results suggest that the buildup and venting of CO_2 are closely associated with LLJ activity during the night. Of significance in quantifying nocturnal fluxes, this paper demonstrates how low-level jet activity introduces sporadic coupling between the canopy and the atmosphere.