Turbulent Air Flow Measurements in the Surface Layer within a Deciduous Forest

抄録

Sensible heat flux is measured using the eddy-correlation method in a deciduous forest.
Estimates of sensible heat flux are found to compensate for most of the heat loss caused by negative net long wave radiation in the afternoon on the snow surface under calm conditions in mid winter. Twenty four hour total heat balance components show that the conductive heat flux from the snow cover occupies 87 to 100% of the net radiation. Sensible heat flux is found to be less than 6% of the net radiation, though it plays an important role in compensating for the daily maximum of difference between air temperature and snow surface temperature during the first 2-3 hours after the net long wave radiation turns negative at 14:00. The Ri number which indicates the criterion for stability achieves a maximum value of 0.1 at 1.5:00-19:00. The turbulent air flow on the snow surface is characterized as intermittent and low turbulent under stable conditions. The sensible heat flux fits the one obtained under strong stable conditions, by using the empirical constant K in the empirical equation known as the bulk method. Power spectra for the vertical, streamwise wind velocity and temperature computed by the Maximum Entropy Method show low spectral density under strong stable conditions.