An Experimental Study of Scalar Turbulence and Advective Exchange

We present methodology, data, and analysis of horizontal CO2 advection at the Wind River Canopy Crane AmeriFlux site. The crane is located in a Pacific Northwest Old-growth Forest with trees up to 500 years old and 65 meters tall. The low elevation, Douglas fir/Western hemlock forest structure is complex, with large amounts of woody debris on the forest floor and a diverse understory. Data were collected using a 3-dimensional CO2/H2O profile system with a total of 15 intakes distributed on the tower, throughout the canopy, and in the understory. Additional data were acquired using permanent eddy covariance stations at 2.5 meters, and an identical system measuring total ecosystem exchange at a height of 70 meters. Supplementary micrometeorological data (½ hour mean wind velocity, wind direction, air temperature, and humidity) were collected at 6 heights (2 m, 10 m, 20 m, 40 m, 60 m, 70 m) along the tower. Advection was calculated using horizontal concentration differences and mean wind velocity. Data show that advection can account for 5-20% of the above canopy, ecosystem exchange as measured by eddy-covariance. Estimates of NEE including advection were consistent with estimates of NEE using more the traditional u* correction methodology, although the advection adjustments yielded stronger sink estimates than the u* correction method.