Estimating the components of the sensible heat budget of a tall forest canopy in complex terrain

Ultrasonic wind measurements, sonic temperature and air temperaturedata at two heights in the advection experiment MORE II were used to establisha complete budget of sensible heat including vertical advection, horizontal advec-tion and horizontal turbulent flux divergence. MORE II took place at the long-termCarbo-Europe IP site in Tharandt, Germany. During the growing period of 2003 threeadditional towers were established to measure all relevant parameters for an estima-tion of advective fluxes, primarily of CO2. Additionally, in relation to other advectionexperiments, a calculation of the horizontal turbulent flux divergence is proposed andthe relation of this flux to atmospheric stability and friction velocity is discussed. Inorder to obtain a complete budget, different scaling heights for horizontal advectionand horizontal turbulent flux divergence are tested. It is shown that neglecting advec-tive fluxes may lead to incorrect results. If advective fluxes are taken into account, thesensible heat budget based upon vertical turbulent flux and storage change only, isreduced by approximately 30%. Additional consideration of horizontal turbulent fluxdivergence would in turn add 5–10% to this sum (i.e., the sum of vertical turbulentflux plus storage change plus horizontal and vertical advection). In comparison withavailable energy horizontal advection is important at night whilst horizontal turbulentflux divergence is rather insignificant. Obviously, advective fluxes typically improvepoor nighttime energy budget closure and might change ecosystem respiration fluxesconsiderably.