Eddy correlation quick-course 1.Background 2.Raw signals Time series covariantie Spectra Footprint 3.Data processing angle of attack dependent calibration detrending rotation Frequency response corrections Schotanus Webb

Background of Eddy correlation 1.We want to measure the fluxes of sensible heat, latent heat (evaporation), carbon dioxide and methane 2.To measure them, we use the turbulent properties of the air 3.For example: during the day: temperaturehumidityCO2 highcolder driernormal 4 m24 oC17 g/kg360 ppm low warmer moisterdepleted 0.1 m25 oC18 g/kg355 ppm

Background of Eddy correlation 25 °C 18 g/kg H 2 O 355 ppm CO 2 25 °C 18 g/kg H 2 O 355 ppm CO 2 24 °C 17 g/kg H 2 O 360 ppm CO 2 17 g/kg 360 ppm 24 °C

Measurements at the Horstermeer

The raw signals

correlation w - T r = 0.55 r 2 = 0.30

covariance covariance = (w – w mean ) x (T – T mean ) or: when defining w’ = (w – w mean ) T’ = (T – T mean ) then covariance = w’T’

covariance w’T’ = 0.33 m/s K to calculate the energy content of this air stream we are actually interested in the covariance of H = w’ (ρ C p T)’ = (ρ– ρ mean ) Cp w’ T’ with ρ ~ 1.2 kg/m3 the air density and C p ~ J/kg the heat capacity of air But (fortunately) ρ does not correlate with w’T’, thus: H = ρ C p w’T’ = 1.2 * 1005 * 0.33 = 397 W/m2

covariance H = ρ C p w’T’ Similarly: LE = λ w’ρ v ’ = ρ λ w’q’ f co2 = w’ρ co2 ’

Angle of Attack Dependent Calibration Gash and Dolman, 2003 van der Molen, Gash and Elbers, 2004

Detrending

Other corrections rotation Frequency response corrections Schotanus

Webb corrections rotation Frequency response corrections Schotanus Webb