A SIMPLE FORMULA FOR ATTENUATION OF EDDY FLUXES MEASURED WITH FIRST-ORDER-RESPONSE SCALAR SENSORS

A simple formula, (1 + (2 pi f(m) tau(c))(alpha))(-1), is proposed to estimate the attenuation of a scalar flux measurement made by eddy-cor relation using a fast-response anemometer and a linear, first-order-re sponse scalar sensor with a characteristic time constant tau(c). In th is formula, alpha = 7/8 for neutral and unstable stratification within the surface-flux layer and alpha = 1 both within the convective bound ary layer (CBL) and for stable stratification in the surface layer. f( m) is the frequency of the peak of the logarithmic cospectrum and can be estimated from f(m) = n(m) (u) over bar/z, where z is the measureme nt height and (u) over bar is the wind speed at that height. The dimen sionless frequency at the cospectral maximum n(m) is estimated here fr om observations of its behavior as a function of atmospheric stability , z/L within the surface layer or z/z(i) within the CBL, where L is th e Obukhov stability length and z(i) is the depth ofthe CBL. The predic ted dependence of flux attenuation on measurement height is discussed.