Fig. 12
(a) Cospectra based on the mean of all sequential 10-minute integration periods from the 10 m tower sensor on two days, 3 and 8 December, 2019, when Fs was predominantly positive (cyan/blue) and negative (yellow/red). Cyan and yellow are data prior to the correction while blue and red are after; at frequencies where only the latter is visible, the spectra are identical. Dashed lines are −8/3 reference, here plotted using a linear y-scale. For reference, data from a nearby Metek USA-1 (that did not contain the artefact) that was mounted to the mast is also shown (greens). The mast height was 4 m on 3 December and was raised from 4 m to 18 m on 8 December. The peak being shifted to higher frequencies at the 4 m height is consistent with the sensor being closer to the surface than the 10 m tower sensor. The data after the mast was raised (light green) show the shift toward peaking at lower frequencies, more similar to the 10 m sensor. (b) Coefficient, β, as a function of frequency under well-mixed (windy and isothermal) conditions. Reds are sensors mounted on the tower and blues are ASFS stations. The number of included times ranged per sensor from N = 3627 (ASFS-40) to N = 7055 (10 m tower).
