Figure. 2.1 Upper figure: Wind speed measured 30 meter above flat homogeneous terrain in
Denmark from Troen and Petersen (1989). The data were obtained from a one-year time series
recorded with 16-Hz resolution. Each graph shows the measured wind speed over the time
period indicated. The number of data points in each graph is 1200; each averaged over 1/1200
of the time period indicated. The vertical axis is wind speed, 0-20 meter/sec. Lower figure:
Similar plot from Jensen and Busch (1982) here based on 1000 points per plot. The lack of fine
structure in the 10 sec plot is due to the onset of viscous dissipation at the highest frequencies
here, see discussion of spectra in the end of this section.