Turbulent dissipation rate in the boundary layer via UHF wind profiler Doppler spectral width measurements

The study is focused on the retrieval and validation of the turbulent kinetic energy dissipation rate epsilon from spectral width measurements made by a UHF wind profiler in the convective atmospheric boundary layer. The possibility to deduce epsilon, which is one of the most important parameters for boundary-layer study and monitoring, from Doppler radar spectral width measurements has a firm theoretical basis established by numerous earlier works. However, the major drawback of this approach lies in various meteorological and instrumental sources of non-turbulent spectral width broadening which have to be recognised and accounted for. In the first part of the study, the theoretical background of the epsilon retrieval is detailed and all possible causes of spectral broadening are listed and evaluated. In the second part, the method is applied to four days of UHF diurnal boundary-layer observations, collected during the TRAC-98 experiment, for which in situ aircraft epsilon measurements were available. Comparison between radar-retrieved epsilon and in situ aircraft measurements yields a fairly good agreement with a linear correlation coefficient of about 0.9 and a residual bias less than 2 x 10(-)4 m(2) s(-3). The analysis of epsilon derived from vertical and off-zenith observation leads to the recommendation, that in the boundary layer, where the wind is usually moderate, data collected by off-zenith beams should be used. Indeed, the measurement of the vertical spectral width, less affected by the large-scale broadening factor, can still be altered by the ground clutter removal.