Observations of the altitude dependence of the logarithmic width of the distribution of the refractive-index structure parameter in the convective boundary layer

In high-Reynolds number turbulence, energy dissipation rates and structure parameters often show a lognormal distribution. According to Kolmogorov's (1962) refined turbulence theory, the logarithmic width of the lognormal distribution increases with Reynolds number, Re. In the convective boundary layer, Re depends on the altitude because the integral length scales depend on altitude.

The US Army's FMCW radar that used to be deployed at White Sands Missile Range, N.M. (now deployed at the US Army Dugway Proving Ground, UT), was operated during the three-week long Profiler-HELIPOD Intercomparison Experiment (PHELIX) at Vandenberg AFB at the Pacific coast near Santa Maria, CA, in Nov. 1997. The FMCW radar sampled the refractive-index structure parameter, C_n², every 13 s at a vertical resolution of down to 2 m. The logarithmic width of the measured histogram of C_n² depends on altitude, as expected. The altitude dependence of histograms of C_n² observed with the FMCW are compared with the altitude dependence of histograms of structure parameters and energy dissipation rates obtained from collocated in situ measurements of the helicopter-borne turbulence instrument HELIPOD.