Flux measurements, flux-estimation techniques, and fine-scale turbulence measurements in the unstable surface layer over land.

Abstract

J.C. Wyngaard NOAA, U.S.A. An AFCRL-UCSD joint experiment in Minnesota in 1973 has provided a comparison of direct and indirect measurements of the surface-layer fluxes of momentum, heat and moisture under unstable conditions. The direct momentum and heat flux measurements of the two groups agreed well, and also agreed well with values inferred by the direct dissipation technique. The moisture flux estimates from the inertial-dissipation technique also agreed well with the directly measured values. Several of the important terms in the budgets of turbulent kinetic energy and turbulent scalar variances were evaluated directly. The imbalance (or pressure transport) term in the energy budget was estimated and the ratio of the imbalance term to the dissipation term determined from the present experiment agrees well with the Kansas results. The dissipation rate of temperature variance exceeded its production rate, in contrast with the Kansas results, implying an imbalanced temperature variance budget. Several possible contributors to this imbalance are discussed. The one-dimensional spectra of the temperature and streamwise velocity fluctuations are presented in Kolmogorov normalized form. Spectral moments to fourth order are shown to agree with earlier results. Values of the universal velocity and temperature spectral constants of ALPHASUP1 0.50+ or !0.02 and BETA 0.45+ or !0.02 were obtained. (A)