Interpretation of Flux-Profile Observations at ITCE (1976)

R. J. Francey CSIRO Division of Atmospheric Physics, Aspendale, Australia 3195

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J. R. Garratt CSIRO Division of Atmospheric Physics, Aspendale, Australia 3195

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Abstract

At an International Turbulence Comparison Experiment (ITCE) in Australia (1976), wind, temperature and humidity profiles, plus vertical fluxes of momentum, sensible heat and latent heat were measured for a limited range of unstable conditions, but with a wide variety of instrumentation.

Comparisons of like instruments, and of flux and profile measurements via the Monin-Obukhov similarity theory, have been used to assess systematic effects. The scatter about conventional flux-profile formulations varies with choice of stability parameter (z/L or Ri) and this also proves an effective means of identifying the source of the scatter. The cup anemometer results exhibit evidence of errors in calibration factors which are the major source of scatter in the unsmoothed measured gradients.

The limited stability range prevents unambiguous solution for all constants in the conventional flux-profile relationships. For momentum transfer, use of Ri as a stability parameter gives least sensitivity to error; adoption of a ΦM(Ri) of Pruitt et al. (1973) leads to kM = 0.33 ± 0.03, significantly below their value of 0.42. Adoption of the ΦM(z/L) of Businger et al. (1971) or Dyer (1974) leads to kM = 0.38 ± 0.04 (cf. their values of 0.35 and 0.41, respectively).

For sensible heat transfer values of kH are significantly lower than those of other workers, while for latent heat kW values similar to previous workers are obtained-this implies a kH < kW for ITCE 1976.

Abstract

At an International Turbulence Comparison Experiment (ITCE) in Australia (1976), wind, temperature and humidity profiles, plus vertical fluxes of momentum, sensible heat and latent heat were measured for a limited range of unstable conditions, but with a wide variety of instrumentation.

Comparisons of like instruments, and of flux and profile measurements via the Monin-Obukhov similarity theory, have been used to assess systematic effects. The scatter about conventional flux-profile formulations varies with choice of stability parameter (z/L or Ri) and this also proves an effective means of identifying the source of the scatter. The cup anemometer results exhibit evidence of errors in calibration factors which are the major source of scatter in the unsmoothed measured gradients.

The limited stability range prevents unambiguous solution for all constants in the conventional flux-profile relationships. For momentum transfer, use of Ri as a stability parameter gives least sensitivity to error; adoption of a ΦM(Ri) of Pruitt et al. (1973) leads to kM = 0.33 ± 0.03, significantly below their value of 0.42. Adoption of the ΦM(z/L) of Businger et al. (1971) or Dyer (1974) leads to kM = 0.38 ± 0.04 (cf. their values of 0.35 and 0.41, respectively).

For sensible heat transfer values of kH are significantly lower than those of other workers, while for latent heat kW values similar to previous workers are obtained-this implies a kH < kW for ITCE 1976.

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