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Laser Scintillation Measurements of the Temperature Spectrum in the Atmospheric Surface Layer

Rod FrehlichCooperative Institute for Research in the Environmental Sciences (CIRES)/NOAA, University of Colorado, Boulder, Colorado

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Abstract

The locally stationary temperature spectrum in the atmospheric surface layer is estimated using laser scintillation. The fluctuations of the parameters of the turbulence spectrum (the structure constant CT2 and inner scale l0) have a lognormal distribution. The average spectrum is calculated by averaging the locally stationary spectrum over these fluctuations. The average spectrum does not have a universal form. The fluctuations in the turbulence parameters produces a bias in measurements of the Obukhov-Corrsin constant and in estimates of energy dissipation rate ε based on average scintillation statistics. The performance of the scintillation technique and the accuracy of scintillation measurements of inner scale and structure constant are estimated using Monte Carlo simulation. One scintillation measurement can provide accurate estimates of the important turbulence parameters and the statistics of the fluctuations of these parameters. The scintillation estimates are true path-averaging estimates and do not require instrumental corrections for the high-frequency region nor the conversion of temporal statistics to spatial statistics.

Abstract

The locally stationary temperature spectrum in the atmospheric surface layer is estimated using laser scintillation. The fluctuations of the parameters of the turbulence spectrum (the structure constant CT2 and inner scale l0) have a lognormal distribution. The average spectrum is calculated by averaging the locally stationary spectrum over these fluctuations. The average spectrum does not have a universal form. The fluctuations in the turbulence parameters produces a bias in measurements of the Obukhov-Corrsin constant and in estimates of energy dissipation rate ε based on average scintillation statistics. The performance of the scintillation technique and the accuracy of scintillation measurements of inner scale and structure constant are estimated using Monte Carlo simulation. One scintillation measurement can provide accurate estimates of the important turbulence parameters and the statistics of the fluctuations of these parameters. The scintillation estimates are true path-averaging estimates and do not require instrumental corrections for the high-frequency region nor the conversion of temporal statistics to spatial statistics.

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