13 Jun 2022
13 Jun 2022
Status: this preprint is currently under review for the journal AMT.

The measurement of mean wind, variances and covariances from an instrumented mobile car in a rural environment

Stefan Miller and Mark Gordon Stefan Miller and Mark Gordon
  • Department of Earth and Space Science and Engineering, York University, Toronto ON, M3J 1P3, Canada

Abstract. On 20 and 22 Aug 2019, a small tripod was outfitted with a sonic anemometer and placed in a highway shoulder to compare with measurements made on an instrumented car as it travelled past the tripod. The rural measurement site in this investigation was selected so that the instrumented car travelled past many upwind surface obstructions and experienced the occasional passing vehicle. To obtain an accurate mean wind speed and mean wind direction on a moving car, it is necessary to correct for flow distortion and remove the vehicle speed from the measured velocity component parallel to vehicle motion (for straight-line motion). In this study, the velocity variances and turbulent fluxes measured by the car are calculated using two approaches: (1) eddy-covariance and (2) wavelet analysis. The results show that wavelet analysis can better resolve low frequency contributions, and this leads to a reduction in the horizontal velocity variances measured on the car, giving a better estimate for some measurement averages when compared to the tripod. A wavelet–based approach to remove the effects of sporadic passing traffic is developed and applied to a measurement period during which a heavy–duty truck passes in the opposite highway lane; removing the times with traffic in this measurement period gives approximately a 10 % reduction in the turbulent kinetic energy. The vertical velocity variance and vertical turbulent heat flux measured on the car are biased low compared to the tripod. This low bias may be related to a mismatch in the flux footprint of the car versus the tripod, or perhaps related to rapid flow distortion at the measurement location on the car. When random measurement uncertainty is considered, the vertical momentum flux is found to be consistent with the tripod in the 95 % confidence interval, and significantly different than zero for most measurement periods.

Stefan Miller and Mark Gordon

Status: open (until 19 Jul 2022)

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Stefan Miller and Mark Gordon

Stefan Miller and Mark Gordon


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Short summary
This research investigates the measurement of atmospheric turbulence using a low-cost instrumented car traveling at near-highway speeds that is impacted by upwind obstructions and other on-road traffic. We show our car design can successfully measure the mean flow and atmospheric turbulence near the surface. We outline a technique to isolate and remove the effects of sporadic passing traffic from car-measured velocity variances and discuss potential measurement uncertainties.