Preprints
https://doi.org/10.5194/amt-2024-47
https://doi.org/10.5194/amt-2024-47
10 Apr 2024
 | 10 Apr 2024
Status: a revised version of this preprint is currently under review for the journal AMT.

Uncertainties in temperature statistics and fluxes determined by sonic anemometer due to wind-induced vibrations of mounting arms

Zhongming Gao, Heping Liu, Dan Li, Bai Yang, Von Walden, Lei Li, and Ivan Bogoev

Abstract. Accurate air temperature measurements are essential in eddy covariance systems, not only for determining sensible heat flux but also for applying the density effect corrections (DEC) to water vapor and CO2 fluxes. However, the influence of wind-induced vibrations of mounting structures on temperature fluctuations remains a subject of investigation. This study examines 30-min average temperature variances and fluxes using eddy covariance systems, combining Campbell Scientific Anemometer Thermometry (CSAT3B) with closely co-located fine-wire thermocouples alongside LI-COR CO2/H2O gas analyzers at multiple heights above a sagebrush ecosystem. The variances of sonic temperature after humidity corrections (Ts) and sensible heat fluxes derived from are underestimated (e.g., by approximately 5 % for temperature variances and 4 % for sensible heat fluxes at 40.2 m, respectively) as compared with those measured by a fine-wire thermocouple (Tc). Spectral analysis illustrates that these underestimated variances and fluxes are caused by the lower energy levels in the Ts spectra than the Tc spectra in the low frequency range (natural frequency < 0.02 Hz). This underestimated Ts spectra in the low frequency range become more pronounced with increasing as wind speeds, especially when wind speed exceeds 10 m s-1. Moreover, the underestimated temperature variances and fluxes cause overestimated water vapor and CO2 fluxes through DEC. Our analysis suggests that these underestimations when using Ts are likely due to wind-induced vibrations affecting the tower and mounting arms, altering the time of flight of ultrasonic signals along three sonic measurement paths. This study underscores the importance of further investigations to develop corrections for these errors.

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Zhongming Gao, Heping Liu, Dan Li, Bai Yang, Von Walden, Lei Li, and Ivan Bogoev

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2024-47', Anonymous Referee #1, 30 Apr 2024
    • AC1: 'Reply on RC1', Zhongming Gao, 16 May 2024
  • RC2: 'Comment on amt-2024-47', Anonymous Referee #2, 03 May 2024
    • AC2: 'Reply on RC2', Zhongming Gao, 16 May 2024
Zhongming Gao, Heping Liu, Dan Li, Bai Yang, Von Walden, Lei Li, and Ivan Bogoev
Zhongming Gao, Heping Liu, Dan Li, Bai Yang, Von Walden, Lei Li, and Ivan Bogoev

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Short summary
Using data collected from three levels of a 62-m tower, we found that both the temperature variances and sensible heat flux obtained from sonic anemometers are consistently lower, by a few percentages, compared to those from fine-wire thermocouples.