Using sonic anemometer temperature to measure sensible heat flux in strong winds
Sonic anemometers simultaneously measure the turbulent fluctuations of vertical wind (<i>w</i>') and sonic temperature (<i>T</i><sub>s</sub>'), and are commonly used to measure sensible heat flux (<i...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2012-09-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | http://www.atmos-meas-tech.net/5/2095/2012/amt-5-2095-2012.pdf |
| _version_ | 1818248166744522752 |
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| author | S. P. Burns T. W. Horst L. Jacobsen P. D. Blanken R. K. Monson |
| author_facet | S. P. Burns T. W. Horst L. Jacobsen P. D. Blanken R. K. Monson |
| author_sort | S. P. Burns |
| collection | DOAJ |
| description | Sonic anemometers simultaneously measure the turbulent fluctuations of vertical wind (<i>w</i>') and sonic temperature (<i>T</i><sub>s</sub>'), and are commonly used to measure sensible heat flux (<i>H</i>). Our study examines 30-min heat fluxes measured with a Campbell Scientific CSAT3 sonic anemometer above a subalpine forest. We compared <i>H</i> calculated with <i>T</i><sub>s</sub> to <i>H</i> calculated with a co-located thermocouple and found that, for horizontal wind speed (<i>U</i>) less than 8 m s<sup>−1</sup>, the agreement was around ±30 W m<sup>−2</sup>. However, for <i>U</i> &asymp; 8 m s<sup>−1</sup>, the CSAT <i>H</i> had a generally positive deviation from <i>H</i> calculated with the thermocouple, reaching a maximum difference of ≈250 W m<sup>−2</sup> at <i>U</i> ≈ 18 m s<sup>−1</sup>. With version 4 of the CSAT firmware, we found significant underestimation of the speed of sound and thus <i>T</i><sub>s</sub> in high winds (due to a delayed detection of the sonic pulse), which resulted in the large CSAT heat flux errors. Although this <i>T</i><sub>s</sub> error is qualitatively similar to the well-known fundamental correction for the crosswind component, it is quantitatively different and directly related to the firmware estimation of the pulse arrival time. For a CSAT running version 3 of the firmware, there does not appear to be a significant underestimation of <i>T</i><sub>s</sub>; however, a <i>T</i><sub>s</sub> error similar to that of version 4 may occur if the CSAT is sufficiently out of calibration. An empirical correction to the CSAT heat flux that is consistent with our conceptual understanding of the <i>T</i><sub>s</sub> error is presented. Within a broader context, the surface energy balance is used to evaluate the heat flux measurements, and the usefulness of side-by-side instrument comparisons is discussed. |
| first_indexed | 2024-12-12T15:16:17Z |
| format | Article |
| id | doaj.art-08962c423a904be4976d62d0f2e4ab27 |
| institution | Directory Open Access Journal |
| issn | 1867-1381 1867-8548 |
| language | English |
| last_indexed | 2024-12-12T15:16:17Z |
| publishDate | 2012-09-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Measurement Techniques |
| spelling | doaj.art-08962c423a904be4976d62d0f2e4ab272022-12-22T00:20:29ZengCopernicus PublicationsAtmospheric Measurement Techniques1867-13811867-85482012-09-01592095211110.5194/amt-5-2095-2012Using sonic anemometer temperature to measure sensible heat flux in strong windsS. P. BurnsT. W. HorstL. JacobsenP. D. BlankenR. K. MonsonSonic anemometers simultaneously measure the turbulent fluctuations of vertical wind (<i>w</i>') and sonic temperature (<i>T</i><sub>s</sub>'), and are commonly used to measure sensible heat flux (<i>H</i>). Our study examines 30-min heat fluxes measured with a Campbell Scientific CSAT3 sonic anemometer above a subalpine forest. We compared <i>H</i> calculated with <i>T</i><sub>s</sub> to <i>H</i> calculated with a co-located thermocouple and found that, for horizontal wind speed (<i>U</i>) less than 8 m s<sup>−1</sup>, the agreement was around ±30 W m<sup>−2</sup>. However, for <i>U</i> &asymp; 8 m s<sup>−1</sup>, the CSAT <i>H</i> had a generally positive deviation from <i>H</i> calculated with the thermocouple, reaching a maximum difference of ≈250 W m<sup>−2</sup> at <i>U</i> ≈ 18 m s<sup>−1</sup>. With version 4 of the CSAT firmware, we found significant underestimation of the speed of sound and thus <i>T</i><sub>s</sub> in high winds (due to a delayed detection of the sonic pulse), which resulted in the large CSAT heat flux errors. Although this <i>T</i><sub>s</sub> error is qualitatively similar to the well-known fundamental correction for the crosswind component, it is quantitatively different and directly related to the firmware estimation of the pulse arrival time. For a CSAT running version 3 of the firmware, there does not appear to be a significant underestimation of <i>T</i><sub>s</sub>; however, a <i>T</i><sub>s</sub> error similar to that of version 4 may occur if the CSAT is sufficiently out of calibration. An empirical correction to the CSAT heat flux that is consistent with our conceptual understanding of the <i>T</i><sub>s</sub> error is presented. Within a broader context, the surface energy balance is used to evaluate the heat flux measurements, and the usefulness of side-by-side instrument comparisons is discussed.http://www.atmos-meas-tech.net/5/2095/2012/amt-5-2095-2012.pdf |
| spellingShingle | S. P. Burns T. W. Horst L. Jacobsen P. D. Blanken R. K. Monson Using sonic anemometer temperature to measure sensible heat flux in strong winds Atmospheric Measurement Techniques |
| title | Using sonic anemometer temperature to measure sensible heat flux in strong winds |
| title_full | Using sonic anemometer temperature to measure sensible heat flux in strong winds |
| title_fullStr | Using sonic anemometer temperature to measure sensible heat flux in strong winds |
| title_full_unstemmed | Using sonic anemometer temperature to measure sensible heat flux in strong winds |
| title_short | Using sonic anemometer temperature to measure sensible heat flux in strong winds |
| title_sort | using sonic anemometer temperature to measure sensible heat flux in strong winds |
| url | http://www.atmos-meas-tech.net/5/2095/2012/amt-5-2095-2012.pdf |
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