An Assessment of Coordinate Rotation Methods in Sonic Anemometer Measurements of Turbulent Fluxes over Complex Mountainous Terrain
Abstract
:1. Introduction
2. Materials and Methods
2.1. Description of the Experiment
2.2. Methods
2.2.1. Ultrasonic Anemometer Data Processing
- Control of the instrumental electronic range, applying the following thresholds: ±30 ms for the three components of the wind velocities u, v, w; 290 ms to 370 ms for the speed of sound c; 700 to 1100 for atmospheric pressure p.
- First, the despiking step over u, v, w, c, using an algorithm that replaces single spikes with the previous non-spike value. The block average and standard deviation () were used in the despike algorithm, and spikes were defined as a point at a distance of more than from the window average. Here, we fixed . Bursts were then removed using a linear regression of the neighbouring points. A burst is a step in instantaneous data that is higher than a fixed threshold (here ) with respect to the previous point. It should not exceed a number of consecutive points (four in this work) because, in this case, the data could represent physical behaviour of the eddies.
- Correction of the speed of sound. A previous calibration [22] was used.
- Calculation of sonic temperature from the speed of sound c with Equation (1)
- Control of the extreme values of using Equation (2)Whenever a value fell outside this range, the entire instantaneous measurement record was nullified (u, v, w, ).
- Second despiking step with a threshold over u, v, w and ; burst control was not applied in this phase.
- Coordinate rotation calculation; all the data were moved from the anemometer reference system to a streamline reference system, according to the three rotation methods: Double Rotation (DR), Triple Rotation (TR) or Planar Fit (PF). The applied methods rotate the coordinate system, as explained in [9,10,11,12,14,23,24] and in the following Section 2.2.2.
- Final control of the valid physical range of the vertical wind speed < 5 ms. In this case, the w range is more restrictive than step 1.
2.2.2. Coordinate Rotation Methods
2.2.3. Turbulent Flux Calculation
2.2.4. Flux Quality Control Assessment
- Physical range control of the SH flux;
- Skewness and kurtosis limit control;
- Uncertainty and stationarity control.
3. Results
3.1. Overview of the Standard Meteorological Data
3.2. Ultrasonic Anemometer Data Analysis
3.2.1. Double Rotation
3.2.2. Triple Rotation
3.2.3. Planar Fit
3.2.4. Comparison of the Sensible Heat Flux Standard Deviations
4. Discussion
5. Conclusions
- The PF method was hard to apply in Alpe Veglia complex terrain because the flow was not planar; instead, the wind flow was on a three-dimensional surface. As suggested by Nadeau et al. [31], it could be useful to apply the directional planar fit.
- The TR method has a much smaller third rotation angle than the threshold suggested by McMillen [10]. This suggests that the TR method could be useful, especially for low wind cases that were mostly experienced at the Alpe Veglia site.
- Two different procedures have been applied to define the trustworthiness of SH flux calculated by the three coordinate rotation methods: the quality control procedure (Section 2.2.4) and the SH standard deviation (Section 3.2.4). Considering the high-quality class, the DR method obtained the best results in the 30 and 60 min integration interval ( and Table 2), whereas, considering the merged classes medium and high, the best result is for the TR method ( and ). Considering the standard deviation on SH, and a threshold of 5 Wm, the best result is given by the TR method, while PF performs the worst. The biggest difference between the two methods arose in the PF, which obtained a high rating with the quality assessment, but very high standard deviations were computed; this reflects the senselessness of the detected PF-plane.
- The stationarity test (or steady-test) is harder to obtain at Alpe Veglia, and this could be linked to the applied test or to the constitution of the turbulence in the Alpe Veglia location.
Author Contributions
Funding
- The Department of Earth Sciences, Università degli Studi di Milano, Piano di sostegno alla ricerca 2015–2017: Linea 2, azione A anno 2017 (PSR2017_AZERBONI);
- The Department of Environmental Science and Policy, Università degli Studi di Milano, PhD course in Environmental Sciences funds;
- The Department of Physics, Università degli Studi di Torino, Fondo per la ricerca scientifica locale 2016–2017.
Acknowledgments
Conflicts of Interest
References
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Instrument | Make and Model | Ground and Mast Distance (±0.01 m) | Range | N Direction of the Instrument |
---|---|---|---|---|
Ultrasonic anemometer | Gill, Solent R2-research | ; | ±30 ms 290 ms to 370 ms | |
Anemometer and wind vane | Siap+Micros, SVDV | ; | 0 ms to 60 ms 0 to 359 | |
Thermometer | Thermocouple type K | ; | −200 to 1260 | |
Snow-meter | HC-SR04 | ; | 0 to 5 | |
Radiometer | Eppley, PSP | ; | 0 Wm to 2000 Wm | |
Barometer | Siap, TBAR | ; | 700 to 1100 | |
Inclinometers | HLPlanar Technik, NS-5/PI | ; |
Variable | Quality Level | DR | TR | PF | |||
---|---|---|---|---|---|---|---|
30 min | 60 min | 30 min | 60 min | 30 min | 60 min | ||
zero | 8.46% | 4.98% | 7.99% | 4.64% | 10.96% | 6.87% | |
low | 0.04% | 0.11% | 0.04% | 0.11% | 0.04% | 0.15% | |
medium | 30.32% | 38.29% | 35.47% | 46.03% | 31.37% | 39.68% | |
high A | 61.18% | 56.58% | 56.46% | 52.18% | 57.62% | 53.25% | |
high B | 0.00% | 0.04% | 0.04% | 0.04% | 0.00% | 0.04% | |
high C | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | |
zero | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | |
low | 0.04% | 0.04% | 0.09% | 0.04% | 0.04% | 0.09% | |
medium | 4.93% | 5.18% | 15.87% | 14.54% | 1.85% | 1.87% | |
high A | 94.90% | 94.67% | 83.91% | 85.27% | 97.83% | 97.90% | |
high B | 0.02% | 0.02% | 0.11% | 0.15% | 0.00% | 0.00% | |
high C | 0.11% | 0.09% | 0.02% | 0.00% | 0.28% | 0.25% | |
zero | 0.00% | 0.00% | 0.00% | 0.00% | |||
low | 0.02% | 0.02% | 0.04% | 0.09% | |||
medium | 4.69% | 4.60% | 1.21% | 1.10% | |||
high A | 95.09% | 95.28% | 98.62% | 98.80% | |||
high B | 0.00% | 0.00% | 0.00% | 0.00% | |||
high C | 0.19% | 0.11% | 0.13% | 0.02% |
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Golzio, A.; Bollati, I.M.; Ferrarese, S. An Assessment of Coordinate Rotation Methods in Sonic Anemometer Measurements of Turbulent Fluxes over Complex Mountainous Terrain. Atmosphere 2019, 10, 324. https://doi.org/10.3390/atmos10060324
Golzio A, Bollati IM, Ferrarese S. An Assessment of Coordinate Rotation Methods in Sonic Anemometer Measurements of Turbulent Fluxes over Complex Mountainous Terrain. Atmosphere. 2019; 10(6):324. https://doi.org/10.3390/atmos10060324
Chicago/Turabian StyleGolzio, Alessio, Irene Maria Bollati, and Silvia Ferrarese. 2019. "An Assessment of Coordinate Rotation Methods in Sonic Anemometer Measurements of Turbulent Fluxes over Complex Mountainous Terrain" Atmosphere 10, no. 6: 324. https://doi.org/10.3390/atmos10060324
APA StyleGolzio, A., Bollati, I. M., & Ferrarese, S. (2019). An Assessment of Coordinate Rotation Methods in Sonic Anemometer Measurements of Turbulent Fluxes over Complex Mountainous Terrain. Atmosphere, 10(6), 324. https://doi.org/10.3390/atmos10060324