The variation in time of the third rotation angle (McMillen, 1988)

In June 2019 the first scientific article dedicated to the data of the MetAlp measurement campaign was released at the Alpe Veglia. In particular, the high-frequency data, acquired with the sonic anemometer, are studied in the first two months of measurement (27 September, 16 November 2018). With the article entitled "An Assessment of Coordinate Rotation Methods in Sonic Anemometer Measurements of Turbulent Fluxes over Complex Mountainous Terrain", we want to investigate how the different methods of analysis of the turbulence can affect their quality, and what is the technique that introduces the smallest error.

The article

An Assessment of Coordinate Rotation Methods in Sonic Anemometer Measurements of Turbulent Fluxes over Complex Mountainous Terrain

Authors: Alessio Golzio, Irene Maria Bollati, Silvia Ferrarese

Abstract

The measurement of turbulent fluxes in the atmospheric boundary layer is usually performed using fast anemometers and the Eddy Covariance technique. This method has been applied here and investigated in a complex mountainous terrain. A field campaign has recently been conducted at Alpe Veglia (the Central-Western Italian Alps, 1746 m a.s.l.) where both standard and micrometeorological data were collected. The measured values obtained from an ultrasonic anemometer were analysed using a filtering procedure and three different coordinate rotation procedures: Double (DR), Triple Rotation (TR) and Planar Fit (PF) on moving temporal windows of 30 and 60 min. A quality assessment was performed on the sensible heat and momentum fluxes and the results show that the measured turbulent fluxes at Alpe Veglia were of a medium-high quality level and rarely passed the stationary flow test. A comparison of the three coordinate procedures, using quality assessment and sensible heat flux standard deviations, revealed that DR and TR were comparable, with significant differences, mainly under low-wind conditions. The PF method failed to satisfy the physical requirement for the multiple planarity of the flow, due to the complexity of the mountainous terrain.

The meteorological variables measured in the first two month of campaign

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