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

Alessio Golzio,Silvia Ferrarese,Irene Maria Bollati

doi:10.3390/atmos10060324

Alessio Golzio, Silvia Ferrarese + Show 1 more

Open Access

https://doi.org/10.3390/atmos10060324

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Journal: Atmosphere	Publication Date: Jun 13, 2019
Citations: 12	License type: CC BY 4.0

Affiliation: University of Milan, University of Turin

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.

Highlights

High mountain environments are rapidly changing as a result of the ongoing climate changes, which are quickly modifying landscapes and ecological components, such as vegetation, including flora and fauna, as well as human fruition and geoheritage [1]
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
The Planar Fit (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

Summary

Introduction

High mountain environments are rapidly changing as a result of the ongoing climate changes, which are quickly modifying landscapes and ecological components, such as vegetation, including flora and fauna, as well as human fruition and geoheritage [1]. Glacier shrinkage is accompanied by a widening of the proglacial areas ([2] and reference ), while some debris-free glaciers are transforming into debris covered ones and a transition is occurring from glacial to paraglacial systems [3]. Debris covered glaciers are progressively being colonized by supraglacial grass, shrubs and trees [4] and new biological successions are emerging [5]. The nearest atmospheric layer to the surface is the Atmospheric Boundary Layer (ABL), where exchanges of momentum, mass and energy with the surface take place. Some authors have defined a specific ABL as a Mountain Boundary

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