In-situ measurements of wind and turbulence by a motor glider in the Andes

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  • 1 Oberpfaffenhofen, Germany
  • 2 Quo Vadis, Serres, France
  • 3 Met Office, Exeter, United Kingdom
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Abstract

A Stemme S10-VT motor glider was equipped with a newly developed sensor suite consisting of a five-hole probe, inertial navigation and global navigation satellite system, two temperature sensors and a humidity sensor. By design, the system provides three-dimensional wind vector data that enable the analysis of atmospheric motion scales up to a temporal resolution of 10 Hz. We give a description of components and installation of the system, its calibration and performance. The accuracy for the measurement of the wind vector is estimated to be of the order of 0.5 ms−1. As part of the SouthTRAC field campaign, 30 research flights were performed from September 2019 to January 2020. We present statistical analysis of the observations, discriminating pure motor flights from soaring flights in the lee waves of the Andes. We present histograms of flight altitude, airspeed, wind speed and direction, temperature and relative humidity to document the atmospheric conditions. Probability density functions of vertical air velocity, turbulence kinetic energy (TKE) and dissipation rate complete the statistical analysis. Altogether, 41% of the flights are in weak, 14% in moderate, and 0.4% in strong mountain wave conditions according to thresholds for the measured vertical air velocity. As an exemplary case study, we compare measurements on 11 September 2019 to a high-resolution numerical weather prediction model. The case study provides a meaningful example of how data from soaring flights might be utilized for model validation on the mesoscale and within the troposphere.

Corresponding author: Norman Wildmann, norman.wildmann@dlr.de

Abstract

A Stemme S10-VT motor glider was equipped with a newly developed sensor suite consisting of a five-hole probe, inertial navigation and global navigation satellite system, two temperature sensors and a humidity sensor. By design, the system provides three-dimensional wind vector data that enable the analysis of atmospheric motion scales up to a temporal resolution of 10 Hz. We give a description of components and installation of the system, its calibration and performance. The accuracy for the measurement of the wind vector is estimated to be of the order of 0.5 ms−1. As part of the SouthTRAC field campaign, 30 research flights were performed from September 2019 to January 2020. We present statistical analysis of the observations, discriminating pure motor flights from soaring flights in the lee waves of the Andes. We present histograms of flight altitude, airspeed, wind speed and direction, temperature and relative humidity to document the atmospheric conditions. Probability density functions of vertical air velocity, turbulence kinetic energy (TKE) and dissipation rate complete the statistical analysis. Altogether, 41% of the flights are in weak, 14% in moderate, and 0.4% in strong mountain wave conditions according to thresholds for the measured vertical air velocity. As an exemplary case study, we compare measurements on 11 September 2019 to a high-resolution numerical weather prediction model. The case study provides a meaningful example of how data from soaring flights might be utilized for model validation on the mesoscale and within the troposphere.

Corresponding author: Norman Wildmann, norman.wildmann@dlr.de
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