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Open AccessArticle

Spatial Variability of the Lower Atmospheric Boundary Layer over Hilly Terrain as Observed with an RPAS

1
Department of Physics, University of the Balearic Islands, 07122 Palma, Mallorca, Spain
2
Technische Hochschule Ostwestfalen-Lippe, An der Wilhelmshöhe 44, D-37671 Höxter, Germany
3
Meteorological and Hydrological Service (DHMZ), 10000 Zagreb, Croatia
4
NorthWest Research Associates, Corvallis, OR 97330, USA
*
Author to whom correspondence should be addressed.
Atmosphere 2019, 10(11), 715; https://doi.org/10.3390/atmos10110715
Received: 28 October 2019 / Accepted: 12 November 2019 / Published: 15 November 2019
(This article belongs to the Special Issue Measurement of Atmospheric Composition by Unmanned Aerial Systems)
The operation of a Remotely Piloted Aircraft System (RPAS) over a hilly area in northern Germany allows inspection of the variability of the profiles of temperature, humidity, and wind speed next to a small hill. Four cases in nearly stationary conditions are analyzed. Two events are windy, one overcast and the other with clear skies, whereas the two other cases have weak winds, one overcast, and one with clear skies and dissipating mist. The profiles are made at five locations surrounding the hill, separated by a distance from each other of 5 km at most, sampling up to 130 m above the ground. The average profiles and their standard deviations indicate that the variability in the windy cases is approximately constant with height, likely linked to the turbulent flow itself, whereas, for the weak wind cases, the variability diminishes with height, and it is probably linked to the surface variability. The variability between soundings is large. The computation of the root mean square error with respect to the average of the soundings for each case shows that the site closest to the average is the one over open terrain and low vegetation, whereas the site in the forest is the farthest from average. Comparison with the profiles to the nearest grid point of the European Centre for Medium-Range Weather Forecasts (ECMWF) model shows that the closest values are provided by the average of the soundings and by the site closest to the average. Despite the small dataset collected during this exercise, the methodology developed here can be used for more cases and locations with the aim to characterize better the local variability in the lower atmosphere. In this sense, a non-dimensional heterogeneity index is proposed to quantify the topographically and thermally induced variability in complex terrain. View Full-Text
Keywords: RPAS; atmospheric profiles; hilly terrain; spatial variability; ECMWF; thermal and topographical heterogeneity index RPAS; atmospheric profiles; hilly terrain; spatial variability; ECMWF; thermal and topographical heterogeneity index
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Cuxart, J.; Wrenger, B.; Matjacic, B.; Mahrt, L. Spatial Variability of the Lower Atmospheric Boundary Layer over Hilly Terrain as Observed with an RPAS. Atmosphere 2019, 10, 715.

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