TY - JOUR

T1 - On the Discrepancy in Simultaneous Observations of the Structure Parameter of Temperature Using Scintillometers and Unmanned Aircraft

AU - Braam, Miranda

AU - Beyrich, Frank

AU - Bange, Jens

AU - Platis, Andreas

AU - Martin, Sabrina

AU - Maronga, Björn

AU - Moene, Arnold F.

N1 - Funding Information: The LITFASS-2009 and LITFASS-2010 experiment were performed as part of the research project "Turbulent structure parameters over heterogeneous terrain—implications for the interpretation of scintillometer data". This project was funded by the German Science Foundation (Deutsche Forschungsgemeinschaft, DFG) through grants BA1988/9-1, BE2044/3-1, RA617/20-1, and by the Dutch Science Foundation (Nederlandse Organisatie voor Wetenschappelijk Onderzoek, NWO) through grant DN76-274. The data analysis and the additional LES sensitivity study have been supported financially by DFG through grant BE2044/3-3 and RA617/20-3. All LES runs were performed on the Cray XC30 at The North-German Supercomputing Alliance (HLRN), Hannover/Berlin. The discussions with Aline van den Kroonenberg (Scintec) and Oscar Hartogensis (Wageningen University) and the comments of Bram van Kesteren (Deutscher Wetterdienst) and Bert Holtslag (Wageningen University) on an early version of the manuscript were very helpful. Finally, that would like to thank the three anonymous reviewers for their constructive comments that helped to improve the paper.

PY - 2016/2

Y1 - 2016/2

N2 - We elaborate on the preliminary results presented in Beyrich et al. (in Boundary-Layer Meteorol 144:83–112, 2012), who compared the structure parameter of temperature (CT2) obtained with the unmanned meteorological mini aerial vehicle (M2 AV) versus CT2 obtained with two large-aperture scintillometers (LASs) for a limited dataset from one single experiment (LITFASS-2009). They found that CT2 obtained from the M2 AV data is significantly larger than that obtained from the LAS data. We investigate if similar differences can be found for the flights on the other six days during LITFASS-2009 and LITFASS-2010, and whether these differences can be reduced or explained through a more elaborate processing of both the LAS data and the M2 AV data. This processing includes different corrections and measures to reduce the differences between the spatial and temporal averaging of the datasets. We conclude that the differences reported in Beyrich et al. can be found for other days as well. For the LAS-derived values the additional processing steps that have the largest effect are the saturation correction and the humidity correction. For the M2 AV-derived values the most important step is the application of the scintillometer path-weighting function. Using the true air speed of the M2 AV to convert from a temporal to a spatial structure function rather than the ground speed (as in Beyrich et al.) does not change the mean discrepancy, but it does affect CT2 values for individual flights. To investigate whether C2T derived from the M2 AV data depends on the fact that the underlying temperature dataset combines spatial and temporal sampling, we used large-eddy simulation data to analyze CT2 from virtual flights with different mean ground speeds. This analysis shows that CT2 does only slightly depends on the true air speed when averaged over many flights.

AB - We elaborate on the preliminary results presented in Beyrich et al. (in Boundary-Layer Meteorol 144:83–112, 2012), who compared the structure parameter of temperature (CT2) obtained with the unmanned meteorological mini aerial vehicle (M2 AV) versus CT2 obtained with two large-aperture scintillometers (LASs) for a limited dataset from one single experiment (LITFASS-2009). They found that CT2 obtained from the M2 AV data is significantly larger than that obtained from the LAS data. We investigate if similar differences can be found for the flights on the other six days during LITFASS-2009 and LITFASS-2010, and whether these differences can be reduced or explained through a more elaborate processing of both the LAS data and the M2 AV data. This processing includes different corrections and measures to reduce the differences between the spatial and temporal averaging of the datasets. We conclude that the differences reported in Beyrich et al. can be found for other days as well. For the LAS-derived values the additional processing steps that have the largest effect are the saturation correction and the humidity correction. For the M2 AV-derived values the most important step is the application of the scintillometer path-weighting function. Using the true air speed of the M2 AV to convert from a temporal to a spatial structure function rather than the ground speed (as in Beyrich et al.) does not change the mean discrepancy, but it does affect CT2 values for individual flights. To investigate whether C2T derived from the M2 AV data depends on the fact that the underlying temperature dataset combines spatial and temporal sampling, we used large-eddy simulation data to analyze CT2 from virtual flights with different mean ground speeds. This analysis shows that CT2 does only slightly depends on the true air speed when averaged over many flights.

KW - Airborne measurements

KW - Large-eddy simulation

KW - LITFASS experiment

KW - Scintillometer measurements

KW - Sonic anemometer measurements

KW - Temperature structure parameter

UR - http://www.scopus.com/inward/record.url?scp=84954369951&partnerID=8YFLogxK

U2 - 10.1007/s10546-015-0086-9

DO - 10.1007/s10546-015-0086-9

M3 - Article

AN - SCOPUS:84954369951

VL - 158

SP - 257

EP - 283

JO - Boundary-Layer Meteorology

JF - Boundary-Layer Meteorology

SN - 0006-8314

IS - 2

ER -