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Volume 16, issue 3 | Copyright

Special issue: HD(CP)2 Observational Prototype Experiment (AMT/ACP...

Atmos. Chem. Phys., 16, 1377-1400, 2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 08 Feb 2016

Research article | 08 Feb 2016

Observed spatiotemporal variability of boundary-layer turbulence over flat, heterogeneous terrain

V. Maurer1, N. Kalthoff1, A. Wieser1, M. Kohler1, M. Mauder2, and L. Gantner1 V. Maurer et al.
  • 1Institut für Meteorologie und Klimaforschung (IMK-TRO), Karlsruher Institut für Technologie (KIT), Karlsruhe, Germany
  • 2Institut für Meteorologie und Klimaforschung (IMK-IFU), Karlsruher Institut für Technologie (KIT), Garmisch-Partenkirchen, Germany

Abstract. In the spring of 2013, extensive measurements with multiple Doppler lidar systems were performed. The instruments were arranged in a triangle with edge lengths of about 3km in a moderately flat, agriculturally used terrain in northwestern Germany. For 6 mostly cloud-free convective days, vertical velocity variance profiles were calculated. Weighted-averaged surface fluxes proved to be more appropriate than data from individual sites for scaling the variance profiles; but even then, the scatter of profiles was mostly larger than the statistical error. The scatter could not be explained by mean wind speed or stability, whereas time periods with significantly increased variance contained broader thermals. Periods with an elevated maximum of the variance profiles could also be related to broad thermals. Moreover, statistically significant spatial differences of variance were found. They were not influenced by the existing surface heterogeneity. Instead, thermals were preserved between two sites when the travel time was shorter than the large-eddy turnover time. At the same time, no thermals passed for more than 2h at a third site that was located perpendicular to the mean wind direction in relation to the first two sites. Organized structures of turbulence with subsidence prevailing in the surroundings of thermals can thus partly explain significant spatial variance differences existing for several hours. Therefore, the representativeness of individual variance profiles derived from measurements at a single site cannot be assumed.

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The measurement of turbulence in the lowest 1–2 km above the land surface is important for our understanding of boundary-layer processes. We compared turbulence profiles measured at three locations lying about 3 km apart and found that the deployment of the instruments in different crop fields has no direct influence on turbulence statistics on cloud-free days. Nevertheless, spatial differences as well as correlations were found, indicating the existence of organized structures of turbulence.
The measurement of turbulence in the lowest 1–2 km above the land surface is important for our...