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Influence of Low-Level Jets and Gravity Waves on Turbulent Fluxes

Title data

Serafimovich, Andrei ; Hübner, Jörg ; Leclerc, Monique Y. ; Duarte, Henrique F. ; Foken, Thomas:
Influence of Low-Level Jets and Gravity Waves on Turbulent Fluxes.
In: Foken, Thomas (ed.): Energy and Matter Fluxes of a Spruce Forest Ecosystem. - Cham : Springer , 2017 . - pp. 247-276 . - (Ecological Studies ; 229 )
ISBN 978-3-319-49387-9
DOI: https://doi.org/10.1007/978-3-319-49389-3_11

Abstract in another language

Atmospheric waves and local wind phenomena in the atmospheric boundary layer are common forms of air motions observed above the forest canopy at night. Low-level jets with duration times of several hours and the gravity wave event were detected by SODAR-RASS and miniSODAR systems installed in the Fichtelgebirge Mountains in Germany. Varying wind directions with low turbulence and wind speed are observed at times of sunrise and sunset. At midday, secondary circulations due to convection over a big clear-cut are possible. The existence of a low-level jet seems to be independent of the general weather situation. At nighttimes and during the morning hours the profile of the wind vector often shows a strong turn of the wind direction with increasing height. As a result, gravity wave generation was connected to the wind shear effect and change of the wind direction observed in the ascending low-level jet. The observed period and vertical wavelength were obtained by application of the wavelet transform, allowing the gravity wave to be filtered from the mean wind flow. A comprehensive study of gravity wave parameters was done using the linear wave theory. The analysis of the wind perturbation profiles indicates a downward wave energy propagation above the canopy level. The eddy-covariance measurements are used to investigate the impact of the gravity wave on the generation of coherent structures and turbulent transport. It was shown that coherent structures have smaller temporal scales when the gravity wave occurs, in contrast to the period before the wave was detected. It was found that there was a significant impact of the gravity wave on the momentum exchange, and that this led to the higher transport of the momentum during the ejection phases of coherent structures, whereas the sweep phases were mostly responsible for transport in the absence of the gravity wave in the mean flow.

Further data

Item Type: Article in a book
Refereed: No
Additional notes: BAYCEER139899
Institutions of the University: Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Earth Sciences > Professorship Micrometeorology
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Earth Sciences > Former Professors > Professorship Micrometeorology - Univ.-Prof. Dr. Thomas Foken
Research Institutions
Research Institutions > Research Centres
Research Institutions > Research Centres > Bayreuth Center of Ecology and Environmental Research- BayCEER
Faculties
Faculties > Faculty of Biology, Chemistry and Earth Sciences
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Earth Sciences
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Earth Sciences > Former Professors
Result of work at the UBT: Yes
DDC Subjects: 500 Science
Date Deposited: 10 Jan 2018 14:11
Last Modified: 10 Jan 2018 14:11
URI: https://eref.uni-bayreuth.de/id/eprint/41263