Observation of gravity waves in a boreal forest

X. Lee, H. H. Neumann, G. Den Hartog, J. D. Fuentes, T. A. Black, R. E. Mickle, P. C. Yang, P. D. Blanken

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Abstract

In this paper we report the results of the analysis of two 60-min wave events that occurred in a boreal aspen forest during the 1994 BOREAS (Boreal Ecosystems-Atmosphere Study) field experiment. High frequency wind and temperature data were provided by three 3-D sonic anemometer/thermometers and fourteen fine-wire thermocouples positioned within and above the forest. Wave phase speeds, estimated from information revealed by spectral analysis and linear plane wave equations, are 2.2 and 1.3 m s-1 for the two events. The wavelengths are 130 m and 65 m respectively and are much larger than the vertical wave displacements. There is strong evidence from the present analysis and from the literature supporting our postulate that these waves are generated by shear instability. We propose that wind shear near the top of the stand is often large enough to reduce the gradient Richardson number below the critical value of 0.25 and thus is able to trigger the instability. When external conditions are favorable, the instability will grow into waves.

Original languageEnglish (US)
Pages (from-to)383-398
Number of pages16
JournalBoundary-Layer Meteorology
Volume84
Issue number3
DOIs
StatePublished - Jan 1 1997

All Science Journal Classification (ASJC) codes

  • Atmospheric Science

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    Lee, X., Neumann, H. H., Den Hartog, G., Fuentes, J. D., Black, T. A., Mickle, R. E., Yang, P. C., & Blanken, P. D. (1997). Observation of gravity waves in a boreal forest. Boundary-Layer Meteorology, 84(3), 383-398. https://doi.org/10.1023/A:1000454030493