ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-10-25759-2010 Estimating the atmospheric boundary layer height over sloped, forested terrain from surface spectral analysis during BEARPEX Choi W. 1 Faloona I. C. 1 McKay M. 2 4 Goldstein A. H. 2 Baker B. 3 University of California, Davis, Dept. of Land, Air, and Water Resources, Davis, California, USA University of California, Berkeley, Dept. of Environmental Science, Policy and Management, Berkeley, California, USA California State University, Sacramento, Dept. of Chemistry, California, USA now at: California Air Resources Board, Sacramento, California, USA 02 11 2010 10 11 25759 25801 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/10/25759/2010/acpd-10-25759-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/10/25759/2010/acpd-10-25759-2010.pdf

In this study the atmospheric boundary layer (ABL) height (<i>z</i><sub><i>i</i></sub>) over complex, forested terrain is estimated based on the power spectra and the integral length scale of horizontal winds obtained from a three-axis sonic anemometer during the BEARPEX (Biosphere Effects on Aerosol and Photochemistry) Experiment. The <i>z</i><sub><i>i</i></sub> values estimated with this technique showed very good agreement with observations obtained from balloon tether sonde (2007) and rawinsonde (2009) measurements under unstable conditions (<i>z/L</i> < 0) at the coniferous forest in the California Sierra Nevada. The behavior of the nocturnal boundary layer height (<i>h</i>) and power spectra of lateral winds and temperature under stable conditions (<i>z/L</i> > 0) is also presented. The nocturnal boundary layer height is found to be fairly well predicted by a recent interpolation formula proposed by Zilitinkevich et al. (2007), although it was observed to only vary from 60–80 m during the experiment. Finally, significant directional wind shear was observed during both day and night with winds backing from the prevailing west-southwesterlies in the ABL (anabatic cross-valley circulation) to consistent southerlies in a layer ~1 km thick just above the ABL before veering to the prevailing westerlies further aloft. We show that this is consistent with the forcing of a thermal wind driven by the regional temperature gradient directed due east in the lower troposphere.

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