ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-11-21013-2011 Analysis of coherent structures and atmosphere-canopy coupling strength during the CABINEX field campaign: implications for atmospheric chemistry Steiner A. L. 1 Pressley S. N. 2 Botros A. 3 Jones E. 4 Chung S. H. 2 Edburg S. L. 5 Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI, USA Department of Civil and Environmental Engineering, Washington State University, Pullman, WA, USA Department of Neuroscience, University of California, Los Angeles, CA, USA Franklin W. Olin College of Engineering, Needham, MA, USA Department of Geography, University of Idaho, Moscow, ID, USA 26 07 2011 11 7 21013 21054 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/11/21013/2011/acpd-11-21013-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/11/21013/2011/acpd-11-21013-2011.pdf

Intermittent coherent structures can be responsible for a large fraction of the chemical exchange between the vegetation canopy and the atmosphere. Quantifying their contribution to fluxes is necessary to interpret measurements of trace gases and aerosols within and above forest canopies. The primary objective of the Community Atmosphere-Biosphere Interactions Experiment (CABINEX) field campaign (10 July 2009 to 9 August 2009) was to study the chemistry of volatile organic compounds (VOC) within and above a forest canopy. In this manuscript, we provide an analysis of coherent structures and canopy-atmosphere exchange during CABINEX to support in-canopy gradient measurements of VOC. We quantify the number and duration of coherent structure events and their percent contribution to momentum and heat fluxes with two methods: (1) quadrant-hole analysis and (2) wavelet analysis. Despite differences in the duration and number of events, both methods predict that coherent structures contribute 40–50 % to total momentum fluxes and 44–65 % to total heat fluxes during the CABINEX campaign. Contributions associated with coherent structures are slightly greater under stable rather than unstable conditions. By comparing heat fluxes within and above the canopy, we determine the degree of coupling between upper canopy and atmosphere and find that they are coupled to the majority of the campaign time period. Uncoupled canopy-atmosphere events occur in the early morning (04:00–08:00 LT) approximately 30 % of the time. This study confirms that coherent structures contribute significantly to the exchange of heat and momentum between the canopy and atmosphere at the CABINEX site, and indicates the need to include these transport processes when studying the mixing and chemical reactions of trace gases and aerosols between a forest canopy and the atmosphere.

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