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Title

Flux attenuation due to sensor displacement over sea

Abstract

When using the eddy correlation method to measure turbulent scalar fluxes, there is often a spatial separation between the instruments measuring the scalar and the vertical velocity. The attenuation of the flux due to this separation is studied here for marine conditions. Measurements of a two-point covariance between vertical velocity and temperature are compared to covariance measurements from collocated sensors for both horizontal and vertical displacements, with the purpose of finding the approximate functions to describe the flux loss for typical separation distances. On the basis of this study’s measurements, there is only a slight directional dependence (i.e., streamwise or crosswind separation) of the flux loss for sensor separation distances less than 1 m but an increasing dependence with increasing displacement distance. For a vertical displacement, observations from this study confirm that flux loss is less with the scalar sensor positioned below the velocity sensor than at an equal distance above. Furthermore, the data show a clear dependence on atmospheric stability with increasing flux loss for increasing stable stratification, but it is not as large as that found in previous studies of flux attenuation over land. For example, the authors compare estimated flux loss for neutral and moderately stable (z/L = 0.3) stratification at a measuring height of z = 10 m and a sensor displacement r = 0.3 m, where L is the Obukhov length. For neutral (stable, z/L = 0.3) stratification the estimated loss of flux is 3% (5%) of the total flux for horizontal displacement. Whereas for an equal vertical separation the estimates are 2% (4%) when the scalar sensor is placed above the anemometer but less than 1% (2%) if it is placed below. Thus, the authors conclude that placing the scalar sensor below the anemometer minimizes the flux loss due to sensor separation, and that a simple correction function can be used to quantify the mean flux loss due to sensor separation over sea.

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http://n2t.net/ark:/85065/d7bp0362

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eng

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geoscientificInformation

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publication

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2016-01-01T00:00:00Z

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publication

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2010-05-01T00:00:00Z

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Copyright 2010 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be "fair use" under Section 107 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Law (17 USC, as revised by P.L. 94-553) does not require the Society's permission. Republication, systematic reproduction, posting in electronic form on servers, or other uses of this material, except as exempted by the above statements, requires written permission or license from the AMS. Additional details are provided in the AMS Copyright Policies, available from the AMS at 617-227-2425 or amspubs@ametsoc.org. Permission to place a copy of this work on this server has been provided by the AMS. The AMS does not guarantee that the copy provided here is an accurate copy of the published work.

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OpenSky Support

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UCAR/NCAR - Library

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PO Box 3000

Boulder

80307-3000

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opensky@ucar.edu

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