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A comparison of the performance of three types of passive fog gauges under conditions of wind-driven fog and precipitation

Authors

  • K. F. Arnoud Frumau,

    Corresponding author
    1. Faculty of Earth and Life Sciences, VU University, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands
    Current affiliation:
    1. Air Quality and Climate Change Group, Energy Research Centre of the Netherlands, P.O. Box 1, 1755 ZG Petten, The Netherlands
    • Faculty of Earth and Life Sciences, VU University, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands.===

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  • Reto Burkard,

    1. Institute of Geography, University of Bern, Hallerstrasse 12, 3012 Bern, Switzerland
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  • Simone Schmid,

    1. Institute of Geography, University of Bern, Hallerstrasse 12, 3012 Bern, Switzerland
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  • L. A. (Sampurno) Bruijnzeel,

    1. Faculty of Earth and Life Sciences, VU University, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands
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  • Conrado Tobón,

    1. Faculty of Earth and Life Sciences, VU University, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands
    Current affiliation:
    1. Departamento de Ciencias Forestales, Universidad Nacional de Colombia, Calle 59a, no. 63–20, Medellín, Colombia
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  • Julio C. Calvo-Alvarado

    1. Forestry Department, Instituto Tecnológico de Costa Rica, Cartago, Costa Rica
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  • This paper is largely reproduced from a chapter previously published as K.F.A. Frumau, R. Burkard, S. Schmid, L.A. Bruijnzeel, C. Tobón, and J.C. Calvo-Alvarado (2010). Fog gage performance under conditions of fog and wind-driven rain. In Tropical Montane Cloud Forests. Science for Conservation and Management, eds. L.A. Bruijnzeel, F.N. Scatena and L.S. Hamilton. Cambridge: Cambridge University Press, pp. 293–301. www.cambridge.org/9780521760355.

Abstract

Understanding of the ‘typical’ amounts of fog intercepted by different types of cloud forests is hampered by a lack of comparative information on local fog climatology. Usually some kind of ‘fog gauge’ is used to characterize fog occurrence and amounts. Moreover, wind-driven fog and precipitation are difficult to measure separately and reported measurements of ‘fog’ often represent a combination of the two. In this paper, the term ‘occult precipitation’ (HP) is used to represent fog in combination with the horizontal component of wind-driven precipitation (WDR). Collection efficiencies of three widely used types of passive fog gauges, viz. a wire harp (WH) screen, a modified cylindrical gauge (MJU, Juvik-type) and a tunnel gauge (TTG, Daube-type), were derived by comparing the volumes of water collected by the respective gauges with horizontal cloud water fluxes (CWFs) derived from wind speed (u) and the fog liquid water content (LWC) as measured by a cloud particle spectrometer during conditions of fog at a windward cloud forest site in northern Costa Rica. Under conditions of fog-only, the collection efficiencies of the three gauges were linearly related to the horizontal CWF as measured by the gauges themselves. Therefore, additional information on wind speed, droplet size and fog LWC was not needed. During conditions of HP, relative collection efficiencies were derived by comparing the volumes collected by the respective gauge types. The modified Juvik gauge had an efficiency close to 100%, independently of the wind speed and direction, whereas the efficiency of the WH depended critically on the wind speed. The tunnel gauge had an efficiency comparable to that of the Juvik gauge, with some additional catch occurring under conditions of low precipitation angles due to the reclined frontal surface of the gauge. Copyright © 2010 John Wiley & Sons, Ltd.

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