Comparison of passive fog gauges for determining fog duration and fog interception by a Puerto Rican elfin cloud forest

摘要

Between 5 March and 10 May 2001, the performance of three types of passive fog gauges (wire harp WH, standard fogncollector SC and Juvik gauge JU) was compared at a wind-exposed Puerto Rican elfin cloud forest site. The gauges were usednto determine the timing and duration of fog, as well as fog-induced crown drip using gauge to canopy conversions factors. Thenlatter were calculated as the average ratio between throughfall, and fog collected by the respective gauges during periods withnfog-only and negligible evaporation loss. The fog gauges indicated very similar timing and fog duration, presumably becausendense fog prevailed for 75–80% of the time whereas winds were generally sufficiently strong (4–5 m su00011) and from a nearlynconstant direction. Resulting gauge to canopy factors were 0D12 for WH and SC, and 0D10 for JU. Estimating fog interceptionnby the elfin forest canopy using these conversion factors gave very similar values for the three gauge types (mean rates ofn0D15 š 0D01 mm hu00011). Throughfall typically started about 5 h after the fog gauges indicated the beginning of a fog event. Thisntime lag probably reflects the filling of the canopy storage capacity. Integrating the estimated fog interception rates over thentime lag suggested an average value of 0D4 mm for the canopy storage capacity during fog-only events. The present resultsnare expected to apply to sites with comparable wind and fog conditions.