Eddy correlation measurements of size-dependent cloud droplet turbulent fluxes to complex terrain

Abstract

An eddy correlation technique was used to measure the turbulent flux of cloud droplets to complex, forested terrain near the coast of Washington State during the spring of 1993. Excellent agreement was achieved for cloud liquid water content measured by two instruments. Substantial downward liquid water fluxes of-1 mm per 24 h were measured at night during "steady and continuous" cloud events, about twice the magnitude of those measured by Beswick et al. in Scotland. Cloud water chemical fluxes were estimated to represent up to 50 % of the chemical deposition associated with precipitation at the site. An observed size-dependence in the turbulent liquid water fluxes suggested that both droplet impaction, which leads to downward fluxes, and phase change processes, which can lead to upward fluxes, consistently are important contributors to the eddy correlation results. The diameter below which phase change processes were important to observed fluxes was shown to depend upon 'hi L, the relative standard deviation of the liquid water content (LWC) within a 30-min averaging period. The crossover from upward to downward L W flux occurs at 8 µm for steady and continuous cloud events but at-13 µm for events with a larger degree of L WC variability. This comparison of the two types of cloud events suggested that evaporation was the most likely cause of upward droplet fluxes for the smaller droplets (dia < 13 µm) during cloud with variable LWC (a LIL> 0.3).

Estimating fog deposition at a Puerto Rican elfin cloud forest site: comparison of the water budget and eddy covariance methods

“…The average fog deposition rate at Pico del Este during periods with VIS < 1000 m, as measured directly with the eddy covariance method, was 0Ð04 mm h 1 (or 10Ð18 mg m 2 s 1 ). This is well in the range (0-15 mg m 2 s 1 ) determined with the same method at various locations outside the tropics (Beswick et al, 1991;Gallagher et al, 1992;Vong and Kowalski, 1995;Vermeulen et al, 1997;Kowalski and Vong, 1999;Thalmann et al, 2002;Burkard et al, 2003). However, it is much lower than the average deposition rate derived with the water budget approach.…”

Nutrient Input Through Occult and Wet Deposition into a Subtropical Montane Cloud Forest

“…This method is often described as the only direct flux measurement technique for fog (Gallagher et al 1992;Vong and Kowalski 1995;Burkard et al 2002). The experimental setup consisted of a Young 81000 ultrasonic anemometer (R.M.…”

It goes both ways: measurements of simultaneous evapotranspiration and fog droplet deposition at a montane cloud forest

“…The objectives of this study are to measure evapotranspiration in a montane cypress forest and to analyse whether evapotranspiration of water does, in fact, occur during the extremely humid conditions associated with fog. It is well documented that turbulent deposition of fog droplets onto vegetation occurs during foggy conditions (Gallagher et al, 1992;Vong and Kowalski, 1995;Kowalski and Vong, 1999;Vermeulen et al, 1997;Thalmann et al, 2002;Eugster et al, 2006;Holwerda et al 2006). However, defining the relationships between evapotranspiration of water vapour and turbulent deposition of liquid water, and discovering whether these processes can occur simultaneously will improve the general understanding of hydrological processes and energy flux partitioning in these ecosystems.…”