Characteristics of fog and fogwater fluxes in a Puerto Rican elfin cloud forest

Abstract

The Luquillo Mountains of northeastern Puerto Rico harbours important fractions of tropical montane cloud forests. Although it is well known that the frequent occurrence of dense fog is a common climatic characteristic of cloud forests around the world, it is poorly understood how fog processes shape and influence these ecosystems. Our study focuses on the physical characteristics of fog and quantifies the fogwater input to elfin cloud forest using direct eddy covariance net flux measurements during a 43-day period in 2002. We used an ultrasonic anemometerthermometer in combination with a size-resolving cloud droplet spectrometer capable of providing number counts in 40 droplet size classes at a rate of 12.5 times per second. Fog occurred during 85% of the time, and dense fog with a visibility <200 m persisted during 74% of the period. Fog droplet size depended linearly on liquid water content (r 2 =0.89) with a volumeweighted mean diameter of 13.8 µm. Due to the high frequency of occurrence of fog the total fogwater deposition measured with the eddy covariance method and corrected for condensation and advection effects in the persistent up-slope air flow, averaged 4.36 mm d −1 , rainfall during the same period was 28 mm d −1 . Thus, our estimates of the contribution of fogwater to the hydrological budget of elfin cloud forests is considerable and higher than in any other location for which comparable data exist but still not a very large component in the hydrological budget. For estimating fogwater fluxes for locations without detailed information about fog droplet distributions we provide simple empirical relationships using visibility data.

Abrupt Change in Forest Height along a Tropical Elevation Gradient Detected Using Airborne Lidar

“…Such changes should be progressive on the volcanoclastic bedrock, since there are no sudden mountain-wide systematic changes in erosion rate, slope, bedrock chemistry or soil properties with elevation. Some changes in the climatic variables with elevation, such as the mean cloud base elevation [14] can potentially produce rapid changes in vegetation height, akin to the effect of the tropical inversion layer as observed on higher tropical mountains. If so they should appear in the volcanoclastic bedrock profile as well as the quartz diorite.…”

Spatiotemporal variations of T/ET (the ratio of transpiration to evapotranspiration) in three forests of Eastern China

“…First, due to the effects of gap-filling in rainy days (Kang et al, 2012), dews (Maestre-Valero et al, 2012), and fogs (Beiderwieden et al, 2008;Eugster et al, 2006), the measured ET may be underestimated. Second, the underestimated ET caused by gap-filling in rainy days (Kang et al, 2012), dews (Maestre-Valero et al, 2012), and fogs (Beiderwieden et al, 2008;Eugster et al, 2006) may overestimate T/ET. Third, during days with open canopy, the low temperature (Shi et al, 2008a) caused small measured water vapor fluxes below the canopy, which made the measured T (the difference between two layers water vapor fluxes) and T/ET overestimated.…”

Evaluating the capabilities and uncertainties of droplet measurements for the fog droplet spectrometer (FM-100)

“…The FM-100 has been used in several ground based studies so far especially as part of an eddy covariance system to quantify fog water deposition fluxes in tropical mountain cloud forests (e.g. Eugster et al, 2006;Holwerda et al, 2006;Beiderwieden, 2007;Beiderwieden et al, 2008;Schmid et al, 2010), in temperate ecosystems (Burkard et al, 2002;Thalmann, 2002;Burkard, 2003), and deposition fluxes in rather arid areas (Westbeld et al, 2009). It has also been used as a single instrument for microphysical studies of fog (Gonser et al, 2011;Liu et al, 2011) and compared to other devices Schmid et al, 2010;Frumau et al, 2011).…”

“…It plays an important role for the radiative characteristic of the cloud and is, for example needed to describe the anthropogenic influence (Gunn and Philips, 1957;Twomey, 1977) and the cloud lifetime effect (Albrecht, 1989;Rosenfeld and Lensky, 1998). Moreover, the knowledge of droplet size distribution is crucial for a better understanding of the onset of precipitation (Gunn and Philips, 1957;Stevens and Feingold, 2009) as well as the occult deposition input of clouds to vegetation, which is known to be a relevant component in the hydrological budget of tropical mountain cloud forests (Bruijnzeel et al, 2005;Eugster et al, 2006). At this stage, there are two different approaches of measuring cloud droplet sizes: in-situ measurements using optical instruments on aircrafts or ground based stations (e.g.…”

“…Lance et al, 2010) and actively ventilated instruments, which are mainly used for ground based or tower based measurements (e.g. Burkard et al, 2002;Eugster et al, 2006). In-situ measurements are very challenging due to various difficulties recently discussed for aircraft devices by Lance et al (2010) and Baumgardner et al (2011) and for the FSSP in general by Baumgardner (1983) and Baumgardner et al (1992).…”