Near‐surface fluxes of cloud water evolve vertically

Kowalski, Andrew S.; Vong, Richard J.

doi:10.1002/qj.49712555916

Cited by 28 publications

(31 citation statements)

References 49 publications

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“…Kowalski and Vong 1999;Holwerda et al 2006). The eddy covariance method only measures net deposition whereas at the leaf level the gross deposition rate is considerably larger.…”

Section: Discussionmentioning

confidence: 99%

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

Eugster

Burkard

Holwerda

et al. 2006

Agricultural and Forest Meteorology

113

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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.

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“…Kowalski and Vong 1999;Holwerda et al 2006). The eddy covariance method only measures net deposition whereas at the leaf level the gross deposition rate is considerably larger.…”

Section: Discussionmentioning

confidence: 99%

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

Eugster

Burkard

Holwerda

et al. 2006

Agricultural and Forest Meteorology

113

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“…There, the rate of potential PAR is high and accessibility to moisture from passing mists is highest due to the diffusion of flow within the canopy (Kowalski and Vong, 1999), which may be exacerbated in the present context due to the outer canopy thickening with high epiphytic growth (Chapter 4). Thus, inside the canopy, establishing epiphytes would be significantly disadvantaged by the lower PAR, lower accessibility to moisture from passing mists (though less evaporation), and a larger metabolic expenditure for root growth in order to secure an attachment on the larger surface area.…”

Section: Inner Canopy Recolonisationmentioning

confidence: 94%

Epiphytic bryophytes and habitat variation in montane rainforest, Peru

Romanski¹,

Pharo

Kirkpatrick³

2011

The Bryologist

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A total of 190 holoepiphytic and 5 hemiepiphytic vascular plant species were collected from the canopy and the trunk of an emergent Ficus L. species host that is common to a Peruvian cloud forest. One hundred and fourteen of the vascular epiphyte species were orchids. A large majority of the vascular species were rare in occurrence. Vascular epiphyte diversity and density was highest in the outer canopy zone of the host crown. In the inner canopy zone there was a dearth of epiphytes, attributed to a high rate of epiphyte slumping on the smooth-barked branches. The trunk had a different suit of species to those found in the canopy.During the wet season, the thickening of epiphytic matter in the outer canopy zone appeared to contribute to a large amelioration of daytime and nocturnal temperatures through evaporation and heat retention respectively.Nocturnal temperatures were highest in the outer canopy zone, and were lowest on the forest floor. The latter was attributed to the downward flow of the product of radiative cooling as a result of the heterogeneous canopy on the steep slope.Epiphyte clumps appear to slump before competition causes the loss of early successional species. Some species showed a preference for more shaded epiphyte clumps and many were more frequent on smaller branch diameters. Most species showed a moderately high niche overlap with a large number of other species, which suggested a high degree of species coexistence.Epiphyte slumping is suggested to be the major driving mechanism for the maintenance of non-equilibrium in the community. Aspects of the phenologies of epiphytes, age-structure of the community and high environmental variation could be other mechanisms for the maintenance of a high degree of species coexistence.iii

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“…One way of addressing the isoaxial sampling is to put the instrument onto a turntable and letting it continually turn into the main wind direction as done by Vong (1995), Kowalski et al (1997), Kowalski (1999), Wrzesinsky (2000), Burkard et al (2002), Thalmann (2002, Burkard (2003), Eugster et al (2006), andHolwerda et al (2006). Nevertheless, these procedures do not assure isokinetic sampling conditions.…”

Section: Sampling Lossesmentioning

confidence: 99%

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

Spiegel¹,

Zieger²,

Bukowiecki³

et al. 2012

Atmos. Meas. Tech.

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Abstract. Droplet size spectra measurements are crucial to obtain a quantitative microphysical description of clouds and fog. However, cloud droplet size measurements are subject to various uncertainties. This work focuses on the error analysis of two key measurement uncertainties arising during cloud droplet size measurements with a conventional droplet size spectrometer (FM-100): first, we addressed the precision with which droplets can be sized with the FM-100 on the basis of the Mie theory. We deduced error assumptions and proposed a new method on how to correct measured size distributions for these errors by redistributing the measured droplet size distribution using a stochastic approach. Second, based on a literature study, we summarized corrections for particle losses during sampling with the FM-100. We applied both corrections to cloud droplet size spectra measured at the high alpine site Jungfraujoch for a temperature range from 0 • C to 11 • C. We showed that Mie scattering led to spikes in the droplet size distributions using the default sizing procedure, while the new stochastic approach reproduced the ambient size distribution adequately. A detailed analysis of the FM-100 sampling efficiency revealed that particle losses were typically below 10 % for droplet diameters up to 10 µm. For larger droplets, particle losses can increase up to 90 % for the largest droplets of 50 µm at ambient wind speeds below 4.4 m s −1 and even to >90 % for larger angles between the instrument orientation and the wind vector (sampling angle) at higher wind speeds. Comparisons of the FM-100 to other reference instruments revealed that the total liquid water content (LWC) measured by the FM-100 was more sensitive to particle losses than to re-sizing based on Mie scattering, while the total number concentration was only marginally influenced by particle losses. Consequently, for further LWC measurements with the FM-100 we strongly recommend to consider (1) the error arising due to Mie scattering, and (2) the particle losses, especially for larger droplets depending on the set-up and wind conditions.

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Near‐surface fluxes of cloud water evolve vertically

Cited by 28 publications

References 49 publications

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

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

Epiphytic bryophytes and habitat variation in montane rainforest, Peru

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

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