Terry J. Gillespie

Estimating dew duration. I. Utilizing micrometeorological data

Abstract The energy balance technique along with heat transfer theory for flat plates was used to develop a computer model to simulate the dew duration (DD) on a single leaf. The DD was inferred from a computation of the latent heat flux. Microclimatic data obtained in an apple orchard and in corn and soybean crops were used to verify the model. Estimates of DD were attempted for exposed and shaded leaves. On the average, the dew duration estimates were within 30 min of observed DD for exposed leaves and within 60 min for shaded leaves.

Estimating dew duration. II. Utilizing standard weather station data

Abstract This paper describes an energy budget approach which allows the estimation of dew duration (DD) from standard weather station measurements of air temperature, dew point temperature, wind speed and cloud cover. Differences between observed and estimated values of DD were, on average, ⩽1 h for an exposed leaf and ⩽1.5 h for a shaded leaf.

Ozone deposition onto a deciduous forest during dry and wet conditions

Abstract Results of an experiment conducted to quantify the ozone deposition onto a deciduous forest stand in an acid-precipitation-impacted area of Canada are presented and discussed. The ozone deposition data were obtained above and within the forest canopy. The deposition process was affected by solar radiation, wind speed and ambient ozone concentration. Solar radiation was likely acting through its influence on stomatal opening and wind speed through its effects on bulk boundary layer resistance. Ozone deposition deep in the canopy was negligibly small compared with that in the upper canopy. The difference is ascribed to a larger biological sink for ozone in the upper canopy and to a lack of efficient transport in the lower canopy. Substantial ozone deposition was measured while the forest canopy remained wet with either dew or rain water, during night-time and daytime conditions. This is contrary to assumptions made in some deposition models that ozone uptake is reduced when foliage is wet.

Review of the physiology of human thermal comfort while exercising in urban landscapes and implications for bioclimatic design

This review comprehensively examines scientific literature pertaining to human physiology during exercise, including mechanisms of heat formation and dissipation, heat stress on the body, the importance of skin temperature monitoring, the effects of clothing, and microclimatic measurements. This provides a critical foundation for microclimatologists and biometeorologists in the understanding of experiments involving human physiology. The importance of the psychological aspects of how an individual perceives an outdoor environment are also reviewed, emphasizing many factors that can indirectly affect thermal comfort (TC). Past and current efforts to develop accurate human comfort models are described, as well as how these models can be used to develop resilient and comfortable outdoor spaces for physical activity. Lack of suitable spaces plays a large role in the deterioration of human health due to physical inactivity, leading to higher rates of illness, heart disease, obesity and heat-related casualties. This trend will continue if urban designers do not make use of current knowledge of bioclimatic urban design, which must be synthesized with physiology, psychology and microclimatology. Increased research is required for furthering our knowledge on the outdoor human energy balance concept and bioclimatic design for health and well-being in urban areas.

Ambient biogenic hydrocarbons and isoprene emissions from a mixed deciduous forest

Experiments were conducted during the growing season of 1993 at a mixed deciduous forest in southern Ontario, Canada to investigate the atmospheric abundance of hydrocarbons from phytogenic origins, and to measure emission rates from foliage of deciduous trees. The most abundant phytogenic chemical species found in the ambient air were isoprene and the monoterpenes α-pinene and β-pinene. Prior to leaf-bud break during spring, ambient hydrocarbon mixing ratios above the forest remained barely above instrument detection limit (∼20 parts per trillion), but they became abundant during the latter part of the growing season. Peak isoprene mixing ratios reached nearly 10 parts per billion (ppbv) during mid-growing season while maximum monoterpene mixing ratios were close to 2 ppbv. Both isoprene and monoterpene mixing ratios exhibited marked diurnal variations. Typical isoprene mixing ratios were highest during mid-afternoon and were lowest during nighttime. Peak isoprene mixing ratios coincided with maximum canopy temperature. The diurnal pattern of ambient isoprene mixing ratio was closely linked to the local emissions from foliage. Isoprene emission rates from foliage were measured by enclosing branches of trees inside environment-controlled cuvette systems and measuring the gas mixing ratio difference between cuvette inlet and outlet airstream. Isoprene emissions depended on tree species, foliage ontogeny, and environmental factors such as foliage temperature and intercepted photosynthetically active radiation (PAR). For instance, young (<1 month old) aspen leaves released approximately 80 times less isoprene than mature (>3 months old) leaves. During the latter part of the growing season the amount of carbon released back to the atmosphere as isoprene by big-tooth and trembling aspen leaves accounted for approximately 2% of the photosynthetically fixed carbon. Significant isoprene mixing ratio gradients existed between the forest crown and at twice canopy height above the ground. The gradient diffusion approach coupled with similarity theory was used to estimate canopy isoprene flux densities. These canopy fluxes compared favorably with values obtained from a multilayered canopy model that utilized locally measured plant microclimate, biomass distribution and leaf isoprene emission rate data. Modeled isoprene fluxes were approximately 30% higher compared to measured fluxes. Further comparisons between measured and modeled canopy biogenic hydrocarbon flux densities are required to assess uncertainties in modeling systems that provide inventories of biogenic hydrocarbons.

A comparison of bowen ratio and eddy correlation sensible and latent heat flux measurements above deciduous forest

AbstractSensible and latent heat flux densities (H and ΛE) were measured above a mature, 18 m deciduous forest during July and August, 1988, using the Bowen ratio-energy balance (BREB) and eddy correlation (EC) methods. EC estimates ofH and ΛE underestimated day-time surface available energy by 11%. EC also partitioned available energy differently than BREB. forź/L<0.0, EC favouredH and BREB favoured ΛE. Practical and theoretical limitations of the BREB and EC methods above forests are discussed. The most plausible causes for the failure of EC to close the surface energy balance are a low frequency loss of flux and the failure of a single point measurement to account for the spatial dispersive flux. The most plausible causes of the EC-BREB energy partitioning anomaly are the invalidity of the BREB similarity assumption and the violation of flux-gradient diffusion assumptions in the near-field diffusion region.

Thermal comfort modelling of body temperature and psychological variations of a human exercising in an outdoor environment

Human thermal comfort assessments pertaining to exercise while in outdoor environments can improve urban and recreational planning. The current study applied a simple four-segment skin temperature approach to the COMFA (COMfort FormulA) outdoor energy balance model. Comparative results of measured mean skin temperature (

Reconsidering Leaf Wetness Duration Determination for Plant Disease Management

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