Instruments have been designed and assembled for the summation of areas of precipitation on a weather radar map. One technique uses the output from a system scanning the map to deflect the trace on the cathoderay tube of an oscilloscope in discrete steps depending on the intensity of the precipitation. This trace is photographed. Since the brightness of the trace is constant, exposure is a function of scan-time. Because scan-time is proportional to area scanned, the density on film resulting from this exposure is a function of area. Densitometry then yields these areas. A more convenient technique makes use of the fact that scan-time is proportional to the number of cycles of the a.c. output from the scanner, and areal summation is accomplished with an electronic counter. Examples of measurements are presented, and their meteorological value is discussed. [...]

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published_or_final_version / Physics / Master / Master of Philosophy

Occult deposition is the direct uptake of cloudwater by vegetation that comes into physical contact with wind-driven cloud droplets. This can be a significant pathway for hydrological and chemical fluxes from the atmosphere to some forests. Methods for estimating cloudwater fluxes to forests are reviewed. Previous studies have neglected the fact that cloudwater is not a conservative atmospheric quantity. This invalidates traditional micrometeorological approaches for estimation of cloudwater fluxes to forests. A theory is developed to predict the change in the cloudwater flux with height due to condensation in the updrafts of orographic cloud, allowing estimation of surface uptake via eddy correlation measurements while accounting for condensation. The performances of three microphysical instruments are examined. From collocated measurements, errors in cloud liquid water content are determined for a Particulate Volume Monitor (PVM) and a Forward Scattering Spectrometer Probe (FSSP) to be less than 0.01 g m⁻³ and 0.035 g m⁻³ respectively. Similarly, the error bounds for surface-normal cloud liquid water fluxes are found to be 2 mg m⁻² s⁻¹ for the PVM and 3.5 mg m⁻² s⁻¹ for the FSSP. Smaller errors are found to be associated with the uncertainty in the direction of the flux relevant to surface uptake. The FSSP is seen to have larger errors when droplet concentrations exceed 600 cm⁻³. A vertical divergence is detected in the cloudwater flux; the downward flux decreases with increasing distance from the surface, usually changing sign by 15 m above ground. Five candidate processes are identified as possible explanations for this measured flux divergence. A scale analysis shows that the liquid water source (condensation due to pseudoadiabatic ascent) is largely responsible for the change in flux with height. Accounting for the change in flux with height results in a near doubling of the estimated surface flux relative to the flux measured at a height of 10 m in the surface layer for this silver fir forest. This factor applies to chemical as well as liquid water fluxes. This source of liquid water also is seen to be important in developing a simple model for cloudwater deposition. / Graduation date: 1997

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