James E. Jiusto

Fog-82: A Cooperative Field Study of Radiation Fog

The Cloud Physics Section of the Atmospheric Sciences Research Center-State University of New York at Albany conducted a cooperative field study (FOG-82) during the autumn of 1982 as part of an ongoing radiation-fog research program. A computer-controlled data-acquisition system consisting of sophisticated soil, surface, and boundary-layer sensors, as well as contemporary aerosol and droplet probes was developed. These data are being used to address a variety of critical problems related to radiation-fog evolution. Scientists from 10 universities and research laboratories participated in portions of FOG-82. Research objectives included studies of fog mesoscale meteorology, radiation studies, low-level water budget, vertical fog structure, fog supersaturation, condensation nuclei, and fog-water chemistry, as well as radiation-fog life cycles. A comprehensive description of the FOG-82 program and objectives is presented.

Measurements of Visual Range and Radiation-Fog (Haze) Microphysics

Abstract An extensive boundary-layer field program was conducted which included simultaneous measurements of visibility and particle size distributions during fog and haze. Several empirical expressions relating changes in visibility to characteristics of the aerosol (droplet) size spectrum and relative humidity are presented and evaluated. Detailed analysis of one evolving dense fog revealed several points of interest regarding the behavior of drop size spectra, including a scheme for approximating fog supersaturation.

A Numerical Evaluation of Radiation Fog Variables

Abstract A numerical model of radiation fog was developed in order to test the sensitivity of variables comprising the model, and evaluate its capability for forecasting the onset of fog from standard radiosonde weather data. Four case studies were considered that included both fog and no-fog occurrences. The variables examined–initial surface temperature and moisture conditions, eddy exchange profiles, radiative flux divergence, and dew formation–were all found to influence critically the models performance. Prediction of fog occurrence and temperature were reasonably encouraging provided a judicious (though somewhat arbitrary) choice of eddy mixing values was made.

Numerical Estimates of Humidity in a Membrane–Filter Ice Nucleus Chamber

Abstract A one-dimensional model was developed to examine humidity fields within a conditioning chamber for measuring ice nucleus concentrations on millipore filters. Representative concentrations of ice and cloud condensation nuclei were assumed, and the interplay among these growing particles (vapor sinks), the supply flux of vapor, and the resultant relative humidity at and above the filter surface investigated. The model suggests that water saturation is not achieved under typical operating conditions of such chambers. Maximum humidifies reached decrease with increasing numbers of either condensation or ice nuclei, thereby offering another possible explanation of the filter volume effect. Most favorable operating conditions for achieving highest chamber humidities are delineated. The results suggest that this technique is capable of detecting mixed condensation-freezing nuclei, deposition nuclei and some contact nuclei, with the former perhaps being most common not only in filter measurements but also...

An Examination of Ice Nucleus Concentrations in Eastern New York State

Abstract This work reports the results from a five-station (remote to highly urbanized) sampling network operated in 1976 in eastern New York State in which daily measurements were made of ice nucleus and condensation nucleus concentrations among the stations at most of the test relative humidities. Generally, semi-urban Albany had the highest concentration of ice nuclei and remote Whiteface Mountain the lowest. Albany also typically had the highest slope values (ice nucleus concentration-supersaturation spectrum) and the highest concentrations of condensation nuclei, while Whiteface Mountain typically had the lowest values for these two parameters. Lower ice nucleus concentrations in the New York City area suggest that the degree of urbanization there did not have a major impact on ice nucleus concentrations.

Some Local Climate Trends in Four Cities of New York State

Abstract From historical weather records, a preliminary assessment was made of local climate changes in four major urban areas of New York State. Particular emphasis was placed on cold season precipitation and possible relationships to mans activities. Total snowfall was found to have increased significantly from about 1940, the start of a period of sharp increases in urbanization and industrialization. The relationship was merely coincidental, with the underlying cause of snowfall increases due to natural causes, apparently in part to a corresponding decline in ambient temperature. A few climate trends appeared linked to anthropogenic causes, particularly in New York City.

Factors Affecting Ice Nucleus Concentration Measurements with a Static Vapor-Diffusion Chamber

Abstract This paper presents some findings and recommendations for obtaining more reliable information from ice nucleus concentration measurements with the membrane filter technique commonly in use. Variables related to chamber design, filter preparation and crystal counting are discussed.