Accession Number : ADA190867

Title :   Fog, Rain and Aerosol Attenuation in the Atmosphere.

Descriptive Note : Final rept. 1 Apr 84-31 Aug 87,

Corporate Author : STATE UNIV OF NEW YORK AT ALBANY ATMOSPHERIC SCIENCES RESEARCH CENTER

Personal Author(s) : Lala, G G ; Fitzjarrald, David R ; Meyer, Michael B

PDF Url : ADA190867

Report Date : 31 Dec 1987

Pagination or Media Count : 60

Abstract : Large scale meteorological influences as well as local fog climatology were investigated and a simple model based on standard weather observations was formulated to explain seasonal trends in fog occurrence. Detailed studies of surface layer and boundary layer structure during fog events are summarized. The importance of initial conditions in determining the potential for fog formation are discussed. The roles of long wave radiational cooling and turbulent transport in promoting fog formation in each of these regions were investigated. In many cases, radiational cooling is the dominant mechanism responsible for bringing a deep layer to saturation. Local winds, such as the channeled flow in the Hudson valley, may act either to promote or to prevent fog formation. From this analysis, it is clear that standard surface and upper air observations alone are inadequate inputs for fog forecasting, but must be augmented with more detailed boundary layer observations. Continuous samples of droplet spectra in fog obtained with a forward scattering droplet spectrometer were analyzed to investigate the shape of the size distribution as a function of time. Over periods of the order of hours, the large drop spectra maintains a similar shape which is well described by the lognormal distribution function. Analysis of the spectra in terms of the distribution parameters indicates that shallow fog distributions are narrower and have smaller mass median diameters than deep fogs. Fogs which begin as shallow fogs and subsequently develop through a deep layer show a corresponding change in the distribution shape.

Descriptors :   *FOG, AEROSOLS, ATTENUATION, BOUNDARY LAYER, COOLING, DISTRIBUTION, DROPS, FORECASTING, FORWARD SCATTERING, LAYERS, LONG WAVELENGTHS, MASS, METEOROLOGICAL DATA, PATTERNS, RADIATION, RAIN, SAMPLING, SATURATION, SEASONAL VARIATIONS, SHALLOW DEPTH, SHAPE, SPECTRA, SPECTROMETERS, SURFACES, TRANSPORT, TURBULENCE, UPPER ATMOSPHERE, WEATHER, WIND, NEW YORK, VALLEYS, PARTICLE SIZE, LIGHT TRANSMISSION

Subject Categories : Meteorology

Distribution Statement : APPROVED FOR PUBLIC RELEASE