Search Results

You are looking at 1 - 4 of 4 items for :

  • Author or Editor: James E. Jiusto x
  • Journal of the Atmospheric Sciences x
  • Refine by Access: Content accessible to me x
Clear All Modify Search
Roland J. Pilié and James E. Jiusto

Abstract

Contrails were produced for laboratory study by burning aircraft fuels under controlled conditions of ambient temperature and humidity at pressure altitudes between 1000 and 300 mb. Observed critical formation temperatures differ from Appleman's theoretical data in a manner similar to that obtained on project CLOUD TRAIL flights. Laboratory experiments with these trails proved that the initial phase of the condensed moisture is liquid and produced strong evidence that, contrary to general belief, the final phase is sometimes liquid. Additional evidence was obtained indicating that Appleman's criterion for a barely visible trail (0.004 g per m3 of condensed moisture) is very nearly correct for ideal conditions of observation such as used in the laboratory, but is probably small by an order of magnitude or more for adverse conditions. By modifying Appleman's theory to allow for the production of a visible quantity of liquid water under adverse viewing conditions, agreement is reached with project CLOUD TRAIL data. Also presented is a simple interpretation of the theory which substantially reduces the labor required to compute critical temperatures for contrail formation.

Full access
Alfred H. Woodcock, Duncan C. Blanchard, and James E. Jiusto

Abstract

In Past 1 of this fog study, the distribution of water with number and size of drops in some New England marine advection fogs was shown to be related to the distribution of number and size of salt particles found in marine air. It was indicated that in saturated air the calculated amounts of water condensed on the salt particles produced water distributions as a function of drop size much like distributions observed in numerous advection fogs. The results suggest that salt particles play an important role in the initiation and growth of marine fogs.

In the present work, photomicrographs of drops and of drop salt nuclei from several New England marine fogs are studied. The results confirm the conclusions of the first study, demonstrating even more clearly the direct relationship of drop weight to nucleus weight. The fog drops must have grown in supersaturated air, because in almost all of them the salt concentrations were below the equilibrium values for saturated air. However, the number and sizes of the salt nuclei in the air and fog support the idea that the fogs probably developed first as moderate haze-droplet fogs in saturated air (i.e., relative humidity 100%). A temperature-mixing ratio diagram is used to explain how saturation may be sustained by mixing, for the time intervals required for these haze-drop fogs to develop.

Full access
G. Garland Lala, Eric Mandel, and James E. Jiusto

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 model's performance. Prediction of fog occurrence and temperature were reasonably encouraging provided a judicious (though somewhat arbitrary) choice of eddy mixing values was made.

Full access
Michael B. Meyer, James E. Jiusto, and G. Garland Lala

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.

Full access