Roland J. Pilie

A LABORATORY STUDY OF CONTRAILS

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 Applemans 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 Applemans 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 Applemans theory to allow for the production of a visible quantity of liquid water under adverse viewing conditions, agreement is reached with project C...

WARM FOG SUPPRESSION IN LARGE-SCALE LABORATORY EXPERIMENTS

Visibility in warm fog produced in a 600-cubic-meter chamber was increased by factors of 3 to 10 by seeding with carefully sized sodium chloride particles. As little as 1.7 milligrams of salt per cubic meter was effective. Extrapolation of these results indicates that clearing a suitable landing zone for aircraft would not involve prohibitive amounts of seeding material.

Aerosol Composition In The Marine And Coastal Boundary Layer

As part of a number of broader-based studies, Calspan acquired a considerable quantity of data describing bcundary-layer aerosol characteristics both at sea and in maritime continental locations. This paper focuses on aerosol composition data obtained in the North Atlantic, in the Mediterranean, in the northern Gulf of Mexico, off the coasts of California, Nova Scotia and Portugal, and on shore on Cape Cod and on the North Sea Coast of West Germany. The data show that the marine aerosol population varies considerably in composition, particularly in coastal areas, and does not necessarily comprise primarily sea salt aerosols. A continental/anthropogenically-derived component to the marine aerosol population is generally always observed, even in remote marine areas. In coastal regions, dramatic changes in aerosol composition occur as a result of wind shifts or airmass changes. As a result of these compositional differences, response of the aerosol to fluctuations in relative humidity is expected to differ from one locale or airmass to another. Therefore, aerosol size spectra alone are not sufficient for the prediction of visibility or the potential performance of EO systems under changing humidity conditions.