Fine-scale measurements of fog-droplet concentrations: a preliminary assessment

Abstract

Measurements of warm fog-droplet concentrations carried out in a site in Mexico were analyzed with the purpose of identifying inhomogeneous sections of clouds. The site, located in the Sierra Madre Oriental of eastern Mexico, is characterized by frequent fog events throughout the year, sometimes accompanied with drizzle. Fog droplet concentrations and size spectra were obtained with a Forward Scattering Spectrometer Probe mounted on a ground-based, instrumented van for in-motion operation. The sampling technique, along with the data retrieval scheme used, allows one to investigate fine-scale microphysical structure of fog and to identify droplet concentration zones in cloud segments over spatial resolutions from hundreds of meters to tens of centimeters. The results show that a broadening of the droplet spectra towards larger sizes occurs in zones of decreased droplet concentration. This provides new information regarding fog microstructure at scales where important droplet growth occurs by condensation and coagulation. It is concluded that detailed knowledge of droplet spectra variations along fog transects provide further information for the characterization of cloud inhomogeneities.