Precipitation from a maritime cloud layer with very low droplet concentrations

• Published in: Atmospheric research 1996, Vol.40 (1), p.99,102-99,107
• Main Authors: Hobbs, P.V., Rangno, A.L.
• Format: Article
• Language: English
• Subjects: Earth, ocean, space; Exact sciences and technology; External geophysics; Meteorology; Water in the atmosphere (humidity, clouds, evaporation, precipitation)
• ISSN: 0169-8095; 1873-2895
• DOI: 10.1016/0169-8095(95)00030-5

In very clean air the total concentrations of droplets in maritime stratiform clouds can be very low (Squires, 1958a, b). Interestingly, these clouds sometimes precipitate. In this note we describe such a case and the meteorological conditions that accompanied it. The measurements were made aboard the University of Washington's Convair C-131A aircraft about 100 km off the Pacific Northwest coastline from about 2000 to 2200 UTC on 2 December 1991. The instrumentation aboard the Convair C131-A for the measurement of aerosol and cloud particles has been described by Hobbs et al. (1991). The synoptic conditions at 850 hPa (the standard pressure level closest to the cloud layers we studied) are shown in a figure. Air that originated from the sub-tropics was approaching the Washington coast after being rotated anticyclonically around a surface high-pressure center (10 hPa) located about 1000 km west of northern California. Consequently, the clouds that we sampled formed in an air mass that had a very long trajectory over the Pacific Ocean.