The 5-6 December 1991 FIRE IFO II jet stream cirrus case study: possible influences of volcanic aerosols

Abstract

Following the local appearance of a spur of stratospheric volcanic debris from the subtropics, a series of jet streams subsequently conditioned the troposphere through tropopause foldings with sulfur-based particles that became effective cloud-forming nuclei in cirrus clouds. Aerosol and ozone measurements suggest a complicated history of stratospheric-tropospheric exchanges embedded within the upper-level flow, and cirrus cloud formation was noted to occur locally at the boundaries of stratospheric aerosol-enriched layers that became humidified through diffusion, precipitation, or advective processes. Apparent cirrus cloud alterations include abnormally high ice crystal concentrations (up to ~600 L-1, complex radial ice crystal types, and relatively large haze particles in cirrus uncinus cell heads at temperatures between -40° and -50°C. Implications for volcanic-cirrus cloud climate effects and usual (nonvolcanic aerosol) jet stream cirrus cloud formation are discussed. -from Authors