Aerosols used as tracers for stratosphere-troposphere exchange in the arctic

Accumulation range particles as well as ozone and meteorological parameters were measured, in situ and on-line, during the 1991/1992 EASOE (European Arctic Stratospheric Ozone Experiment) aircraft measurement campaigns. Some interesting and significant findings relate to one flight in 31 January, 1992 from Kiruna (67°48′N, 20°18′E) to Spitsbergen (79°00′N 30°13′E) and back. At 390 mb the aircraft encountered stratospheric air, characterised by strong increases in concentrations of accumulation mode particles and ozone. The concentrations of particles with diameters between 0.31 and 0.79 μm were, moreover, highly correlated with ozone mixing ratios (R = 0.95). In the regions where stratospheric air was sampled the particle number size distribution showed a predominant mode centred at around 0.5 μm diameter. This mode was the signature of the stratospheric aerosol transported down into the upper troposphere where the measurements were conducted. There are indications that the measured stratospheric air originated from a folded tropopause. An approach to study the mixing between the intrusions of stratospheric air and the free tropospheric air has been used to quantify mixing coefficients (fractions of stratospheric air) along the flight route and absolute levels of particles and ozone in the lower stratosphere. This approach can be applied to study the dilution process during stratosphere-troposphere exchange. The requirement is that at least two conservative stratospheric tracers are measured simultaneously.