Measurements of condensation nuclei above the jet stream: Evidence for cross jet transport by waves and new particle formation at high altitudes

Abstract

Condensation nuclei (CN) were used as a tracer in mid‐latitude aircraft experiments in April and May 1984 designed to study transport in the stratosphere. A very large scale, mean distribution of CN was determined for April 20 in the plane perpendicular to the jet stream using smoothed CN measurements and very large scale, mean potential vorticity isopleths. This very large scale, mean distribution was constructed to exclude the structures associated with waves of short vertical wavelengths. A second analysis was done on filtered CN data by Danielsen et al. [this issue] to produce a CN cross section which included the effects of waves having vertical wavelengths of the order of 1 to 3 km. These two analyses and the waves inferred from the meteorological and tracer data produce a self‐consistent explanation for the observed spatial distribution of CN on April 20. The very large scale, mean CN distribution was distorted by waves which had the effect of transporting air with anticyclonic properties several degrees to the cyclonic side of the jet and created a strongly layered structure in the CN distribution.The unfiltered CN data revealed short wavelength oscillations in the CN distribution at the interface between the transported anticyclonic air parcel and the adjacent cyclonic air mass. These oscillations were also seen in the ozone data, and they increase the potential for mixing along that interface. If the mixing does occur, then a wave mechanism for cross jet transport has been observed.At altitudes above about 17 km, CN mixing ratios were affected by a high altitude source of new particles.