Book Description

Stratospheric aerosols are important to both chemical and radiational processes in the atmosphere. The University of Wyoming maintains one the longest stratospheric aerosol records in the world, which includes unique measurements of stratospheric condensation nuclei (CN) that are made with optical particle counters in series with a particle growth chamber. In this dissertation, balloon-borne stratospheric CN measurements are presented since 1982 over Laramie, Wyoming (41°N) and since 1986 over McMurdo Station, Antarctica (78°S). In the Antarctic region, the climatology shows the formation of a ubiquitous stratospheric CN layer between 21 - 27 km around mid August (late winter), reaching its maximum extent between September and early October (spring). CN concentrations increase from 10 - 20 cm−3 to over 100 cm−3 . In the northern mid-latitudes, the climatology shows a quasi-annual and smaller CN increase (1-10 cm−3 to over 20 cm−3 ), which is observed between 25 - 31 km in late winter and early spring. Major volcanic eruptions appear to enhance CN layers over Laramie and McMurdo. The Arctic Oscillation generally correlates with the magnitude of the Laramie CN layer, suggesting the importance of meridional transport. Volatility measurements and nucleation modeling support a sulfuric acid and water composition, and binary homogeneous nucleation as the primary observed CN layer formation mechanism in both locations. Bi-monthly CN measurements above Laramie support coagulation as the main reason for the dissipation of the CN layer, and suggest that the layer has a global extent. Air parcel trajectory analyses indicated that Arctic conditions and the associated ambient temperature changes during transport to Laramie, impacts the magnitude of the mid-latitude CN layer. Run specifically for 2010, the NCAR Community Earth System Model Version 1, with the high top component, the Whole Atmosphere Community Climate Model, indicates that the CN layer indeed has a global extent, and that the winter/spring mid-stratospheric layer possibly extends to 15°S in August and 30° N in February. Although preliminary, the CN layer over Antarctica may be associated with the decrease in springtime ozone loss above 20 km.