Evidence for the Widespread Presence of Liquid-Phase Particles During the 1999-2000 Arctic Winter
Research Staff: Katja Drdla
In-situ Multi-Angle Spectrometer Probe (MASP) particle measurements have been analysed to determine the typical behaviour of sulphate particles during the SOLVE campaign. The study has explored variations in the total particle concentration measured by MASP. A new analysis method has been developed which accounts for several known sources of variability in MASP concentrations. In the resulting dataset, variations in MASP concentration reveal the growth characteristics of small particles (those which are smaller than 0.2mm in radius at mid-latitudes). The method also allows all of the MASP measurements made during the SOLVE campaign to be incorporated in a single analysis.
At all levels of the stratosphere, the total MASP concentration varies continuously with temperature. This behaviour is well-reproduced by assuming that the sulphate aerosols are liquid solutions, but cannot be reproduced if the aerosol is assumed to be frozen. At sufficiently cold temperatures, larger increases in the MASP concentration are consistently seen; the observed onset temperature for this increase is in good agreement with model expectations for liquid ternary solutions. Liquid-like behaviour is apparent for all measurements made during SOLVE, both inside and outside the vortex, and even at the coldest temperatures sampled during the campaign. The only anomalous measurements were made during the flight of January 14th, 2001; however, this mid-latitude flight was very unlikely to contain sulphuric acid tetrahydrate particles based on the recent warm temperatures experienced by the air. At the levels with the coldest measured temperatures, which cause maximum particle sizes and thus the greatest total MASP concentrations, 90% of the particles grow as liquids. Therefore, the freezing that occurred during the 1999-2000 Arctic winter was selective, causing most of the particles to remain liquid even in the presence of a small number of frozen particles.
Collaborators: B. W. Gandrud and D. Baumgardner, NCAR; J. C. Wilson, University of Denver; T. P. Bui, SGG branch; D. Hurst, S. M. Schauffler, NCAR; H. Jost, SGG branch; J. Greenblatt, SGG branch; C. R. Webster, JPL
Point of Contact: Katja Drdla, 650/604-5663, firstname.lastname@example.org