HR: 13:30h
AN: A53B-01    [Abstracts]
TI: Highlights of the SPARC Assessment of Stratospheric Aerosol Properties
AU: * Thomason, L W
EM: l.w.thomason@nasa.gov
AF: NASA Langley Research Center, Mail Stop 475, Hampton, VA 23681 United States
AU: Peter, T
EM: thomas.peter@env.ethz.ch
AF: Institute for Atmospheric and Climate Science, Hoenggerberg HPP L8.2 , Zuerich, CH-8093 Switzerland
AB: The SPARC Assessment of Stratospheric Aerosol Properties (ASAP) is a broad survey of the state of knowledge of aerosol precursors, measurements, and modeling and an extensive report will be released in 2005. This presentation will highlight key findings of this effort that are summarized herein. During the past three decades, aerosol loading in the stratosphere has primarily reflected the effects of a few volcanic eruptions that inject aerosol and its gaseous precursors (primarily SO2) into the stratosphere. The most noteworthy of these eruptions are El Chichon (1982) and Pinatubo (1991). The 1991 Pinatubo eruption likely had the largest impact of any event in the 20th century producing ~30 Tg of aerosol (compared to El Chichon's ~12 Tg) that persisted into at least the late 1990's. Current loading, which is at lowest levels observed, is less than 0.5 Tg and the Pinatubo event represents nearly a factor of 100 enhancement relative to a non-volcanic level. Many parameters that are useful for either scientific or intercomparison purposes are derived indirectly from observations. This is particularly true for space-based measurements where only bulk extinction is measured but also true in degree for most ground-based and in situ systems as well. Space-based and in situ measurements of aerosol parameters tend to be consistent following significant volcanic events. However, during periods of very low aerosol loading, this consistency breaks down and significant differences exist between systems for key parameters including aerosol surface area density and extinction. The source of the non-volcanic aerosol is primarily OCS and there is general agreement between measured OCS and modeling of its transformation to sulfate aerosol, and observed aerosols. However, there is a significant dearth of SO2 measurements, and the role of tropospheric SO2 in the stratospheric aerosol budget - while significant - remains a matter of some guesswork. In addition, it is not well understood whether decreasing global human-derived SO2 emissions or increasing emissions in low latitude developing countries such as China dominate the human component of SO2 transport across the tropical tropopause. While the actual removal of aerosol from the stratosphere to the troposphere is predominately associated with tropopause folds, sedimentation plays a crucial role in the vertical distribution of aerosol throughout the stratosphere including its abundance in the vicinity of the tropopause. Given the high variability of stratospheric aerosol loading, it is difficult to detect trends in the non-volcanic component. Trends derived from the late 1970's to the current period are likely to encompass a value of zero.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0340 Middle atmosphere--composition and chemistry
DE: 0370 Volcanic effects (8409)
SC: Atmospheric Sciences [A]
MN: 2005 Joint Assembly