Stratospheric aerosols

Assessments of stratospheric ozone have been conducted for nearly two decades and have evolved from describing ozone morphology to estimating ozone trends, and then to attribution of those trends. Stratospheric aerosol has only been integrated in assessments in the context of their effects on ozone chemistry and has not been critically evaluated. The objective of the SPARC Report No. 4 (2006) was to present a systematic analysis of the state of knowledge of stratospheric aerosols including their precursors. The report included an examination of precursor concentrations and trends, measurements of stratospheric aerosol properties, trends in those properties, and modeling of aerosol formation, transport, and distribution in both background and volcanic conditions. The scope of the report is extensive; however, some aspects of stratospheric aerosol science have been deliberately excluded. For instance, no examination was included of polar stratospheric clouds (PSCs) or other clouds (such as cirrus clouds) occurring at or above the tropopause.

The report produced a gap-free aerosol data base for use beyond this assessment. This required some new analysis that has not previously appeared in the technical literature. Similarly, the trend analysis required the development of a new analysis technique.

Activity leaders:

T. Peter, ETH Zurich, Switzerland

L. Thomason, NASA Langley, USA

Published results:

SPARC report:

SPARC Report No. 4 (2006) Assessment of Stratospheric Aerosol Properties (ASAP). L Thomason and T. Peter (eds.) WCRP-124, WMO/TD- No. 1295.

Middle Atmosphere Climatology

The aim of the SPARC Working Group on Middle Atmosphere Climatology led by David Karoly, Monash University, Australia, was to provide, to the the climate modelling community, the current best estimates of appropriate parameters that determine stratospheric aspects of recent time-varying climate forcing. The approach has been to consolidate existing information and provide estimates of time-varying forcings over the periods since about 1880 associated with stratospheric ozone, stratospheric volcanic aerosols and solar variations.

The activity produced stratospheric climate forcing data sets which were made available to the climate modelling community through the SPARC Data Center and used in the IPCC Third Assessment Report (2001).

Published results:

SPARC Science Report:

SPARC Report No. 3 (2002) Intercomparison of Middle Atmosphere Climatologies. Randel, M.-L. Chanin and C. Michaut (Editors).

SPARC activity report:

SPARC Newsletter No. 14 (2000), p. 15: Stratospheric Aspects of Climate Forcing, by D. Karoly

Journal publication:

Randel, W., P. Udelhofen, E. Fleming, M. Geller, M. Gelman, K. Hamilton, D. Karoly, D. Ortland, S. Pawson, R. Swinbank, F. Wu, M. Baldwin, M.-L. Chanin, P. Keckhut, K. Labitzke, E. Remsberg, A. Simmons, and D. Wu (2004) The SPARC Intercomparison of Middle Atmosphere Climatologies. Journal of Climate 17, p. 987-1003