Insightsts gained from field measurements of aerosols and clouds in the upper troposphere/lower stratosphere

摘要

The tropopause region UT/LS is an altitude band in the Earth's atmosphere which is subjected to stratospheric as well as tropospheric influences.Here abundances of trace gases like ozone increase with altitude from levels of tens of ppbvs to ppmv while water vapor decreases from hundreds to a few ppmv.The tropopause temperatures may be as low as -90 deg C with pressures ranging roughly from 210 hPa to 90 hPa.These thermodynamic conditions in the UT/LS allow for complex cloud and aerosol formation and interaction mechanisms [Lynch et al.,2002].Before anthropogenic effects like the possible influence of aircraft emissions on radiative budget,cloud formation and air chemistry can be assessed,fundamental questions need to be addressed.Some of these are [IPCC,1999]:Which properties of aerosol particles in the UT/LS determine ice cloud formation ? What forms and maintains the Junge aerosol layer ? Which mechanisms are causing the dryness in the stratosphere ? Do the recently discussed veils of subvisual cirrus clouds in the tropical tropopause region [Thomas et al.,2002] contribute to this dehydration ? What is the role of tropical upper tropospheric ice clouds in general ? To what degree is supersaturation with respect to ice possible in the upper troposphere ? [Gettleman et al.,2000] What is the chemical composition of the aerosol particles in the UT/LS and how does this influence cloud formation and radiative transfer?In this invited presentation the results obtained from various field campaigns concerning these and other questions are presented.