GACP Projects
Improved Exploitation of Field Data Sets to Address Aerosol Radiative-Climatic Effects and Development of a Global Aerosol Climatology
Philip B. Russell, PI
John M. Livingston, Co-I
Beat Schmid, Co-I
Abstract: The Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) and the second Aerosol Characterization Experiment (ACE-2) gathered extensive data sets on aerosol properties and radiative effects. TARFOX focused on the urban-industrial haze plume flowing from the eastern United States over the western Atlantic Ocean, whereas ACE-2 studied aerosols carried over the eastern Atlantic from both European urban/industrial and African mineral sources. We participated in TARFOX and ACE-2 by playing overall coordinating roles, by making aircraft and ship sunphotometer measurements, by analyzing the data in terms of aerosol-induced radiative flux changes, and by participating in closure studies that test the mutual consistency of a variety of measurements and the models that link them. The sunphotometer data set includes optical depth spectra (380-1020 nm and 380-1556 nm) in horizontal transects and vertical profiles, retrieved aerosol size distributions, water vapor columns and profiles, and ozone columns. Our current TARFOX funding has supported the archival of the optical depth data, their use in the flux-change studies mentioned above, and their comparison to optical depths retrieved from the satellite sensors AVHRR, GOES Imager, and ATSR-2, and from the MODIS Airborne Simulator. Our ACE-2 funding will support analogous archival and studies, with increased emphasis on water vapor retrievals and vertically resolved aerosol and water vapor intercomparisons. Our current TARFOX funding will be exhausted by the middle of this year, and our ACE-2 funding will be exhausted by the end of FY 1999.
For the funding requested here we propose to conduct additional analyses of the TARFOX, ACE-2, and related data sets, with the goals of greatly increasing their exploitation in aerosol radiative/climatic studies and in the development of a global aerosol climatology. In particular, we propose to: (1) Improve the cloud-screening in the sunphotometer optical depth data set, perform more general quality checks, and archive reprocessed data as necessary, (2) Investigate the question of the best aerosol optical models (e.g., complex refractive indices, internal vs. external mixtures, shapes) to account for observed aerosol compositions (e.g., water, carbonaceous material, sulfates, minerals) and sources, (3) Develop and test a new, more automated technique for retrieving particle size distributions from optical depth spectra, and apply it to the TARFOX and ACE-2 data sets, (4) Compare results of the new retrievals to those of previous retrievals, to size distributions measured in situ, and to models used in retrievals from imaging spectrometers on satellites and aircraft, and (5) Investigate the relationship between column water vapor and aerosol properties, with the goal of using water vapor information to improve satellite retrievals of aerosol optical depth and radiative forcing. We will use the results of these investigations in collaborative studies with other members of the Aerosol Radiative Forcing Science Team, so as to advance the development of a global aerosol climatology and to reduce uncertainties in aerosol effects on climate.
