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Published December 16, 2003 | public
Journal Article

Column closure studies of lower tropospheric aerosol and water vapor during ACE-Asia using airborne Sun photometer and airborne in situ and ship-based lidar measurements


We assess the consistency (closure) between solar beam attenuation by aerosols and water vapor measured by airborne Sun photometry and derived from airborne in situ and ship-based lidar measurements during the April 2001 Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia). The airborne data presented here were obtained aboard the Twin Otter aircraft. Comparing aerosol extinction σ_(ep)(550 nm) from four different techniques shows good agreement for the vertical distribution of aerosol layers. However, the level of agreement in absolute magnitude of the derived aerosol extinction varied among the aerosol layers sampled. The σ_(ep)(550 nm) computed from airborne in situ size distribution and composition measurements shows good agreement with airborne Sun photometry in the marine boundary layer but is considerably lower in layers dominated by dust if the particles are assumed to be spherical. The σ_(ep)(550 nm) from airborne in situ scattering and absorption measurements are about ∼13% lower than those obtained from airborne Sun photometry during 14 vertical profiles. Combining lidar and the airborne Sun photometer measurements reveals the prevalence of dust layers at altitudes up to 10 km with layer aerosol optical depth (from 3.5 to 10 km altitude) of ∼0.1 to 0.2 (500 nm) and extinction-to-backscatter ratios of 59–71 sr (523 nm). The airborne Sun photometer aboard the Twin Otter reveals a relatively dry atmosphere during ACE-Asia with all water vapor columns <1.5 cm and water vapor densities ρ_w < 12 g/m³. Comparing layer water vapor amounts and ρ_w from the airborne Sun photometer to the same quantities measured with aircraft in situ sensors leads to a high correlation (r² = 0.96), but the Sun photometer tends to underestimate ρ_w by 7%.

Additional Information

This research was conducted as part of the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia). It is a contribution to the International Global Atmospheric Chemistry (IGAC) Core Project of the International Geosphere Biosphere Program (IGBP) and is part of the IGAC Aerosol Characterization Experiments (ACE). Funding to NASA Ames was provided by NASA's Earth Observing System Inter-Disciplinary Science (EOS-IDS) Program, NASA's Radiation Sciences Program, and the Office of Naval Research. Funding to the Department of Atmospheric Sciences, University of Washington, was provided by Office of Naval Research grant N00014-97-1-0132. We thank the Ozone Processing Team at NASA Goddard Space Flight Center for making available TOMS EP data. We also would like to thank Edward T. Peltzer for making available Matlab shell-scripts for linear regression analysis (www.mbaeri.org/~etp3/regressindex.htm), and Atmospheric and Environmental Research Inc. (AER) for making LBLRTM available at http://www.rtweb.aer.com/.

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