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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D14210, doi:10.1029/2005JD006812, 2006

Airborne measurements of spectral direct aerosol radiative forcing in the Intercontinental chemical Transport Experiment/Intercontinental Transport and Chemical Transformation of anthropogenic pollution, 2004

Jens Redemann

Bay Area Environmental Research Institute, Sonoma, California, USA


Peter Pilewskie

Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA


Philip B. Russell

NASA Ames Research Center, Moffett Field, California, USA


John M. Livingston

SRI International, Menlo Park, California, USA


Steve Howard

Bay Area Environmental Research Institute, Sonoma, California, USA


Beat Schmid

Bay Area Environmental Research Institute, Sonoma, California, USA


John Pommier

Bay Area Environmental Research Institute, Sonoma, California, USA


Warren Gore

NASA Ames Research Center, Moffett Field, California, USA


James Eilers

NASA Ames Research Center, Moffett Field, California, USA


Manfred Wendisch

Leibniz Institute for Tropospheric Research, Leipzig, Germany


Abstract

As part of the INTEX-NA (Intercontinental chemical Transport Experiment–North America) and ITCT (Intercontinental Transport and Chemical Transformation of anthropogenic pollution) field studies, the NASA Ames 14-channel Airborne Tracking Sunphotometer (AATS-14) and a pair of Solar Spectral Flux Radiometers (SSFR) took measurements from aboard a Sky Research Jet stream 31 (J31) aircraft during 19 science flights over the Gulf of Maine during 12 July to 8 August 2004. The combination of coincident AATS-14 and SSFR measurements yields plots of net (downwelling minus upwelling) spectral irradiance as a function of aerosol optical depth (AOD) as measured along horizontal flight legs. By definition, the slope of these plots yields the instantaneous change in net irradiance per unit AOD change and is referred to as the instantaneous spectral aerosol radiative forcing efficiency, E i (W m−2 nm−1). Numerical integration over a given spectral range yields the instantaneous broadband aerosol radiative forcing efficiency (W m−2). This technique for deriving E i is called the aerosol gradient method. Within 10 case studies considered suitable for our analysis we found a high variability in the derived instantaneous aerosol forcing efficiencies for the visible wavelength range (350–700 nm), with a mean of −79.6 W m−2 and a standard deviation of 21.8 W m−2 (27%). An analytical conversion of the instantaneous forcing efficiencies to 24-hour-average values yielded −45.8 ± 13.1 W m−2 (mean ± std). We present spectrally resolved aerosol forcing efficiencies between 350 and 1670 nm, estimates of the midvisible aerosol single scattering albedo and a comparison of observed broadband forcing efficiencies to previously reported values.

Received 25 October 2005; accepted 27 March 2006; published 26 July 2006.

Keywords: aerosol radiative forcing; aerosol remote sensing.

Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801, 4906); 1616 Global Change: Climate variability (1635, 3305, 3309, 4215, 4513); 1637 Global Change: Regional climate change; 1640 Global Change: Remote sensing (1855).

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Citation: Redemann, J., P. Pilewskie, P. B. Russell, J. M. Livingston, S. Howard, B. Schmid, J. Pommier, W. Gore, J. Eilers, and M. Wendisch (2006), Airborne measurements of spectral direct aerosol radiative forcing in the Intercontinental chemical Transport Experiment/Intercontinental Transport and Chemical Transformation of anthropogenic pollution, 2004, J. Geophys. Res., 111, D14210, doi:10.1029/2005JD006812.