Redemann, ICARTT workshop, Durham, NH, Aug.9-12, 2005 Redemann, ICARTT workshop, Durham, NH, Aug.9-12, 2005 Airborne measurements of spectral direct aerosol radiative forcing - a new aerosol gradient method applied to data collected in INTEX/ITCT/ICARTT, 2004 J. Redemann (1) , P. Pilewskie (2) , P. Russell (4) , J. Livingston (3) , S. Howard (1) , J. Pommier (1) , B. Schmid (1) , W. Gore (4) , J. Eilers (4) , M. Wendisch (5) (1) Bay Area Environmental Research Institute, Sonoma, USA, (2) University of Colorado, Boulder, USA, (3) SRI International, Menlo Park, USA, (4) NASA Ames Research Center, Moffett Field, USA, (5) Institute for Tropospheric Research, Leipzig, Germany
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Redemann, ICARTT workshop, Durham, NH, Aug.9-12, 2005 Airborne measurements of spectral direct aerosol radiative forcing - a new aerosol gradient method.
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1. In INTEX/ICARTT/ITCT, we observed a total of 14 horizontal AOD gradients, with 10 gradients well suited for an analysis using the gradient forcing method.
2. More than half of the AOD gradients (at a wavelength of 499 nm) were greater than 0.1 and extended over distances less than 40 km.
3. We found cos()/«1 && nm>0.05 to be necessary criteria for the gradient forcing method.
4. Within the 10 case studies we found a high variability in the derived instantaneous aerosol forcing efficiencies (forcing per unit optical depth) for the visible wavelength range (350-700nm), with a mean of -79.6Wm-2 and a standard deviation of 21.8Wm-2(27%).
5. The mean instantaneous forcing efficiency for the visible plus near-IR wavelength range (350-1670nm) was derived to be ‑135.3Wm-2 with a standard deviation of 36.0Wm-2(27%).
6. An analytical conversion of the instantaneous forcing efficiencies to 24h-average values based on a 2-stream approximation yielded -45.8±13.1Wm-2 (mean±std) for the visible and -82.9±23.1Wm-2 (mean±std) for the visible plus near-IR wavelength range, respectively.
Funding for the J-31 aircraft modifications through NASA RSP, TCP + SSP, and for ICARTT measurements and data analysis through NOAA ACCP are gratefully acknowledged.