Airborne measurements of spectral direct aerosol radiative forcing in INTEX/ICARTT (2004) and comparisons to previous campaigns

HR: 17:00h
AN: A14B-05 INVITED [Abstracts]
TI: Airborne measurements of spectral direct aerosol radiative forcing in INTEX/ICARTT (2004) and comparisons to previous campaigns
AU: * Redemann, J
EM: jredemann@mail.arc.nasa.gov
AF: BAER Institute, 4742 Suffolk Ct., Ventura, CA 93003 United States
AU: Pilewskie, P
EM: Peter.Pilewskie@lasp.colorado.edu
AF: University of Colorado, Campus Box 311, Boulder, CO 80309 United States
AU: Russell, P
EM: prussell@mail.arc.nasa.gov
AF: NASA Ames Research Center, MS 245-5, Moffett Field, CA 94035 United States
AU: Livingston, J
EM: jlivingston@mail.arc.nasa.gov
AF: SRI International, 333 Ravenswood Ave., Menlo Park, CA 94025
AU: Howard, S
EM: howard@solat.arc.nasa.gov
AF: BAER Institute, 4742 Suffolk Ct., Ventura, CA 93003 United States
AU: Schmid, B
EM: bschmid@mail.arc.nasa.gov
AF: BAER Institute, 4742 Suffolk Ct., Ventura, CA 93003 United States
AU: Pommier, J
EM: jpommier@mail.arc.nasa.gov
AF: NASA Ames Research Center, MS 245-5, Moffett Field, CA 94035 United States
AU: Gore, W
EM: wgore@mail.arc.nasa.gov
AF: NASA Ames Research Center, MS 245-5, Moffett Field, CA 94035 United States
AU: Eilers, J
EM: jeilers@mail.arc.nasa.gov
AF: NASA Ames Research Center, MS 245-5, Moffett Field, CA 94035 United States
AU: Wendisch, M
EM: wendisch@tropos.de
AF: Leibniz-Inst. for Trop. Res., Permoserstr. 15, Leipzig, D-04318 Germany
AU: Bush, B
EM: bbush@kumo.ucsd.edu
AF: UCSD - Scripps, 9500 Gilman Drive, Dept. 0242, La Jolla, CA 92093 United States
AU: Valero, F
EM: fvalero@ucsd.edu
AF: UCSD - Scripps, 9500 Gilman Drive, Dept. 0242, La Jolla, CA 92093 United States
AB: 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 Jetstream 31 (J31) aircraft during 19 science flights (~ 53 flight hours) over the Gulf of Maine between 12 July and 8 August 2004. AATS-14 measures the direct solar beam transmission at 14 discrete wavelengths (354-2138 nm), yielding aerosol optical depth (AOD) spectra, while the SSFR system yields down- and upwelling solar irradiance at a spectral resolution of ~ 8-12 nm over the wavelength range 300-1700 nm. The combination of simultaneous AATS and SSFR measurements yields plots of net spectral irradiance as a function of aerosol optical depth as measured along horizontal flight legs. From the slope of these plots we determine the instantaneous aerosol-induced change in net radiative flux per change in AOD. By normalization to an aerosol optical depth change of unity we derive the spectral aerosol radiative forcing efficiency [W m^-2 nm^-1]. Numerical integration of the irradiance measurements over a given spectral range yields the broadband aerosol radiative forcing efficiency [W m^-2]. In INTEX/ITCT, we observed a total of 16 horizontal AOD gradients, with 10 gradients well suited for our analysis because of the small changes in solar zenith angle. Within the 10 case studies 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%). The mean instantaneous forcing efficiency for the visible plus near-IR wavelength range (350-1670 nm) was derived to be 135.3 W m^-2 with a standard deviation of 36.0 W m^-2 (27%). An analytical conversion of the instantaneous forcing efficiencies to 24h-average values yielded -45.8ń13.1 W m^-2 (meanństd) for the visible and -82.9ń23.1 W m^-2 (meanństd) for the visible plus near-IR wavelength range, respectively. We present spectrally resolved aerosol forcing efficiencies and compare the range of observed broadband forcing efficiencies to previously reported values. We further show the consistency in broadband single scattering albedos derived from the gradient measurements with the presence of biomass burning aerosol from Canadian forest fires during the first half of the ICARTT experiment.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 1640 Remote sensing (1855)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005