ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-7829-2010 A new method for deriving aerosol solar radiative forcing and its first application within MILAGRO/INTEX-B Schmidt K. S. 1 Pilewskie P. 1 Bergstrom R. 2 Coddington O. 1 Redemann J. 2 Livingston J. 3 Russell P. 4 Bierwirth E. 5 Wendisch M. 5 Gore W. 4 Dubey M. K. 6 Mazzoleni C. 6 7 Laboratory for Atmospheric and Space Physics, Boulder, CO, USA Bay Area Environmental Research Institute, Sonoma, CA, USA SRI International, Menlo Park, CA, USA NASA Ames Research Center, Moffett Field, CA, USA Leipzig Institute for Meteorology, University of Leipzig, Germany Los Alamos National Laboratory, Los Alamos, NM, USA Michigan Technological University, MI, USA 24 08 2010 10 16 7829 7843 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/7829/2010/acp-10-7829-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/7829/2010/acp-10-7829-2010.pdf

We introduce a method for deriving aerosol spectral radiative forcing along with single scattering albedo, asymmetry parameter, and surface albedo from airborne vertical profile measurements of shortwave spectral irradiance and spectral aerosol optical thickness. The new method complements the traditional, direct measurement of aerosol radiative forcing efficiency from horizontal flight legs below gradients of aerosol optical thickness, and is particularly useful over heterogeneous land surfaces and for homogeneous aerosol layers where the horizontal gradient method is impractical. Using data collected by the Solar Spectral Flux Radiometer (SSFR) and the Ames Airborne Tracking Sunphotometer (AATS-14) during the MILAGRO (Megacity Initiative: Local and Global Research Observations) experiment, we validate an over-ocean spectral aerosol forcing efficiency from the new method by comparing with the traditional method. Retrieved over-land aerosol optical properties are compared with in-situ measurements and AERONET retrievals. The spectral forcing efficiencies over ocean and land are remarkably similar and agree with results from other field experiments.

 References Arnott, W. P., Moosmüller, H., Rogers, C. F., Jin, T., and Bruch, R.: Photoacoustic spectrometer for measuring light absorption by aerosols: Instrument description, Atmos. Environ., 33, 2845–2852, 1999. Bannehr, L. and Schwiesow, R.: A technique to account for the misalignment of pyranometers installed on aircraft, J. Atmos. Oceanic Technol., $10$, 774–777, 1993. Barnard, J. C., Volkamer, R., and Kassianov, E. I.: Estimation of the mass absorption cross section of the organic carbon component of aerosols in the Mexico City Metropolitan Area, Atmos. Chem. Phys., 8, 6665–6679, doi:10.5194/acp-8-6665-2008, 2008. Bergstrom, R. W., Pilewskie, P., Russell, P. B., Redemann, J., Bond, T. C., Quinn, P. K., and Sierau, B.: Spectral absorption properties of atmospheric aerosols, Atmos. Chem. Phys., 7,~5937–5943,~doi:10.5194/acp-7-5937-2007, 2007. Bergstrom, R. W., Schmidt, K. S., Coddington, O., Pilewskie, P., Guan, H., Livingston, J. M., Redemann, J., and Russell, P. B.: Aerosol spectral absorption in the Mexico City area: results from airborne measurements during MILAGRO/INTEX B, Atmos. Chem. Phys., 10, 6333–6343, doi:10.5194/acp-10-6333-2010, 2010. Bierwirth, E., Wendisch, W., Ehrlich, E., Heese, B., Tesche, M., Althausen, D., Schladitz, A., Müller, D., Otto, S., Trautmann, T., Dinter, T., Hoyningen-Huene, W., and Kahn, R.: Spectral surface albedo over Morocco and its impact on radiative forcing of Saharan dust, Tellus, 61B, 252-269, doi10.1111/j.1600-0889.2008.00395.x, 2009. Bucholtz, A., Bluth, R. T., Kelly, B., Taylor, S., Batson, K., Sarto, A. W., Tooman, T. P., and McCoy Jr., R. F.: The Stabilized Radiometer Platform (STRAP) – An Actively Stabilized Horizontally Level Platform for Improved Aircraft Irradiance Measurements, J. Atmos. Oceanic Technol., 25, 2161–2175, 2008. Chandrasekhar, S., Radiative transfer, Dover Publications Inc., New York, USA, 10–11, 1960. %\blackbox\bf add page range Coakley, J. and Chylek, P.: The two-stream approximation in radiative transfer: Including the angle of the incident radition, J. Atmos. Sci., $32$, 409–418, 1975. Coddington, O., Schmidt, K. S., Pilewskie, P., Gore, W. J., Bergstrom, R. W., Román, M., Redemann, J., Russell, P. B., Liu, J., and Schaaf, C. C.: Aircraft measurements of spectral surface albedo and its consistency with ground-based and space-borne observations, J. Geophys. Res., 113, D17209, doi:10.1029/2008JD010089, 2008. Corr, C. A., Krotkov, N., Madronich, S., Slusser, J. R., Holben, B., Gao, W., Flynn, J., Lefer, B., and Kreidenweis, S. M.: Retrieval of aerosol single scattering albedo at ultraviolet wavelengths at the T1 site during MILAGRO, Atmos. Chem. Phys., $9$, 5813–5827, doi:10.5194/acp-9-5813-2009, 2009. Doran, J. C., Barnard, J. C., Arnott, W. P., Cary, R., Coulter, R., Fast, J. D., Kassianov, E. I., Kleinman, L., Laulainen, N. S., Martin, T., Paredes-Miranda, G., Pekour, M. S., Shaw, W. J., Smith, D. F., Springston, S. R., and Yu, X.-Y.: The T1-T2 study: evolution of aerosol properties downwind of Mexico City, Atmos. Chem. Phys., $7$, 1585–1598, doi:10.5194/acp-7-1585-2007, 2007. Dubovik, O., Smirnov, A., Holben, B. N., King, M. D., Kaufman, Y. J., Eck, T. F., and Slutsker, I.: Accuracy assessments of aerosol optical properties retrieved from Aerosol Robotic Network (AERONET) Sun and sky radiance measurements, J. Geophys. Res., 105(D8), 9791–9806, 2000. Hair, J. W., Hostetler, C. A., Cook, A. L., Harper, D. B., Ferrare, R. A., Mack, T. L., Welch, W., Isquierdo, L. R., and Hovis, F. E.: Airborne high spectral resolution lidar for profiling aerosol optical properties, Appl. Opt., $47$, 6734–6752, 2008. Kassianov, E. I., Flynn, C. J., Ackerman, T. P., and Barnard, J. C.: Aerosol single-scattering albedo and asymmetry parameter from MFRSR observations during the ARM Aerosol IOP 2003, Atmos. Chem. Phys., 7, 3341–3351, doi:10.5194/acp-7-3341-2007, 2007. Kurucz, R. L.: Synthetic infrared spectra, in Infrared Solar Physics: Proceedings of the 154th Symposium of the International Astronomical Union, edited by D. M. Rabin, J. T. Jefferies, and C. Lindsey, pp. 523Ð531, Kluwer Acad., Dordrecht, Netherlands, 1992. Livingston, J. M., Redemann, J., Russell, P. B., Torres, O., Veihelmann, B., Veefkind, P., Braak, R., Smirnov, A., Remer, L., Bergstrom, R. W., Coddington, O., Schmidt, K. S., Pilewskie, P., Johnson, R., and Zhang, Q.: Comparison of aerosol optical depths from the Ozone Monitoring Instrument (OMI) on Aura with results from airborne sunphotometry, other space and ground measurements during MILAGRO/INTEX-B, Atmos. Chem. Phys., 9, 6743–6765, doi:10.5194/acp-9-6743-2009, 2009. Magi, B. I., Fu, Q., Redemann, J., and Schmid, B.: Using aircraft measurements to estimate the magnitude and uncertainty of the shortwave direct radiative forcing of southern African biomass burning aerosol, J. Geophys. Res., 113, D05213, doi:10.1029/2007JD009258, 2008. Marley, N. A., Gaffney, J. S., Castro, T., Salcido, A., and Frederick, J.: Measurements of aerosol absorption and scattering in the Mexico City Metropolitan Area during the MILAGRO field campaign: a comparison of results from the T0 and T1 sites, Atmos. Chem. Phys., 9, 189–206, doi:10.5194/acp-9-189-2009, 2009. Mayer, B. and Kylling, A.: Technical note: The libRadtran software package for radiative transfer calculations – description and examples of use, Atmos. Chem. Phys., 5, 1855–1877, doi:10.5194/acp-5-1855-2005, 2005. Molina, L. T., Madronich, S., Gaffney, J. S., Apel, E., de Foy, B., Fast, J., Ferrare, R., Herndon, S., Jimenez, J. L., Lamb, B., Osornio-Vargas, A. R., Russell, P., Schauer, J. J., Stevens, P. S., and Zavala, M.: An overview of the MILAGRO 2006 campaign: Mexico City emissions and their transport and transformation, Atmos. Chem. Phys. Discuss., 10, 7819–7983, doi:10.5194/acpd-10-7819-2010, 2010. Paredes-Miranda, G., Arnott, W. P., Jimenez, J. L., Aiken, A. C., Gaffney, J. S., and Marley, N. A.: Primary and secondary contributions to aerosol light scattering and absorption in Mexico City during the MILAGRO 2006 campaign, Atmos. Chem. Phys., 9, 3721–3730, doi:10.5194/acp-9-3721-2009, 2009. Pilewskie, P., Pommier, J., Bergstrom, R., Gore, W., Howard, S., Rabbette, M., Schmid, B., Hobbs, P. V., and Tsay, S. C.: Solar spectral radiative forcing during the Southern African Regional Science Initiative, J. Geophys. Res., 108(D13), 8486, doi:10.1029/2002JD002411, 2003. Redemann, J., Pilewskie, P., Russell, P. B., Livingston, J. M., Howard, S., Schmid, B., Pommier, J., Gore, W., Eilers, J., and Wendisch, M.: 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, 2006. Redemann, J., Zhang, Q., Livingston, J., Russell, P., Shinozuka, Y., Clarke, A., Johnson, R., and Levy, R.: Testing aerosol properties in MODIS Collection 4 and 5 using airborne sunphotometer observations in INTEX-B/MILAGRO, Atmos. Chem. Phys., 9, 8159-8172, doi:10.5194/acp-9-8159-2009, 2009. Ricchiazzi, P., Yang, S. R., Gautier, C., and Sowle, D.: SBDART: A research and teaching software tool for Plane-parallell radiative transfer in the earth's atmosphere. Bulletin of the American Meteorological Society 79 (10) : 2101-2114, 1998. Russell, P. B., Kinne, S., and Bergstrom, R.: Aerosol Climate Effects: Local Radiative Forcing and Column Closure Experiments, J. Geophys. Res., 102, 9397–9407, 1997. Russell, P. B., Livingston, J. M., Hignett, P., Kinne, S., Wong, J., and Hobbs, P. V.: Aerosol-induced radiative flux changes off the United States Mid-Atlantic coast: Comparison of values calculated from sunphotometer and in situ data with those measured by airborne pyranometer, J. Geophys. Res., $104$, 2289–2307, 1999. Russell, P. B., J. Redemann, B. Schmid, R. W. Bergstrom, J. M. Livingston, D. M. McIntosh, S. Hartley, P. V. Hobbs, P. K. Quinn, C. M. Carrico, M. J. Rood, E. Öström, K. J. Noone, W. von Hoyningen-Huene, and L. Remer, Comparison of aerosol single scattering albedos derived by diverse techniques in two North Atlantic experiments, J. Atmos. Sci., $59$, 609–619, 2002. Wendisch, M., Müller, D., Schell, D., and Heintzenberg, J.: An airborne spectral albedometer with active horizontal stabilization, J. Atmos. Oceanic Technol., $18$, 1856–1866, 2001. Wendisch, M., Pilewskie, P., Jäkel, E., Schmidt, S., Pommier, J., Howard, S., Jonsson, H. H., Guan, H., Schröder, M., and Mayer, B.: Airborne measurements of areal spectral surface albedo over different sea and land surfaces. J. Geophys. Res., 109, D08203, doi:10.1029/2003JD004392, 2004. Wiscombe, W. J., and Grams, G. W.: The backscattered fraction in two-stream approximations, J. Atmos. Sci., 33, 2440–2451, 1976.