ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-10-14557-2010 Spectral invariant behavior of zenith radiance around cloud edges simulated by radiative transfer Chiu J. C. 1 Marshak A. 2 Knyazikhin Y. 3 Wiscombe W. J. 2 4 University of Maryland Baltimore County, Baltimore, MD, USA NASA/Goddard Space Flight Center, Greenbelt, MD, USA Boston University, Boston, MA, USA Brookhaven National Laboratory, New York, NY, USA 11 06 2010 10 6 14557 14581 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-discuss.net/10/14557/2010/acpd-10-14557-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/10/14557/2010/acpd-10-14557-2010.pdf

A previous paper discovered a surprising spectral-invariant relationship in shortwave spectrometer observations taken by the Atmospheric Radiation Measurement (ARM) program. Here, using radiative transfer simulations, we study the sensitivity of this relationship to the properties of aerosols and clouds, to the underlying surface type, and to the finite field-of-view (FOV) of the spectrometer. Overall, the relationship is mostly sensitive to cloud properties and has little sensitivity to the other factors. At visible wavelengths, the relationship primarily depends on cloud optical depth regardless of cloud thermodynamic phase and drop size. At water-absorbing wavelengths, the slope of the spectral-invariant relationship depends primarily on cloud optical depth; the intercept, by contrast, depends primarily on cloud absorption properties, suggesting a new retrieval method for cloud drop effective radius. These results suggest that the spectral-invariant relationship can be used to infer cloud properties even with insufficient or no knowledge about spectral surface albedo and aerosol properties.

 References Baker, M. B. and Latham, J.: The evolution of droplet spectra and the rate of production of embryonic raindrops in small cumulus clouds, J. Atmos. Sci., 36, 1612–1615, 1979. Baker, M. B., Corbin, R. G., and Latham, J.: The influence of entrainment on the evolution of cloud droplet spectra: 1 A model of inhomogeneous mixing. Q. J. Roy. Meteor. Soc., 106, 581–598, 1980. Charlson, R. J., Ackerman, A. S., Bender, F. A.-M., Anderson, T. L., and Liu, Z.: On the climate forcing consequences of the albedo continuum between cloudy and clear air, Tellus B, 59, 715–727, doi:10.1111/j.1600-0889.2007.00297.x, 2007. Chiu, J. C., Marshak, A., Knyazikhin, Y., Pilewski, P., and Wiscombe, W. J.: Physical interpretation of the spectral radiative signature in the transition zone between cloud-free and cloudy regions, Atmos. Chem. Phys., 9, 1419–1430, doi:10.5194/acp-9-1419-2009, 2009. Jiang, H., Feingold, G., and Koren, I.: Effect of aerosol on trade cumulus cloud morphology, J. Geophys. Res., 114, D11209, doi:10.1029/2009JD011750, 2009. Koren, I., Remer, L. A., Kaufman, Y. J., Rudich, Y., and Martins, J. V.: On the twilight zone between clouds and aerosols, Geophys. Res. Lett., 34, L08805, doi:10.1029/2007GL029253, 2007. Koren, I., Oreopoulos, L., Feingold, G., Remer, L. A., and Altaratz, O.: How small is a small cloud?, Atmos. Chem. Phys., 8, 3855–3864, doi:10.5194/acp-8-3855-2008, 2008. Koren, I., Feingold, G., Jiang, H., and Altaratz, O.: Aerosol effects on the inter-cloud region of a small cumulus cloud field, Geophys. Res. Lett., 36, L14805, doi:10.1029/2009GL037424, 2009. Latham, J and Reed, R. L.: Laboratory studies of effects of mixing on evolution of cloud droplet spectra, Q. J. Roy. Meteor. Soc., 103, 297–306, 1977. Lu, M.-L., Mcclatchey, R. A., and Seinfeld, J. H.: Cloud Halos: Numerical Simulation of Dynamical Structure and Radiative Impact, J. App. Meteo., 41, 832–848, 2002. Lu, M.-L., Wang, J., Freedman, A., Jonsson, H. H., Flagan, R. C., McClatchey, R. A., and Seinfeld, J. H.: Analysis of humidity halos around trade wind cumulus clouds, J. Atmos. Sci., 60, 1041–1059, 2003. Marshak, A., Knyazikhin, Y., Chiu, J. C., and Wiscombe, W. J.: Spectral invariant behavior of zenith radiance around cloud edges observed by ARM SWS, Geophys. Res. Lett., 36, L16802, doi:10.1029/2009GL039366, 2009. Marshak, A., Wen, G., Coakley, J., Remer, L., Loeb, N. G., and Cahalan, R. F.: A simple model for the cloud adjacency effect and the apparent bluing of aerosols near clouds, J. Geophys. Res., 113, D14S17, doi:10.1029/2007JD009196, 2008. Mason, B. J., and Jonas, P. R.: The evolution of droplet spectra and large droplets by condensation in cumulus clouds, Q. J. R. Meteor. Soc., 100, 23–38, 1974. Perry, K. D. and Hobbs, P. V.: Influences of isolated cumulus clouds on the humidity of their surroundings, J. Atmos. Sci., 53, 159–174, 1996. Platt, C. M. R. and Gambling, D. J.: Laser radar reflexions and downward infrared flux enhancement near small cumulus clouds, Nature, 232, 182–185, 1971. Redemann, J., Zhang, Q., Russell, P. B., Livingston, J. M., and Remer, L. A.: Case studies of aerosol remote sensing in the vicinity of clouds, J. Geophys. Res., 114, D06209, doi:10.1029/2008JD010774, 2009. Ricchiazzi, P., Yang, S. R., Gautier, C., and Sowle, D.: SBDART: A research and teaching software tool for plane-parallel radiative transfer in the Earth's atmosphere, B. Am. Meteorol. Soc., 79, 2101–2114, 1998. Su, W., Schuster, G. L., Loeb, N. G., Rogers, R. R., Ferrare, R. A., Hostetler, C. A., Hair, J. W., and Obland , M. D.: Aerosol and cloud interaction observed from high spec-tral resolution lidar data, J. Geophys. Res., 113, D24202, doi:10.1029/2008JD010588, 2008. Tackett, J. L. and Di Girolamo, L.: Enhanced aerosol backscatter adjacent to tropical trade wind clouds revealed by satellite-based lidar, Geophys. Res. Lett., 36, L14804, doi:10.1029/2009GL039264, 2009. Twohy, C. H., Coakley, J. A. Jr., and Tahnk, W. R.: Effect of changes in relative humidity on aerosol scattering near clouds, J. Geophys. Res., 114, D05205, doi:10.1029/2008JD01099, 2009. Wen, G., Marshak, A., Cahalan, R. F., Remer, L. A., and Kleidman, R. G.: 3-D aerosol-cloud radiative interaction observed in collocated MODIS and ASTER images of cumulus cloud fields, J. Geophys. Res., 112, D13204, doi:10.1029/2006JD008267, 2007. Várnai, T. and Marshak, A.: Global CALIPSO observations of aerosol changes near clouds, IEEE Remote. Sens. Lett., in press, 2010. Zhang, J. L., Reid, J. S., and Holben, B. N.: An analysis of potential cloud artifacts in MODIS over ocean aerosol optical thickness products, Geophys. Res. Lett., 32, L15803, doi:10.1029/2005GL023254, 2005.