References

ACP

Atmospheric Chemistry and Physics

ACP

1680-7324

Copernicus GmbH

Göttingen, Germany

10.5194/acp-11-191-2011

Global analysis of cloud field coverage and radiative properties, using morphological methods and MODIS observations

Bar-Or

R. Z.

¹ Altaratz

¹ Koren

Department of Environmental Sciences and Energy Research, Weizmann Institute of Science, Rehovot, Israel

11 01 2011

11 1 191 200

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/11/191/2011/acp-11-191-2011.html

The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/191/2011/acp-11-191-2011.pdf

The recently recognized continuous transition zone between detectable clouds and cloud-free atmosphere ("the twilight zone") is affected by undetectable clouds and humidified aerosol. In this study, we suggest to distinguish cloud fields (including the detectable clouds and the surrounding twilight zone) from cloud-free areas, which are not affected by clouds. For this classification, a robust and simple-to-implement cloud field masking algorithm which uses only the spatial distribution of clouds, is presented in detail. A global analysis, estimating Earth's cloud field coverage (50° S–50° N) for 28 July 2008, using the Moderate Resolution Imaging Spectroradiometer (MODIS) data, finds that while the declared cloud fraction is 51%, the global cloud field coverage reaches 88%. The results reveal the low likelihood for finding a cloud-free pixel and suggest that this likelihood may decrease as the pixel size becomes larger. A global latitudinal analysis of cloud fields finds that unlike oceans, which are more uniformly covered by cloud fields, land areas located under the subsidence zones of the Hadley cell (the desert belts), contain proper areas for investigating cloud-free atmosphere as there is 40–80% probability to detect clear sky over them. Usually these golden-pixels, with higher likelihood to be free of clouds, are over deserts. Independent global statistical analysis, using MODIS aerosol and cloud products, reveals a sharp exponential decay of the global mean aerosol optical depth (AOD) as a function of the distance from the nearest detectable cloud, both above ocean and land. Similar statistical analysis finds an exponential growth of mean aerosol fine-mode fraction (FMF) over oceans when the distance from the nearest cloud increases. A 30 km scale break clearly appears in several analyses here, suggesting this is a typical natural scale of cloud fields. This work shows different microphysical and optical properties of cloud fields, urging to separately investigate cloud fields and cloud-free atmosphere in future climate research.

References 1

Ackerman, S. A., Strabala, K. I., Menzel, W. P., Frey, R. A., Moeller, C. C., and Gumley, L. E.: Discriminating clear sky from clouds with MODIS, J.Geophys. Res.-Atmos., 103, 32141–32157, 1998.

Adler, J. and Hancock, D.: Advantages of using a distance transform function in the measurement of fractal dimensions by the dilation method, Powder Technol., 78, 191–196, 1994.

Astin, I. and Latter, B. G.: A case for exponential cloud fields?, J. Appl. Meteorol., 37, 1375–1382, 1998.

Bar-Or, R. Z., Koren, I., and Altaratz, O.: Estimating cloud field coverage using morphological analysis, Environ. Res. Lett., 5, 014022, doi:10.1088/1748-9326/5/1/014022, 2010.

Cahalan, R. F. and Joseph, J. H.: Fractal statistics of cloud fields, Mon. Weather Rev., 117, 261–272, 1989.

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.

Davis, T. J.: A simple parameterization scheme for joint statistics of cloud field morphology and physical parameters, J. Appl. Meteorol., 29, 776–782, 1990.

Dybbroe, A., Karlsson, K. G., and Thoss, A.: NWCSAF AVHRR cloud detection and analysis using dynamic thresholds and radiative transfer modeling. Part I: Algorithm description, J. Appl. Meteorol., 44, 39–54, 2005.

Feingold, G. and Morley, B.: Aerosol hygroscopic properties as measured by lidar and comparison with in situ measurements, J. Geophys. Res.-Atmos., 108, 4327, doi:10.1029/2002jd002842, 2003.

Joseph, J. H. and Cahalan, R. F.: Nearest neighbor spacing of fair weather cumulus clouds, J. Appl. Meteorol., 29, 793–805, 1990.

Kaufman, Y. J., Tanre, D., and Boucher, O.: A satellite view of aerosols in the climate system, Nature, 419, 215–223, doi:10.1038/nature01091, 2002.

King, M. D., Menzel, W. P., Kaufman, Y. J., Tanre, D., Gao, B. C., Platnick, S., Ackerman, S. A., Remer, L. A., Pincus, R., and Hubanks, P. A.: Cloud and aerosol properties, precipitable water, and profiles of temperature and water vapor from MODIS, IEEE T. Geosci. Remote., 41, 442–458, doi:10.1109/tgrs.2002.808226, 2003.

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. L., 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.

Lee, J., Chou, J., Weger, R. C., and Welch, R. M.: Clustering, randomness, and regularity in-cloud fields.4. Stratocumulus cloud fields, J. Geophys. Res.-Atmos., 99, 14461–14480, 1994.

Levy, R. C., Remer, L. A., Mattoo, S., Vermote, E. F., and Kaufman, Y. J.: Second-generation operational algorithm: Retrieval of aerosol properties over land from inversion of Moderate Resolution Imaging Spectroradiometer spectral reflectance, J. Geophys. Res.-Atmos., 112, D13211, doi:10.1029/2006jd007811, 2007.

Lovejoy, S. and Mandelbrot, B. B.: Fractal properties of rain, and a fractal model, Tellus A, 37, 209–232, 1985.

Lovejoy, S. and Schertzer, D.: Fractals, raindrops and resolution dependence of rain measurements, J. Appl. Meteorol., 29, 1167–1170, 1990.

Lovejoy, S. and Schertzer, D.: Multifractals, cloud radiances and rain, J. Hydrol., 322, 59–88, doi:10.1016/j.jhydro1.2005.02.042, 2006.

Luo, Y., Trishchenko, A. P., and Khlopenkov, K. V.: Developing clear-sky, cloud and cloud shadow mask for producing clear-sky composites at 250-meter spatial resolution for the seven MODIS land bands over Canada and North America, Remote Sens. Environ., 112, 4167–4185, doi:10.1016/j.rse.2008.06.010, 2008.

Marshak, A., Platnick, S., Varnai, T., Wen, G. Y., and Cahalan, R. F.: Impact of three-dimensional radiative effects on satellite retrievals of cloud droplet sizes, J. Geophys. Res.-Atmos., 111, D09207, doi:10.1029/2005jd006686, 2006.

Marshak, A., Wen, G., Coakley, J. A., Remer, L. A., 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.-Atmos., 113, D14S17, doi:10.1029/2007jd009196, 2008.

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.

Nair, U. S., Weger, R. C., Kuo, K. S., and Welch, R. M.: Clustering, randomness, and regularity in cloud fields – 5. The nature of regular cumulus cloud fields, J. Geophys. Res.-Atmos., 103, 11363–11380, 1998.

Pahlow, M., Feingold, G., Jefferson, A., Andrews, E., Ogren, J. A., Wang, J., Lee, Y. N., Ferrare, R. A., and Turner, D. D.: Comparison between lidar and nephelometer measurements of aerosol hygroscopicity at the Southern Great Plains Atmospheric Radiation Measurement site, J. Geophys. Res.-Atmos., 111(8), D05s15, doi:10.1029/2004jd005646, 2006.

Platnick, S., King, M. D., Ackerman, S. A., Menzel, W. P., Baum, B. A., Riedi, J. C., and Frey, R. A.: The MODIS cloud products: Algorithms and examples from Terra, IEEE T. Geosci. Remote., 41, 459–473, doi:10.1109/tgrs.2002.808301, 2003.

Radke, L. F. and Hobbs, P. V.: Humidity and particle fields around some small cumulus clouds, J. Atmos. Sci., 48, 1190–1193, 1991.

Remer, L. A., Kaufman, Y. J., Tanre, D., Mattoo, S., Chu, D. A., Martins, J. V., Li, R. R., Ichoku, C., Levy, R. C., Kleidman, R. G., Eck, T. F., Vermote, E., and Holben, B. N.: The MODIS aerosol algorithm, products, and validation, J. Atmos. Sci., 62, 947–973, 2005.

Remer, L. A., Kleidman, R. G., Levy, R. C., Kaufman, Y. J., Tanre, D., Mattoo, S., Martins, J. V., Ichoku, C., Koren, I., Yu, H. B., and Holben, B. N.: Global aerosol climatology from the MODIS satellite sensors, J. Geophys. Res.-Atmos., 113(18), D14s07, doi:10.1029/2007jd009661, 2008.

Rosin, P. L.: A simple method for detecting salient regions, Pattern Recognit., 42, 2363–2371, doi:10.1016/j.patcog.2009.04.021, 2009.

Sankaranarayanan, J., Samet, H., and Varshney, A.: A fast all nearest neighbor algorithm for applications involving large point-clouds, Computers & Graphics-Uk, 31, 157–174, doi:10.1016/j.cag.2006.11.011, 2007.

Sengupta, S. K., Welch, R. M., Navar, M. S., Berendes, T. A., and Chen, D. W.: Cumulus cloud field morphology and spatial patterns derived from high spatial-resolution landsat imagery, J. Appl. Meteorol., 29, 1245–1267, 1990.

Tessier, Y., Lovejoy, S., and Schertzer, D.: Universal multifractals – theory and observations for rain and clouds, J. Appl. Meteorol., 32, 223–250, 1993.

Twohy, C. H., Coakley, J. A., and Tahnk, W. R.: Effect of changes in relative humidity on aerosol scattering near clouds, J. Geophys. Res.-Atmos., 114, D05205, doi:10.1029/2008jd010991, 2009.

Varnai, T. and Marshak, A.: MODIS observations of enhanced clear sky reflectance near clouds, Geophys. Res. Lett., 36, L06807, doi:10.1029/2008gl037089, 2009.

Venema, V., Meyer, S., Garcia, S. G., Kniffka, A., Simmer, C., Crewell, S., Lohnert, U., Trautmann, T., and Macke, A.: Surrogate cloud fields generated with the iterative amplitude adapted Fourier transform algorithm, Tellus A, 58, 104–120, 2006.

Weger, R. C., Lee, J., Zhu, T. R., and Welch, R. M.: Clustering, randomness and regularity in cloud fields .1. Theoretical considerations, J. Geophys. Res.-Atmos., 97, 20519–20536, 1992.

Weger, R. C., Lee, J., and Welch, R. M.: Clustering, randomness, and regularity in-cloud fields .3. The nature and distribution of clusters, J. Geophys. Res.-Atmos., 98, 18449–18463, 1993.

Wen, G. Y., 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.-Atmos., 112, D13204, doi:10.1029/2006jd008267, 2007.

Wen, G. Y., Marshak, A., and Cahalan, R. F.: Importance of molecular Rayleigh scattering in the enhancement of clear sky reflectance in the vicinity of boundary layer cumulus clouds, J. Geophys. Res.-Atmos., 113(10), D24207, doi:10.1029/2008jd010592, 2008.

Zhu, T., Lee, J., Weger, R. C., and Welch, R. M.: Clustering, randomness, and regularity in cloud fields .2. Cumulus cloud fields, J. Geophys. Res.-Atmos., 97, 20537–20558, 1992.

Zinner, T., Marshak, A., Lang, S., Martins, J. V., and Mayer, B.: Remote sensing of cloud sides of deep convection: towards a three-dimensional retrieval of cloud particle size profiles, Atmos. Chem. Phys., 8, 4741–4757, doi:10.5194/acp-8-4741-2008, 2008.