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Volume 14, issue 21 | Copyright

Special issue: Meso-scale aerosol processes, comparison and validation studies...

Atmos. Chem. Phys., 14, 11633-11656, 2014
https://doi.org/10.5194/acp-14-11633-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 06 Nov 2014

Research article | 06 Nov 2014

Observations of rapid aerosol optical depth enhancements in the vicinity of polluted cumulus clouds

T. F. Eck1,2, B. N. Holben2, J. S. Reid3, A. Arola4, R. A. Ferrare5, C. A. Hostetler5, S. N. Crumeyrolle5,6, T. A. Berkoff5,7, E. J. Welton2, S. Lolli2,7, A. Lyapustin2, Y. Wang2,7, J. S. Schafer2,8, D. M. Giles2,8, B. E. Anderson5, K. L. Thornhill5,9, P. Minnis5, K. E. Pickering2, C. P. Loughner2,10, A. Smirnov2,8, and A. Sinyuk2,8 T. F. Eck et al.
  • 1Universities Space Research Association, GESTAR, Columbia, MD, USA
  • 2NASA, GSFC, Greenbelt, MD, USA
  • 3Naval Research Laboratory, Monterey, CA, USA
  • 4Finnish Meteorological Institute, Kuopio, Finland
  • 5NASA LRC, Hampton, VA, USA
  • 6LOA, UMR8518, CNRS – Université Lille1, Villeneuve d'Ascq, France
  • 7University of Maryland Baltimore County, JCET, Baltimore, MD, USA
  • 8Sigma Space Corporation, Lanham, MD, USA
  • 9Science Systems and Applications, Inc., Lanham, MD, USA
  • 10University of Maryland, ESSIC, College Park, MD, USA

Abstract. During the July 2011 Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) field experiment in Maryland, significant enhancements in Aerosol Robotic Network (AERONET) sun–sky radiometer measured aerosol optical depth (AOD) were observed in the immediate vicinity of non-precipitating cumulus clouds on some days. Both measured Ångström exponents and aerosol size distribution retrievals made before, during and after cumulus development often suggest little change in fine mode particle size; therefore, implying possible new particle formation in addition to cloud processing and humidification of existing particles. In addition to sun–sky radiometer measurements of large enhancements of fine mode AOD, lidar measurements made from both ground-based and aircraft-based instruments during the experiment also measured large increases in aerosol signal at altitudes associated with the presence of fair weather cumulus clouds. These data show modifications of the aerosol vertical profile as a result of the aerosol enhancements at and below cloud altitudes. The airborne lidar data were utilized to estimate the spatial extent of these aerosol enhancements, finding increased AOD, backscatter and extinction out to 2.5 km distance from the cloud edge. Furthermore, in situ measurements made from aircraft vertical profiles over an AERONET site during the experiment also showed large increases in aerosol scattering and aerosol volume after cloud formation as compared to before. The 15-year AERONET database of AOD measurements at the Goddard Space Flight Center (GSFC), Maryland site, was investigated in order to obtain a climatological perspective of this phenomenon of AOD enhancement. Analysis of the diurnal cycle of AOD in summer showed significant increases in AOD from morning to late afternoon, corresponding to the diurnal cycle of cumulus development.

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