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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 16, issue 17 | Copyright
Atmos. Chem. Phys., 16, 11301-11318, 2016
https://doi.org/10.5194/acp-16-11301-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 13 Sep 2016

Research article | 13 Sep 2016

A long-term study of aerosol–cloud interactions and their radiative effect at the Southern Great Plains using ground-based measurements

Elisa T. Sena1,2, Allison McComiskey3, and Graham Feingold2 Elisa T. Sena et al.
  • 1Institute of Physics, University of São Paulo, São Paulo, Brazil
  • 2NOAA Chemical Sciences Division, Boulder, CO, USA
  • 3NOAA Global Monitoring Division, Boulder, CO, USA

Abstract. Empirical estimates of the microphysical response of cloud droplet size distribution to aerosol perturbations are commonly used to constrain aerosol–cloud interactions in climate models. Instead of empirical microphysical estimates, here macroscopic variables are analyzed to address the influence of aerosol particles and meteorological descriptors on instantaneous cloud albedo and the radiative effect of shallow liquid water clouds. Long-term ground-based measurements from the Atmospheric Radiation Measurement (ARM) program over the Southern Great Plains are used. A broad statistical analysis was performed on 14 years of coincident measurements of low clouds, aerosol, and meteorological properties. Two cases representing conflicting results regarding the relationship between the aerosol and the cloud radiative effect were selected and studied in greater detail. Microphysical estimates are shown to be very uncertain and to depend strongly on the methodology, retrieval technique and averaging scale. For this continental site, the results indicate that the influence of the aerosol on the shallow cloud radiative effect and albedo is weak and that macroscopic cloud properties and dynamics play a much larger role in determining the instantaneous cloud radiative effect compared to microphysical effects. On a daily basis, aerosol shows no correlation with cloud radiative properties (correlation = −0.01±0.03), whereas the liquid water path shows a clear signal (correlation = 0.56±0.02).

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A new method for assessing aerosol effects on clouds is proposed. For the first time, 14 years of collocated, coincident ground-based observations have been used to study cloud–aerosol–meteorology–radiation interactions in the USA. For this site, the results indicate that the influence of the aerosol on cloud radiative effect and cloud albedo is weak, and that macroscopic cloud properties play a much larger role in determining the cloud radiative effect compared to aerosol effects.
A new method for assessing aerosol effects on clouds is proposed. For the first time, 14 years...
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