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

Abstract

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).

The Radiative Forcing of Aerosol–Cloud Interactions in Liquid Clouds: Wrestling and Embracing Uncertainty

“…This typically occurs in more polluted conditions [2,21,56,149,158]. Analysis of very large data sets sometimes shows no clear aerosol signal in the cloud radiative effect [129], and even massive aerosol perturbations from effusive volcanoes may not result in L and cloud fraction responses large enough to be detected above the meteorological noise over a few months [84]. 4.…”

“…Between the Darwinian ACI metrics and the Newtonian A -cloud fraction analysis lies fertile ground for additional analyses. Examples include (1) the radar reflectivity Zcloud optical depth τ c phase diagram [143], which sheds light on microphysical processes like the balance of condensation vs. collision-coalescence growth, (2) measurements that elucidate the radiative properties of a cloud field very directly such as the probability distribution function of up-or downward shortwave irradiance [120] or the cloud radiative forcing/effect-L phase diagram [129], and (3) cloud field properties such as cloud size distributions. Similar analyses of independent components/parameters would, when compounded, provide confidence in the predictive power of the model.…”

“…The Darwinian approach focuses on details of elements of the aerosol-cloud system. A merging of Newtonian and Darwinian approaches can be achieved via a balance between metrics that constrain processes at various levels of detail: (i) traditional aerosolcloud interaction metrics (e.g., [33,37,42]); (ii) (joint) PDFs that illuminate physical processes [120,143]; (iii) high-level analyses that address key ERF aci -relevant components [10,129]; and (iv) emergent constraints [110,148]. Analyses of all components can be derived from both observations and modeling.…”

Analysis of aerosol effects on warm clouds over the Yangtze River Delta from multi-sensor satellite observations

“…This process, described as the "second AIE", may further influence the cloud fraction (CF) (Albrecht, 1989;Feingold et al, 2001). The interaction mechanisms between aerosols and clouds remain among the most uncertain processes in the global climate system in spite of a large number of studies made using both observations Koren et al, 2005;Krüger et al, 2004) and models (Suzuki et al, 2004;Quaas et al, 2009;Sena et al, 2016).…”

Effects of Continental Clouds on Surface Aitken and Accumulation Modes

“…ARM SGP groundbased instrumentation has previously been used to study aerosol-cloud interactions (Feingold et al, 2003;Garrett et al, 2004;Kim et al, 2008Kim et al, , 2003McComiskey et al, 2009). Sena et al (2016) successfully related surface aerosol measurements at SGP to remote cloud microphysics measurements. The basis of that research was the demonstration that relationships between surface and cloud level aerosol measurements are uncorrelated with the degree of boundary layer vertical mixing (Delle Monache et al, 2004).…”