Multisensor satellite observations of aerosol effects on warm clouds

Abstract

[1] A global multisensor satellite examination of aerosol indirect effects on warm oceanic clouds is presented. The study centers on the water path response of cloud to aerosol burden. A unique element of the study is a rigorous rain screening methodology that is utilized to separate the responses of nonraining and raining clouds. It is demonstrated that high aerosol environments are associated with reduced liquid water path in nonprecipitating clouds and that the reduction in liquid water path reduces the albedo enhancement expected from decreasing effective radius. Furthermore the reduction in liquid water path is greater in thermodynamically unstable environments than in stable environments suggesting a greater sensitivity of cumulus cloud than stratiform cloud liquid water path to aerosol. In sharp contrast with nonprecipitating clouds, the cloud liquid water path of transitional and precipitating clouds increases dramatically with aerosol, which may be indicative of an inhibited coalescence process. The evidence further indicates that increasing aerosol requires greater amounts of cloud condensate before the onset of precipitation. Additional support for this hypothesis is found in a reduction in the probability of precipitation by as much as 10% depending on the thermodynamical state of the environment. Independent estimates of the broadband cloudy-sky albedo are used to confirm that the cloud albedo responds to the trends that are identified in the liquid water path. In particular, it is found that the water path effect dominates the cloud albedo response for precipitating and transitional clouds. Finally, regional analysis demonstrates that the magnitude of the relationship between aerosol and cloud albedo is greatest in the extratropics and subtropical stratus regions primarily in the winter hemisphere. These relationships are used to estimate the magnitude of the first indirect effect as À0.42 W/m 2 .

Cloud-resolving modelling of aerosol indirect effects in idealised radiative-convective equilibrium with interactive and fixed sea surface temperature

“…Higher CCN counts and, hence, smaller cloud droplets result in suppression of warm rain production and, consequently, in increase of the liquid water path (Fig. 5a), which is consistent with the observational study by Lebsock et al (2008) for the case of precipitating clouds. Corresponding relative susceptibility in the fSST case is about twice as high as in the iSST case (4.6 vs. 2.3 g m −3 , or 14 % vs. 7 % with respect to the control).…”

Investigating potential biases in observed and modeled metrics of aerosol-cloud-precipitation interactions

“…The methodology in a number of studies has included obtaining data for rain and cloud properties from CloudSat and MODIS with a spatial resolution on the order of 1 km, while aerosol data are retrieved from a significantly larger spatial domain (1 • × 1 • ) (Lebsock et al, 2008;Sorooshian et al, 2009aSorooshian et al, , 2010. The effect of wet scavenging is tested using data for the months of June through August (JJA) between 2006-2008 and just the year 2007 within the tropics for shallow cumulus clouds.…”

“…The description of all satellite products and data filtering methodology are described extensively elsewhere (Lebsock et al, 2008;Sorooshian et al, 2010). Briefly, data are only used for warm maritime clouds in conditions of single cloud layers.…”

The scientific basis for a satellite mission to retrieve CCN concentrations and their impacts on convective clouds

“…With greater N d smaller droplets are formed, reducing coalescence and inhibiting rain production (Gunn and Phillips, 1957;Squires, 1958). The dynamic response to the rain suppression lengthens the life-time and increases the cloud cover when suppressing precipitation in clouds, at least in the case of shallow heavily drizzling marine stratocumulus (Albrecht, 1989;Rosenfeld et al, 2006;Lebsock et al, 2008;Wang et al, 2011;Goren and Rosenfeld, 2012). In contrast, adding CCN to non-precipitating clouds can enhance their evaporation and mixing with the ambient air due to the decrease in cloud drop size (e.g., Wood, 2007;Jiang et al, 2009;Chen et al, 2011).…”