Low-level stratiform clouds have been a topic of considerable interest since the publication of the classic paper describing their physics (Lilly, 1968) because the radiative effect of these clouds contributes to one of the largest uncertainties in climate modeling (IPCC, 2013). They have significant effects on the hydrological cycle and the Earth's radiation budget and consequently on the regional and global climate (Garreaud et al.
Atmospheric aerosols are widely recognized to give rise to a substantial radiative forcing of climate by scattering and absorbing radiation (direct effects) and by modifying the microphysical, optical, and radiative properties of clouds, affecting their reflectivity and persistence (indirect effects). One example of the aerosol indirect effects (AIEs) is Marine Cloud Brightening (MCB, Latham et al., 2012). The basic principle behind the idea is to seed marine stratocumulus clouds with numerous aerosols generated at or near the ocean surface. These particles would have a sufficiently large salt mass to ensure their activation and subsequent growth within the clouds, but not large enough to generate drizzle or precipitation. Moreover, these particles would be sufficiently numerous to enhance the cloud-droplet number concentration (N C ) to values substantially higher than the natural ones. This will result in two effects: (a) the marine boundary layer (MBL) cloud droplets become smaller and thus the MBL clouds are more reflective of incoming solar radiation (Twomey, 1977), and (b) the MBL clouds become more persistent, occupy a broader areal extent, and suppress precipitation (Albrecht, 1989). Both effects reduce the amount of solar radiation reaching the Earth's surface and therefore have a cooling effect on the planet.Understanding how aerosols influence MBL clouds remains vital in determining cloud properties and lifecycle. Each cloud droplet requires an aerosol particle to initiate growth by condensation in the real atmosphere; however, factors including the aerosol size, chemistry, and meteorological condition will determine whether a particle will become activated to allow condensation (Kohler, 1936;Zheng et al., 2020). Aerosol particles which satisfy these conditions at a given supersaturation are known as cloud condensation nuclei (CCN). Theoretically, CCN number concentrations (N CCN ) increase monotonically with increasing supersaturation until all condensation nuclei (CN) are activated. Hence, measurements of N CCN as a function of supersaturation can provide important information on the relationship between aerosols and clouds. It has long been hypothesized that aerosol concentration can affect cloud-droplet number concentration (N C ) and cloud albedo (Twomey, 1977). N CCN will also influence cloud-droplet effective radius (r c ), further affecting cloud to drizzle initiation when cloud droplets outweigh the updraft buoyancy force for drizzle to begin. Moreover, Yamaguchi et al. (2017) found that drizzle rates can affect the cloud's lifetime and the transition from stratocumulus to cumulus clouds. These indirect aerosol effects
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