Abstract
Abstract. Better representation of cloud–aerosol interactions is crucial for an improved understanding of natural and anthropogenic effects on climate. Recent studies have shown that the overall aerosol effect on warm convective clouds is non-monotonic. Here, we reduce the system's dimensions to its center of gravity (COG), enabling distillation and simplification of the overall trend and its temporal evolution. Within the COG framework, we show that the aerosol effects are nicely reflected by the interplay of the system's characteristic vertical velocities, namely the updraft (w) and the effective terminal velocity (η). The system's vertical velocities can be regarded as a sensitive measure for the evolution of the overall trends with time. Using a bin-microphysics cloud-scale model, we analyze and follow the trends of the aerosol effect on the magnitude and timing of w and η, and therefore the overall vertical COG velocity. Large eddy simulation (LES) model runs are used to upscale the analyzed trends to the cloud-field scale and study how the aerosol effects on the temporal evolution of the field's thermodynamic properties are reflected by the interplay between the two velocities. Our results suggest that aerosol effects on air vertical motion and droplet mobility imply an effect on the way in which water is distributed along the atmospheric column. Moreover, the interplay between w and η predicts the overall trend of the field's thermodynamic instability. These factors have an important effect on the local energy balance.
Highlights
Clouds are key players in the Earth’s climate system via their influence on the energy balance (Baker and Peter, 2008; Trenberth et al, 2009) and hydrological cycle
From an early stage of the cloud’s evolution, the cleanest cloud (25CCN) had the lowest center of gravity (COG). This was a result of the lower w (Fig. 1a) and larger absolute value of the negative η, which together cause a lower VCOG (Fig. 1c)
The 500CCN had lower values of η than the 10000CCN, which decreased the height of its COG compared to the 10000CCN
Summary
Clouds are key players in the Earth’s climate system via their influence on the energy balance (Baker and Peter, 2008; Trenberth et al, 2009) and hydrological cycle. The onset of significant collision events between droplets in polluted clouds, which are initially smaller and more numerous than in clean clouds (Squires, 1958), is delayed (Gunn and Phillips, 1957; Rosenfeld, 1999, 2000; Squires, 1958; Warner, 1968) This delay can have opposing effects on cloud development by increasing both the water loading (which reduces cloud buoyancy and vertical development) and the latent heat release resulting from the longer and more efficient condensation (increasing cloud buoyancy and vertical development) (Dagan et al, 2015a, b; Pinsky et al, 2013; Koren et al, 2014). Often, these opposing effects act at different stages of the cloud’s lifetime, further complicating the prediction of overall trends
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
