Interactions between trade wind shallow cumuli and their environment

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The shallow cumulus cloud is the most prevalent cloud type on Earth; ubiquitous in the trade winds of the Tropics, their behaviour is critical to our understanding of the atmosphere, and yet is still poorly understood. These small, shallow convective clouds low in the atmosphere play an important role in regulating the thermodynamics and dynamics of their environment; warming the cloud layer through condensation, transporting moisture to the inversion layer above, and cooling of both the inversion, and the sub-cloud layer, through the evaporation of cloud droplets and precipitation (Zhu and Bretherton 2004, Neggers et al. 2007). Additionally, these clouds exert a cooling radiative effect, reflecting shortwave radiation. One particularly uncertain aspect of the behaviour of shallow cumuli is their relationship and response to a changing climate, and aerosol perturbations. The interactions of shallow convection with the troposphere have large implications for climate sensitivity, and their feedbacks are responsible for much of the spread in climate sensitivity between models (Sherwood et al. 2014). Previous works have shown contesting responses of quantities such as cloud abundance and precipitation to increases in aerosol (Xue et al. 2008, Lonitz et al. 2015). Another interesting feature of these clouds is that, despite their small individual size, and depending on local conditions, they are capable of producing mesoscale circulations which result in large organised patterns and clusters of clouds. Changes in this organisation can have large impacts on cloud amount (Vogel et al., 2016), which, given the ubiquitous nature of these clouds and their effects on their environment, is highly significant.