The interaction between deep convective clouds and their environment

Abstract

Deep convective clouds play a key role in tropical weather patterns, summertime rainfall, and the global transport of energy from the tropics to higher latitudes. Current weather and climate models struggle to realistically represent the development and behavior of these clouds. Both the timing of the convection and the role of humidity in the environment are often poorly represented in these models. In this thesis, detailed numerical simulations serve as a virtual laboratory where the influence of the environment on cloud formation is investigated. The evaporation of rain is shown to result in a positive feedback loop that causes the clouds to become wider and deeper. These wider and deeper clouds tend to form at preferential locations. Subsequently, the relative influence of the temperature profile and humidity in the environment is systematically explored. A simple model captures the response of the clouds to these conditions. Flow trajectories are used to investigate the mixing between the clouds and their environment in more detail. These trajectories show that in essence clouds consist of rising air that mixes horizontally with the environment. Finally, we show that the presence of small particulates (aerosols) can delay the formation of precipitation, but nevertheless lead to larger accumulated rainfall.