In WP1, we constrained the precipitation response to aerosol perturbations top down through energy and water budget constraints. Through a hierarchy of simulations of increasing complexity, we demonstrated for the first time a strong regional dependence of the precipitation susceptibility to aerosol perturbation, which we could underpin with a physical framework of budgetary and dynamical constraints. We analysed the atmospheric water budget to elucidate the spatial scale of precipitation changes and combine energy and water budgets to further strengthen the constraint on the precipitation response under climate change climate change. We transitioned our idealized setup to more realistic climate model configurations to probe the global precipitation susceptibility and systematically test the regional dependence. We further separated the contrasting behaviour of scattering and absorbing aerosol. Together, RECAP publications provide an authoritative body of literature energy and water budget constraints on regional and global precipitation.
In WP2 we investigated drivers of aerosol effects on precipitation bottom up employing and developing a hierarchy of advanced high-resolution atmospheric models of increasing complexity. We demonstrated a strong sensitivity of convective ice to variations in cloud droplet numbers (as proxy for aerosol perturbations) over the North Atlantic – with moderate precipitation responses. We used large-scale high-resolution atmospheric simulations with idealised aerosol perturbation to isolate smoke impacts on cloud and precipitation processes over the Amazon, highlighting the importance of aerosol-radiation interactions and the complex diurnal response of cloud systems. We capitalized on the emergence of global high-resolution km-scale climate models to investigate global aerosol-cloud-precipitation interactions and set out to develop a novel reduced complexity aerosol module HAM-Lite.
In WP3, we developed novel observational constraints, capitalizing on emerging opportunities and advancements in the field, in particular of Artificial Intelligence (AI) and Machine Learning (ML). We derived a novel framework for satellite data analysis to provide the first observational evidence that aerosols enhance cloud lifetime and brightness. We developed a novel framework for the detection of convective cores and anvils in satellite data that we have applied to derive the first full climatology of the convective lifecycle and aerosol effects thereon. We seized the opportunities provided by opportunistic experiments, such as pollution tracks from ships, to provide novel constraints on aerosol-cloud-precipitation interactions. We also developed a new ML framework for the definition of regimes of cloud controlling factors for cloud forcing and feedback studies.
In WP4, we synthesized aerosol effects on precipitation. Internationally, we co-led the first intercomparison project of cloud resolving models to study aerosol effects on convection and precipitation under the umbrella of the Aerosols, Clouds, Precipitation and Climate (ACPC) initiative and have been invited to co-lead the World Climate Research Programme’s GEWEX Aerosol Precipitation (GAP) initiative – pushing the frontiers through a proposed global km-scale model intercomparison of aerosol effects. We held three expert RECAP workshop at Oxford providing authoritative overview papers of key RECAP topics and activities: the first RECAP expert workshop on aerosol effects on precipitation under the umbrella of GAP; a second RECAP / GAP expert workshop, synthesizing our understanding of satellite-based assessments of aerosol effects on precipitation; and the third RECAP expert workshop on cloud tracking, synthesizing science opportunities and tools and serving as key dissemination route for our tobac cloud tracking tool developed under RECAP.
