Aerosol Effects on Precipitation and the Hydrological Cycle-A Discussion

A wide range of aerosol effects on precipitation and the global hydrological cycle have been proposed. These can be broadly categorised into radiatively and cloud-microphysically mediated effects. Aerosol effects on precipitation have traditionally been assessed bottom-up, modelling or observing the processes involved from aerosol emissions via microphysical processes all the way to precipitation formation. However, such assessments rely on a complete understanding of a very complex and uncertain process chain and have been shown to be subject to large uncertainties.

In this presentation, Prof. Philip Stier will provide a comprehensive overview of aerosol effects on precipitation, summarising the findings of a number of recent expert workshops. He will also show that the response of regional precipitation to idealised and realistic aerosol radiative perturbations can be constrained top-down through an energy and water balance framework because associated changes in the net diabatic heating / water transport need to be balanced by latent heat release, surface or top-of-atmosphere fluxes or compensated for by energy / water divergence.

However, this physical perspective of aerosol effects on precipitation has its limitations and provides no answers to key questions about their impact: which kind of precipitation changes have the biggest impact for mankind and ecosystems? Which regions of the globe are most vulnerable? What aspects of precipitation changes (in terms of changes of its intensity distribution and location) should we concentrate on? Are there objective ways to answer these questions? Please come ready to discuss these questions and more!

*Please note that registration for this event will close 3 hours before the event takes place. You must be registered to participate.

About the Speaker

Philip Stier is a Professor of Atmospheric Physics and Head of Atmospheric, Oceanic and Planetary Physics in the Department of Physics and a Fellow of the new Reuben College. His research addresses physical climate processes in the context of anthropogenic perturbations to the earth system as the underlying cause of climate change and air pollution. Focal points of his research are aerosol and cloud physics, their interactions and their role in the climate system. He also heads the Climate Processes Group and serve on the steering group of the Oxford Climate Research Network.