CoSy seminar: "Simulation of extreme events and rare transitions in climate models with rare event algorithms"

Everyone is welcome and the first 40 people to register will be treated to a free lunch sandwich. If you do not want lunch, you are still welcome to join.

Register for a lunch sandwich (deadline: Sunday 26 May)

Abstract: The analysis of extreme and rare events is one of the main areas of application of numerical climate models. Extremes like heat waves, floods or wind storms, as well as rare abrupt transitions associated with tipping elements of the climate system, can have severe impacts on human societies and ecosystems. Studying these events on a robust statistical basis with complex climate models is however computationally challenging, as very long simulations and/or very large ensembles are necessary to sample a sufficient number of events to keep statistical uncertainties small enough. This problem can be tackled using rare event algorithms, numerical tools designed to reduce the computational effort required to sample rare events in numerical models. These methods typically take the form of genetic algorithms, where a set of suppression and cloning rules are applied to the members of an ensemble simulation, in order to oversample trajectories leading to the events of interest. In this talk we first show recent applications of these methods to the simulation of heat waves and warm summers in the Northern hemisphere. We show how a rare event algorithm allows to efficiently sample extreme events characterised by persistency of high regional surface temperatures on subseasonal to seasonal scales, and we analyse the emergence of atmospheric teleconnections during the events. We then present applications to extremes of Arctic sea ice reduction, and to abrupt transitions associated to the weakening and collapse of the Atlantic Meridional Overturning Circulation. Finally we discuss how these results open the way to further applications to a wide range of problems.

This is a lecture in the seminar series held by CIM 
(Centre for Interdisciplinary Mathematics).