Revisiting the dynamic and thermodynamic processes driving the record-breaking January 2014 precipitation in the southern UK

Boutheina Oueslati,Aglaé Jézéquel,Pascal Yiou

doi:10.1038/s41598-019-39306-y

Abstract

Many attribution studies of precipitation extreme events have attempted to estimate the thermodynamic contribution (linked to temperature changes) and the dynamic contribution (linked to the atmospheric circulation). Those studies are based on statistical decompositions of atmospheric fields, and essentially focus on the horizontal motion of the atmosphere. This paper proposes a framework that decomposes those terms from first physical principles, which include the vertical atmospheric motion that has often been overlooked. The goal is to take into account the driving processes of the extreme event. We revisit a recent example of extreme precipitation that was extensively investigated through its relation with the atmospheric circulation. We find that although the horizontal motion plays a minor (but important) role, the vertical motion yields a dominating contribution to the event that is larger than the thermodynamic contribution. This analysis quantifies the processes leading to high winter precipitation rates, and can be extended for further attribution studies.

Highlights

During the 2013/14 winter, southern UK was affected by a spate of winter storms associated with a strengthening of the North Atlantic jet stream[1]
We propose an alternative framework to disentangle the dynamic and thermodynamic contributions
This framework has been widely used in the tropics to relate local changes in precipitation to changes in atmospheric water vapor and circulation [e.g.16,20,21]. This method is applied to January 2014 precipitation to understand the physical drivers of this extreme event. It provides a physically-based quantification of dynamic and thermodynamic contributions that might be useful for extreme event attribution

Summary

Introduction

During the 2013/14 winter, southern UK was affected by a spate of winter storms associated with a strengthening of the North Atlantic jet stream[1]. The statistical approaches that have been used might provide a partial view of the atmospheric circulation and estimate only a part of the dynamic contribution to extreme events. Changes in extreme precipitation are decomposed using a robust physical approach based on the atmospheric water budget (see Methods). It provides a physically-based quantification of dynamic and thermodynamic contributions that might be useful for extreme event attribution.

Results

Conclusion