Tropical atmospheric drivers of wintertime European precipitation events

Ronald K K Li,Chris O'Reilly,Tim Woollings,Adam A Scaife

doi:10.1002/qj.3708

Abstract

AbstractFrom observations, we identify a wave‐like pattern associated with northwestern European seasonal precipitation events. These events are associated with tropical precipitation anomalies, prompting us to investigate if there are any tropical–extratropical teleconnections, in particular the role of tropical anomalies in driving extratropical dynamics through Rossby wave propagation. Using a hierarchy of models from ray tracing to barotropic and baroclinic models, we investigate the Rossby wave mechanism and test potential tropical drivers and yield qualitative results. Using a barotropic model, we identify potential Rossby wave source regions which are consistent between the observations and the model. These regions include the tropical western and eastern Atlantic, the subtropical eastern Atlantic and, to a smaller degree, the subtropical eastern Pacific. Zonal wavenumber 2 and 3 components of the barotropic model responses match well with the observations and ray tracing supports the importance of these components. We use a baroclinic model to investigate the link between the observed Rossby wave source anomalies and the observed tropical precipitation anomalies. The reduced precipitation observed in the tropical Atlantic just north of the Equator can generate some of the observed Rossby wave source anomalies in the tropical Atlantic, while the increased precipitation observed in the tropical eastern Pacific can generate some of the observed Rossby wave source anomalies in the subtropical eastern Pacific. Our results can also be applied to European drought events because of the qualitative linearity in the observations and in our linear methods.

Highlights

Many studies have looked at recent wet European winters. Scaife et al (2017a) showed that seasonal forecasts of the wet UK and northwestern Europe in the early winter of December 2015 were likely driven by the extreme El Niño of that winter. Knight et al (2017) found that the extratropical pattern associated with the record UKQ J R Meteorol Soc. 2020;1–15.wileyonlinelibrary.com/journal/qj 1rainfall of winter 2013–2014 could be partly reproduced by relaxing models especially over the tropical Atlantic, and suggested that enhanced Amazonian convection could be an atmospheric driver of the extratropical Rossby wave
Rainfall of winter 2013–2014 could be partly reproduced by relaxing models especially over the tropical Atlantic, and suggested that enhanced Amazonian convection could be an atmospheric driver of the extratropical Rossby wave
We have identified a large-scale wave pattern associated with seasonal European precipitation events, which is qualitatively linear with respect to the dry and wet events

Summary

Introduction

Many studies have looked at recent wet European winters. Rainfall of winter 2013–2014 could be partly reproduced by relaxing models especially over the tropical Atlantic, and suggested that enhanced Amazonian convection could be an atmospheric driver of the extratropical Rossby wave. Their analysis might suggest similar atmospheric drivers contributing to extreme precipitation events across neighbouring regions in the North Atlantic–European sector. Studies have found predictability in the QBO (Scaife et al, 2014b) and in its northern winter teleconnection on seasonal time-scales(O'Reilly et al, 2019)

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