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Tropical atmospheric drivers of wintertime European precipitation events

From 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 tr...

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Bibliographic Details
Published in:Quarterly journal of the Royal Meteorological Society 2020-01, Vol.146 (727), p.780-794
Main Authors: Li, Ronald K. K., Woollings, Tim, O'Reilly, Chris, Scaife, Adam A.
Format: Article
Language:English
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Summary:From 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. Climate anomalies are often related to each other at large distances, known as teleconnections. This study looks at the atmospheric teleconnections between heavy precipitation in the tropics, namely the tropical Atlantic and the tropical Pacific, and heavy precipitation in northwestern Europe in the winter. It is found that heavy tropical precipitation can trigger planetary scale Rossby waves that propagate to Europe and affect its precipitation.
ISSN:0035-9009
1477-870X
DOI:10.1002/qj.3708