Abrupt transitions in the NAO control of explosive North Atlantic cyclone development
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Explosive cyclones are intense extra-tropical low pressure systems featuring large deepening rates. In the Euro-Atlantic sector, they are a major source of life-threatening weather impacts due to their associated strong wind gusts, heavy precipitation and storm surges. The wintertime variability of the North Atlantic cyclonic activity is primarily modulated by the North Atlantic Oscillation (NAO). In this study, we investigate the interannual and multi-decadal variability of explosive North Atlantic cyclones using track density data from two reanalysis datasets (NCEP and ERA-40) and a control simulation of an atmosphere/ocean coupled General Circulation Model (GCM—ECHAM5/MPIOM1). The leading interannual and multi-decadal modes of variability of explosive cyclone track density are characterized by a strengthening/weakening pattern between Newfoundland and Iceland, which is mainly modulated by the NAO at both timescales. However, the NAO control of interannual cyclone variability is not stationary in time and abruptly fluctuates during periods of 20–25 years long both in NCEP and ECHAM5/MPIOM1. These transitions are accompanied by structural changes in the leading mode of explosive cyclone variability, and by decreased/enhanced baroclinicity over the sub-polar/sub-tropical North Atlantic. The influence of the ocean is apparently important for both the occurrence and persistence of such anomalous periods. In the GCM, the Atlantic Meridional Overturning Circulation appears to influence the large-scale baroclinicity and explosive cyclone development over the North Atlantic. These results permit a better understanding of explosive cyclogenesis variability at different climatic timescales and might help to improve predictions of these hazardous events.
KeywordsExtra-tropical cyclones Explosive cyclogenesis NAO Jet stream Ocean variability AMOC
We thank the National Centers for Environmental Prediction and the European Centre for Medium-Range Weather Forecasts for the NCEP and ERA-40 reanalysis. We thank the Met Office Hadley Centre for the SST and sea ice data (HadISST) and the University of Maryland for the Simple Ocean Data Assimilation (SODA) reanalysis. We are indebted to the Max Plank Institute and the Deutsches Klimarechenzentrum (DKRZ) for the ECHAM5/MPIOM1 data. In particular, we thank Hans Winter, Hannes Thiemann, Helmuth Haak and Monika Esch for help with the MPIOM1 data. IG is supported by the research projects MULCLIVAR (CGL-2012-38923-C02-01—Spanish Ministry of Economy and Competitiveness) and PREFACE (EUFP7/2007–2013 Grant Agreement 603521). We thank Irene Polo, Marta Martín-Rey, Jorge López-Parages, Rubén Banderas, Tim Woollings and Christoph Raible for constructive remarks. We thank Gwendal Rivière and another anonymous reviewer for their pertinent comments and suggestions, which have contributed to improve this manuscript.
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