We thank the Natural Environment Research Council (NERC) mesosphere–stratosphere–troposphere radar facility for providing MST radar data for this study, and the Met Office for the weather radar data. Both datasets were supplied by the British Atmospheric Data Center (BADC). The NAO index values are provided by the Climatic Research Unit, University of East Anglia, Norwich, available online at http://www.cru.uea.ac.uk. Thanks to Harold Brooks for providing the dataset used in section 3c. The work was supported by NERC as part of the Tropopause Folding, Stratospheric Intrusions and Deep Convection (TROSIAD) project, Grant NE/H008225/1.
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