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Franziska Teubler and Michael Riemer

wave packets (RWPs) for weather forecasting has long been recognized ( Cressman 1948 ; Hovmöller 1949 ). The role of RWPs as precursors to high-impact weather events has more recently been given special attention ( Shapiro and Thorpe 2004 ; Chang 2005 ; Martius et al. 2008 ; Wirth and Eichhorn 2014 ; Piaget et al. 2015 ). The investigation of RWPs along the midlatitude waveguide is the focus of this study. It is generally expected that RWPs, as large-scale flow features obeying balanced

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Michael Riemer, Marlene Baumgart, and Sven Eiermann

). This brief analysis supports Grams et al.’s hypothesis that the downstream cyclone exhibited characteristics of a diabatic Rossby vortex during this time. 6. Summary and conclusions The formation of a jet streak and an amplified trough are archetypical features of the modification of the midlatitude flow during ET. Both features are well known to promote cyclogenesis. Downstream cyclogenesis may lead to high-impact weather and has been shown to constitute an important step in the further dispersion

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Simon T. K. Lang, Sarah C. Jones, Martin Leutbecher, Melinda S. Peng, and Carolyn A. Reynolds

1. Introduction In the Ensemble Prediction System (EPS) of the European Centre for Medium-Range Weather Forecasts (ECMWF), singular vectors (SVs) are used to generate perturbations to the initial condition ( Leutbecher and Palmer 2008 ; Buizza et al. 2008 ). The rationale behind using SVs, the fastest-growing perturbations over a finite time interval, is to sample the dynamically most relevant structures that will dominate the uncertainty sometime in the future ( Ehrendorfer and Tribbia 1997

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Olivia Martius and Heini Wernli

-scale modification of subtropical jets. The remainder of this paper is organized as follows: the details of the Lagrangian approach are specified in the next section. Section 3 discusses three episodes of subtropical jet formation, followed by generalization of the case study results in section 4 . The final section provides a discussion of the results and some concluding remarks. 2. Data and methods Interim European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim) data ( Dee et al

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