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Peter Vogel, Peter Knippertz, Andreas H. Fink, Andreas Schlueter, and Tilmann Gneiting

other datasets. We defined in total ten climatic regions with similar characteristics (see color shadings in Fig. 2a ). For the most frequent main climates Equatorial (A) and Arid (B), we added continental labels: Arid North (N) Africa, Tropical Africa, Arid South (S) Africa, Arid Americas (mostly Mexico, eastern Brazil, and areas near the Andes), Tropical Americas, Arid Asia (mostly southwestern Asia and parts of India), Tropical Asia (including the Maritime Continent and northern Australia), and

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Julia H. Keller, Christian M. Grams, Michael Riemer, Heather M. Archambault, Lance Bosart, James D. Doyle, Jenni L. Evans, Thomas J. Galarneau Jr., Kyle Griffin, Patrick A. Harr, Naoko Kitabatake, Ron McTaggart-Cowan, Florian Pantillon, Julian F. Quinting, Carolyn A. Reynolds, Elizabeth A. Ritchie, Ryan D. Torn, and Fuqing Zhang

downstream, and the next downstream ridge builds, which signifies the downstream propagation that arises from the initial local changes in the jet near the site of ET ( Fig. 1c ). Meanwhile, Nuri reintensifies into a strong extratropical cyclone and initiates cyclonic wave breaking over the western North Pacific ( Fig. 1c ). Subsequently, the upper-level wave pattern amplifies farther downstream, establishing a high-amplitude ridge–trough couplet over North America. A heat wave develops in the high

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Jacopo Riboldi, Christian M. Grams, Michael Riemer, and Heather M. Archambault

) documented how a series of three TCs (Florence, Helene, and Leslie), recurving in the North Atlantic between September and October 2000, led to the continuous invigoration of atmospheric blocks over the North Atlantic and to repeated Rossby wave breaking over western Europe associated with extreme flooding over southern Switzerland and northern Italy. It has been hypothesized that a link exists between ET in the western North Pacific and enhanced blocking activity over western North America during the

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Andreas Schäfler, George Craig, Heini Wernli, Philippe Arbogast, James D. Doyle, Ron McTaggart-Cowan, John Methven, Gwendal Rivière, Felix Ament, Maxi Boettcher, Martina Bramberger, Quitterie Cazenave, Richard Cotton, Susanne Crewell, Julien Delanoë, Andreas Dörnbrack, André Ehrlich, Florian Ewald, Andreas Fix, Christian M. Grams, Suzanne L. Gray, Hans Grob, Silke Groß, Martin Hagen, Ben Harvey, Lutz Hirsch, Marek Jacob, Tobias Kölling, Heike Konow, Christian Lemmerz, Oliver Lux, Linus Magnusson, Bernhard Mayer, Mario Mech, Richard Moore, Jacques Pelon, Julian Quinting, Stephan Rahm, Markus Rapp, Marc Rautenhaus, Oliver Reitebuch, Carolyn A. Reynolds, Harald Sodemann, Thomas Spengler, Geraint Vaughan, Manfred Wendisch, Martin Wirth, Benjamin Witschas, Kevin Wolf, and Tobias Zinner

meridional potential vorticity (PV) gradient associated with the jet stream serves as a waveguide for propagating Rossby waves. Frequently, small disturbances in the jet entrance region over eastern North America grow in baroclinic weather systems and evolve into large-amplitude features in the European sector ( Schwierz et al. 2004 ). Figure 1 portrays an idealized North Atlantic flow situation that could result in HIW in the form of high winds and heavy precipitation over northern Europe. In addition

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Volkmar Wirth, Michael Riemer, Edmund K. M. Chang, and Olivia Martius

gradual than that of the carrier wave (dotted) or the RWP signal (blue). Fig . 1. Schematic of a Rossby wave packet (RWP) at a specific time. The blue line represents , the black dotted line is the underlying carrier wave , and the two red lines depict plus (upper line) and minus (lower line) the amplitude . A real world example is presented in Fig. 2 . Figure 2a shows the midlatitude jet with large meridional undulations over North America. Over the rest of hemisphere, the jet is more zonally

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Joaquim G. Pinto, Florian Pantillon, Patrick Ludwig, Madeleine-Sophie Déroche, Giovanni Leoncini, Christoph C. Raible, Len C. Shaffrey, and David B. Stephenson

.5194/nhess-14-2487-2014 Scaife , A. A. , and Coauthors , 2014 : Skillful long-range prediction of European and North American winters . Geophys. Res. Lett. , 41 , 2514 – 2519 , https://doi.org/10.1002/2014GL059637 . 10.1002/2014GL059637 Schäfer , S. A. K. , and A. Voigt , 2018 : Radiation weakens idealized midlatitude cyclones . Geophys. Res. Lett. , 45 , 2833 – 2841 , https://doi.org/10.1002/2017GL076726 . 10.1002/2017GL076726

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Georgios Fragkoulidis and Volkmar Wirth

E 0 threshold of 15 m s −1 that is used in this case results in the two RWPs to appear connected or under the process of merging over North America, a situation that illustrates the challenge in selecting the identification threshold for RWP tracking [see Wolf and Wirth (2017) for an extensive discussion of the issue]. The resulting c p values of the ridge over western Europe and the upstream trough centered at ~20°W amount to 1–4 m s −1 , which indicates a quasi-stationary wave ( Fig. 3d

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Paolo Ghinassi, Georgios Fragkoulidis, and Volkmar Wirth

bust” for the majority of the operational forecast models, showing a huge drop in the medium-range forecast skill over Europe ( Rodwell et al. 2013 ). The authors associated this poor performance to the misrepresentation of moist convective processes over North America a few days earlier, and this error was subsequently communicated downstream embedded in a RWP. Data are retrieved from the ERA-Interim reanalyses ( Dee et al. 2011 ) with a horizontal resolution of 2° × 2° on 20 pressure levels

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Michael Maier-Gerber, Michael Riemer, Andreas H. Fink, Peter Knippertz, Enrico Di Muzio, and Ron McTaggart-Cowan

events, because they primarily occur in proximity to the eastern seaboard of North America ( McTaggart-Cowan et al. 2008 ). In a recent study, Wang et al. (2018) examine reforecasts in terms of their skill to predict tropical cyclogenesis in the North Atlantic, using the pathway classification of McTaggart-Cowan et al. (2013) . The authors conclude that the two TT categories are less predictable than the others, a finding that they attribute to forecast errors of the deep-layer shear and the

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Roderick van der Linden, Andreas H. Fink, Joaquim G. Pinto, and Tan Phan-Van

, northeastern Vietnam is also frequently affected by the rainbands that are associated with this front ( Xu et al. 2009 ). The South China Sea usually is the main moisture source, but sometimes moisture is also transported from the Bay of Bengal to the mei-yu front ( American Meteorological Society 2016 ). Other synoptic systems affecting the study region with copious rains are tropical cyclones (TCs) that originate in the northwest Pacific and enter the South China Sea. Although the TC season peaks in

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