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Maxi Boettcher and Heini Wernli

” constitutes a clear example for a two-phase development. The precursor rapidly crossed the North Atlantic as a DRW before it intensified to one of the most harmful storms in central Europe in the last few decades. Wernli et al. (2002) identified an intensive straight zonal jet during the DRW propagation phase of Lothar far to the north of the low-level vortex and excluded a significant upper-level forcing of the surface low due to the absence of waves on the intense jet. They demonstrated that later in

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Kirstin Kober, Annette M. Foerster, and George C. Craig

idealized setup ( Keane and Plant 2012 ). Groenemeijer and Craig (2012) implemented it in a limited-area model to show that the scheme adds a significant amount of variability to an ensemble. They found as well that this effect depends on the strength of the synoptic forcing. Keane et al. (2014) showed in global aquaplanet simulations that the variability introduced by the scheme adapts correctly to changes in model resolution. In this study, we investigate if the additional variability introduced

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Julian F. Quinting, Michael M. Bell, Patrick A. Harr, and Sarah C. Jones

structures. For the first time, airborne observations were collected simultaneously by three research aircraft [Naval Research Laboratory-P3 (NRL-P3), U.S. Air Force-WC130 (USAF-WC130), and DLR-Falcon] during ET and provided unique and detailed insight into a TC approaching a midlatitude baroclinic zone. On 20 September the NRL-P3 and the USAF-WC130 measured the structure and the environment of a deep convective system that developed as Sinlaku was close to the primary midlatitude baroclinic zone. The

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Maxi Boettcher and Heini Wernli

models were cloud-diabatic heating in a baroclinic background atmosphere producing a positive potential vorticity (PV) anomaly at low-tropospheric levels. The following basic conditions for DRW existence and propagation emerged from these simulations. The vortex of the positive low-level PV anomaly (that is accompanied by a weak SLP minimum) induces a poleward low-level jet of warm moist air at its downstream side. This stream ascends along the poleward-sloping isentropes until condensation occurs

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Andrea Schneidereit, Dieter H. W. Peters, Christian M. Grams, Julian F. Quinting, Julia H. Keller, Gabriel Wolf, Franziska Teubler, Michael Riemer, and Olivia Martius

.g., Labitzke 1987 ; van Loon and Labitzke 1987 ), zonally asymmetric ozone changes (e.g., Peters et al. 2015 ), El Niño–Southern Oscillation (ENSO) (e.g., Butler and Polvani 2011 ), and the Madden–Julian oscillation (MJO) (e.g., Garfinkel et al. 2012 ; Liu et al. 2014 ). All these processes change the forcing of planetary waves in the troposphere or change the wave propagation into and in the stratosphere (mainly wavenumbers 1–3; Charney and Drazin 1961 ; Dickinson 1969 ). The strong mean

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Martin Weissmann, Florian Harnisch, Chun-Chieh Wu, Po-Hsiung Lin, Yoichiro Ohta, Koji Yamashita, Yeon-Hee Kim, Eun-Hee Jeon, Tetsuo Nakazawa, and Sim Aberson

connected to two other projects that coordinated their observations: the operational DOTSTAR program enhanced its flight activity and the U.S. Navy conducted the Tropical Cyclone Structure Experiment (TCS-08). Altogether, up to four aircraft were simultaneously available in a two month period: One U.S. Air Force WC-130 aircraft, which could penetrate into the eye of TCs; one U.S. Navy P-3 aircraft, which focused on rainbands and the structure of convection; the Falcon 20 aircraft of the Deutsches

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Christian M. Grams and Heather M. Archambault

enhanced poleward moisture transport that occurs often on the eastern side of a transitioning TC. When this moisture impinges on a midlatitude baroclinic zone in a region of upper-level forcing for ascent [e.g., near the equatorward entrance region of an upper-level jet streak; Uccellini and Johnson (1979) ] several days prior to ET, heavy precipitation and flooding may occur as a result of quasi-stationary convection in that region (e.g., Wang et al. 2009 ; Galarneau et al. 2010 ; Byun and Lee

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Yannick Barton, Paraskevi Giannakaki, Harald von Waldow, Clément Chevalier, Stephan Pfahl, and Olivia Martius

data from the International Satellite Cloud Climatology Project (ISCCP) were used ( Knapp 2008 ). b. Statistical procedures Daily precipitation sums may exhibit temporal dependence, even at high quantiles. In southern Switzerland regional-scale precipitation extremes are triggered by long-lived synoptic systems ( Hoinka et al. 2006 ; Pfahl and Wernli 2012 ). This leads to temporal clusters of extreme precipitation days on the time scale of the synoptic systems. Here, we are interested in the time

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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

, S. , D. M. Schultz , and G. Vaughan , 2017a : Early evolution of the 23–26 September 2012 U.K. Floods: Tropical Storm Nadine and diabatic heating due to cloud microphysics . Mon. Wea. Rev. , 145 , 543 – 563 , https://doi.org/10.1175/MWR-D-16-0200.1 . 10.1175/MWR-D-16-0200.1 Hardy , S. , D. M. Schultz , and G. Vaughan , 2017b : The 23–26 September 2012 U.K. Floods: Using PV surgery to quantify sensitivity to upper-level forcing . Mon. Wea. Rev. , 145 , 4055 – 4079 , https

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Hilke S. Lentink, Christian M. Grams, Michael Riemer, and Sarah C. Jones

offshore by the vortex outer circulation (>100 km from the center) and advected upward ( Chan and Liang 2003 ). When dry air moves over moist air, this reduces the moist static stability on the offshore side, and an asymmetric convection and cloud pattern is expected ( Chan and Liang 2003 ). Subsequently, when a TC moves closer to the shore and is situated partly over land and partly over the ocean, the difference in surface roughness has a dominant effect on vertical motion asymmetries, compared to

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