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Stephan Rasp, Tobias Selz, and George C. Craig

upper-level PV structure and can strongly impact downstream development. For WCBs this has, for example, been shown by Grams et al. (2011) and Madonna et al. (2015) . Since the PV anomaly in the outflow usually acts to strengthen the already existing upper-level ridge, a systematic underestimation of low-PV transport by WCBs could contribute to the decrease in Rossby wave amplitude with increasing forecast time found by Gray et al. (2014) . In the continental warm season, only a small fraction

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

1. Introduction Tropical transition (TT) describes the phenomenon when a tropical cyclone (TC) emerges from an extratropical cyclone ( Davis and Bosart 2003 , 2004 ). During TT, the extratropical cyclone transforms from a cold- to a warm-core system. A cascade of events commonly precedes the TT: anticyclonic wave breaking (e.g., Thorncroft et al. 1993 ; Postel and Hitchman 1999 ) causes an upper-level precursor potential vorticity (PV) trough to penetrate into the (sub)tropics ( Galarneau et

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Christian Barthlott and Corinna Hoose

profiles then lead to differences in the stability and relative humidity, both of which are highly relevant to cloud formation and precipitation. The advantage of this method is that the dominating weather regime and the environmental conditions in the planetary boundary layer and at cloud base are not changed. To cover different weather regimes, this technique is applied to days with weak synoptic forcing (airmass convection) and strong synoptic forcing (passage of frontal zones). In each of these

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

) and http://www.cosmo-model.org for more details on the computational methods]. The model is set up with a horizontal resolution of 0.025° (about 2.5 km at 35°N) and 57 vertical levels up to 30-km height, with an enhanced vertical resolution in the planetary boundary layer. Shallow convection is parameterized using the mass-flux scheme of Tiedtke (1989) , while middle and high convection are explicitly computed. For all parameterized processes, the default setup of COSMO is used ( Doms et al

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Joël Arnault, Thomas Rummler, Florian Baur, Sebastian Lerch, Sven Wagner, Benjamin Fersch, Zhenyu Zhang, Noah Kerandi, Christian Keil, and Harald Kunstmann

noticeable in a 100 × 100 km 2 domain, but not in a 500 × 2500 km 2 domain. WRF-Hydro also produced daily discharge moderately close to observations according to the Nash–Sutcliffe model efficiency coefficient (NSE; Nash and Sutcliffe 1970 ): 0.27 in the case of Senatore et al. (2015) , 0.43 in the case of Arnault et al. (2016) , and 0.02 in the case of Kerandi et al. (2018) . The above studies show that the representation of terrestrial water flow indeed impacts the surface fluxes and planetary

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Christian Euler, Michael Riemer, Tobias Kremer, and Elmar Schömer

structural evolution In this section the storm structure and environmental conditions in the simulation will briefly be described at four selected stages during Karl’s transition. This description provides the context for the Lagrangian analysis presented in the subsequent sections. a. Synoptic overview A synoptic overview of Karl is given by Pasch and Zelinsky (2016) : Karl originated from a low pressure system close to the Cabo Verde Islands that developed from an easterly wave crossing the west coast

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