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

1. Introduction Regional-scale extreme precipitation events in the mountainous terrain of the Alpine region can have severe impacts on human populations and the environment ( Frei et al. 2000 ). They can trigger floods, which are the main natural hazard in terms of financial damage in Switzerland ( Hilker et al. 2009 ). The potential damage of these regional-scale extreme precipitation events can be substantial because they can affect the entire watershed of a river or a lake. For example, in

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

the forecast errors associated with these changes. For mature TCs that make landfall, on the other hand, many (idealized) studies document the influence of either a flat coastal region or an orographic barrier (e.g., Taiwan) on the track and structural development. When a TC vortex impinges on land, regardless of orography, it has two effects: a reduction of moisture supply and an increase of surface roughness. First, when the inner core is still over the ocean, dry air from land is transported

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Olivia Martius and Heini Wernli

al. 2009 ) but also coincide with areas of frequent tropopause folding and attendant enhanced vertical exchange between the stratosphere and the troposphere ( Sprenger et al. 2003 ). On decadal time scales observations reveal a poleward shift of the climatological zonal mean subtropical jet in conjunction with a widening of the tropical belt ( Seidel et al. 2008 , and references therein). However, regionally a southward shift of the subtropical jet over the eastern North Atlantic and Africa is

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Lisa-Ann Quandt, Julia H. Keller, Olivia Martius, and Sarah C. Jones

clusters are stronger than the differences among members of the same cluster. We did not use the cluster mean for the comparison of the development scenarios of the block, in order to omit the neutralizing effects that averaging produces on small-scale structures and on synoptic fields (which is a particular problem at the end of the forecast when forecast variability is high). d. Identification of atmospheric blocking We used two blocking indices. The first index is one-dimensional and identifies

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

. However, high-resolution observations of the structural changes of a TC during ET and its environment are still rare and have not been investigated yet in detail. One of the aims of The Observing System Research and Predictability Experiment (THORPEX) Pacific Asian Regional Campaign (T-PARC) in 2008 was to extend the knowledge of the various physical processes involved in ET using aircraft observations. During this field campaign one of the major typhoons in the western North Pacific Ocean in 2008

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Andreas Schäfler, Andreas Dörnbrack, Christoph Kiemle, Stephan Rahm, and Martin Wirth

fields, the authors identified the inaccurate representation of diabatic effects in the IFS as a possible cause of an inaccurate cyclone forecast. An extratropical cyclone very efficiently transports moisture upward ahead of the cold front. The associated diabatic heating can, in turn, generate an upper-level negative potential vorticity (PV) anomaly, which considerably influences the large-scale dynamics and, subsequently, the precipitation distribution ( Massacand et al. 2001 ). Despite all of the

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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

forecast uncertainty is the representation of diabatic processes in NWP models. The convective parameterization schemes employed in all global models, and in some regional models, might underrepresent divergent outflow aloft, in part because the divergent outflow is a gridscale response to resolved precipitation processes, as well as parameterized convective heating and moistening ( Zadra et al. 2018 ). This error in the representation of diabatic processes affects the correct simulation of initial

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Andrea Schneidereit, Silke Schubert, Pavel Vargin, Frank Lunkeit, Xiuhua Zhu, Dieter H. W. Peters, and Klaus Fraedrich

contributors to the blocking high in 2010. Dole et al. (2011) demonstrate that the natural variability is the main cause of the long-lasting blocking high. It has hypothesized that such an event could occur more often due to climate change and the expected change in the year-to-year variability ( Schär et al. 2004 ). Global and regional model simulations indicate its improbability that such an event may occur over eastern Europe until the second half of the twenty-first century ( Dole et al. 2011

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Christian M. Grams and Heather M. Archambault

of the downstream trough (T2) in the presence of ET ( Fig. 6c ). The dipoles of strong upper-level and lower-level QG ascent reflect the effects of differential vorticity advection at upper levels and differential temperature advection at low levels ( Fig. 7c ). Farther downstream, QG ascent increases ahead of amplifying trough T2. The vertical cross section indicates the merging of the remnants of the TC inner core (1400 km; Fig. 8c ) with the PRE ahead of the now much stronger low

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

conservation of mass and circulation within a PV isoline on an isentropic surface. The computation of the MLM results in a stronger background flow than the climatological time average and, hence, stronger PV gradients. If one transcends linear theory and accounts for nonlinear effects, the waves do have an impact on the background state. In practice it may, therefore, be an advantage to use a nonstationary background flow, which implicitly accounts for the feedback of the waves on the waveguide. For

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