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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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Maxi Boettcher and Heini Wernli

neglecting latent heat release (and surface fluxes in the later study). In these experiments the DRW mechanism came to a halt and the subsequent intensification was significantly weaker or even quasi-absent. Moore and Montgomery (2004 , 2005) conducted further idealized two- and three-dimensional model studies of DRWs. They suggested that regarding the environmental conditions, the baroclinicity and the low-level moisture supply are the most important parameters determining the size and amplitude of

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Kirstin Kober and George C. Craig

relevant to the initiation of convection. In general, the initiation of convection requires certain atmospheric conditions. In synoptic situations without large-scale forcing, convection can develop if instability, measurable by the convective available potential energy (CAPE), as well as local triggers to overcome a possible inversion above the boundary layer, measurable by the convective inhibition (CIN), are available together with moisture in specific heights ( Done et al. 2012 ). The distribution

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

air mass is advected in a southerly flow toward the Alpine ridge and then orographically forced to ascend (e.g., Massacand et al. 1998 ; Martius et al. 2006b ). The low-level southerly flow, typically transporting moisture from the Atlantic Ocean and the Mediterranean Sea ( Winschall et al. 2014 ), can be related to the presence of a positive upper-tropospheric potential vorticity (PV) anomaly over western Europe ( Doswell et al. 1998 ; Massacand et al. 1998 ; Martius et al. 2006b ). These

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

; Matsueda 2009 ). These troughs (hereafter referred to as flanks) have a special role as they are the transition zones from the quasi-stationary persistent core of the block to the environmental flow. An impressive example of atmospheric blocking is the spatially extensive high pressure system over Russia during summer 2010 ( Fig. 1 ) that blocked the zonal flow from mid-June to mid-August ( Trenberth and Fasullo 2012 ). Favorable large-scale sea surface temperatures and local soil moisture conditions

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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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Maxi Boettcher and Heini Wernli

. Below the level of maximum latent heating a positive diabatic PV tendency occurs, which leads to the reformation of the DRW downstream of its original position. Once generated, a DRW can be regarded as a self-preserving system that propagates rapidly by continuous diabatic PV regeneration under the conditions of at least moderate baroclinicity and sufficient moisture supply. With this characterization of DRWs we emphasize the aspect of wavelike regeneration and propagation (as opposed to material

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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

moves poleward and starts to interact with the midlatitude flow ( Fig. 1a ). This results in the formation of a jet streak ( Fig. 1b ) and a poleward deflection of the jet near the transitioning cyclone in conjunction with the development of a ridge–trough couplet ( Fig. 1b ). At the same time, a region of enhanced moisture flux—a so-called atmospheric river ( Zhu and Newell 1998 )—forms ahead of the downstream trough. The ridge–trough couplet continues to amplify, a new cyclone develops farther

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

convection. The two convection parameterizations differ not only in the fact that one is deterministic and is one stochastic. Both are mass-flux-based schemes, but differ in two major ways: the closure assumption (Tiedtke parameterization is based on moisture convergence and PC08 is based on CAPE) and the trigger (Tiedtke: temperature threshold; PC08 : vertical velocity) ( Dierer et al. 2009 ). Groenemeijer and Craig (2012) implemented the PC08 scheme in COSMO, version 4.8, and performed ensemble

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Jana Čampa and Heini Wernli

distributed over the whole cyclone area. Field and Wood (2007) composited cyclones according to their intensity (in terms of surface wind speed) and moisture content. They show that for cyclones of the same wind speed intensity, those with more moisture have a slightly higher sea level pressure (SLP) than the drier ones. Therefore the dynamical effect of precipitation processes is also to produce stronger winds in the cyclones that do not have very low SLP. Rudeva and Gulev (2011) found similar

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