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Paolo Ghinassi
,
Georgios Fragkoulidis
, and
Volkmar Wirth

1. Introduction An important feature of midlatitude atmospheric dynamics is the existence of upper-tropospheric Rossby waves with synoptic- to planetary-scale wavenumbers. Often a Rossby wave is not strictly circumglobal; rather, its amplitude is spatially inhomogeneous with a relative maximum at a specific location decaying to smaller values at larger distances. This gives rise to so-called Rossby wave packets [RWPs; for a recent review see Wirth et al. (2018) ]. A key feature of RWPs is the

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Marlene Baumgart
,
Paolo Ghinassi
,
Volkmar Wirth
,
Tobias Selz
,
George C. Craig
, and
Michael Riemer

phase. Beyond this synoptic-scale phase saturation at long lead times (beyond 2 weeks), the results of Buizza and Leutbecher (2015) indicate that there is still forecast skill for large-scale fields. To investigate error growth up to the planetary scale, we employ a complementary diagnostic that filters out phase information and identifies the envelope of the upper-level Rossby waves. This diagnostic is based on finite-amplitude local wave activity (LWA) in the primitive-equation, isentropic

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

. As in Fig. 3 , but for the N = 49 recurving TCs in the DECEL subset. Fig . 15. As in Fig. 3 , but for the N = 49 recurving TCs in the ACCEL subset. The planetary wave pattern strongly influences where the genesis of atmospheric blocking occurs. It still needs to be assessed whether significant differences in planetary-scale flow, which could be related to the different observed blocking patterns, exist between ACCEL and DECEL. For instance, the presence of significantly positive over

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Mirjam Hirt
,
Stephan Rasp
,
Ulrich Blahak
, and
George C. Craig

for a deceleration of the flow by unresolved orography, either by modifying the roughness length or by including an orographic drag term. Here, we aim to account for the mechanical lifting caused by SSO and its effect on convective initiation with a newly developed stochastic perturbation scheme, called SSOSP. The new scheme closely follows the formulation of the PSP scheme: wind tendencies are randomly perturbed with an amplitude that scales with theoretical gravity waves excited by SSO

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Florian Pantillon
,
Bianca Adler
,
Ulrich Corsmeier
,
Peter Knippertz
,
Andreas Wieser
, and
Akio Hansen

warming during a typical foehn event. Nevertheless, the pattern of near-surface dry air downstream of mountain ranges in ensemble member 17 clearly indicates an orographic contribution upstream of the WASTEX site ( Fig. 9a ) and a wave pattern over the warm sector can be recognized in satellite imagery ( Fig. 2 ). Accordingly, mountain waves with wavelength of about 20 km are found in the lee of the Vosges Mountains in ensemble member 17 ( Fig. 11a ). Their amplitude decreases at the northern tip of

Open access
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

Open access
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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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

Open access
Tobias Necker
,
Martin Weissmann
,
Yvonne Ruckstuhl
,
Jeffrey Anderson
, and
Takemasa Miyoshi

Research project (Project ID:ra000015, ra001011). Finally, this study was partly funded by the Transregional Collaborative Research Center SFB/TRR 165 “Waves to Weather” funded by the German Science Foundation (DFG). APPENDIX List of Variable Abbreviations TOT_PREC Hourly accumulated precipitation T _2M 2-m temperature U _10M 10-m zonal wind PS Sea level pressure DBZ_CMAX Column maximum radar reflectivity T _500 500-hPa temperature U _500 500-hPa zonal wind W _500 500-hPa vertical wind QV_500 500-hPa

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