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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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Volkmar Wirth and Christopher Polster

.0.CO;2 . 10.1175/1520-0469(1981)038<1179:TSLROA>2.0.CO;2 Hoskins , B. J. , and T. Ambrizzi , 1993 : Rossby wave propagation on a realistic longitudinally varying flow . J. Atmos. Sci. , 50 , 1661 – 1671 ,<1661:RWPOAR>2.0.CO;2 . 10.1175/1520-0469(1993)050<1661:RWPOAR>2.0.CO;2 Huntingford , C. , D. Mitchell , K. Kornhuber , D. Coumou , S. Osprey , and M. Allen , 2018 : Assessing changes in risk of amplified planetary waves in a

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Jan Wandel, Julian F. Quinting, and Christian M. Grams

smoothed with a Gaussian filter. Next we focus on week 3, the time when WCB outflow frequency biases saturate ( Fig. 9 ). Similar results are found for weeks 2 and 4 (not shown). First we investigate if a link of WCB outflow biases and biases in the upper-tropospheric large-scale flow, as depicted by geopotential height at 300 hPa, exist. Generally the forecasted large-scale extratropical flow in winter is too zonal and the planetary wave pattern is slightly shifted in week 3 ( Fig. 9b ): over the

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Benedikt Schulz and Sebastian Lerch

of the stationwise (left) mean bias of the ensemble median and (right) mean ensemble range of the EPS as functions of the lead time. The black line indicates the average over all samples. The temporal development of the bias and ensemble range shown in Fig. 4 indicates another meteorological effect, the evening transition of the planetary boundary layer. When the sun sets, the surface and low-level air that have been heated over the course of the day cool down and thermally driven

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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

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Andreas Schlueter, Andreas H. Fink, Peter Knippertz, and Peter Vogel

( Matsuno 1966 ). Two other major wave types have been observed in the tropical belt that are not obtained from the shallow-water equations: the Madden–Julian oscillation (MJO; Madden and Julian 1971 ) and westward traveling tropical disturbances (TDs) including easterly waves ( Riehl 1945 ). All these waves are collectively termed “tropical waves” in this paper. The spatiotemporal scales range from planetary and 30–90 days in the case of the MJO to synoptic and 1–3 days in the case of inertio

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George C. Craig, Andreas H. Fink, Corinna Hoose, Tijana Janjić, Peter Knippertz, Audine Laurian, Sebastian Lerch, Bernhard Mayer, Annette Miltenberger, Robert Redl, Michael Riemer, Kirsten I. Tempest, and Volkmar Wirth

Waves to Weather (W2W) is a collaborative research center formed to investigate the limits of predictability of weather. Our ability to make forecasts up to a week or more in advance contributes to a strong economy and protects human life and property. Although we commonly speak of “weather,” particularly high-impact weather events take many different forms that result from different physical processes. The most destructive weather disasters in recent years have been associated with floods and

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Tobias Selz

background spectrum and thus likely involve a climatological component. For example, orography and the land–sea distribution may hinder the largest planetary waves from freely evolving. In addition the ICON simulations have fixed sea surface temperatures. d. Comparison to simulations with a deterministic convection scheme A second set of simulations has been performed using the ICON model but this time in its standard setup with the deterministic TB convection scheme ( Bechtold et al. 2001 ). With this

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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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