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

organization and coupling to larger-scale circulations. The most important example of such a coupling on weather time scales are equatorial waves, classically referring to planetary-scale solutions of the shallow water equations for the tropics ( Matsuno 1966 ; Wheeler and Kiladis 1999 ). The coupling relies on a wave-induced modification of environmental conditions for convection such as convergence, stability, moisture availability, and shear ( Schlueter et al. 2019a , b ). Although a relatively high

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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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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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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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