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Volkmar Wirth and Christopher Polster

stationary wavenumber of free Rossby waves in a zonal channel approaches the dominant wavenumber of the stationary forcing due to orography or diabatic heating ( Charney and Eliassen 1949 ; Held 1983 ). The mechanism requires Rossby waves to travel around the entire globe in the zonal direction ( Yang et al. 1997 ; Wirth 2020a , 1–3), and this is facilitated in the real atmosphere by a circumglobal jet with strong waveguidability ( Branstator 1983 , 2002 ; Manola et al. 2013 ). Resonance appears

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

outflow height ( Schäfler and Harnisch 2015 ). During WCB ascent air rises ahead of the cold front and across the warm front in a region of quasigeostrophic forcing for ascent ( Binder et al. 2016 ) which results in precipitation below the WCB airstream. The strong latent heat release due to condensation further contributes to upward motion through cross-isentropic ascent. On average, this latent heat release amounts to 20 K within 48 h ( Madonna et al. 2014 ). In the following, we use the potential

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Christian Barthlott and Corinna Hoose

profiles then lead to differences in the stability and relative humidity, both of which are highly relevant to cloud formation and precipitation. The advantage of this method is that the dominating weather regime and the environmental conditions in the planetary boundary layer and at cloud base are not changed. To cover different weather regimes, this technique is applied to days with weak synoptic forcing (airmass convection) and strong synoptic forcing (passage of frontal zones). In each of these

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Kirstin Kober and George C. Craig

2006 ). Multiple integrations of NWP models (ensembles) can be used to provide probabilistic information but can be set up in different ways, depending on the represented sources of uncertainty. Recent studies have shown that in different weather regimes, different sources of uncertainty dominate: in cases of strong large-scale forcing, initial and boundary conditions uncertainty contributes more to the overall uncertainty, whereas in weak large-scale forcing, model error is more important

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Kevin Bachmann, Christian Keil, George C. Craig, Martin Weissmann, and Christian A. Welzbacher

hours ( Hohenegger and Schär 2007a , b ; Zhang et al. 2015 , 2016 ). However, there are steady Earth surface features such as orography or transient dynamical forcing patterns such as weather regimes that potentially provide the means to extend those predictability estimates ( Anthes 1986 ). The prevailing synoptic weather regime exerts a decisive influence on the predictability of convective precipitation. In case studies, Hanley et al. (2011 , 2013) and Barrett et al. (2015) showed how the

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Roderick van der Linden, Andreas H. Fink, Joaquim G. Pinto, and Tan Phan-Van

period of heavy precipitation was even shorter and ended at about 1200 UTC 27 July 2015. In the following, the focus is put on the first period because of 1) the persistence of rainfall, 2) the fact that the highest (station) rainfall amounts were almost exclusively observed in regions close to the coast, and 3) the large-scale dynamical forcing (see section 4 ). 4. Synoptic–dynamic development Strong convection was linked to a weak surface low in the Gulf of Tonkin and northeastern Vietnam during

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Thomas Engel, Andreas H. Fink, Peter Knippertz, Gregor Pante, and Jan Bliefernicht

–trough system, the former being located over Guinea and Sierra Leone. To the west of the trough, the 0600 UTC analysis shows enhanced lower-tropospheric wind shear of 10–20 m s −1 over northern Burkina Faso and westernmost Niger, but because of the early morning hours, CAPE is lower than 1000 J kg −1 ( Fig. 4b ). From this, we conclude that the convective invigoration must be related to synoptic forcing from the AEW that provided strong convergence and record amounts of moisture. Canonical squall lines

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

relevant when synoptic forcing is weak and local mechanisms are the main driver for overcoming convection inhibition ( Keil et al. 2014 ). In these situations insufficient convective initiation has been commonly observed for kilometer-scale models (see e.g., Clark et al. 2016 ). In operational NWP systems such biases are often compensated by tuning other parameters, such as the turbulent length scale in the boundary layer parameterization ( Hanley et al. 2015 ). Smaller mixing lengths allow the lowest

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Stephan Rasp, Tobias Selz, and George C. Craig

second moment can be expressed in terms of the normalized variance or in terms of the unnormalized standard deviation b. Previous tests of the CC06 theory So far, few studies have directly tested the assumptions and predictions of CC06. Cohen and Craig (2006) used a convection-permitting model in a radiative–convective equilibrium setup with different large-scale forcing and vertical wind shear strengths and found that p ( m ) was well approximated by an exponential distribution for all settings

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Joël Arnault, Thomas Rummler, Florian Baur, Sebastian Lerch, Sven Wagner, Benjamin Fersch, Zhenyu Zhang, Noah Kerandi, Christian Keil, and Harald Kunstmann

drainage. However, the change in precipitation between WRF and WRF-Hydro was modest due to strong oceanic and orographic forcing in their study region. Differences between WRF and WRF-Hydro seasonal precipitation were also small in the case of a steep catchment at the foothills of Mount Kenya, East Africa ( Kerandi et al. 2018 ). In West Africa, Arnault et al. (2016) found that the impact of overland flow and runoff–infiltration partitioning on precipitation was scale dependent, that is, much more

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