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

forecasting ( Alley et al. 2019 ). Why is there so little progress in tropical weather forecasting, although many challenges have been realized for decades (e.g., Smith et al. 2001 )? First, initial uncertainties tend to be largest in equatorial regions ( Žagar 2017 ). This is caused by an insufficient observational network, data assimilation algorithms optimized for midlatitude conditions, and large model errors, which also contribute to a fast degradation of forecast quality ( Privé and Errico 2013

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Tobias Kremer, Elmar Schömer, Christian Euler, and Michael Riemer

settings have been used for the parameterization schemes: inter alia a turbulent kinetic energy-based turbulence scheme, a shallow-convection scheme with mass-flux closure after Tiedtke (1989) , and a single-moment ice microphysics scheme (including graupel). The parameterization schemes are described in Doms et al. (2011) and more details on the setup of the simulation are given in Euler et al. (2019) . Our simulation domain spans from 22° to 54°N and from 40° to 70°W. Boundary and initial

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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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Stephan Rasp, Tobias Selz, and George C. Craig

Germany at 50°N, 10°E. For the analysis, a 256 × 256 gridpoint subdomain, roughly 717 km × 717 km, at the center of the simulation domain is considered to avoid boundary spinup effects. The 50-member ensemble simulations are started at 0000 UTC on each of the 12 consecutive days (see section 3 ) with a simulation time of 24 h. For initial and boundary conditions, we use hourly interpolated deterministic COSMO European version (COSMO-EU) analyses, which have a horizontal resolution of 7 km. Each

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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

microphysics scheme accounting for cloud water, rainwater, cloud ice, snow, and graupel ( Lin et al. 1983 ; Reinhardt and Seifert 2006 ); as well as a two-stream radiation scheme ( Ritter and Geleyn 1992 ). The asymptotic vertical mixing length of the boundary layer turbulence scheme is set to 500 m. All idealized experiments are initialized with horizontally homogeneous initial conditions (IC), based on a sounding from Payerne in Switzerland (CH, Radiosonde 06610; Fig. 1 ), observed at 1200 UTC 30 July

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

our experiments we only use the deterministic analysis. Using initial conditions provided by a convective-scale data assimilation system reduces the model spinup compared to downscaled initial conditions. Boundary conditions are provided by global ICON forecasts. Our simulations are started at 0000 UTC on each of the simulation days and extend for 24 h. A simulation without stochastic perturbations, also with tur_len = 500 m, is denoted as Reference . c. Observations We compare our simulations to

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Stephan Rasp, Tobias Selz, and George C. Craig

origin and the horizontal extent of the domain are listed in Table 1 for each simulation case. Initial and boundary conditions were taken from the analysis and the deterministic forecast of the European Centre for Medium-Range Weather Forecasts (ECMWF) using a COSMO simulation with coarser horizontal grid spacing of 7 km and parameterized convection as an intermediate step. Table 1. Details of model simulations. An online trajectory calculation tool by Miltenberger et al. (2013) , developed for

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Marlene Baumgart, Michael Riemer, Volkmar Wirth, Franziska Teubler, and Simon T. K. Lang

PV inversion (PPVI) under nonlinear balance ( Charney 1955 ; Davis 1992 ). The PPVI is performed on the Northern Hemisphere between 25° and 85°N on 15 evenly spaced pressure levels, with vertical boundary conditions specified at 875 and 125 hPa. Anomalies are defined as deviations from a background state, which is here defined as the 30-day mean (centered at 0000 UTC 14 November 2013) of the analysis. We use a midtropospheric pressure level (600 hPa) as the separation level between upper- and

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Tobias Selz, Lucas Fischer, and George C. Craig

. 1999 ), increasing exponents with height ( Tjemkes and Visser 1994 ; Kahn et al. 2011 ), boundary layer versus free troposphere ( Cho et al. 2000 ; Pressel and Collins 2012 ), and anisotropic scaling ( Lovejoy et al. 2010 ). The implications of the different observed exponents for the existence of universal power laws are not clear, since the data used in each case are limited, and the results may not be comparable. It is, however, interesting to consider whether distinct physical mechanisms may

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