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Andrea Schneidereit, Dieter H. W. Peters, Christian M. Grams, Julian F. Quinting, Julia H. Keller, Gabriel Wolf, Franziska Teubler, Michael Riemer, and Olivia Martius

( Tripathi et al. 2015 ). Matsuno (1971) developed a dynamical model of the stratospheric sudden warming phenomena in which tropospheric forced planetary wave packets propagate upward into the stratosphere. The deposition of their easterly angular momentum [Eliassen–Palm flux (EP flux) convergence] leads to a weakening and breakdown of the polar night jet. Several processes influence the occurrence of MSSW events in the Northern Hemisphere: the quasi-biennial oscillation (QBO) and the solar cycle (e

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Gabriel Wolf and Volkmar Wirth

of RWPs at any given time; rather, it can only be derived by reference to a sequence of consecutive points in time. This is in contrast to diagnostics involving some form of a flux, which by design is a vector and may be designed such as to indicate the direction of propagation. In this study we make use of wave activity and its associated flux. The concept of wave activity and wave activity flux is attractive, because it involves a conservation relation for conservative flows, in distinct

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Volkmar Wirth, Michael Riemer, Edmund K. M. Chang, and Olivia Martius

conservation of total energy following the 3D flow); is the velocity vector, ω is the pressure vertical velocity, and α is the specific volume. In (3) , the first two terms on the right-hand side represent baroclinic and barotropic conversion, respectively. The third term on the right-hand side also represents an energy transfer between the mean flow and the eddies, but averages out to zero in the time mean. Following Orlanski and Sheldon (1993) , the energy flux can be written as follows: where

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Julia H. Keller, Sarah C. Jones, and Patrick A. Harr

. Advective and dispersive K e fluxes, together with baroclinic conversion from eddy available potential into eddy kinetic energy then enable investigation of the intensification and downstream propagation of individual K e maxima and the interaction between neighboring features. The analysis method was already applied successfully to examine the development and amplification of wave patterns in the midlatitudes due to extratropical cyclones ( McLay and Martin 2002 ; Decker and Martin 2005

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Julia H. Keller

conversion of when eddy available potential energy is converted into through lifting of warm and sinking of cold air masses [first term on the right-hand side in Eq. (2) ], and the divergence of the ageostrophic geopotential flux (second term), which disperses from one center to another (i.e., downstream propagation by group velocity). As in Harr and Dea (2009) , all quantities are vertically integrated between and , and normalized by the standard gravity , to obtain units of joules per

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Andrea Schneidereit, Silke Schubert, Pavel Vargin, Frank Lunkeit, Xiuhua Zhu, Dieter H. W. Peters, and Klaus Fraedrich

its long persistence extending to mid-August is not ( Matsueda 2011 ). Thus, the question arises: what are the causes of this long-lasting heat wave or rather the blocking high? Blocking, in general, denotes the effect of a synoptic system acting as a barrier to the westerly flow splitting the jet stream ( Elliott and Smith 1949 ). The formation of a block over Europe can be ascribed to the convergence (or absorption) of wave activity density flux associated with an incoming anomalous quasi

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Simon T. K. Lang, Sarah C. Jones, Martin Leutbecher, Melinda S. Peng, and Carolyn A. Reynolds

initial SVs we apply the energy flow analysis ( Kwon and Frank 2008 ) to our EPS experiments (see section 3b ). We calculate the conversion terms for the unperturbed control forecasts and the perturbed forecasts. To analyze how the conversion terms are changed by the SV perturbations, the conversion terms of the unperturbed forecast are subtracted from the conversion terms of the perturbed forecasts. Since we focus on the initial SVs, and therefore investigate the energy fluxes at t = 0, the

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Kirstin Kober, Annette M. Foerster, and George C. Craig

study. The PC08 parameterization is based on the closure assumption and the cloud model of the Kain–Fritsch convection parameterization ( Kain and Fritsch 1990 ), and it maintains quasi equilibrium on large scales while creating small-scale variability by drawing plumes from a probability density function computed from the closure mass flux in the convection scheme. As a result, different realizations for the same large-scale conditions provide a representation of the intrinsic stochasticity of

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Julian F. Quinting and Sarah C. Jones

of a time mean (subscript m ) and a perturbation. The horizontal wind field is then defined as and scalar variables, including the vertical velocity ω , are defined as . The time mean is defined as a 30-day running mean. The time tendency of is defined in pressure coordinates as where ϕ denotes the geopotential height, α the specific volume, and the horizontal gradient operator. The first term on the right-hand side is the ageostrophic (subscript a ) geopotential flux divergence

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Andreas Schäfler, Andreas Dörnbrack, Christoph Kiemle, Stephan Rahm, and Martin Wirth

2008 ; Miglietta and Rotunno 2009 ), or low-level moisture supply ( Boutle et al. 2010 ; Keil et al. 2008 ), and their physical representation in NWP models has emerged to play a crucial role for QPF. In particular, the supply of low-level moisture by latent heat fluxes or through advective transport is crucial for the evolution of midlatitude weather systems. As pointed out by Boutle et al. (2010) , large-scale moisture advection is the process that maintains the structure of the boundary layer

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