The German Research Foundation (DFG) is gratefully acknowledged for funding the research group PANDOWAE (FOR896) that enabled this work. The code for the quasigeostrophic vertical motion diagnostic was derived from routines in NDDIAG, a diagnostics package developed and supported by NCAS-CMS (U.K. National Centre for Atmospheric Science Computational Modelling Services). We thank Sue Gray (University of Reading) for making this package available to us. We are also grateful to Patricia Heckendorn for providing us with an initial version of the DRW tracking algorithm. Finally, we thank Ron McTaggart-Cowan and an anonymous reviewer for their constructive, in-depth reviews that helped to improve this paper.
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The term “anomaly” is used to indicate significant deviations from a climatological value, which, in the lower extratropical troposphere is typically around 0.5 PVU.
Although the system shows a localized vortexlike circulation (and not a wavelike vorticity structure), we prefer to refer to this system as a DRW (instead of a diabatic Rossby vortex, cf. Moore and Montgomery 2004) in order to highlight the wavelike propagation mechanism (as opposed to the advection of a coherent vortex).
Note that we cannot expect a perfect correlation between the two quantities, since precipitation is at best an integral measure of diabatic heating whereas the diabatic PV production depends strongly on the vertical gradient of the latent heating.