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Thomas H. A. Frame, John Methven, Nigel M. Roberts, and Helen A. Titley

we shall give a brief outline of the tracking method used. See Hewson and Titley (2010) for a full description of the objective feature identification and tracking methodology. The tracking algorithm aims to identify and track developing cyclonic storms through their entire life cycle from small kinks in fronts (labeled diminutive frontal waves) through developed frontal waves to closed low pressure centers (labeled barotropic lows). The algorithm uses a hybrid of objective fronts, pressure

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Jeffrey M. Chagnon and Suzanne L. Gray

), diabatic Rossby waves (e.g., Parker and Thorpe 1995 ; Moore and Montgomery 2004 ; Moore et al. 2013 ), and forecast error growth (e.g., Brennan et al. 2008 ; Davies and Didone 2013 ). In the absence of frictional and diabatic processes, PV is materially conserved. Therefore, PV provides a convenient means to characterize the large-scale structure of the atmosphere and its evolution in mid- and high latitudes where the planetary vorticity is nonnegligible. Climatologically, PV increases with height

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Jesse Norris, Geraint Vaughan, and David M. Schultz

with greater spaces between. In this paper we investigate how the synoptic environment determines which of the many possible morphologies the cores and gaps can adopt. The study builds on that of Norris et al. (2014) who compared the distribution and evolution of precipitation bands in idealized baroclinic wave simulations where roughness length, latent-heat release, and surface fluxes of sensible and latent heat were varied. Norris et al. (2014) simulated, at 20-km grid spacing, precipitation

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Matthew R. Clark and Douglas J. Parker

the frontal updraft by vertical shear- and buoyancy-induced wavelike disturbances above the front ( Kawashima 2007 ) and the modulation of the frontal updraft by trapped gravity waves, triggered by regions of stronger updraft along the cold front ( Brown et al. 1999 ). Locatelli et al. (1995) defined “large” gaps as those greater than 10–12 km in the alongfront direction, and suggested that they may be dynamically different from smaller gaps. Intense NCFRs often produce damaging wind gusts and

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David M. Schultz, Bogdan Antonescu, and Alessandro Chiariello

1200 UTC 3 January 2003, a large-scale sub 980-mb (1 mb = 1 hPa) cyclone south of Greenland occupied the western half of the North Atlantic Ocean ( Fig. 3a ). A frontal wave was traveling around the larger cyclone on its south side. Petterssen (1936) frontogenesis at 850 mb was used to diagnose the regions of locations where the magnitude of the horizontal temperature gradient was increasing, indicating active fronts. The wave possessed three regions of Petterssen frontogenesis: a region along

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G. Vaughan, J. Methven, D. Anderson, B. Antonescu, L. Baker, T. P. Baker, S. P. Ballard, K. N. Bower, P. R. A. Brown, J. Chagnon, T. W. Choularton, J. Chylik, P. J. Connolly, P. A. Cook, R. J. Cotton, J. Crosier, C. Dearden, J. R. Dorsey, T. H. A. Frame, M. W. Gallagher, M. Goodliff, S. L. Gray, B. J. Harvey, P. Knippertz, H. W. Lean, D. Li, G. Lloyd, O. Martínez–Alvarado, J. Nicol, J. Norris, E. Öström, J. Owen, D. J. Parker, R. S. Plant, I. A. Renfrew, N. M. Roberts, P. Rosenberg, A. C. Rudd, D. M. Schultz, J. P. Taylor, T. Trzeciak, R. Tubbs, A. K. Vance, P. J. van Leeuwen, A. Wellpott, and A. Woolley

weather systems. PV combines the vertical stability of the atmosphere with the horizontal shear and rotation of the wind field and is materially conserved in the absence of diabatic and frictional processes. It is a local measure of circulation about a point and its distribution is fundamental to our understanding of Rossby waves and the evolution of cyclones (e.g., Hoskins et al. 1985 ). Cyclone development typically arises through interaction between a Rossby wave on the tropopause and large

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Sam Hardy, David M. Schultz, and Geraint Vaughan

, and H. Wernli , 2014 : Atmospheric processes triggering the central European floods in June 2013 . Nat. Hazards Earth Syst. Sci. , 14 , 1691 – 1702 , doi: 10.5194/nhess-14-1691-2014 . 10.5194/nhess-14-1691-2014 Hakim , G. J. , D. Keyser , and L. F. Bosart , 1996 : The Ohio valley wave-merger cyclogenesis event of 25–26 January 1978. Part II: Diagnosis using quasigeostrophic potential vorticity inversion . Mon. Wea. Rev. , 124 , 2176 – 2205 , doi: 10

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Oscar Martínez-Alvarado, Laura H. Baker, Suzanne L. Gray, John Methven, and Robert S. Plant

. , 1973 : Mechanisms influencing distribution of precipitation within baroclinic disturbances . Quart. J. Roy. Meteor. Soc. , 99 , 232 – 251 , doi: 10.1002/qj.49709942003 . Hoskins , B. J. , and F. P. Bretherton , 1972 : Atmospheric frontogenesis models: Mathematical formulation and solution . J. Atmos. Sci. , 29 , 11 – 37 , doi: 10.1175/1520-0469(1972)029<0011:AFMMFA>2.0.CO;2 . Janssen , P. , 2004 : The Interaction of Ocean Waves and Wind . Cambridge University Press, 300 pp . Lock

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Ben Harvey, John Methven, Chloe Eagle, and Humphrey Lean

1. Introduction Atmospheric frontal systems are associated with numerous high-impact weather phenomena. The majority of extreme precipitation events in midlatitudes are associated with fronts ( Catto and Pfahl 2013 ), and intense wind gusts, including tornadoes, commonly occur near frontal rainbands ( Clark and Parker 2014 ). Despite being embedded within large-scale weather systems, often stretching over thousands of kilometers, the narrow cross-frontal scale of frontal systems coupled with

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Oscar Martínez-Alvarado, Suzanne L. Gray, and John Methven

sea level pressure) on 24 February 1987, Stoelinga (1996) showed that its intensity was 70% stronger as a result of coupling between baroclinic wave growth and latent heat release. Until now, studies on latent heat release and cyclone intensification have focused on Northern Hemisphere extratropical cyclones occurring mostly during wintertime (December–February), but also during spring (March–May) and autumn (September–November). On the other hand, the importance of latent heat release, and

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