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

Hemisphere Shapiro–Keyser cyclone in development stage 3: surface cold front (SCF); surface warm front (SWF); bent-back front (BBF); cold conveyor belt (CCB); sting jet airstream (SJ); dry intrusion (DI); warm conveyor belt (WCB); WCB anticyclonic branch (WCB1); WCB cyclonic branch (WCB2); and the large × represents the cyclone center at the surface, and the gray shading represents cloud top (see also Fig. 2 ). There are two separate regions usually associated with strong winds in Shapiro

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Jesse Norris, Geraint Vaughan, and David M. Schultz

. 2008 ). As in Norris et al. (2014) , WRF was initialized with the baroclinic-wave test case, which consists of a zonal jet on an f plane ( s −1 ) in thermal wind balance with a horizontal temperature gradient at the surface of roughly 20 K (1000 km) −1 . The jet is obtained by inverting a baroclinically unstable potential vorticity distribution in the y – z plane, as in Rotunno et al. (1994) . The computational domain is 8000 km in the north–south direction. In the east–west direction, the

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David M. Schultz, Bogdan Antonescu, and Alessandro Chiariello

lengthen and narrow ( Fig. 3c ). At 300 mb, an 80 m s −1 jet upstream of a strong diffluent trough was associated with the surface pressure center ( Fig. 4 ). That the large-scale flow environment in which the cyclone was embedded was diffluent supports the formation of a Norwegian cyclone, weak warm front, and meridionally oriented occluded front (e.g., Schultz et al. 1998 ; Schultz and Zhang 2007 ). Fig . 3. Sea level pressure (black lines every 4 hPa), 850-mb potential temperature (green lines

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

, while that of and is shown in Fig. 3c . In this case, the flow moves westward across the whole dropsonde curtain ( Fig. 3a ). The maximum zonal velocity ( ) is located at midtropospheric levels around 450 hPa, constituting the system’s WCB. At lower levels, the maximum zonal velocity ( ) is located within a low-level jet (LLJ) toward the section’s northern edge behind the system’s cold front. The cold front is located around 55.5°N near the surface. A column with extends over the cold front

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Matthew R. Clark and Douglas J. Parker

; Browning 1995 ). This could explain the absence of a well-defined prefrontal low-level jet and associated strong alongfront component of prefrontal winds at low levels, such as is usually observed ahead of NCFRs associated with rearward-sloping fronts ( Browning and Pardoe 1973 ; Browning et al. 1998 ), and as observed in the other NCFR cases analyzed herein. b. Vorticity, convergence, and stretching The NCFR of 29 November 2011 was marked by a line of large vertical vorticity, horizontal convergence

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Jeffrey M. Chagnon and Suzanne L. Gray

depend on whether convection is parameterized or explicitly resolved, but the mesoscale convective systems analyzed were more convectively unstable than the cases presented in this paper. Finally, the characteristics of the dipole were not uniform across the large domains in which the simulations were performed. In case I, positive net diabatic PV accumulated at the level of the tropopause (i.e., 1.5–5 PVU) within a subdomain confined to low latitudes south of the primary jet (not shown). This

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Geraint Vaughan, Bogdan Antonescu, David M. Schultz, and Christopher Dearden

. , 136 , 1582 – 1592 , doi: 10.1175/2007MWR2091.1 . 10.1175/2007MWR2091.1 Parton , G. , G. Vaughan , E. G. Norton , K. A. Browning , and P. A. Clark , 2009 : Wind profiler observations of a sting jet . Quart. J. Roy. Meteor. Soc. , 135 , 663 – 680 , doi: 10.1002/qj.398 . 10.1002/qj.398 Rao , T. N. , J. Arvelius , and S. Kirkwood , 2008 : Climatology of tropopause folds over a European Arctic station (Esrange) . J. Geophys. Res. , 113 , 1 – 10 , doi: 10.1029/2007JD009638

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Sam Hardy, David M. Schultz, and Geraint Vaughan

, 2008 : The impact of extratropical transition on the downstream flow: An idealized modelling study with a straight jet . Quart. J. Roy. Meteor. Soc. , 134 , 69 – 91 , doi: 10.1002/qj.189 . 10.1002/qj.189 Ritchie , E. , and R. L. Elsberry , 2007 : Simulations of the extratropical transition of tropical cyclones: Phasing between the upper-level trough and tropical cyclones . Mon. Wea. Rev. , 135 , 862 – 876 , doi: 10.1175/MWR3303.1 . 10.1175/MWR3303.1 Roebber , P. J. , D. M. Schultz

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G. Lloyd, C. Dearden, T. W. Choularton, J. Crosier, and K. N. Bower

study of the effect of velocity on Hallett–Mossop ice crystal multiplication . Atmos. Res. , 59–60 , 3 – 14 , doi: 10.1016/S0169-8095(01)00106-5 . Shapiro , M. A. , and D. Keyser , 1990 : Fronts, jet streams and the tropopause. Extratropical Cyclones: The Erik Palmen Memorial Volume, C. W. Newton and E. O. Holopainen, Eds., Amer. Meteor. Soc., 167–191 . Ulbrich , U. , A. H. Fink , M. Klawa , and G. Pinto , 2001 : Three extreme storms over Europe in December 1999 . Weather

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