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Jeffrey M. Chagnon and Suzanne L. Gray

numerical simulation of a rapidly intensifying extratropical marine cyclone . Mon. Wea. Rev. , 119 , 368 – 384 , doi: 10.1175/1520-0493(1991)119<0368:TIBBAD>2.0.CO;2 . Kurosaki , S. , M. Yamamoto , H. Hashiguchi , T. Sato , and S. Fukao , 1996 : Vertical eddy diffusivity in the lower and middle atmosphere: A climatology based on the MU radar observations during 1986-1992 . J. Atmos. Sol.-Terr. Phys. , 58 , 727 – 734 , doi: 10.1016/0021-9169(95)00070-4 . Lock , A. P. , A. R

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

). However, the system’s CCB extends farther up in the model than in observations, reaching 850 hPa. The column with also extends higher in the model than in observations, indicating that the model’s atmosphere is too moist. This wet bias is a deficiency that has been previously identified in other studies using the MetUM version 7.3 (e.g., Martínez-Alvarado et al. 2014a ). A systematic wet bias in a model could be leading to an overestimation of WCB intensities and outflow levels as well as

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

for dry air, and J kg −1 K −1 is the latent heat of vaporization. Cook and Renfrew (2015) apply a surface-layer correction to τ in order to obtain an estimate of the value at the surface; this correction is not applied here, since the values are compared directly with the model output at the aircraft altitude. b. Numerical model The simulations presented here are performed with the Met Office Unified Model (UM), version 8.4, which employs a nonhydrostatic, deep-atmosphere dynamical core

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

was 10 min, limiting the average sonde spacing to 5 min along the flight track or 30 km at the aircraft science speed of 100 m s −1 . The vertical resolution is about 10 m. Table 1 lists the sonde release times along the three dropsonde curtains across the cyclone. Table 1. Dropsonde release times. b. Numerical model The case study has been simulated using the MetUM version 7.3. The MetUM is a finite-difference model that solves the nonhydrostatic deep atmosphere dynamical equations with a semi

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Sam Hardy, David M. Schultz, and Geraint Vaughan

cloud microphysics . Mon. Wea. Rev. , 145 , 543 – 563 , doi: 10.1175/MWR-D-16-0200.1 . 10.1175/MWR-D-16-0200.1 Hong , S.-Y. , Y. Noh , and J. Dudhia , 2006 : A new vertical diffusion package with an explicit treatment of entrainment processes . Mon. Wea. Rev. , 134 , 2318 – 2341 , doi: 10.1175/MWR3199.1 . 10.1175/MWR3199.1 Hoskins , B. J. , and M. A. Pedder , 1980 : The diagnosis of middle latitude synoptic development . Quart. J. Roy. Meteor. Soc. , 106 , 707 – 719 , doi: 10

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