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

to the gravity waves evident in the 100-m simulation is not explored further here. Finally, it is also noted that the 100-m simulation appears to exhibit a numerical instability lying along the front from where it leaves the domain at the northern boundary. Together, these shortcomings of the 100-m simulation highlight the current limitations of trying to attain high-resolution simulations of nonstationary dynamic features such as fronts. Further, 100-m simulations with a larger domain will prove

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

–Keyser cyclones. The first region is the low-level jet ahead of the cold front in the warm sector of the cyclone. This low-level jet is part of the broader airstream known as the warm conveyor belt, which transports heat and moisture northward and eastward while ascending from the boundary layer to the upper troposphere ( Browning 1971 ; Harrold 1973 ). The second region of strong winds develops to the southwest and south of the cyclone center as a bent-back front wraps around the cyclone. The strong winds

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Jesse Norris, Geraint Vaughan, and David M. Schultz

bands resembling those observed in the real atmosphere that were sensitive to all of these influences. The variation of the bands between simulations occurred via variations in the synoptic- and mesoscale structure of the flow environment. The current study aims to do the same, but for finer-scale precipitation cores. Therefore, a simulation from Norris et al. (2014) with all these diabatic factors appropriate to an extratropical cyclone over the open ocean, after 132 h when the surface cold front

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

.11° (~12 km) in both longitude and latitude on a rotated grid centered around 52.5°N, 2.5°W. The North Atlantic–European domain extends approximately from 30° to 70°N in latitude and from 60°W to 40°E in longitude. The vertical coordinate is discretized in 70 vertical levels with the lid around 80 km. The initial conditions were given by Met Office operational analyses valid at 1200 UTC 17 July 2012 for IOP13 and at 1800 UTC 14 August 2012 for IOP14. The lateral boundary conditions (LBCs) consisted of

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

enhances CAPE downstream of it, but has little effect on winds near the lower boundary. Further, Schlemmer et al. (2010) , examining a PV streamer approaching the Alps (a recognized harbinger of heavy convective rainfall), concluded that, although the streamer decreased the static stability throughout the troposphere directly beneath it, “destabilization [was] a second-order effect in the formation of heavy precipitation in the Alps” (p. 2352). Understanding the low-level conditions (moisture and

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Sam Hardy, David M. Schultz, and Geraint Vaughan

simulations in this study, employing a single domain ( Fig. 2 ) with 60 vertical levels (extending to 50 hPa), horizontal grid spacing of 15 km, and a time step of 75 s. Global Forecast System (GFS) analyses from the National Centers for Environmental Prediction (NCEP) at 0.5° × 0.5° horizontal and 50-hPa vertical grid spacing (25 hPa below 750 hPa) were used as initial and lateral boundary conditions, input every 6 h. The Thompson microphysics scheme was used ( Thompson et al. 2008 ) with the Yonsei

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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

-moving air was around 42%, suggesting a descent of around 150 hPa from initial saturation. Turbulent mixing was intense at low levels on this flight—the turbulent kinetic energy, calculated from the 32-Hz turbulence probe, was 7–10 m 2 s –2 —and the aircraft became coated in sea salt even when flying at 500 m above sea level. [Observations of turbulence throughout the DIAMET experiment are reported in Cook and Renfrew (2014) .] On this boundary layer leg (lasting 30 min), the gradient in potential

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C. Dearden, G. Vaughan, T. Tsai, and J.-P. Chen

of temperature. Dearden et al. (2014) showed that local diabatic heating rates associated with vapor growth of ice crystals can differ by a factor of 2 or more depending on the assumptions made in bulk models concerning the treatment of shape and size. Whether this uncertainty range is large enough to have any significant impact on the dynamics of cyclones in general is currently unknown. Thus, the outstanding question is the following: How complex does a microphysics scheme need to be to

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