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  • Diabatic Influence on Mesoscale Structures in Extratropical Storms (DIAMET) x
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Ben Harvey, John Methven, Chloe Eagle, and Humphrey Lean

. Together with observations of local wind speeds and vertical turbulent fluxes, the circuit integrals provide a detailed evaluation of the convergence of the model with resolution against reality at a range of spatial scales. A series of nested numerical simulations is employed, spanning the range from a traditional NWP model (12-km grid spacing) in which both tropospheric and boundary layer convective mixing are performed by parameterization schemes, through convection-permitting resolutions in which

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

beginning of the study period. In spite of this, the simulations can be considered a realistic representation of the development of both cyclones. Several quantities derived from the dropsonde observations during the first IOP13 leg are shown in a vertical cross section in Figs. 2a and 2c . Figure 2a shows zonal velocity u , θ , and relative humidity with respect to ice ; Fig. 2c shows and water vapor flux defined as , where q is specific humidity and is the horizontal wind component

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David M. Schultz and Joseph M. Sienkiewicz

surface sensible heat flux ( Fig. 3c ). Indeed, this sensible heat flux exceeding 400 W m −2 is comparable in magnitude to the sensible heat fluxes of other rapidly developing marine cyclones from observations (e.g., Neiman et al. 1990 ; Crescenti and Weller 1992 ) and model simulations (e.g., Chang et al. 1996 ; Gozzo and da Rocha 2013 ). Fig . 3. The 925-hPa potential temperature (thin solid lines every 1 K) and 925-hPa wind speed (m s −1 , shaded according to scale at the left side of the

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H. F. Dacre, P. A. Clark, O. Martinez-Alvarado, M. A. Stringer, and D. A. Lavers

-hPa relative vorticity value. The water vapor budget in a column of air is given by where P is the surface precipitation flux (kg m –2 s –1 ), E is the surface evaporation flux (kg m –2 s –1 ), g is the acceleration due to gravity (m s –2 ), q is the specific humidity (kg kg –1 ), t is time (s), and is the horizontal wind vector (m s –1 ). Terms on the right-hand side of the equation are integrated from the surface to 500 hPa as water vapor transport above 500 hPa is found to contribute

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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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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

by diabatic processes (those that add or remove heat from the air) such as latent heating and cooling associated with phase changes of water, fluxes of heat and moisture from the Earth’s surface, and radiative flux convergence. Key elements in diabatic processes are turbulence, convection, and cloud physics—small-scale phenomena that cannot be represented explicitly in numerical weather prediction models. They must therefore be parameterized, introducing a source of systematic uncertainty in the

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

developed to study the creation and destruction of potential vorticity ( Stoelinga 1996 ; Gray 2006 ). Potential temperature is decomposed in a series of tracers so that . Each tracer Δ θ P accumulates the changes in θ that can be attributed to the parameterized process P . The parameterized processes considered in this work are (i) surface fluxes and turbulent mixing in the boundary layer, (ii) convection, (iii) radiation, and (iv) large-scale cloud and precipitation. The tracer θ 0 matches θ

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Jeffrey M. Chagnon and Suzanne L. Gray

represent subgridscale processes. The model uses an Arakawa C grid in the horizontal with Charney–Phillips staggering in the vertical. The MetUM utilizes a height-based terrain-following vertical coordinate. Davies et al. (2005) provide a comprehensive summary of the model’s design. The parameterization schemes include the mass-flux convection scheme of Gregory and Rowntree (1990) , the MOSES-II boundary layer scheme ( Lock et al. 2000 ), the Edwards and Slingo (1996) radiation scheme, and the

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David M. Schultz, Bogdan Antonescu, and Alessandro Chiariello

. (2002 , 717–718) to explain stability differences between the cold and warm fronts: differential cloud cover, surface fluxes, or friction. We argue that such storms with weak or nonexistent warm fronts tend to form cold-type occlusions rather than warm-type occlusions. Specifically, by Stoelinga et al.’s (2002) static stability rule, the warm front must be less stable than the cold front. One way this can happen is to have a relatively weak warm front, possibly in diffluent flow. Such a weak warm

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Sam Hardy, David M. Schultz, and Geraint Vaughan

.5*PV compared with 5 mm h −1 in CNTRL; cf. Figs. 18c and 18e ). Stronger lower-tropospheric moisture flux, mainly associated with stronger easterly flow poleward of the lower-tropospheric geopotential height trough, likely also contributed somewhat to the higher rainfall rates in CNTRL relative to 0.5*PV (not shown). However, because the heaviest rain along the frontal band mostly fell to the south of the low center, in westerly rather than easterly flow, we hypothesize that the impact of moist

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