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  • Diabatic Influence on Mesoscale Structures in Extratropical Storms (DIAMET) x
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H. F. Dacre, P. A. Clark, O. Martinez-Alvarado, M. A. Stringer, and D. A. Lavers

Identifying the source of atmospheric rivers: Are they rivers of moisture exported from the subtropics or footprints left behind by poleward traveling storms? Studies of heavy precipitation occurring in the winter over land in the midlatitudes have found that these events are almost always associated with extratropical cyclones ( Lackmann and Gyakum 1999 ; Viale and Nunez 2011 ; Hawcroft et al. 2012 ). These heavy precipitation events often occur when warm moist air, located in the cyclone

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

strong, elongated upper-level PV anomalies. How does this conceptual model for PV thinking overlap with that for deep moist convection? Specifically, all environments favorable for deep moist convection are characterized by three necessary and sufficient ingredients: moisture, low static stability, and a lifting mechanism for the parcels to ascend to their level of free convection (LFC) ( Johns and Doswell 1992 ; Doswell and Bosart 2001 ). Although the cyclonic upper-level PV anomaly is associated

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

, including measurements of the associated moisture transport. The warm conveyor belt observations are discussed in Martínez-Alvarado et al. (2014) ; the focus of the present study is on the near-surface frontal structure and its representation in the numerical simulations. Figure 1 depicts the route of the flight track together with the approximate position of the front at 1500 UTC 24 November 2009. The FAAM BAe-146 aircraft took off from Cranfield Airport, England, at 1311 UTC and flew southwestward

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Jeffrey M. Chagnon and Suzanne L. Gray

heat and moisture are transported from the boundary layer poleward and into the upper troposphere. These features are typical of extratropical cyclones in the North Atlantic. Fig . 1. Meteosat visible channel satellite images over the North Atlantic and western Europe, valid at (a) 1200 UTC 23 Sep 2011 (case I), (b) 1200 UTC 29 Nov 2011 (case II), and (c) 1100 UTC 24 Nov 2009 (case III). Images provided courtesy of EUMETSAT. Figure 2 presents the full PV in each of the three cases after 24 h of

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

PV has also been computed but is much smaller in comparison with processes (i)–(iv) and therefore is not shown. Each tracer is selectively affected by the p th parameterized process and governed by the equation where represents the source due to the p th parameterized process so that Equations (2) , (3) , and (5) are solved using the same numerical methods implemented in the MetUM to solve the evolution equations of the model’s prognostic variables (velocity components, θ , and moisture

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Sam Hardy, David M. Schultz, and Geraint Vaughan

Atlantic on 21 September 2012, as an equatorward-moving PV streamer approached Nadine from the northwest and tropical moisture was drawn poleward over a lower-tropospheric baroclinic zone ( Hardy et al. 2017 ). The cyclone deepened further (20 hPa in 36 h) over the United Kingdom on 24–25 September as an upper-level PV anomaly approached from the west, elongating into a PV streamer and wrapping around the cyclone. A band of moderate rain (5 mm h −1 ) developed ahead of this PV streamer to the northwest

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

generation of mesoscale potential vorticity (PV) and moisture anomalies in cyclonic storms and the impact these may have on the weather. The aims of the campaign most relevant to the work presented here are the measurement of microphysical properties and variability in mesoscale structures. Here we present data from three intensive observation periods (IOPs) of a cold front, warm front, and occluded frontal system during the DIAMET campaign. We discuss the large-scale features associated with these

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

simpler in comparison, and are standard microphysics options available for use within existing versions of WRF. These additional schemes were chosen because they are more representative of the level of parameterization used in typical operational models. For instance, WSM3 is a single-moment scheme that predicts the mass mixing ratios for three classes of moisture. In addition to water vapor, a single variable is used to represent cloud condensate, which can be liquid droplets or ice depending on

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