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

-level air masses is to detect filaments of high total column water vapor (TCWV) extending from the subtropics using satellite data. These 2D filamentary structures suggest long-distance, riverlike moisture transport and are routinely used as a proxy for identifying regions of strong water vapor transport (atmospheric rivers). High TCWV and strong low-level winds in the pre–cold frontal region lead to intense poleward moisture transport ( Ralph et al. 2004 , 2013 ) and have been associated with flooding

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

Kingdom, northern Europe, and Scandinavia. Heavy precipitation can have an important societal impact, as it can lead to extreme weather events, such as flash flooding. Water vapor condensation in the rising air also releases latent heat, which typically intensifies the ascending motion and the cyclone near the surface (e.g., Tracton 1973 ; Davis 1992 ; Stoelinga 1996 ; Ahmadi-Givi et al. 2004 ; Grams et al. 2011 ). For example, studying a cyclone that reached its maximum intensity (based on mean

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

), mean diameter ( Fig. 11d ), and ice water content ( Fig. 8d ) as a function of altitude show the change in the microphysics between runs B1 and B2. During the highest altitude run (B1) at a temperature of ~−43°C ice crystal number concentrations ~25 L −1 were observed. With decreasing altitude the process of aggregation gradually increased the mean size while some vapor growth of the ice crystals present increased the IWCs. Around 4 km (−15°C) a more significant increase occurred as the median ice

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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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Jeffrey M. Chagnon and Suzanne L. Gray

values of 1.5–5 PVU estimated by Kunz et al. (2011) . Furthermore, Hoerling et al. (1991) determined that the thermal tropopause is on average located near 3.5 PVU in the extratropics. We present two hypothesized mechanisms causing the node of the dipole in diabatic PV to be close to the tropopause height: (i) the vertical profile of longwave cooling is regulated by the vertical profile of water vapor, which is in turn very sharp at the level of the tropopause; and (ii) PV material modified in the

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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

objectives of DIAMET was to quantify diabatic heating and cooling rates using the observed microphysics, to compare with and improve model simulations. As an example of this, the method described in Dearden et al. (2014) has been used to calculate instantaneous diabatic heating and cooling rates associated with the growth and evaporation of ice crystals by vapor diffusion along this section of the flight ( Fig. 8e ). The calculations made use of relative humidity derived from the Water Vapor Sensing

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