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Alan Shapiro, Evgeni Fedorovich, and Joshua G. Gebauer

model for the nocturnal motion. We consider, in turn, lateral variations in the free-atmosphere geostrophic wind and CBL buoyancy. The nocturnal state following the shutdown of mixing is modeled as a two-dimensional (2D) inviscid flow of a stably stratified fluid. In this scenario, flow convergence cannot occur at the terminus of a jet (there is no terminus) but is parallel to the jet axis. The shutdown of mixing that triggers the convergence in our theory is the same mechanism that triggers an

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Aaron Johnson, Xuguang Wang, Kevin R. Haghi, and David B. Parsons

observed bore dissipation to the weakening of the wave duct in the near-surface stable layer. Blake et al. (2017) used the simulation to investigate the role of a bore in the maintenance of a nocturnal MCS. The basic theory of bores as hydraulic jumps in the depth of the stable layer, maintained by the ducting of vertically propagating wave energy, has been confirmed by numerous laboratory experiments and by analytically using a simple two-layer model of the atmosphere (e.g., Maxworthy 1980

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Evgeni Fedorovich, Jeremy A. Gibbs, and Alan Shapiro

documented over the Great Plains of the United States (e.g., Blackadar 1957 ; Hoecker 1963 ; Bonner 1968 ; Parish et al. 1988 ; Mitchell et al. 1995 ; Zhong et al. 1996 ; Whiteman et al. 1997 ; Banta et al. 2002 ; Song et al. 2005 ; Banta 2008 ; Walters et al. 2008 ; Klein et al. 2016 ). The LLJ wind speed profile has a pronounced maximum that typically occurs at levels within 500 m above the ground. The maximum wind often exceeds the free-atmosphere geostrophic value by up to 70%. However

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Kevin R. Haghi, Bart Geerts, Hristo G. Chipilski, Aaron Johnson, Samuel Degelia, David Imy, David B. Parsons, Rebecca D. Adams-Selin, David D. Turner, and Xuguang Wang

observed in numerous estuaries over the globe. It took until the twentieth century before bores were recognized to also exist in the atmosphere. A convectively induced bore was not identified until the night of 16–17 May 1948 in Ohio ( Tepper 1950 ) during the Thunderstorm Project. A network of 50 surface stations with a typical spacing of 3 km was placed in a rectangular area. Station pressure, temperature, and wind signatures identified a wave disturbance leading the arrival of an MCS. It was not

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Aaron Johnson and Xuguang Wang

have demonstrated the sensitivity to features such as atmospheric bores, LLJs, elevated frontal zones, mesoscale regions of elevated ascent, and land–atmosphere interactions during the previous day. Therefore, the goal of this study is to determine the sensitivity of nocturnal convection forecasts to different aspects of the ensemble data assimilation (DA) and forecast system design in order to improve its configuration for the unique foci of PECAN. In particular, this paper will focus on the

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W. G. Blumberg, T. J. Wagner, D. D. Turner, and J. Correia Jr.

1. Introduction The radiosonde is widely considered to be the gold standard for measuring vertical profiles of thermodynamic and kinematic variables. The in situ nature of radiosonde observations allows scientists to obtain a high-vertical-resolution (roughly every 10 m) picture of the atmosphere. Because of this, radiosondes are used for several different applications. Meteorologists use these profiles to understand the current atmospheric state, initialize models, verify model forecasts, and

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Jonathan E. Thielen and William A. Gallus Jr.

have urged caution with reducing grid spacing to certain levels. For instance, Schumacher (2015) demonstrated that, for the destructive tornado/flash flood case of 31 May–1 June 2013 in central Oklahoma, a 4-km grid spacing simulation performed best, and that increased-resolution runs experienced degraded performance. This was due to the planetary boundary layer schemes operating with grid scales of the same order as the turbulent motions, a situation Wyngaard (2004) terms the “terra incognita

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John M. Peters, Erik R. Nielsen, Matthew D. Parker, Stacey M. Hitchcock, and Russ S. Schumacher

1. Introduction Nocturnal mesoscale convective systems (MCSs) are responsible for a large percentage of warm season rainfall in the central United States ( Fritsch et al. 1986 ), and are capable of producing extreme rainfall events and flash flooding (e.g., Moore et al. 2003 ; Schumacher and Johnson 2005 ). Whereas daytime convection frequently derives convective energy from the planetary boundary layer (PBL) (these types of systems are referred to as “surface based”), nocturnal MCSs often

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Elizabeth N. Smith, Joshua G. Gebauer, Petra M. Klein, Evgeni Fedorovich, and Jeremy A. Gibbs

1. Introduction Wind maxima called nocturnal low-level jets (NLLJs) often occur during the night in the lowest kilometer of the atmosphere. In the most general sense, the NLLJ is the result of the disruption of the daytime force balance between the Coriolis, pressure gradient, and frictional forces. Once the sun sets, thermally generated turbulence decays, and the stable boundary layer (SBL) forms. The frictional force weakens above the surface, which eliminates the force balance and leads to

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Aaron Johnson and Xuguang Wang

( Wyngaard 2004 ; Verrelle et al. 2015 ). This complicates the choice of a closure model for vertical mixing by turbulence. Neither a planetary boundary layer (PBL) parameterization as the closure model [denoted herein as convection permitting model (CPM)] nor a subgrid-scale closure model like the Smagorinsky (1963) scheme are quite justified ( Verrelle et al. 2015 ). Since the Smagorinsky closure presumes the largest turbulent eddies to be resolvable, we refer to this as a large-eddy simulation (LES

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