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Rachel L. Miller, Conrad L. Ziegler, and Michael I. Biggerstaff

1. Introduction The Plains Elevated Convection At Night (PECAN) field program ( Geerts et al. 2017 ) was designed to study nocturnal weather features, including mesoscale convective systems (MCSs), bores, convection initiation (CI) events, and the nocturnal low-level jet (NLLJ). The comprehensive PECAN observing strategy included both mobile and fixed observations obtained by radars, sounding systems, PECAN integrated sounding array (PISA) profilers, research aircraft, and mesonets ( Geerts

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Aaron Johnson and Xuguang Wang

1. Introduction Atmospheric bores are commonly observed in the nocturnal convective environment in the Great Plains ( Haghi et al. 2017 ). This is because the stable boundary layer and low-level jet often provide a suitable wave duct, while convectively generated cold pools frequently provide an obstacle to this stable and ducted low-level flow ( Rottman and Simpson 1989 ; Johnson et al. 2018 ). Several studies have demonstrated the importance of bores in both the initiation and maintenance of

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

characterized by a southwesterly low-level jet (LLJ) that extended from Texas through Kansas and Missouri, and terminated along an east–west-oriented frontal boundary in southeastern Nebraska and southern Iowa ( Figs. 1a,b ). An MCS had moved through northeastern Nebraska and central Iowa earlier in the day (not shown), and had produced a surface cold pool that strengthened the north–south low-level temperature gradient along a preexisting synoptic front ( Figs. 1a,b ). A mesoscale region of low-level warm

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Dana Mueller, Bart Geerts, Zhien Wang, Min Deng, and Coltin Grasmick

listed above are satisfied when l 2 becomes negative (or decreases rapidly with height), and when a region of maximum curvature falls within a layer of low stability ( Crook 1988 ). Such wave trapping mechanism commonly applies in the Great Plains in cases of south-bound bores encountering the southerly nocturnal low-level jet (LLJ) ( Koch et al. 1991 ). A critical layer, where C b equals U and the Richardson number is less than 0.25, can also prolong bore lifetime due to wave reflectance. The

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Hristo G. Chipilski, Xuguang Wang, and David B. Parsons

, 2010 : The response of simulated nocturnal convective systems to a developing low-level jet . J. Atmos. Sci. , 67 , 3384 – 3408 , . 10.1175/2010JAS3329.1 Geerts , B. , and Coauthors , 2017 : The 2015 Plains Elevated Convection at Night field project . Bull. Amer. Meteor. Soc. , 98 , 767 – 786 , . 10.1175/BAMS-D-15-00257.1 Gentine , P. , A. Garelli , S.-B. Park , J. Nie , G. Torri , and Z

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