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Chuan-Chi Tu, Yi-Leng Chen, Pay-Liam Lin, and Yu Du

1. Introduction The low-level jet (LLJ) is considered one of the important factors for producing heavy orographic precipitation in many different parts of the world, such as China; Japan; Korea; the European Alps; the U.S. Sierra Nevada, Rockies, and Appalachians; and the New Zealand Alps ( Lin et al. 2001 ; Lin 2005 ; Witcraft et al. 2005 ). Du et al. (2014) and many other previous studies classified LLJs during the early summer over East Asia into two types: 1) synoptic system–related low

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Thomas R. Parish, Richard D. Clark, and Todd D. Sikora

1. Introduction The Great Plains low-level jet (LLJ) was a major topic of research as part of the Plains Elevated Convection at Night (PECAN) field study, which was conducted from 1 June to 15 July 2015 (e.g., Geerts et al. 2017 ). The LLJ is a nocturnal wind speed maximum that develops in the lowest kilometer of the atmosphere during warm-season months. Winds associated with the LLJ are predominantly from the south, with peak wind speeds often in excess of 20 m s −1 . LLJ frequency is highest

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Brian J. Vanderwende, Julie K. Lundquist, Michael E. Rhodes, Eugene S. Takle, and Samantha L. Irvin

1. Introduction On many nights in the central United States, the weather is largely determined by the evolution of low-level winds near the top of the boundary layer. During the summer months, winds aloft accelerate after sunset with remarkable consistency in numerous regions throughout the central plains and Midwest states. These wind accelerations are known as low-level jets (LLJs), and their influence has been noted in many fields of study, such as clear-air turbulence (e.g., Banta et al

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Paola Salio, Matilde Nicolini, and Edward J. Zipser

America (SESA), mostly covers the continental latitudes to the east of the Andes between 23° and 40°S and is identified by a box in Fig. 1 . This northern flow is present throughout the year and shows an intense maximum during the spring ( Berbery and Barros 2002 ; Vera et al. 2002 ; Campetella and Vera 2002 ; Berbery and Collini 2000 ). On some occasions the flow shows a low-level jet profile in its vertical structure favoring an intense horizontal transport of humidity at low levels of the

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Shuguang Wang and Fuqing Zhang

, hereinafter UK87 ), after a survey of 13 observational case studies, found that mesoscale gravity waves frequently occur in the exit region of upper-level jet streaks and on the cold-air side of surface frontal boundaries. They speculated that the flow imbalance and subsequent geostrophic adjustment near the jet streak are likely responsible for generating these gravity waves. The preferred region of gravity wave activity in UK87 was also later verified in many other observational studies (e

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Paul J. Neiman, Ellen M. Sukovich, F. Martin Ralph, and Mimi Hughes

barrier jet paralleling the long axis of the high terrain. Barrier jet flows, which are maintained by a statically stable pressure ridge dammed against the windward slope, have been documented across North America (and elsewhere), including Appalachia (e.g., Bell and Bosart 1988 ), the Rockies (e.g., Dunn 1992 ; Colle and Mass 1995 ; Cox et al. 2005 ), coastal Alaska and British Columbia (e.g., Loescher et al. 2006 ; Olson et al. 2007 ; Yu and Bond 2002 ; Overland and Bond 1995 ), the Pacific

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Yu Du and Guixing Chen

1. Introduction The close relationship between low-level jets (LLJs) and heavy rainfall has been widely documented in previous studies (e.g., Stensrud 1996 ; Means 1952 ; Chen and Yu 1988 ; Rasmussen and Houze 2016 ). Generally, the LLJs provide favorable thermodynamic conditions for heavy rainfall ( Astling et al. 1985 ; Tuttle and Davis 2006 ; Trier and Parsons 1993 ). The LLJs not only transport warm moist air and produce convergence at their termini to destabilize the environment

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Oscar Martínez-Alvarado, Florian Weidle, and Suzanne L. Gray

1. Introduction The detailed analysis of the Great Storm in southeastern England in October 1987 using both observations ( Browning 2004 ; Browning and Field 2004 ) and high-resolution numerical simulations ( Clark et al. 2005 ) led to the concept of sting jet as a transient, highly localized, low-level jet occurring within rapidly deepening extratropical cyclones that develop according to the Shapiro–Keyser model of cyclogenesis ( Shapiro and Keyser 1990 ). Forecasters

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Andrew C. Winters, Daniel Keyser, and Lance F. Bosart

1. Introduction Polar–subtropical jet superpositions represent a type of synoptic-scale environment conducive to high-impact weather ( Winters and Martin 2014 , 2016 , 2017 ; Handlos and Martin 2016 ; Christenson et al. 2017 ; Winters et al. 2020 ). The development of a jet superposition is conceptualized by Winters and Martin (2017 ; their Fig. 2) and Winters et al. (2020 ; their Fig. 1) using a potential vorticity (PV) framework. The forthcoming discussion of this conceptual model

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Peter M. Finocchio and James D. Doyle

recurving TCs on medium-range to subseasonal time scales requires a deeper understanding of the initiation of Rossby waves along the jet stream and the amplification of these waves as they propagate downstream. This study uses a set of idealized, full-physics simulations in order to address how characteristics of the jet stream modulate each of these processes. Diabatic heating and the development of an upper-tropospheric, irrotational outflow are hypothesized to be key processes by which TCs initiate

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