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Levi P. Cowan and Robert E. Hart

1. Introduction Upper-tropospheric jets are among the most conspicuous environmental asymmetries that influence tropical cyclones (TCs), and have been argued to do so through a multitude of physical processes. While prior work has examined TC–jet interactions in case studies and modeling experiments, no systematic identification and cataloging of jets in proximity to TCs has been performed. Such a dataset would prove useful for analyzing specific TC–jet configurations and studying how TCs

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Andrew C. Winters, Daniel Keyser, Lance F. Bosart, and Jonathan E. Martin

1. Introduction The instantaneous positions of the polar and subtropical jets are closely related to the pole-to-equator tropopause structure, as indicated by the idealized vertical cross section in Fig. 1a . In the Northern Hemisphere, the average location of the polar jet is near 50°N in the region where the tropopause height abruptly rises from the polar tropopause (~350 hPa) to the subtropical tropopause (~250 hPa). The polar jet also resides atop the strongly baroclinic- and tropospheric

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Clemens Spensberger, Thomas Spengler, and Camille Li

1. Introduction Jet streams are often identified using a wind speed threshold that defines the perimeter and hence the body of a jet stream (e.g., Koch et al. 2006 ; Strong and Davis 2007 ). Such identification schemes often detect large coherent areas as one jet body, thereby obscuring the existence of multiple wind speed maxima within one body. For example, in the winter snapshots in Figs. 2b and 2c of Koch et al. (2006) , almost all visible wind maxima are encompassed by only one jet body

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Joseph B. Olson, Brian A. Colle, Nicholas A. Bond, and Nathaniel Winstead

1. Introduction Strong low-level terrain-parallel winds, known as barrier jets ( Parish 1982 ), can reach high wind speeds (>30 m s −1 ) along prominent two-dimensional mountain ranges. This phenomenon occurs frequently during the cool season along coastal southeastern Alaska ( Loescher et al. 2006 ; Overland and Bond 1993 , 1995 ; Macklin et al. 1990 ), and can result in hazardous conditions that affect the local fishing, shipping, and aviation industries ( Macklin et al. 1990 ). Alaskan

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Joseph B. Olson, Brian A. Colle, Nicholas A. Bond, and Nathaniel Winstead

1. Introduction Strong low-level terrain-parallel winds , known as barrier jets ( Parish 1982 ), can reach high wind speeds (>30 m s −1 ) along prominent two-dimensional mountain ranges. This phenomenon occurs frequently during the cool season along coastal southeastern Alaska ( Loescher et al. 2006 ; Overland and Bond 1993 , 1995 ; Macklin et al. 1990 ), and can result in hazardous conditions that affect the local fishing, shipping, and aviation industries ( Macklin et al. 1990 ). Alaskan

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Edward I. Tollerud, Fernando Caracena, Steven E. Koch, Brian D. Jamison, R. Michael Hardesty, Brandi J. McCarty, Christoph Kiemle, Randall S. Collander, Diana L. Bartels, Steven Albers, Brent Shaw, Daniel L. Birkenheuer, and W. Alan Brewer

1. Introduction Previous studies of the low-level jet (LLJ) have helped to establish its role as the major conveyor of low-level moisture from the Gulf of Mexico into the central United States ( Stensrud 1996 ; Higgins et al. 1996 ). Higgins et al. (1997) estimate that the contribution of the LLJ to low-level moisture transport over the central plains is almost 50% above average non-LLJ values. A major factor in the LLJ contribution to central plains precipitation is the relationship between

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Andrew C. Winters and Jonathan E. Martin

1. Introduction The atmosphere typically exhibits the three-step pole-to-equator tropopause structure shown in Fig. 1a , with each break in the tropopause height associated with a jet stream. 1 The polar jet (PJ) stream resides at midlatitudes in the break between the polar (~350 hPa) and subtropical (~250 hPa) tropopauses and is situated atop the strongly baroclinic, tropospheric-deep polar front (e.g., Palmén and Newton 1948 ; Namias and Clapp 1949 ; Newton 1954 ; Palmén and Newton 1969

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Yu Du and Guixing Chen

. 2007 ). A southwesterly low-level jet (LLJ) related to the synoptic or subsynoptic front transports warm and moist air to the front and destabilizes the environment, which favors the development of heavy rainfall near the front ( Chen and Yu 1988 ; Tao and Chen 1987 ; Akiyama 1973 ; Chen et al. 1994 ; Trier et al. 1990 ). However, an obvious synoptic-scale boundary, such as a front, is absent for the warm-sector heavy rainfall; thus, the forecast of their location and timing is still very

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Yu Du, Yi-Leng Chen, and Qinghong Zhang

1. Introduction Boundary layer jets (BLJs), which are one type of low-level jet (LLJ) [below 1 km; Du et al. (2014) ], frequently occur next to a large mountain range or in regions with land–sea thermal contrast ( Stensrud 1996 ; Rife et al. 2010 ). In addition to boundary layer jets east of the Rocky Mountains over the U.S. Great Plains (e.g., Bonner 1968 ; Blackadar 1957 ; Parish and Oolman 2010 ; Du and Rotunno 2014 ), coastal boundary layer jets around the world ( Ranjha et al. 2013

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L. Besson and Y. Lemaître

Darfur mountains (Sudan), and the Ethiopian Highlands ( Tetzlaff and Peters 1988 ; Laing and Fritsch 1993 ; Redelsperger et al. 2002 ; Laing et al. 2008 ; Rickenbach et al. 2009 ). Other works suggest an important role of dynamical entities such as the African easterly jet (AEJ), the tropical easterly jet (TEJ) (see Fig. 1 ), African easterly waves (AEWs), and of the convergence term of horizontal moisture flux convergence ( Reiter 1969 ; Payne and McGarry 1977 ; Bolton 1984 ; Bayo Omotosho

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