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Adam J. Clark, Christopher J. Schaffer, William A. Gallus Jr., and Kaj Johnson-O’Mara

1. Introduction A conceptual “four quadrant” model (4QM hereafter; e.g., Bluestein 1993 ; Rose et al. 2004 ) of upper-tropospheric linear jet streak circulations was first hypothesized by Namias and Clapp (1949) and later inferred through observations by Murray and Daniels (1953) . Using the quasigeostrophic momentum equation, it easily can be shown that the ageostrophic wind is directed perpendicular and to the left (in the Northern Hemisphere) of the acceleration of the wind. The

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Teruhisa Shimada, Osamu Isoguchi, and Hiroshi Kawamura

1. Introduction A gap-exiting wind over the ocean is a strong wind blowing from terrestrial gaps such as straits, mountain gaps, and chains of mountainous islands. The low-level strong wind, called a wind jet hereafter, is generally characterized by its short duration, high spatial variability, and highly localized strong wind in the gap exit region, depending on the terrain configurations and atmospheric structures. The wind jets have been an area of investigation for a long time (e

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Andrew C. Winters and Jonathan E. Martin

forced precipitation events (e.g., Ralph et al. 2006 ; Stohl et al. 2008 ; Guan et al. 2010 ), the M12 study demonstrated that atmospheric rivers can also play a considerable role in heavy rainfall events that are synoptically forced, such as those that occur over the central and eastern United States. Specifically, M12 found that a southerly low-level jet, driven by a strong geopotential height gradient between a lee trough along the east coast of Mexico and a strong subtropical ridge north

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Oreste Reale, K. M. Lau, and Arlindo da Silva

more correct representation of the African easterly jet (namely, a northward and upward shift, in agreement with observations). In this article, a further step is made in this direction: climatologically varying aerosols are replaced with interactive aerosols that are fully consistent with the meteorology at every time. This is one of the first successful attempts to insert the radiative effects of realistically varying aerosols into a global operational framework, designed to produce real

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David E. Jahn and William A. Gallus Jr.

1. Introduction The influence of the Great Plains low-level jet (LLJ) on the initiation and evolution of nocturnal convection in the central United States, through its northward transport of heat and moisture and an increase in low-level convergence, has been investigated by several studies as reviewed in Stensrud (1996) . Climatologically, linkages between the LLJ and a maximum in moisture transport and associated precipitation in spring and summer over the Great Plains have been identified

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Brian J. Squitieri and William A. Gallus Jr.

1. Introduction The Great Plains nocturnal low-level jet (LLJ) has been found to be an important ingredient for fueling nocturnal convective events ( Means 1952 ; Bonner 1966 ; Augustine and Caracena 1994 ; Stensrud 1996 ; Schumacher and Johnson 2009 ). Understanding the Great Plains LLJ climatology and being able to differentiate between strongly and weakly forced LLJ environments is important since the LLJ and its supporting synoptic environment influences the amount of moisture, low

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

conducive to the development of ETEs in a particular geographic location, and 2) to increase understanding of the synoptic–dynamic mechanisms that support the development of large-scale meteorological flow patterns associated with ETEs. These two recommendations motivate the present study. Case studies of extreme weather events (EWEs) over North America demonstrate that the state and evolution of the North Pacific jet (NPJ) stream can support the establishment of a downstream environment that is

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

1. Introduction Anchored downstream of the Asian continent at midlatitudes, the North Pacific jet (NPJ) stream is a narrow, meandering current of strong upper-tropospheric wind speeds bounded by appreciable horizontal and vertical shear. The position and intensity of the NPJ is modulated by a number of external factors, including tropical convection (e.g., Hoskins and Karoly 1981 ; Madden and Julian 1994 ; Harr and Dea 2009 ; Archambault et al. 2013 , 2015 ; Torn and Hakim 2015 ; Grams

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Brian J. Squitieri and William A. Gallus Jr.

Plains southerly low-level jet (LLJ) ( Cotton et al. 1989 ; Augustine and Caracena 1994 ; Mitchell et al. 1995 ; Higgins et al. 1997 ; French and Parker 2010 ), a narrow current of air with a wind speed maximum located between 300 and 1000 m above ground level (AGL) ( Bonner and Paegle 1970 ; Mitchell et al. 1995 ; Whiteman et al. 1997 ; Song et al. 2005 ). Uccellini (1980) classified LLJs based on their synoptic environments, finding that LLJs were typically produced by lee cyclogenesis

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J. Tenenbaum

188 VOLUME 11 WEATHER AND FORECASTING Jet Stream Winds: Comparisons of Aircraft Observations with Analyses J. TENENBAUM State University of New York at Purchase, Purchase, New York (Manuscript received 29 December 1994, in final form 9 January 1996) ABSTRACT Wind measurements have been obtained from commercial aircraft crossing the 1992 winter subtropical jet streams over southwest and east Asia. Comparisons of these data with new, high-resolution analyses from four of the

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