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Everson D. Piva, Manoel A. Gan, and V. Brahmananda Rao

data. They used the methodology developed by Murray and Simmonds (1991) and improved by Simmonds and Murray (1999) . Their results show that throughout the year there is a high density of cyclones in the latitude of the circumpolar trough with secondary maxima in the Chaco region and west coast of South America. Cyclogenesis regions are observed over Antarctica and New Zealand, and over the tip of South America. Cyclolysis is observed over Antarctica with secondary maxima over the Pacific Ocean

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Melissa Payer, Neil F. Laird, Richard J. Maliawco Jr., and Eric G. Hoffman

associated with moderate or intense baroclinic zones, and this discrepancy was particularly large for cold fronts. The passage of fronts and troughs across the Great Lakes is a critical factor in influencing the weather that affects millions of people living in the region. Fronts often play a role in the initiation and evolution of severe thunderstorms, winter storms, and lake-effect snowstorms, which may potentially affect transportation, utilities, municipal decisions, and recreational activities

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Everson Dal Piva, Manoel A. Gan, and V. Brahmananda Rao

in lower levels, and the upper-level trough develops during the evolution of the cyclone associated with temperature advection. In type B, the surface cyclogenesis happens when the preexisting upper-level trough is located over an area favorable to cyclogenesis, such as the presence of warm advection in lower levels. In the 1980s, Radinovic (1986) proposed the existence of another cyclone development called type C, which would be associated with orographic effects, known as lee cyclogenesis

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Biao Geng, Kunio Yoneyama, and Ryuichi Shirooka

1. Introduction The monsoon trough is a directional shear line in a region of low atmospheric pressure at sea level, with southwesterly monsoonal winds on the equatorward side and easterly trade winds on the poleward side ( Sadler 1964 ). The monsoon trough is one of the most important features of monsoon systems in various monsoon regimes and has a great impact on regional climate and weather phenomena. In the western North Pacific Ocean, the mean location of the monsoon trough advances

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William A. Komaromi and James D. Doyle

conditions, namely, during the interaction between a TC and an upper-level trough. Several explanations exist in the literature as to why trough interaction would affect either the TC intensity or vortex structure. A number of studies argue trough interaction can enhance upper-level divergence, creating a more favorable environment for sustained convection ( Sadler 1976 ; Merrill 1988a , b ; Bosart et al. 2000 ). Other studies have argued that enhanced ascent associated with the trough’s secondary

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Nicholas D. Metz, Zachary S. Bruick, Peyton K. Capute, Molly M. Neureuter, Emily W. Ott, and Michael F. Sessa

-tropospheric phenomenon, less focus is typically given to upper-level features, such as short-wave troughs. Short-wave troughs are upper-level progressive waves that feature cyclonic circulation and move in the same general direction as the upper-level flow ( American Meteorology Society 2018 ). Differential cyclonic vorticity advection (CVA) found ahead of short-wave troughs provides forcing for ascent and can lead to atmospheric destabilization (e.g., Jiusto et al. 1970 ; Niziol et al. 1995 ; Lackmann 2001

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Tao Feng, Xiu-Qun Yang, Xuguang Sun, Dejian Yang, and Cuijiao Chu

1. Introduction The lower-tropospheric monsoon trough in the western North Pacific is a vital component of the East Asian summer monsoon system. The monsoon trough exhibits a planetary-scale cyclonic flow, which consists of southwesterlies from the Southern Hemisphere and trade easterlies from the tropical central Pacific. The monsoon trough is sometimes called a monsoon depression as it displays a region with low sea level pressure. The trough is the main region in which most of the monsoon

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Zachary O. Finch and Richard H. Johnson

of the most important circulation systems to traverse the NAM region is the upper-level inverted trough (IV) associated with either midlatitude breaking Rossby waves ( Thorncroft et al. 1993 ) or tropical upper-tropospheric troughs (TUTTs; Sadler 1967 ). The IV disturbances have been observed to progress westward over the NAM region on the southern periphery of the subtropical ridge and impact weather over the southern United States and northern Mexico ( Whitfield and Lyons 1992 ; Douglas and

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Dian Wen, Ying Li, Da-Lin Zhang, Lin Xue, and Na Wei

1. Introduction An upper-level cold-core low is a cyclonic low pressure system in the upper troposphere that may produce important influences on the development of surface cyclones. Wang et al. (2012) classified upper-level cold-core lows into Palmén and Palmer types according to their locations and movements. The Palmén-type cold-core lows commonly come from cutoff lows of midlatitude troughs and thus mostly move eastward ( Palmén and Nagler 1949 ), whereas the Palmer-type cold-core lows are

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Chanil Park, Seok-Woo Son, and Jung-Hoon Kim

streak. Fig . 2. Schematic illustration of the typical QG vertical motion by (a) the transverse Q vector and (b) the shearwise Q vector around the jet streak, and (c) the shearwise Q vector around the trough in the Northern Hemisphere. Gray dotted lines denote the isentropes with warm air to the south, and black and purple arrows indicate the geostrophic streamlines and Q vectors, respectively. The shaded regions in pink and apricot, respectively, denote the QG descent and ascent. The n and s

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