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Michelle M. Gierach, Mark A. Bourassa, Philip Cunningham, James J. O’Brien, and Paul D. Reasor

1. Introduction Although tropical cyclogenesis (TCG) is a very active area of research, it remains a highly debatable and unresolved topic. While considerable attention has been paid to tropical cyclone formation, little attention has focused on observational studies of the very early stages of TCG, otherwise referred to as the genesis stage. In the past, the early stages of TCG were unverifiable in surface observations because of the paucity of meteorological data over the tropical oceans. The

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Ron McTaggart-Cowan, Glenn D. Deane, Lance F. Bosart, Christopher A. Davis, and Thomas J. Galarneau Jr.

the Sixth International Workshop on Tropical Cyclones that research be focused on TC structural changes during genesis and on finding objective ways to quantify the influence of trough forcing on TC outflow ( IWTC-VI 2006 ). This investigation develops a dynamically based categorization scheme for tropical cyclogenesis in the North Atlantic basin. The result provides an objective method for framing studies and discussions of tropical cyclogenesis in analyses, forecast models, and climate

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Zhenhai Zhang and F. Martin Ralph

1. Introduction This paper builds on the long history of research in extratropical cyclones (ETC), and the more recent understanding of atmospheric rivers (ARs). ARs are recognized as the primary region of strong horizontal water vapor transport often created by ETCs ( Ralph et al. 2020a ). However, it is clear that extratropical cyclogenesis (ETC-genesis) can occur in an environment with a preexisting, or “antecedent” AR ( Sodemann and Stohl 2013 ; Zhang et al. 2019 ). This study uses modern

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Clifford S. Felton, Bulusu Subrahmanyam, and V. S. N. Murty

emerge in the central Pacific Ocean during April–June and peaking later during November–January. Though research on the effects of ENSO on tropical cyclones in the Atlantic and Pacific Oceans is well documented, far less research has been conducted over the BoB. Alterations in SST and relative vorticity during El Niño facilitate increased cyclogenesis during July–August of El Niño years in the BoB ( Singh et al. 2001 ). Camargo et al. (2007) found that vertical wind shear played the primary role in

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Brian H. Tang

1. Introduction Tropical cyclogenesis is a multiscale process with a strong coupling between the dynamics of the circulation and the thermodynamics of moist convection ( Simpson et al. 1997 ). While numerical modeling of tropical cyclogenesis has become increasingly sophisticated and skillful from an operational perspective ( Halperin et al. 2013 ), there remain a number of open questions and hypotheses concerning the relevant or dominant physical processes during tropical cyclogenesis. One

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Man-Li C. Wu, Oreste Reale, Siegfried D. Schubert, Max J. Suarez, and Chris D. Thorncroft

1. Introduction This article investigates some large-scale properties of the atmospheric circulation over western Africa and the northern tropical Atlantic across seasonal and subseasonal time scales. In particular, relationships between instability of the atmospheric flow computed on a seasonal time scale, African easterly wave (AEW) activity, and the spatial distribution of tropical genesis points are investigated. The problem of tropical cyclogenesis can be studied from a variety of

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Sebastian Schemm, Gwendal Rivière, Laura M. Ciasto, and Camille Li

during El Niño winters to produce a negative NAO-like response ( Li and Lau 2012b , a ; Drouard et al. 2015 ). The described mechanism has been confirmed using quasigeostrophic modeling experiments ( Drouard et al. 2013 ). A preliminary first link between the different downstream propagating upper-level transient eddies and the North Atlantic surface storm track is provided by Schemm et al. (2016) , who showed a preference for Gulf Stream cyclogenesis to occur below the North Atlantic jet exit

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Kenneth D. Leppert II, Walter A. Petersen, and Daniel J. Cecil

1. Introduction African easterly waves (AEWs) form in the tropical easterlies over east-central Africa (e.g., Burpee 1972 ; Norquist et al. 1977 ; Reed et al. 1977 ; Berry and Thorncroft 2005 ; Thorncroft et al. 2008 ) and often form the necessary precursor low-level disturbance for tropical cyclogenesis ( Kurihara and Tuleya 1981 ). These waves are important for tropical cyclogenesis not only in the Atlantic Ocean (e.g., Landsea 1993 ), but also in the east Pacific Ocean (e.g., Avila

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Paul J. Roebber

1. Introduction The role of cyclogenesis in producing substantial reorganization of the large-scale atmospheric flow remains somewhat unclear. Numerous observational and modeling studies have implicated the role of cyclones in producing one characteristic flow reorganization: the atmospheric block ( Berggren et al. 1949 ; Rex 1950 ; Schilling 1982 ; Hansen and Chen 1982 ; Shutts 1983 ; Colucci 1985 ; Mullen 1987 ; Vautard and Legras 1988 ; Konrad and Colucci 1988 ; Malguzzi 1993

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Carl J. Schreck III, John Molinari, and Anantha Aiyyer

)-type disturbances, commonly referred to as easterly waves ( Bessafi and Wheeler 2006 ; Frank and Roundy 2006 ; Schreck et al. 2011 , hereafter SMM11 ). For brevity, all of these features will be referred to as equatorial waves because they reside in equatorial regions and share wavelike properties. SMM11 examined tropical cyclone precursors over the western North Pacific using rainfall data. Tropical cyclogenesis was attributed to wave-enhanced convection when the wave-filtered rainfall anomaly exceeded a

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