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Dayton G. Vincent

accompanyingcloud band are reviewed and discussed. The paper focuses on the following topics: location, structure, andcharacteristics of the SPCZ; theories and observations concerning its existence; the significance and scope ofthe SPCZ in global-scale circulation patterns; quasi-periodic changes in its location and strength; and synopficscale features within its regional influence (e.g., cyclones, subtropical jets). It concludes with some challengingproblems for the future.1. Introductory remarks The South

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Clifford Mass and Brigid Dotson

al. 1988 ; Burt and Mansfield 1988 ), the Burns’ Day Storm of 25 January 1990 ( McCallum 1990 ), the Christmas Eve Storm of 24 December 1997 ( Young and Grahame 1999 ), and the series of three storms that struck northern Europe in December 1999 ( Ulbrich et al. 2001 ). Browning 2004 , Browning and Field (2004) , and Clark et al. (2005) present evidence that a limited area of strong winds associated with evaporative cooling and descent (termed a sting jet) occurred during the October 1987

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Julia H. Keller, Christian M. Grams, Michael Riemer, Heather M. Archambault, Lance Bosart, James D. Doyle, Jenni L. Evans, Thomas J. Galarneau Jr., Kyle Griffin, Patrick A. Harr, Naoko Kitabatake, Ron McTaggart-Cowan, Florian Pantillon, Julian F. Quinting, Carolyn A. Reynolds, Elizabeth A. Ritchie, Ryan D. Torn, and Fuqing Zhang

moves poleward and starts to interact with the midlatitude flow ( Fig. 1a ). This results in the formation of a jet streak ( Fig. 1b ) and a poleward deflection of the jet near the transitioning cyclone in conjunction with the development of a ridge–trough couplet ( Fig. 1b ). At the same time, a region of enhanced moisture flux—a so-called atmospheric river ( Zhu and Newell 1998 )—forms ahead of the downstream trough. The ridge–trough couplet continues to amplify, a new cyclone develops farther

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Volkmar Wirth, Michael Riemer, Edmund K. M. Chang, and Olivia Martius

gradual than that of the carrier wave (dotted) or the RWP signal (blue). Fig . 1. Schematic of a Rossby wave packet (RWP) at a specific time. The blue line represents , the black dotted line is the underlying carrier wave , and the two red lines depict plus (upper line) and minus (lower line) the amplitude . A real world example is presented in Fig. 2 . Figure 2a shows the midlatitude jet with large meridional undulations over North America. Over the rest of hemisphere, the jet is more zonally

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T. N. Krishnamurti

--ishighlighted. The planetary boundary layer is another area of investigation which has drawn much interest, especially overthe western Arabian Sea where the Somali jet exhibits interesting properties during summer monsoon. Thesestudies cover modeling, theoretical and observational areas. The onset and active monsoons were monitored by a large array of ship and research aircraR during MONEX.Studies in this area place an empfiasis on observational, theoretical stability analysis and numerical weatherprediction

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Daniel Keyser and M. A. Shapiro

forcing for the irrotational part of theageostrophic circulation, which contains the divergenceand vertical motion fields. The divergence patterns associated with upper-level frontal systems and their accompanying jet streaks~ play an active part in midlatitude cyclogenesis by contributing to low-level geopotential height (mass) changes. The vertical circulations associated with upper-level and surface frontal zones also are a component in the development andorganization of midlatitude cloud and

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Huw C. Davies

-scale development and subsynoptic across-frontal circulation patterns (e.g., Keyser et al. 1989 ; Martin 1999 ); explore the relative amplitude and nature of the forcing at different elevations (e.g., Trenberth 1978 ; Durran and Snellman 1987 ); infer qualitatively the major regions of ascent (e.g., Hoskins and Pedder 1980 ; Sanders and Hoskins 1990 ); examine the contribution of diabatic heating to cyclogenesis (e.g., Chang et al. 1984 ; Tsou et al. 1987 ; Strahl and Smith 2001 ); study jet flow and

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Robert A. Houze Jr.

) analyzed aircraft observations showing that rainbands tend to have a “secondary horizontal wind maximum,” or jet located along the axis of the rainband. Hence and Houze (2008) found that the principal rainbands in the category-5 stages of Hurricanes Katrina (2005) and Rita (2005) had well defined jets along their axes. The occurrence of the jet suggests that the rainbands have dynamics somewhat in common with eyewalls, which are tied closely to the RMW, and the outward-sloping updrafts seen in Figs

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Tammy M. Weckwerth and David B. Parsons

–150-km-long arcs in radar reflectivity) along a gust front were the preferred locations for surface convergence and for convective development. Deep convection occurred along the gust front only after interaction with the dryline and/or low-level jet. This outflow boundary first propagated as a density current and evolved toward an internal undular bore. Dual-Doppler radar analyses also showed waves generated atop the cold-air outflow (e.g., Mueller and Carbone 1987 ; Weckwerth and Wakimoto 1992

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Clark Evans, Kimberly M. Wood, Sim D. Aberson, Heather M. Archambault, Shawn M. Milrad, Lance F. Bosart, Kristen L. Corbosiero, Christopher A. Davis, João R. Dias Pinto, James Doyle, Chris Fogarty, Thomas J. Galarneau Jr., Christian M. Grams, Kyle S. Griffin, John Gyakum, Robert E. Hart, Naoko Kitabatake, Hilke S. Lentink, Ron McTaggart-Cowan, William Perrie, Julian F. D. Quinting, Carolyn A. Reynolds, Michael Riemer, Elizabeth A. Ritchie, Yujuan Sun, and Fuqing Zhang

), likely due to the lower probability of a TC interacting with the midlatitude flow associated with the climatological poleward retreat of the polar jet in boreal summer. September is also the month in which the greatest percentage of recurving WNP TCs reintensify after becoming extratropical ( Klein et al. 2000 ; Archambault et al. 2013 ). The ET frequency varies both between and within WNP typhoon seasons: it occurs less frequently when the subtropical high is anomalously strong, such that TCs are

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