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Yoshio Kawatani, Kevin Hamilton, and Shingo Watanabe

1. Introduction The quasi-biennial oscillation (QBO) is a persistent, quasi-periodic, large-amplitude oscillation of the low-latitude stratospheric circulation [see Baldwin et al. (2001) for a review]. The QBO is most evident in the zonal mean zonal wind near the equator, which undergoes reversals from strong easterlies to strong westerlies through each QBO cycle, but has clear observable signals in temperature and meridional circulation as well as the concentration of ozone and other trace

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Rolando R. Garcia and Jadwiga H. Richter

1. Introduction The quasi-biennial oscillation (QBO) is the principal mode of variability of the tropical stratosphere, from the near-tropopause region at 100 hPa (16 km) to the upper stratosphere near 3 hPa (40 km), where the circulation begins to be dominated by the semiannual oscillation ( Baldwin et al. 2001 ). In addition to its role in the dynamics of the deep tropics, eddy and mean meridional circulation transports associated with the QBO are an important source of variability in the

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Lawrence Coy, Paul A. Newman, Steven Pawson, and Leslie R. Lait

1. Introduction The quasi-biennial oscillation (QBO) consists of downward descending easterly and westerly zonal wind regimes that dominate the zonal mean wind variability in the tropical lower stratosphere (100–10 hPa, ~18–30 km in altitude) with a varying (~28 month) period [see Baldwin et al. (2001) and references therein]. The QBO has been a persistent characteristic of the tropical lower stratosphere since observations began in 1953. However, a significant disruption of the QBO occurred

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Pu Lin, Isaac Held, and Yi Ming

1. Introduction The quasi-biennial oscillation (QBO) is the most prominent circulation pattern in the tropical stratosphere, featuring alternating easterlies and westerlies that slowly descend from the stratopause to the tropopause ( Baldwin et al. 2001 , and references therein). It is mainly driven by the vertically propagating waves with easterly and westerly phase speeds that dissipate in the corresponding shear zones, leading to easterly acceleration in easterly shear zones (where

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Kylash Rajendran, Irene M. Moroz, Scott M. Osprey, and Peter L. Read

1. Introduction The quasi-biennial oscillation (QBO) is the dominant mode of variability of zonal-mean zonal winds in the tropical stratosphere between 100 and 5 hPa. It consists of alternating bands of descending westerly and easterly wind regimes that form in the tropical upper stratosphere and descend to the tropical tropopause at an average rate of approximately 1 km month −1 . A review of the basic properties and dynamics of the QBO is given in Baldwin et al. (2001) . The period of the

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Eriko Nishimoto and Shigeo Yoden

mesoscale moist convection is the predominant source driving the atmospheric motions. Recently, several studies have shown the influence of some stratospheric phenomena on tropical deep convection and its organizations, including the influence of stratospheric sudden warming ( Eguchi and Kodera 2010 ; Kodera et al. 2011 ; Albers et al. 2016 ), the stratospheric quasi-biennial oscillation (QBO; Collimore et al. 1998 , 2003 ; Giorgetta et al. 1999 ; Huang et al. 2012 ) and its dynamical analog

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Bei-Wei Lu, Lionel Pandolfo, and Kevin Hamilton

1. Introduction The familiar quasi-biennial oscillation (QBO) dominates variations of the zonal winds in the stratosphere (from about 16- to 50-km altitudes) around the equator. In general, the zonal wind at each pressure level alternates between easterly and westerly with a period varying between about 20 and 36 months with a relatively rapid transition over about 2 to 4 months. The wind regimes consistently propagate downward through the equatorial stratosphere. The wind amplitude, associated

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Jian Rao, Chaim I. Garfinkel, and Ian P. White

1. Introduction The quasi-biennial oscillation (QBO) is one of the most dominant, periodic, and therefore predictable modes in the tropical stratosphere on interannual time scales ( Scaife et al. 2014 ), with alternate easterlies and westerlies descending from the equatorial upper stratosphere to the tropopause every 21–32 (~28 on average) months ( Baldwin et al. 2001 and references therein). The QBO is driven by various waves propagating upward that deposit westerly and easterly momentum in

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S. Abhik, Harry H. Hendon, and Matthew C. Wheeler

1. Introduction The quasi-biennial oscillation (QBO) refers to the alternating westerly and easterly winds in the equatorial stratosphere that descend from the upper to lower stratosphere with period of ~28 months (e.g., Baldwin et al. 2001 ). The QBO is well understood to be driven by the momentum fluxes associated with upward-propagating waves that originate in the equatorial troposphere, primarily forced by tropical convection ( Lindzen and Holton 1968 ). Although the QBO is a stratospheric

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Hiroaki Naoe, Makoto Deushi, Kohei Yoshida, and Kiyotaka Shibata

in tropical upwelling and also that the shallow branch is modulated by the subtropical transport barriers. The projected future evolution of total column ozone in the tropics was particularly sensitive to changes in tropical upwelling ( World Meteorological Organization 2014 ). The large spread among ozone projections obtained from diagnostics of chemistry–climate model (CCM) simulations indicate that the confidence level remains low (e.g., Strahan et al. 2011 ). The quasi-biennial oscillation

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