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Dongmin Kim, Sang-Ki Lee, and Hosmay Lopez

.e., 14–30 days of lead time), several studies have explored a potential link between U.S. tornado activity and the Madden–Julian oscillation (MJO; Madden and Julian 1972 ), which is defined by the convective activity over the Maritime Continent propagating eastward around the equatorial tropics with a 30–90-day period (e.g., Thompson and Roundy 2013 ; Barrett and Gensini 2013 ; Barrett and Henley 2015 ; Gensini and Marinaro 2016 ; Tippett 2018 ; Baggett et al. 2018 ; Moore and McGuire 2020

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Emily J. Becker, Ernesto Hugo Berbery, and R. Wayne Higgins

1. Introduction The Madden–Julian oscillation (MJO) is a large-scale pattern of coupled atmospheric circulation and deep convection. First documented by Madden and Julian (1971 , 1972) , it features a prominent area of enhanced deep convection and rainfall that propagates eastward along the equator through the Indian and Pacific Oceans at the relatively slow speed of about 5 m s −1 , with an intraseasonal period of between 30 and 90 days (see Zhang 2005 , and references therein). The

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Emily M. Riley, Brian E. Mapes, and Stefan N. Tulich

1. Introduction The Madden–Julian oscillation (MJO) is the dominant coherent mode of intraseasonal variability in the tropics ( Madden and Julian 1972 ; Zhang 2005 ). At its most basic level, the MJO can be described as a multiscale envelope of organized convection and cloudiness that moves slowly eastward over the Indo-Pacific at approximately 5 m s −1 . Motivation for studying the MJO comes from its profound influence on tropical weather over the Indo-Pacific, monsoon rains over the nearby

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Hai Lin, Gilbert Brunet, and Ruping Mo

-range prediction, especially in precipitation. Beyond about a week, a forecast can no longer rely on the evolution of extratropical cyclones and anticyclones, because of the fast growth of initial error in the highly nonlinear flow. 1 A low-frequency signal source is essential for such an extended-range forecast. There is indication that the Madden–Julian oscillation (MJO), with its intraseasonal time scale, can provide an important signal for subseasonal weather predictions (e.g., Waliser et al. 2003 ). The

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B. Pohl, N. Fauchereau, C. J. C. Reason, and M. Rouault

the Madden–Julian oscillation (MJO) ( Madden and Julian 1994 ; Zhang 2005 ) activity by Carvalho et al. (2005) and Matthews and Meredith (2004 , hereafter MM04 ). The MJO is the dominant mode of atmospheric variability at the intraseasonal time scale and its periodicity typically varies between 30 and 60 days. It is mostly found at low latitudes, where it is associated with a mean eastward propagation of large-scale convective clusters (∼10 000 km across) from the Indian Ocean to the Maritime

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Richard H. Johnson and Paul E. Ciesielski

1. Introduction The Madden–Julian oscillation (MJO; Madden and Julian 1972 ) is the most dominant signal of intraseasonal variability in the tropics. Its impacts are far reaching. They extend into the subtropics and midlatitudes; specifically, there are influences on tropical cyclone frequency, monsoon onset and rainfall variability, ENSO, midlatitude storm tracks, the North Atlantic Oscillation, the Arctic and Antarctic Oscillations, the Indian Ocean dipole, Wyrtki jets, Indonesian

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Hirohiko Masunaga, Tristan S. L’Ecuyer, and Christian D. Kummerow

1. Introduction Since first documented by Madden and Julian (1971 , 1972 ), the Madden–Julian oscillation (MJO) has been extensively studied to explore its physical mechanism. In contrast to other low-frequency modes such as the Kelvin wave, however, the MJO has no apparent counterpart in the linear shallow-water theory described by Matsuno (1966) . Numerous attempts have been made to explain the physical processes that give rise to the MJO. In the framework of the linear theory, the

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Yanjuan Guo, Xianan Jiang, and Duane E. Waliser

1. Introduction Deep convection in the tropics is observed to be organized in part by a hierarchy of zonally propagating wavelike disturbances with a broad spectrum in both space and time ( Nakazawa 1988 ). These tropical modes constitute a major fraction of the tropical convective variability (e.g., Takayabu 1994 ; Wheeler and Kiladis 1999 , hereafter WK99 ; Kiladis et al. 2009 ). Among them, the Madden–Julian oscillation (MJO) has received extensive attention since its discovery in the

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Hai Lin, Gilbert Brunet, and Jacques Derome

in extended-range (7–30 days) forecasts (e.g., Waliser et al. 2006 ), which reflects the need to fill the historical gap between the short-range weather forecast and seasonal predictions. The strong amplitude and low-frequency nature of the Madden–Julian oscillation (MJO) provide an important signal for the extended-range forecast in a global domain (e.g., Madden and Julian 1971 ; Lau and Phillips 1986 ; Matthews et al. 2004 ). Thus, a skillful forecast of the MJO is both highly desirable and

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Michael Goss and Steven B. Feldstein

1. Introduction The Madden–Julian oscillation (MJO), the primary mode of tropical variability on the intraseasonal time scale, is known to affect the extratropical circulation through the excitation of poleward-propagating Rossby waves. In the context of idealized model calculations, the Pacific–North American (PNA) teleconnection pattern has been shown to arise in response to MJO forcing (e.g., Seo and Son 2012 ; Yoo et al. 2012a ). Support for this driving of the PNA-like anomalies by MJO

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