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Tapio Schneider
and
Paul A. O’Gorman

1. Introduction The thermal stratification of the troposphere mediates many aspects of the response of climate to perturbations. For example, it determines the strength of the greenhouse effect and influences the energies and scales of the large-scale eddies that effect most of the transport of heat, mass, momentum, and water vapor in Earth’s extratropical troposphere. Understanding the dynamic processes that control it is therefore essential for understanding the response of climate to

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Tao Zhu
,
Jing Yang
,
Bin Wang
, and
Qing Bao

the Asian monsoon regions in boreal summer (e.g., Wang and Xie 1997 ; Annamalai and Slingo 2001 ; Kemball-Cook and Wang 2001 ; Jiang et al. 2004 ; Yang et al. 2008 ; Wang et al. 2021 ). Since the tropical ISO significantly affects both tropical and extratropical weather and climate ( Hendon and Liebmann 1990 ; Liebmann et al. 1994 ; Maloney and Hartmann 2000 ; Sultan et al. 2003 ), several effective indices have been well-constructed for the real-time monitoring and subseasonal prediction

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Pallav Ray
and
Chidong Zhang

and extratropics (e.g., Ferranti et al. 1990 ; Mo and Higgins 1998 ; Jones and Schemm 2000 ). Major features of the extratropical low-frequency variability could be reproduced by specifying a time-dependent tropical forcing that mimics the convective heating associated with the MJO ( Matthews et al. 2004 ). Thus, forecast of the MJO is essential for the skillful prediction in the tropics and extratropics on the intraseasonal time scale. An important step toward achieving this is to understand

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Tianying Liu
,
Zhengyu Liu
,
Yuchu Zhao
, and
Shaoqing Zhang

equatorial Kelvin waves, thus triggering or disrupting the charging of WWV and thus the development of ENSO, explaining the irregular onset of ENSO events. Later studies suggest that ENSO can also be triggered or disrupted by external forcing from the extratropics, notably via the North Pacific meridional mode (NPMM) ( Vimont et al. 2003a , b ; Chiang and Vimont 2004 ; Chang et al. 2007 ; Vimont et al. 2009 ). The NPMM is suggested to be excited by the southern node of the North Pacific Oscillation

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David J. Lorenz
and
Eric T. DeWeaver

1. Introduction It is well known that the global-mean precipitation response to global warming predicted by the current generation of climate models is more uncertain than the temperature response ( Wild et al. 1997 ; Watterson 1998 ; Roeckner et al. 1999 ; Boer et al. 2000 ; Allen and Ingram 2002 ; Yang et al. 2003 ; Meehl et al. 2005 ). Because the global-mean precipitation is dominated by the Tropics, however, the uncertainty in the response of extratropical precipitation to global

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Peter Knippertz
and
Andreas H. Fink

-level disturbances intruding from the extratropical North Atlantic into the tropics ( Seck 1962 ; Griffiths 1972 ; Borgne 1979 ; Gaye et al. 1994 ; Issar 1995 ; Buckle 1996 ; Leroux 2001 ). Recently, Knippertz and Fink 2008a , hereafter KF08 ) documented a case of an unusual northward penetration of the rain zone into the countries of Ghana, Togo, Benin, and Nigeria in January 2004. Despite their rare occurrence, dry-season wet events can have substantial impacts on the local hydrology and human

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Y. Yu
and
D-Z. Sun

). Among the global factors that have been suggested to be potentially important in influencing ENSO are the subtropical–extratropical cooling or heating. Using a coupled model, Bush and Philander (1998) investigated the impact of extratropical cooling associated with the Last Glacial Maximum on the tropical Pacific SST. They found that the tropical air–sea interaction amplifies the cooling effect from the high latitudes on the tropics. The attributed this amplification to two factors: 1) the

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Y. Ming
,
V. Ramaswamy
, and
Gang Chen

1. Introduction The Earth’s climate system comprises distinct regimes, depending mainly on latitude and season. When one moves from the tropics into the wintertime extratropics, stationary Rossby waves and baroclinic eddies overtake the time-mean flow as the main mechanism of poleward energy and moisture transport. In light of the fundamental differences between the two climate regimes, we use this paper to examine specifically the impacts of aerosols on the boreal winter extratropical

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Peter Knippertz
and
Andreas H. Fink

, underlining the substantial disturbance of the hydrology brought about by this single event. Naturally, studies on precipitation in tropical West Africa have focused on the rainy season from June to September, while work on rainfall during the boreal cool and transition seasons have concentrated on events in subtropical North Africa. The latter are often related to equatorward-penetrating extratropical disturbances, termed diagonal troughs due to their orientation from southwest to northeast ( Flohn 1975

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Soumi Chakravorty
,
Renellys C. Perez
,
Bruce T. Anderson
,
Sarah M. Larson
,
Benjamin S. Giese
, and
Valentina Pivotti

been influenced by low-frequency extratropical Pacific atmospheric variability ( Amaya et al. 2019 ; Lu et al. 2017 ). Further, some aspects of ENSO diversity arise from extratropical atmospheric variability ( Pegion et al. 2020 ). Thus, understanding the influence of extratropical climate variability on the tropical Pacific is a crucial aspect of ENSO predictability ( Larson et al. 2018a ) and forecast skill ( Tippett et al. 2012 ). A key source of extratropical atmospheric variability is the

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