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Akira Kuwano-Yoshida, Bunmei Taguchi, and Shang-Ping Xie

broad region of East Asia, causing local disasters such as floods and mudslides by heavy rain. Recently Sampe and Xie (2010) proposed a hypothesis linking the subtropical jet and baiu rainband. They suggest that horizontal warm advection by the subtropical jet induces upward motion in the midtroposphere using the thermodynamic energy equation. Specifically, the warm air mass over the Tibetan Plateau flows westward on the upper jet over East Asia, and the adiabatic ascent on isentropic surfaces

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Ryusuke Masunaga, Hisashi Nakamura, Takafumi Miyasaka, Kazuaki Nishii, and Bo Qiu

more meandering, compared to its stable regime. From the unstable KE jet, more warm-core oceanic eddies are pinched off northward, leading to higher SST and enhanced upward SHF and LHF to the north of the mean KE path ( Sugimoto and Hanawa 2011 ; Sasaki and Minobe 2015 ). Iizuka (2010) indicated through regional atmospheric model simulations that the warm SST anomaly can enhance winter precipitation, and its imprints can reach the free troposphere. Using their own measures of the KE regimes

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Akira Kuwano-Yoshida and Shoshiro Minobe

( Nakamura et al. 2004 ; Minobe et al. 2008 ; Taguchi et al. 2009 ; Sampe et al. 2010 ; Kuwano-Yoshida et al. 2010b ; Frankignoul et al. 2011 ; Booth et al. 2012 ; Ogawa et al. 2012 ; Taguchi et al. 2012 ; Iizuka et al. 2013 ; Kuwano-Yoshida et al. 2013 ; Small et al. 2014 ; Smirnov et al. 2015 ; O’Reilly and Czaja 2015 ; O’Reilly et al. 2016 ; Ma et al. 2015 ; Parfitt et al. 2016 ). Nakamura et al. (2004) summarized the relationship among storm tracks, jet streams, and midlatitude

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A. Foussard, G. Lapeyre, and R. Plougonven

( Held et al. 1989 ; Lau 1997 ; Cassou and Terray 2001 ; Shapiro et al. 2001 ). The Hadley cell contributes as well to the midlatitude variability through the interaction between the subtropical jet stream and the midlatitude eddy-driven jet (e.g., Lee and Kim 2003 ; Michel and Rivière 2014 ). The stratosphere is another element affecting the storm-track variability through mechanisms such as the so-called downward control (e.g., Kidston et al. 2015 ). In the midlatitudes, large-scale SST

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Kazutoshi Sato, Atsuyoshi Manda, Qoosaku Moteki, Kensuke K. Komatsu, Koto Ogata, Hatsumi Nishikawa, Miki Oshika, Yuriko Otomi, Shiori Kunoki, Hisao Kanehara, Takashi Aoshima, Kenichi Shimizu, Jun Uchida, Masako Shimoda, Mitsuharu Yagi, Shoshiro Minobe, and Yoshihiro Tachibana

the upper troposphere shows that at 1800 UTC 22 May, the upper jet was directed eastward around 40°N ( Fig. 3a ). A shortwave trough, indicated by a high potential vorticity (PV) anomaly, was near 37°N, 119°E, at the southern periphery of the jet. By 1200 UTC 23 May, this trough had moved eastward to 37°N, 127°E ( Fig. 3b ). Marking the BFZ was an east–west band with strong gradient of θ e in the lower troposphere (850-hPa level), which was accompanied by a relatively strong PV anomaly ( Figs. 3

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Hyodae Seo

feature in the Indian Ocean during the summer monsoon ( Schott and McCreary 2001 ). Many previous studies have examined mechanisms for formation and maintenance of the GW. Some point to local wind curl east of the Findlater (or Somali) Jet ( Leetmaa et al. 1982 ; Luther and O’Brien 1989 ), while others attribute the formation and maintenance to the remote influence of the westward-propagating Rossby waves ( Schott and Quadfasel 1982 ; Brandt et al. 2003 ; Beal and Donohue 2013 ). Jensen (1991

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Bunmei Taguchi, Niklas Schneider, Masami Nonaka, and Hideharu Sasaki

latter. The westward intensification and concentration of the signals with initially broad meridional scale is consistent with jet-trapped Rossby waves proposed by Sasaki et al. (2013) . Fig . 6. (a) Lagged correlation (color shading) and regression (contours, every 0.1 K) coefficients of annual mean based on the Ishii analysis associated with the standardized reference time series of averaged over the KE region (33°–38°N, 145°–170°E; cyan boxes in the panels for lag 0 yr). Positive (negative

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Xiaohui Ma, Ping Chang, R. Saravanan, Raffaele Montuoro, Hisashi Nakamura, Dexing Wu, Xiaopei Lin, and Lixin Wu

frontal regions, on the other hand, can lead to an equatorward shift of the entire low-level atmospheric circulation system, including the surface westerlies, jet streams, and subtropical high pressure belt ( Sampe et al. 2010 ). By comparing atmosphere-only model simulations forced by prescribed SSTs, Taguchi et al. (2009) showed a reduced storm-track activity in response to a weakened SST gradient forcing due to the decreased meridional gradient of turbulent heat fluxes and moisture fluxes across

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Hyodae Seo, Young-Oh Kwon, Terrence M. Joyce, and Caroline C. Ummenhofer

Atlantic eddy-driven jet and the increase in European blocking frequency in response to the GS SST front (see also O’Reilly et al. 2016 ). Fig . 1. (a) Detrended and normalized (to unit standard deviation) JFM GSI ( Joyce et al. 2000 ) for the period 1954–2012. (bottom) The linearly regressed (b) SST (color shading, °C) and (c) column-integrated (1000–50 hPa) northward synoptic eddy heat flux (color shading, 10 7 W m −1 ) overlaid with the Z 250 (m, CI = 2) when the JFM GSI leads by 1 yr ( Kwon and

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Yi-Hui Wang and W. Timothy Liu

) proposed the role of oceanic fronts in modulating downstream storm tracks and westerly jets. Storm-track and jet responses are revealed when sharp oceanic fronts are resolved in models (e.g., Taguchi et al. 2009 ). Frontal and regional atmospheric responses to western boundary currents have been observed within the boundary layer [see the review by Small et al. (2008) , and references therein]. Observational evidence of the deep-tropospheric response is provided by several studies ( Liu et al. 2007

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