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Claude Frankignoul, Nathalie Sennéchael, Young-Oh Kwon, and Michael A. Alexander

be rather persistent because of SST anomaly reemergence, sustained forcing from the tropics, and low-frequency changes in oceanic heat advection. The extratropical SST variability is large near the strong SST gradients along the oceanic fronts associated with western boundary currents and their extensions (hereafter WBCs), especially at decadal time scales ( Nakamura et al. 1997 ; Nakamura and Kazmin 2003 ; Kwon et al. 2010a ), when the changes in the oceanic circulation are particularly

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Takeaki Sampe, Hisashi Nakamura, Atsushi Goto, and Wataru Ohfuchi

boundary with no landmass. In our experiments, we attempt to differentiate between the influence of the midlatitude SST gradient and that of a STJ on the extratropical atmosphere by assigning different meridional SST profiles. As shown in Fig. 1 , and as summarized in Table 1 , we adopted six SST profiles, each of which consists of a combination of one of the two profiles for midlatitudes and one of the three for the tropics. In our control (CTL) experiment, we used a SST profile based on the

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Young-Oh Kwon, Michael A. Alexander, Nicholas A. Bond, Claude Frankignoul, Hisashi Nakamura, Bo Qiu, and Lu Anne Thompson

1. Introduction Atmosphere–ocean interactions are exceptionally strong over western boundary currents and their eastward extensions (hereafter collectively WBCs): for example, the largest mean and variance at interannual and longer time scales of the net surface heat flux (Q net ) over the global ocean occurs in WBC regions ( Wallace and Hobbs 2006 ). Poleward heat transports by the ocean and atmosphere are comparable in the tropics, until the ocean transfers ~70% of its heat transport to the

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Haiming Xu, Hiroki Tokinaga, and Shang-Ping Xie

satellite observations of SST, sea surface height (SSH), sea surface wind, cloud liquid water (CLW), and precipitation by microwave sensors on different platforms. The TMI measures SST free of clouds over the global tropics within 38°N/S. It also measures rain rate and column-integrated cloud liquid water content. We use a monthly TMI product on a 0.25°grid ( Wentz et al. 2000 ). The microwave scatterometer on the QuikSCAT satellite measures daily surface wind velocity over the World Ocean ( Liu et al

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Shoshiro Minobe, Masato Miyashita, Akira Kuwano-Yoshida, Hiroki Tokinaga, and Shang-Ping Xie

layer of conditional instability that enables deep convection in summer over the Gulf Stream, consistent with our observational results. Our results suggest two necessary conditions for the deep heating mode. First, SST needs to exceed a certain threshold . In current climate, the SST threshold for deep convection is ~26°–27°C in the tropics, depending upon region and season ( Graham and Barnett 1987 ; Waliser et al. 1993 ). A visual inspection of rain rate, high-level cloud, and vertical winds in

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Bunmei Taguchi, Hisashi Nakamura, Masami Nonaka, and Shang-Ping Xie

evidence is emerging that the midlatitude atmosphere does respond to fine structures of SST associated with oceanic fronts and eddies ( Nonaka and Xie 2003 ; Chelton et al. 2004 ; Xie 2004 ; Tokinaga et al. 2006 ; Small et al. 2008 ), but the response is localized and mostly confined to the atmospheric planetary boundary layer (PBL). Climatologically, a western boundary current associated with a subtropical gyre transports a huge amount of heat from the tropics into a midlatitude oceanic frontal

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Akira Kuwano-Yoshida, Shoshiro Minobe, and Shang-Ping Xie

of an atmospheric general circulation model to prescribed SST changes: Feedback effects associated with the simulation of cloud optical properties. Climate Dyn. , 5 , 175 – 182 . Lindzen , R. S. , and S. Nigam , 1987 : On the role of sea surface temperature gradients in forcing low-level winds and convergence in the tropics. J. Atmos. Sci. , 44 , 2418 – 2436 . Minobe , S. , A. Kuwano-Yoshida , N. Komori , S-P. Xie , and R. J. Small , 2008 : Influence of the Gulf

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Lu Anne Thompson and Young-Oh Kwon

1. Introduction Observations of a shift in the climate of the North Pacific Ocean around 1976–77 and the link to large-scale patterns in sea surface temperature (SST; Mantua et al. 1997 ) have lead to a search for potential sources of decadal variability in the ocean–atmosphere system in the North Pacific sector. Observations show two modes of variability in SST in the Pacific Ocean ( Deser and Blackmon 1995 ), the first with a large expression in the tropics and a maximum of a different sign

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Terrence M. Joyce, Young-Oh Kwon, and Lisan Yu

transport and storage to mid-latitude ocean-atmosphere interaction. Earth’s Climate: The Ocean-Atmosphere Interaction, Geophys. Monogr., Vol. 147, Amer. Geophys. Union, 347–363 . Lindzen , R. S. , and S. Nigam , 1987 : On the role of sea surface temperature gradients in forcing low-level winds and convergence in the tropics. J. Atmos. Sci. , 44 , 2418 – 2436 . Minobe , S. , A. Kuwano-Yoshida , N. Komori , S. Xie , and R. J. Small , 2008 : Influence of the Gulf Stream on the

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Masami Nonaka, Hisashi Nakamura, Bunmei Taguchi, Nobumasa Komori, Akira Kuwano-Yoshida, and Koutarou Takaya

J. W. Hurrell , 2004 : Pacific interdecadal climate variability: Linkages between the tropics and North Pacific during boreal winter since 1900. J. Climate , 17 , 3109 – 3124 . Enomoto , T. , A. Kuwano-Yoshida , N. Komori , and W. Ohfuchi , 2008 : Description of AFES 2: Improvements for high-resolution and coupled simulations. High Resolution Numerical Modelling of the Atmosphere and Ocean, K. Hamilton and W. Ohfuchi, Eds., Springer, 77–97 . Frankignoul , C. , 1985

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