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Hailan Wang, Siegfried Schubert, Max Suarez, and Randal Koster

-depth investigation of the physical and dynamical mechanisms through which the cold Pacific and warm Atlantic SST patterns, the two major U.S. drought-inducing SST patterns, influence the U.S. precipitation in the NSIPP-1 model. We focus on the NSIPP-1 AGCM experiments because we have available to us a complete set of model outputs, including daily data and three-dimensional (3D) monthly diabatic heating fields, that are necessary for assessing budgets and various dynamical forcing fields. We do, however, address

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Daisuke Hotta and Hisashi Nakamura

mechanism of atmospheric baroclinicity (e.g., Stone 1978 ); however, it cannot explain the existence of such meridionally narrow baroclinic zones, as observed near the surface along the storm tracks. HV90 was the first to address this issue. Using a planetary wave model linearized about the observed wintertime zonal-mean flow with each of the transient eddy momentum and heat fluxes and diabatic heating imposed in the NH storm-track regions—namely, the North Atlantic and the North Pacific—as forcing

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

the surface and is referred to as sensible heating. We now examine the seasonal variations of these heating rates over the Gulf Stream proper and the Florida Current. We focus on the latent and sensible heating rates, as they are much larger than the radiative heating rates. Figure 14a shows that the diabatic heating rate has its maximum in the winter season over the Gulf Stream proper (rectangle in Fig. 11a ). This reflects the fact that both sensible and latent heating reaches a maximum in

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

. Contribution of diabatic heating on storm-track energetics The horizontal distributions of the simulated latent heating rate due to the atmospheric convection and large-scale condensation vertically averaged between the 1000- and 100-hPa levels is quite similar to that of the precipitation rate, with the maximum heating rate reaching up to 2 K day −1 along the warm ocean currents (not shown). The oceanic frontal signatures on the latent heating rate are characterized by confinement of the heating regions

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Kathryn A. Kelly, R. Justin Small, R. M. Samelson, Bo Qiu, Terrence M. Joyce, Young-Oh Kwon, and Meghan F. Cronin

activity was strongly influenced by the baroclinicity in the atmospheric boundary layer, which is, in turn, closely related to the SST gradient. The relationship between storm tracks and ocean fronts in all ocean basins has been reviewed by Nakamura et al. (2004) . In addition to the influence on baroclinicity, ocean fronts affect the diabatic heating of the atmosphere through surface fluxes. Differential diabatic heating at the surface can act to either enhance or reduce the low-level thermal

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

of the former to the latter in this bimonthly period is 0.34, although they have a high correlation of r = 0.76), which is likely because no contributions from diabatic heating and entrainment at the top of the ML to the heat budget in the ML are included in our evaluation. Although the contribution of diabatic heating cannot be estimated quantitatively, time series of cloud cover and outgoing longwave radiation (OLR; Fig. 6c ) imply the formation of low-level clouds immediately after some

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

the oceanic western boundary currents is important for strong diabatic heating in storm-track regions, which excites planetary waves that enhance baroclinicity around the storm-track regions. Nakamura et al. (2004 , 2008) argued that, because of the large heat capacity of the oceanic mixed layer and the strong thermal advection by confluent ocean currents, the presence of an oceanic front can exert a strong restoring effect on baroclinicity of the overlying atmosphere that is subject to

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

wintertime signal. Our results indicate that rms storm-related sensible and latent fluxes of 60 and 90 W m −2 , respectively, are found over the GS ( Figs. 8 and 7 ), and that these are appreciable in terms of mean values, approaching 30%–50% of the mean turbulent fluxes. Similar results apply to the KE region. Thus, winter storms must contribute significantly to the mean signal of diabatic heating throughout the troposphere over the GS and KE and to the energetics that create the storm tracks in the

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

updraft anchored over the surface convergence extends to the upper troposphere based on outgoing longwave radiation (OLR) observations and an atmospheric analysis product from the European Centre for Medium-Range Weather Forecasts (ECMWF). In an AGCM with 50-km horizontal resolution, the Gulf Stream–trapped structures of surface wind convergence, precipitation, and cyclone activity disappear when the SST data are smoothed. Their linear model response to diabatic heating over the Gulf Stream indicates

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

and 0.6 hPa for SLP, so that the response to the KE shifts is at least twice weaker than in the OE case. This is broadly consistent with the smaller SST signature of the KEI (cf. Figs. 5 and 6 ), leading to smaller diabatic heating of the atmosphere. 6. Summary and discussion After removing the ENSO teleconnections in a seasonally varying, asymmetric way, the meridional shifts of the OE and the KE were shown to have a significant influence on the large-scale tropospheric circulation. The

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