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Hidetaka Hirata, Ryuichi Kawamura, Masaya Kato, and Taro Shinoda

–O cyclone forecasting errors. Over the northwestern Pacific Ocean and northwestern Atlantic Ocean, the Kuroshio/Kuroshio Extension and the Gulf Stream (i.e., western boundary currents) supply a large amount of heat and moisture to the midlatitude atmosphere (e.g., Kelly et al. 2010 ; Kwon et al. 2010 ). Several previous studies have shown that the supply of heat and moisture contributed to the rapid development of extratropical cyclones through decreased atmospheric stability and increased latent

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Youichi Tanimoto, Kou Shimoyama, and Shoichi Mori

1. Introduction Continuous and repeated in situ observations of the marine atmospheric boundary layer (MABL) along specific cross sections are very scarce over coastal regions and even rarer over the open oceans. Several previous studies, however, have conducted shipboard atmospheric soundings along a single cross section using a global positioning system (GPS) sonde. These studies have been successful in showing the distinct transition of temperature and moisture in the MABL across the steep

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Hidetaka Hirata, Ryuichi Kawamura, Masaya Kato, and Taro Shinoda

-Givi et al. 2004 ; Kuwano-Yoshida and Asuma 2008 ). Previous studies indicate that the moisture and sensible heat supply around warm currents is one of the factors responsible for the enhanced latent heating in extratropical cyclones (e.g., Davis and Emanuel 1988 ; Nuss and Kamikawa 1990 ; Kuo et al. 1991a ; Reed et al. 1993 ; Gyakum and Danielson 2000 ; Booth et al. 2012 ; Kuwano-Yoshida and Minobe 2017 ). To clarify how the moisture and sensible heat supply from the warm currents affect the

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

1. Introduction The baiu is a quasi-stationary rainband over East Asia and the northwestern Pacific in early summer between June and July, often characterized as a subtropical front in moisture between the tropics and extratropics ( Ninomiya 1984 ; Ninomiya and Akiyama 1992 ). The baiu rainband shows multiscale structures from meso- to synoptic scales ( Ninomiya and Akiyama 1992 ). Because of the multiscale nature, the baiu rainband provides much needed rainfall to supply precious water to a

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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

associated with the BFZ during the study period. In section 5 , we discuss oceanic influences on the BFZ and, in particular, the importance of evaporation and moisture supply to the lower troposphere. Section 6 is a summary and discussion. 2. Observations, data, and methods The field campaign on board the training vessel (T/V) Nagasaki-Maru (Nagasaki University, Japan) was conducted in the East China Sea from 21 to 23 May 2011 as part of project “Hot Spot in Climate System: Coupled Ocean

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Dimitry Smirnov, Matthew Newman, Michael A. Alexander, Young-Oh Kwon, and Claude Frankignoul

), but this upward motion in HR extends to the tropopause, whereas it is limited to the lower troposphere in LR. In the upper troposphere the circulation forms two cells with northward (southward) flow north (south) of the front in HR, whereas the flow is southward at all latitudes in LR. The larger low-level θ E anomaly in HR over the warm SST, reflecting both warmer temperatures and enhanced low-level moisture, also reduces the low-level stability (not shown), in a region that is frequently

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Akira Kuwano-Yoshida and Shoshiro Minobe

second term is the vertically integrated virtual temperature tendency (ITT), and the third term is the moisture mass budget (EP). The ITT can be expanded as follows: where v is the horizontal velocity vector, ω is the vertical pressure velocity, T is the temperature, c p is the specific heat capacity, Q is the diabatic heating rate, and RES ITT is the residuum due to discretization. The first term on the right-hand side indicates horizontal temperature advection (HADV), the second term

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Adèle Révelard, Claude Frankignoul, Nathalie Sennéchael, Young-Oh Kwon, and Bo Qiu

dominated by geostrophic advection, with a clear signature in SST. Sugimoto and Hanawa (2011) showed that SST changes are primarily responsible for turbulent heat flux variations. Because of the strong ocean-to-atmosphere fluxes of heat and moisture, the KOE is a region of large cyclogenesis, as major storm tracks are organized along or just downstream of the main oceanic frontal zones ( Hoskins and Hodges 2002 ; Bengtsson et al. 2006 ). Nakamura et al. (2004) and Taguchi et al. (2009) have

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Hyodae Seo

upwelling. Related to the enhanced SST is the significantly increased evaporation over the Southern Gyre and GW as well as along the coast of Oman ( Fig. 12f ). Fig . 12. The 10-yr JJAS climatologies of (a)–(c) SST (°C), (d)–(f) evaporation (Evp; cm day −1 ), and (g)–(i) vertically integrated moisture flux transport (kg m −1 s −1 ). The overlay in (a),(d),(g) is the CTL SST climatology (CI = 1); in (b),(e),(h) the overlay is the SST difference between CTL and noT e (CI = 0.25; positive solid; negative

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Satoru Okajima, Hisashi Nakamura, Kazuaki Nishii, Takafumi Miyasaka, and Akira Kuwano-Yoshida

Abstract

Sets of atmospheric general circulation model (AGCM) experiments are conducted to assess the importance of prominent positive anomalies in sea surface temperature (SST) observed over the midlatitude North Pacific in forcing a persistent basin-scale anticyclonic circulation anomaly and its downstream influence in 2011 summer and autumn. The anticyclonic anomaly observed in October is well reproduced as a robust response of an AGCM forced only with the warm SST anomaly associated with the poleward-shifted oceanic frontal zone in the midlatitude Pacific. The equivalent barotropic anticyclonic anomaly over the North Pacific is maintained under strong transient eddy feedback forcing associated with the poleward-deflected storm track. As the downstream influence of the anomaly, abnormal warmth and dryness observed over the northern United States and southern Canada in October are also reproduced to some extent. The corresponding AGCM response over the North Pacific to the tropical SST anomalies is similar but substantially weaker and less robust, suggesting the primary importance of the prominent midlatitude SST anomaly in forcing the large-scale atmospheric anomalies observed in October 2011. In contrast, the model reproduction of the atmospheric anomalies observed in summer was unsuccessful. This appears to arise from the fact that, unlike in October, the midlatitude SST anomalies accompanied reduction of heat and moisture release from the ocean, indicative of the atmospheric thermodynamic forcing on the SST anomalies. Furthermore, the distinct seasonality in the AGCM responses to the warm SST anomalies may also be contributed to by the seasonality of background westerlies and storm track.

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