著者

Ayako Seiki Yu Kosaka Satoru Yokoi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17, pp.177-183, 2021 (Released:2021-10-10)

参考文献数

25

被引用文献数

3

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The relationship between the boreal summer intraseasonal oscillation (BSISO) in the tropics and the summertime tropical-extratropical teleconnection called the Pacific-Japan (PJ) pattern is investigated. The positive correlation between the BSISO and intraseasonal PJ pattern peaks during BSISO phase 8 when the convective center of the BSISO reaches the vicinity of the Philippines. A composite analysis based on the BSISO events shows that intraseasonal responses to the migration of the BSISO extend to the midlatitudes and form circulation anomalies reminiscent of the PJ pattern. During phases 7-8, cyclonic wind anomalies with low-pressure signals drastically intensify north of the Philippines and southeasterly wind anomalies blow into midlatitude East Asia, influencing the summer climate. Other apparent intraseasonal signals in pressure and surface air temperature are found over the midlatitude central Pacific and eastern Eurasia, respectively. The intraseasonal variability in the PJ pattern associated with the BSISO undergoes strong interannual modulations, with enhanced intraseasonal signals in summers of the positive seasonal-mean PJ pattern and suppressed signals in those of the negative PJ pattern. This asymmetry between the positive and negative PJ summers highlights the importance of cross-scale interactions for a better understanding of summer climate in East Asia.

著者

Kazuaki Nishii Bunmei Taguchi Masato Mori Yu Kosaka Hisashi Nakamura

出版者

公益社団法人 日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.18, pp.199-204, 2022 (Released:2022-09-12)

参考文献数

23

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Anomalous coldness was observed over midlatitude Eurasia in December 2020 and over subpolar Eurasia in January 2021. The former was accompanied by the Warm Arctic and Cold Eurasia (WACE) pattern, while the latter by the negative phase of the Arctic Oscillation (AO). A set of large ensemble experiments with an atmospheric general circulation model suggests a contribution of reduced Arctic Sea ice to the midlatitude cooling and WACE pattern in December 2020. The tropical and extratropical sea surface temperature (SST) anomalies, however, contribute to warming over midlatitude Eurasia. In January 2021, neither the sea ice nor SST anomalies can explain the subpolar Eurasian cooling and the negative AO in our experiments.

著者

Ayako Seiki Yu Kosaka Satoru Yokoi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-031, (Released:2021-09-02)

被引用文献数

3

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The relationship between the boreal summer intraseasonal oscillation (BSISO) in the tropics and the summertime tropical-extratropical teleconnection called the Pacific-Japan (PJ) pattern is investigated. The positive correlation between the BSISO and intraseasonal PJ pattern peaks during BSISO phase 8 when the convective center of the BSISO reaches the vicinity of the Philippines. A composite analysis based on the BSISO events shows that intraseasonal responses to the migration of the BSISO extend to the midlatitudes and form circulation anomalies reminiscent of the PJ pattern. During phases 7-8, cyclonic wind anomalies with low-pressure signals drastically intensify north of the Philippines and southeasterly wind anomalies blow into midlatitude East Asia, influencing the summer climate. Other apparent intraseasonal signals in pressure and surface air temperature are found over the midlatitude central Pacific and eastern Eurasia, respectively. The intraseasonal variability in the PJ pattern associated with the BSISO undergoes strong interannual modulations, with enhanced intraseasonal signals in summers of the positive seasonal-mean PJ pattern and suppressed signals in those of the negative PJ pattern. This asymmetry between the positive and negative PJ summers highlights the importance of cross-scale interactions for a better understanding of summer climate in East Asia.

著者

Takeshi Horinouchi Yu Kosaka Hiroshi Nakamigawa Hisashi Nakamura Norihisa Fujikawa Yukari N. Takayabu

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17B, no.Special_Edition, pp.1-8, 2021 (Released:2021-06-01)

参考文献数

30

被引用文献数

14

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A prolonged heavy rainfall event occurred in Kyushu in early July 2020. Its large-scale environmental factors are investigated with observational and reanalysis data. Seven-day precipitation and moisture flux convergence around Kyushu were the greatest among the last 30 years. This pronounced convergence was maintained by nearly steady moisture influx, and the persistent upper-level trough to the northwest enhanced the ratio of moisture convergence to the influx. The magnitude of instantaneous moisture flux, however, was not particularly large among those along the subtropical jet axis or the Meiyu-Baiu rainband. What made this event unique is the persistence of the moisture flux peak anchored around Kyushu under the influence of the Silk-Road teleconnection. In June 2020, three upper-level troughs, whose easternmost one corresponding to the aforementioned trough, tend to form along the subtropical Asian jet. This wave train was persistent in the month and lasted until mid-July, 2020. Our analysis suggests that, prior to the rainfall event, the Silk-Road teleconnection was intensified through an interaction with a wave train at subpolar latitudes, which involves nonlinear processes including trough cut-off.

著者

Takeshi Horinouchi Yu Kosaka Hiroshi Nakamigawa Hisashi Nakamura Norihisa Fujikawa Yukari N. Takayabu

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-019, (Released:2021-04-28)

被引用文献数

14

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A prolonged heavy rainfall event occurred in Kyushu in early July 2020. Its large-scale environmental factors are investigated with observational and reanalysis data. Seven-day precipitation and moisture flux convergence around Kyushu were the greatest among the last 30 years. This pronounced convergence was maintained by nearly steady moisture influx, and the persistent upper-level trough to the northwest enhanced the ratio of moisture convergence to the influx. The magnitude of instantaneous moisture flux, however, was not particularly large among those along the subtropical jet axis or the Meiyu-Baiu rainband. What made this event unique is the persistence of the moisture flux peak anchored around Kyushu under the influence of the Silk-Road teleconnection. In June 2020, three upper-level troughs, whose easternmost one corresponding to the aforementioned trough, tend to form along the subtropical Asian jet. This wave train was persistent in the month and lasted until mid-July, 2020. Our analysis suggests that, prior to the rainfall event, the Silk-Road teleconnection was intensified through an interaction with a wave train at subpolar latitudes, which involves nonlinear processes including trough cut-off.

著者

Kazuaki NISHII Takafumi MIYASAKA Yu KOSAKA Hisashi NAKAMURA

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.87, no.3, pp.581-588, 2009 (Released:2009-07-08)

参考文献数

17

被引用文献数

10 11

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A reanalysis dataset is used to establish the relationship between the year-to-year fluctuations in the midwinter storm-track activity over the Far East measured by poleward heat flux associated with subweekly disturbances and the occurrence of the first spring storm with strong southerly winds over Japan (Haru-Ichiban). Our analysis reveals that its early (delayed) occurrence tends to follow the enhanced (suppressed) winter storm-track activity with less (more) apparent minimum in midwinter in the course of the seasonal march. A metric is defined on the basis of the eddy heat flux to measure the reproducibility of the particular seasonal march of the Far East storm-track activity simulated in each of the Coupled Model Intercomparison Project Phase 3 climate models under the present climate. Under a particular global warming scenario, ensemble projection based only on the several models that show the highest reproducibility of the storm-track activity measured with the particular metric indicates that the future enhancement is likely in the midwinter storm-track activity associated with the weakening of the East Asian winter monsoon, implying that Haru-Ichiban is likely to occur earlier in the late 21st century than in the 20th century.

著者

柴田 拓志 大王 拓哉 小阪 湧 今村 祐太 鈴木 大貴 岡本 真悟 杉山 博信 内貴 猛 Hiroshi Shibata Takuya Daiou Yu Kosaka Yuta Imamura Daiki Suzuki Shingo Okamoto Hironobu Sugiyama Takeru Naiki 岡山理科大学大学院工学研究科修士課程生体医工学専攻 岡山理科大学工学部生体医工学科 岡山理科大学工学部生体医工学科 岡山理科大学工学部生体医工学科 岡山理科大学工学部生体医工学科 日機装株式会社メディカル技術センター 日機装株式会社メディカル技術センター 岡山理科大学工学部生命医療工学科 Graduate School of Engineering Okayama University of Science Department of Biomedical Engineering Faculty of Engineering Okayama University of Science Department of Biomedical Engineering Faculty of Engineering Okayama University of Science Department of Biomedical Engineering Faculty of Engineering Okayama University of Science Department of Biomedical Engineering Faculty of Engineering Okayama University of Science Biomedical Engineering Center Nikkiso Corporation Biomedical Engineering Center Nikkiso Corporation Department of Biomedical Engineering Faculty of Engineering Okayama University of Science

巻号頁・発行日

vol.53, pp.131-136, 2018-02