著者
Shion Sekizawa Takafumi Miyasaka Hisashi Nakamura Akihiko Shimpo Kazuto Takemura Shuhei Maeda
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
pp.15A-005, (Released:2019-05-22)
被引用文献数
26

During a torrential rainfall event in early July 2018, profound enhancement of moisture influx from the south and its convergence occurred over western Japan, which is investigated in this study on the basis of objective analysis and forecast data from the Japan Meteorological Agency Meso-Scale Model. The heavy rainfall over western Japan is found to accompany enhanced oceanic evaporation extensively around Japan, especially around the Kuroshio and entirely over the Sea of Japan. Linear decompositions of the anomalous moisture flux and surface latent heat flux anomalies applied to the high-resolution data reveals that the intensified speed of the low-level southerlies was the primary factor for the pronounced enhancement of both the moisture transport into the heavy rainfall region, especially in its western portion, and evaporation around the Kuroshio into the southerlies. An additional contribution is found from positive sea-surface temperature anomalies to the enhanced southerly moisture inflow into the eastern portion of the rainfall region. These findings have been confirmed through a backward trajectory analysis, which suggests that anomalous moisture supply to air parcels into the rainfall region primarily through the enhanced wind-forced evaporation roughly corresponds to about 10% of the precipitable water anomaly over western Japan.
著者
Akihiko Shimpo Kazuto Takemura Shunya Wakamatsu Hiroki Togawa Yasushi Mochizuki Motoaki Takekawa Shotaro Tanaka Kazuya Yamashita Shuhei Maeda Ryuta Kurora Hirokazu Murai Naoko Kitabatake Hiroshige Tsuguti Hitoshi Mukougawa Toshiki Iwasaki Ryuichi Kawamura Masahide Kimoto Izuru Takayabu Yukari N. Takayabu Youichi Tanimoto Toshihiko Hirooka Yukio Masumoto Masahiro Watanabe Kazuhisa Tsuboki Hisashi Nakamura
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.15A, pp.13-18, 2019 (Released:2019-06-15)
参考文献数
22
被引用文献数
54

An extreme rainfall event occurred over western Japan and the adjacent Tokai region mainly in early July, named “the Heavy Rain Event of July 2018”, which caused widespread havoc. It was followed by heat wave that persisted in many regions over Japan in setting the highest temperature on record since 1946 over eastern Japan as the July and summertime means. The rain event was attributable to two extremely moist airflows of tropical origins confluent persistently into western Japan and large-scale ascent along the stationary Baiu front. The heat wave was attributable to the enhanced surface North Pacific Subtropical High and upper-tropospheric Tibetan High, with a prominent barotropic anticyclonic anomaly around the Korean Peninsula. The consecutive occurrence of these extreme events was related to persistent meandering of the upper-level subtropical jet, indicating remote influence from the upstream. The heat wave can also be influenced by enhanced summertime convective activity around the Philippines and possibly by extremely anomalous warmth over the Northern Hemisphere midlatitude in July 2018. The global warming can also influence not only the heat wave but also the rain event, consistent with a long-term increasing trend in intensity of extreme precipitation observed over Japan.
著者
Kazuto Takemura Shunya Wakamatsu Hiroki Togawa Akihiko Shimpo Chiaki Kobayashi Shuhei Maeda Hisashi Nakamura
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.15A, pp.49-54, 2019 (Released:2019-08-09)
参考文献数
21
被引用文献数
1 23

This study investigates the influence of strong southerly moisture flux on an extreme rainfall event over western Japan in early July 2018, by using a global atmospheric reanalysis dataset. During its peak period from 5 to 7 July, extensive and unprecedented rainfall observed along the well-defined quasi-stationary Baiu front was attributed to two branches of extremely moist inflow from the southern confluence into western Japan. One was a shallow southerly airstream enhanced by the surface North Pacific Subtropical High, and the other was a deeper southwesterly airstream accompanying enhanced convection over the East China Sea. Both the vertically integrated moisture flux from the south and its convergence into western Japan reached the highest levels for 60 years due to an overwhelming contribution from the intensified southerlies. Anomalous diabatic heating associated with the active convection over the East China Sea acted to maintain the southwesterly moisture flux by inducing low-level cyclonic potential vorticity anomalies. During the rainfall event, a strong meander of the upper-level subtropical jet associated with the intensified surface North Pacific Subtropical High accompanied an amplified upper-level trough over the Korean Peninsula, which acted to induce ascent dynamically along the Baiu front.
著者
Shion Sekizawa Takafumi Miyasaka Hisashi Nakamura Akihiko Shimpo Kazuto Takemura Shuhei Maeda
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.15A, pp.25-30, 2019 (Released:2019-06-22)
参考文献数
10
被引用文献数
26

During a torrential rainfall event in early July 2018, profound enhancement of moisture influx from the south and its convergence occurred over western Japan, which is investigated in this study on the basis of objective analysis and forecast data from the Japan Meteorological Agency Meso-Scale Model. The heavy rainfall over western Japan is found to accompany enhanced oceanic evaporation extensively around Japan, especially around the Kuroshio and entirely over the Sea of Japan. Linear decompositions of the anomalous moisture flux and surface latent heat flux anomalies applied to the high-resolution data reveal that the intensified speed of the low-level southerlies was the primary factor for the pronounced enhancement of both the moisture transport into the heavy rainfall region, especially in its western portion, and evaporation around the Kuroshio into the southerlies. An additional contribution is found from positive sea-surface temperature anomalies to the enhanced southerly moisture inflow into the eastern portion of the rainfall region. These findings have been confirmed through a backward trajectory analysis, which suggests that anomalous moisture supply to air parcels into the rainfall region primarily through the enhanced wind-forced evaporation roughly corresponds to about 10% of the precipitable water anomaly over western Japan.
著者
Kazuto Takemura Hitoshi Mukougawa
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
pp.2021-029, (Released:2021-08-20)

This study presents a possible large-scale factor of tropical cyclogenesis over the western North Pacific, which is triggered by Rossby wave breaking to the east of Japan. More than half of the wave breaking cases is accompanied by the tropical cyclogenesis. Results from a composite analysis for the wave breaking cases indicate that the genesis and development of tropical cyclones are dominant over the southwest quadrant of the wave breaking center, where an intrusion of the upper-level potential vorticity caused by the wave breaking and the consequent enhanced convection are seen. The number of tropical cyclones in the wave breaking cases exponentially increases in time during the developing stage of the wave breaking. The results of composite analysis further indicate that lower-level strong wind convergence and the associated enhanced convection, which are resulting from the wave breaking, is favorable conditions for the tropical cyclogenesis. An enhanced monsoon trough accompanied by the Pacific–Japan pattern resulting from the enhanced convection can regulate tracks of the tropical cyclones. These results show that the Rossby wave breaking can trigger the tropical cyclogenesis over the western North Pacific, through the southwestward intrusion of the upper-level potential vorticity and the consequent enhanced convection.
著者
Kazuto Takemura Akihiko Shimpo
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.15, pp.75-79, 2019 (Released:2019-04-06)
参考文献数
20

Herein, (i) the remote influence of positive Indian Ocean Dipole (P-IOD) events in enhancing Tibetan High and (ii) its impact on the East Asian climate, from July to September, is analyzed based on composite analysis and linear baroclinic model experiment. In the equatorial Indian Ocean, convective activity enhances over the western part and suppresses over the eastern, which is associated with the zonal contrast of the sea surface temperature anomaly during P-IOD events. A lower-tropospheric clockwise circulation anomaly is evident from the eastern equatorial Indian Ocean where the suppressed convection is seen to the Indochina Peninsula. The streamlines arrive at the seas east of the Philippines, contributing to the enhancement of the monsoon trough. In the upper troposphere, crucial divergence anomaly over a wide area in the western North Pacific and the associated stronger-than-normal northward divergent winds toward East Asia cause strong northward negative-vorticity advection over the northern part of East Asia, contributing to the northeastward extension of the Tibetan High. This circulation anomaly contributes to both the significantly hot conditions in boreal summer and the late-summer heat over East Asia.
著者
Kazuto Takemura Yoshihiro Nakae Yoshihisa Fujihara Hirotaka Sato Hitoshi Sato Atsushi Goto Hiroaki Naoe
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.18A, no.Special_Edition, pp.21-26, 2022 (Released:2022-09-21)
参考文献数
17

Several regions in western Japan experienced a record-breaking early onset of the rainy season called Baiu in mid-May 2021, which is attributed to the northward movement and enhancement of the Baiu frontal zone. This study investigates large-scale atmospheric circulation that contributes to the early onset of Baiu. Diagnostic and statistical analyses based on reanalysis datasets reveal that both enhanced convection over the western Indian Ocean associated with the Madden–Julian oscillation and a blocking high near western Russia promote the excitation of Rossby waves to propagate downstream along the upper-tropospheric jet, and thus contributing to the northward movement of the Baiu frontal zone. The anomalous convection over the western Indian Ocean and the subtropical western North Pacific also may affect anticyclonic circulation anomalies to the northeast of the Philippines in the lower troposphere, which promotes moisture inflow toward western Japan and consequently intensifies the Baiu frontal zone. Numerical and quantitative analyses of the circulation anomalies near Japan based on a linear baroclinic model confirm the aforementioned results. The results indicate that the anomalous convection over the Asian monsoon region and the blocking high near western Russia are the primary factors contributing to the early onset of Baiu.
著者
Kazuto Takemura Yoshihiro Nakae Yoshihisa Fujihara Hirotaka Sato Hitoshi Sato Atsushi Goto Hiroaki Naoe
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
pp.18A-004, (Released:2022-08-18)

Several regions in western Japan experienced a record-breaking early onset of the rainy season called Baiu in mid-May 2021, which is attributed to the northward movement and enhancement of the Baiu frontal zone. This study investigates large-scale atmospheric circulation that contributes to the early onset of Baiu. Diagnostic and statistical analyses based on reanalysis datasets reveal that both enhanced convection over the western Indian Ocean associated with the Madden–Julian oscillation and a blocking high near western Russia promotes the excitation of Rossby waves to propagate downstream along the upper-tropospheric jet, and thus contributing to the northward movement of the Baiu frontal zone. The anomalous convection over the western Indian Ocean and the subtropical western North Pacific also may affect anticyclonic circulation anomalies to the northeast of the Philippines in the lower troposphere, which promotes moisture inflow toward western Japan and consequently intensifies the Baiu frontal zone. Numerical and quantitative analyses of the circulation anomalies near Japan based on a linear baroclinic model confirms the aforementioned results. The results indicate that the anomalous convection over the Asian monsoon region and the blocking high near western Russia are the primary factors contributing to the early onset of Baiu.
著者
Kazuto Takemura Hitoshi Mukougawa Yuhei Takaya Shuhei Maeda
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.18, pp.19-24, 2022 (Released:2022-02-11)
参考文献数
18

Seasonal predictability of summertime Asian jet deceleration near Japan is examined using monthly mean data of hindcasts based on an operational seasonal prediction system of the Japan Meteorological Agency. Interannual variabilities of the Asian jet deceleration averaged during July–August are generally well predicted with moderate to high forecast skill starting from initial months from January to June. The seasonal predictability of the Asian jet deceleration in specific years is, by contrast, limited with large forecast errors. An inter-member regression analysis for the forecast errors of the Asian jet deceleration using ensembles shows that the forecast errors of the Asian jet are associated with those of the Asian jet deceleration near Japan. Furthermore, the forecast errors of El Niño Southern Oscillation (ENSO)-related excessive upper-tropospheric divergence near Southeast Asia can account for the errors of the northward shifted Asian jet. The above-mentioned results indicate that more accurate seasonal prediction of ENSO can further improve the seasonal prediction skill of the Asian jet deceleration and summer climate near Japan.
著者
Kazuto Takemura Hitoshi Mukougawa Yuhei Takaya Shuhei Maeda
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
pp.2022-004, (Released:2022-01-13)

Seasonal predictability of summertime Asian jet deceleration near Japan is examined using monthly mean data of hindcasts based on an operational seasonal prediction system of the Japan Meteorological Agency. Interannual variabilities of the Asian jet deceleration averaged during July–August are generally well predicted with moderate to high forecast skill starting from initial months from January to June. The seasonal predictability of the Asian jet deceleration in specific years is, by contrast, limited with large forecast errors. An inter-member regression analysis for the forecast errors of the Asian jet deceleration using ensembles shows that the forecast errors of the Asian jet are associated with those of the Asian jet deceleration near Japan. Furthermore, the forecast errors of El Niño Southern Oscillation (ENSO)-related excessive upper-tropospheric divergence near Southeast Asia can account for the errors of the northward shifted Asian jet. The above-mentioned results indicate that more accurate seasonal prediction of ENSO can further improve the seasonal prediction skill of the Asian jet deceleration and summer climate near Japan.
著者
Kazuto Takemura Hitoshi Mukougawa
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.17, pp.164-169, 2021 (Released:2021-09-25)
参考文献数
24

This study presents a possible large-scale factor of tropical cyclogenesis over the western North Pacific, which is triggered by Rossby wave breaking to the east of Japan. More than half of the wave breaking cases is accompanied by the tropical cyclogenesis. Results from a composite analysis for the wave breaking cases indicate that the genesis and development of tropical cyclones are dominant over the southwest quadrant of the wave breaking center, where an intrusion of the upper-level potential vorticity caused by the wave breaking and the consequent enhanced convection are seen. The number of tropical cyclones in the wave breaking cases exponentially increases in time during the developing stage of the wave breaking. The results of composite analysis further indicate that lower-level strong wind convergence and the associated enhanced convection, which are resulting from the wave breaking, is favorable conditions for the tropical cyclogenesis. An enhanced monsoon trough accompanied by the Pacific–Japan pattern resulting from the enhanced convection can regulate tracks of the tropical cyclones. These results show that the Rossby wave breaking can trigger the tropical cyclogenesis over the western North Pacific, through the southwestward intrusion of the upper-level potential vorticity and the consequent enhanced convection.
著者
Akihiko Shimpo Kazuto Takemura Shunya Wakamatsu Hiroki Togawa Yasushi Mochizuki Motoaki Takekawa Shotaro Tanaka Kazuya Yamashita Shuhei Maeda Ryuta Kurora Hirokazu Murai Naoko Kitabatake Hiroshige Tsuguti Hitoshi Mukougawa Toshiki Iwasaki Ryuichi Kawamura Masahide Kimoto Izuru Takayabu Yukari N. Takayabu Youichi Tanimoto Toshihiko Hirooka Yukio Masumoto Masahiro Watanabe Kazuhisa Tsuboki Hisashi Nakamura
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
pp.15A-003, (Released:2019-05-17)
被引用文献数
54

An extreme rainfall event occurred over western Japan and the adjacent Tokai region mainly in early July, named “the Heavy Rain Event of July 2018”, which caused widespread havoc. It was followed by heat wave that persisted in many regions over Japan in setting the highest temperature on record since 1946 over eastern Japan as the July and summertime means. The rain event was attributable to two extremely moist airflows of tropical origins confluent persistently into western Japan and large-scale ascent along the stationary Baiu front. The heat wave was attributable to the enhanced surface North Pacific Subtropical High and upper-tropospheric Tibetan High, with a prominent barotropic anticyclonic anomaly around the Korean Peninsula. The consecutive occurrence of these extreme events was related to persistent meandering of the upper-level subtropical jet, indicating remote influence from the upstream. The heat wave can also be influenced by enhanced summertime convective activity around the Philippines and possibly by extremely anomalous warmth over the Northern Hemisphere midlatitude in July 2018. The global warming can also influence not only the heat wave but also the rain event, consistent with a long-term increasing trend in intensity of extreme precipitation observed over Japan.
著者
Shuhei Maeda Yusuke Urabe Kazuto Takemura Tamaki Yasuda Youichi Tanimoto
出版者
(公社)日本気象学会
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.12, pp.17-21, 2016 (Released:2016-02-11)
参考文献数
19
被引用文献数
2 10

We investigated features of the atmosphere and ocean to seek a possible candidate that suppressed the growth of the El Niño event in 2014. In the boreal summer-fall season, equatorially antisymmetric sea surface temperature (SST) anomalies with a positive (negative) sign to the north (south) of the equator prevailed in the central and eastern tropical Pacific. In association with the SST anomalies, cumulus convective activity was enhanced in the region of the climatological Intertropical Convergence Zone (ITCZ). Anomalous southerly surface winds flowing across the equator toward the ITCZ induced upward latent heat flux anomalies and lowered SST in the near-equatorial region. These coherent spatial patterns between SST, wind, and latent heat flux anomalies suggested that the wind-evaporation-SST (WES) feedback sustained the suppression of the El Niño growth. A linear baroclinic model experiment indicated that the enhanced convective heating in the ITCZ also contributed to sustain the anomalous surface southerlies across the equator by the intense meridional atmospheric circulation over the equator. These results indicate that the anomalous southerlies across the equator sustained by the WES feedback and intense convective heating in the ITCZ contributed to the suppression of the El Niño growth.
著者
Kazuto Takemura Hitoshi Mukougawa Shuhei Maeda
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.17, pp.125-129, 2021 (Released:2021-06-26)
参考文献数
18

Rossby waves propagating along the Asian jet frequently cause the breaking near the jet exit region. This study examines characteristics of oceanographic condition and atmospheric circulation associated with interdecadal variability of Rossby wave breaking frequency near Japan in August. Sea surface temperature during a period of the higher Rossby wave breaking frequency is cooler over the central part of the tropical North Pacific, compared with that during a period of the lower frequency. Convective activities are suppressed over the region consistent with the cooler sea surface temperature, contributing to an enhanced and southwestward extended mid-Pacific trough. Deceleration and diffluence of the Asian jet are stronger during the period of the higher frequency than that during the period of the lower one. The enhanced deceleration and diffluence of the jet are associated with the enhanced and southwestward extended mid-Pacific trough. The abovementioned dynamical influence is also shown by a numerical simulation using an atmospheric linear baroclinic model. These results indicate that the interdecadal variability of sea surface temperature over the central part of the tropical North Pacific has an impact on that of the Rossby wave breaking frequency near Japan, through the modulated convective activities and mid-Pacific trough.
著者
Kazuto Takemura Hitoshi Mukougawa Shuhei Maeda
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
pp.2021-021, (Released:2021-05-18)

Rossby waves propagating along the Asian jet frequently cause the breaking near the jet exit region. This study examines characteristics of oceanographic condition and atmospheric circulation associated with interdecadal variability of Rossby wave breaking frequency near Japan in August. Sea surface temperature during a period of the higher Rossby wave breaking frequency is cooler over the central part of the tropical North Pacific, compared with that during a period of the lower frequency. Convective activities are suppressed over the region consistent with the cooler sea surface temperature, contributing to an enhanced and southwestward extended mid-Pacific trough. Deceleration and diffluence of the Asian jet are stronger during the period of the higher frequency than that during the period of the lower one. The enhanced deceleration and diffluence of the jet are associated with the enhanced and southwestward extended mid-Pacific trough. The abovementioned dynamical influence is also shown by a numerical simulation using an atmospheric linear baroclinic model. These results indicate that the interdecadal variability of sea surface temperature over the central part of the tropical North Pacific has an impact on that of the Rossby wave breaking frequency near Japan, through the modulated convective activities and mid-Pacific trough.
著者
関澤 偲温 宮坂 貴文 中村 尚 Akihiko Shinpo Kazuto Takemura 前田 修平
出版者
日本地球惑星科学連合
雑誌
日本地球惑星科学連合2019年大会
巻号頁・発行日
2019-03-14

Western Japan experienced torrential rainfall in early July 2018, which caused severe floods and landslides especially over western Japan. Japan Meteorological Agency (JMA) reported that this extreme event was associated with extreme enhancement of northward moisture flux and its convergence over western Japan. Some recent studies have pointed out an essential role of surrounding oceans for extreme rainfall events through the anomalous heat and moisture supply to the warm, moist monsoonal airflow. This study investigates anomalous oceanic evaporation during the torrential rainfall event over western Japan based on the objective analysis data from the JMA Meso-Scale Model. We have found that the heavy rainfall was associated with enhanced oceanic evaporation extensively around Japan, especially along the Kuroshio and entirely over the Japan Sea. We then conducted a linear decomposition of local surface latent heat flux anomalies based on the bulk formula to determine factors for the enhanced evaporation. Our results show that the enhanced evaporation under the pronounced southerly inflow toward the extreme rainfall region was mainly due to increase in the surface wind speed along the Kuroshio south of Japan, with an additional contribution from warm SST anomalies to the enhanced moisture inflow into central Japan. In order to quantitatively assess contribution of the enhanced evaporation to anomalous moisture transport in the mixed layer, we also performed a backward trajectory analysis for moist air parcels. It reveals that anomalous moisture supply from the ocean to air parcels along trajectories is dominated by enhanced evaporation due to the stronger surface wind speed, which corresponds to about 20 % of the column water vapor anomaly and about 5 % of the total column water vapor.