著者

Hiroaki Ueda Mikihiro Yokoi Masaya Kuramochi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17B, no.Special_Edition, pp.14-18, 2021 (Released:2021-09-09)

参考文献数

28

被引用文献数

7

---

During the early summer of 2020, a stagnation of the Meiyu-Baiu front brought torrential rainfall over East Asia. Meanwhile, the anticyclone was much enhanced over the subtropical western Pacific (SWP), which contributed abundant moisture to the Meiyu-Baiu rainband along the western rim of the anticyclone. Based on the sensitivity experiments of the linear baroclinic model by prescribing the observed diabatic heating anomalies, a combination of anomalous convection over the Indian Ocean and reduced rainfall over the western Pacific can account for the maintenance of zonally elongated SWP anticyclone. Interestingly, this period corresponded to the developing stage of La Niña, while the convective activities were notably suppressed over the warmed western Pacific. The sensitivity experiments to SST anomalies using the atmospheric general circulation model shows that the attenuated convection over the western Pacific can be ascribed to the warmed Indian Ocean associated with an atmospheric Kelvin wave wedge from the Indian Ocean. Overall, the suppressant SST effect of the Indian Ocean opposes and is greater than that of tropical Pacific. We issue a caveat regarding the additivity of the remote influence across the maritime continent. These results have important implications for the predictability of early summer rainfall over East Asia.

著者

Masaya Kuramochi Hiroaki Ueda Chiaki Kobayashi Youichi Kamae Koutarou Takaya

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17B, no.Special_Edition, pp.9-13, 2021 (Released:2021-08-26)

参考文献数

29

被引用文献数

7

---

The anomalous warm winter from December 2019 to February 2020 over East Asia, particularly the anticyclonic anomaly around Japan, was examined from the teleconnection perspective anchored by a warmed Indian Ocean and the El Niño Modoki. In the upper troposphere, high–low–high wave patterns progressing from the Arabian Sea toward Japan via the southern region of China, coupled with the wave-activity flux diagnosis, implicate the propagation of stationary Rossby waves caused by enhanced convection in the western Indian Ocean and suppressed convection around the Maritime Continent. These anomalous convective activities could be responsible for the northward displacement of the subtropical jet and the ensuing warm conditions over East Asia. The atmospheric response to the observed diabatic heating by means of the linear baroclinic model well reproduced the observations. Moreover, sensitivity experiments of the atmospheric general circulation model to sea surface temperature (SST) anomalies, especially in the warmed western Indian and central Pacific oceans, can help understand the anomalous subsidence over the Maritime Continent sector and subsequently weakened convection. The warmer SST observed around the Maritime Continent alone reproduces the enhancement of rainfall and subsequent cold anomalies around Japan, suggesting the importance of trans-basin interaction for teleconnection towards East Asia.

著者

Masaya Kuramochi Hiroaki Ueda Chiaki Kobayashi Youichi Kamae Koutarou Takaya

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.17B-001, (Released:2021-08-05)

被引用文献数

7

---

The anomalous warm winter from December 2019 to February 2020 over East Asia, particularly the anticyclonic anomaly around Japan, was examined from the teleconnection perspective anchored by a warmed Indian Ocean and the El Niño Modoki. In the upper troposphere, high–low–high wave patterns progressing from the Arabian Sea toward Japan via the southern region of China, coupled with the wave-activity flux diagnosis, implicate the propagation of stationary Rossby waves caused by enhanced convection in the western Indian Ocean and suppressed convection around the Maritime Continent. These anomalous convective activities could be responsible for the northward displacement of the subtropical jet and the ensuing warm conditions over East Asia. The atmospheric response to the observed diabatic heating by means of the linear baroclinic model well reproduced the observations. Moreover, sensitivity experiments of the atmospheric general circulation model to sea surface temperature (SST) anomalies, especially in the warmed western Indian and central Pacific oceans, can help understand the anomalous subsidence over the Maritime Continent sector and subsequently weakened convection. The warmer SST observed around the Maritime Continent alone reproduces the enhancement of rainfall and subsequent cold anomalies around Japan, suggesting the importance of trans-basin interaction for teleconnection towards East Asia.

著者

Masamichi OHBA Hiroaki UEDA

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.85, no.3, pp.335-348, 2007 (Released:2007-08-09)

参考文献数

46

被引用文献数

59 77

---

One possible impact of sea surface temperature (SST) anomalies in the Indian Ocean (IO) on the ongoing El Niño is investigated using an air-sea coupled general circulation model (CGCM). A suite of CGCM experiments by imposing the IO basin-wide warming (BW) and IO dipole/zonal mode (IODZM) are conducted to assess the feedback effects of the El Niño-related SST anomalies on the Pacific. While the IODZM during boreal fall does not have a significant impact on the Pacific sector, the BW during boreal winter enhances the surface easterlies over the equatorial Western Pacific (WP) during the maturedecay phase of El Niño. The strengthened easterlies act to enhance the SST cooling over the WP, thereby the zonal gradient of SST between the IO and WP is greater than the climatology. These enhanced WP easterlies induce an advanced transition to the La Niña phase, which is caused by the upwelling ocean Kelvin waves. These results imply that the BW in the IO, to some extent, can be hastening the El Niño to La Niña transition.

著者

Hiroaki Ueda Mikihiro Yokoi Masaya Kuramochi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.17B-002, (Released:2021-08-04)

被引用文献数

7

---

During the early summer of 2020, a stagnation of the Meiyu-Baiu front brought torrential rainfall over East Asia. Meanwhile, the anticyclone was much enhanced over the subtropical western Pacific (SWP), which contributed abundant moisture to the Meiyu-Baiu rainband along the western rim of the anticyclone. Based on the sensitivity experiments of the linear baroclinic model by prescribing the observed diabatic heating anomalies, a combination of anomalous convection over the Indian Ocean and reduced rainfall over the western Pacific can account for the maintenance of zonally elongated SWP anticyclone. Interestingly, this period corresponded to the developing stage of La Niña, while the convective activities were notably suppressed over the warmed western Pacific. The sensitivity experiments to SST anomalies using the atmospheric general circulation model shows that the attenuated convection over the western Pacific can be ascribed to the warmed Indian Ocean associated with an atmospheric Kelvin wave wedge from the Indian Ocean. Overall, the suppressant SST effect of the Indian Ocean opposes and is greater than that of tropical Pacific. We issue a caveat regarding the additivity of the remote influence across the maritime continent. These results have important implications for the predictability of early summer rainfall over East Asia.

著者

Hirokazu Endo Akio Kitoh Hiroaki Ueda

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.14, pp.57-63, 2018 (Released:2018-04-28)

参考文献数

39

被引用文献数

33

---

Recent studies indicate that the view of a general weakening of the monsoon circulation in a warmer climate cannot be simply applied in the Asian monsoon regions. To understand the Asian summer monsoon response to global warming, idealized multi-model experiments are analyzed. In the coupled model response to increased CO2, monsoon westerlies in the lower troposphere are shifted poleward and slightly strengthened over land including South Asia and East Asia, while the tropical easterly jet in the upper troposphere are broadly weakened. The different circulation responses between the lower and upper troposphere is associated with vertically opposite changes in the meridional temperature gradient (MTG) between the Eurasian continent and the tropical Indian Ocean, with a strengthening (weakening) in the lower (upper) troposphere. Atmospheric model experiments to separate the effects of CO2 radiative forcing and sea surface temperature warming reveal that the strengthened MTG in the lower troposphere is explained by the CO2 forcing. On a global perspective, CO2-induced enhancement of the land–sea thermal contrast and resultant circulation changes are the most influential in the South Asian monsoon. This study emphasizes an important role of the land warming on the Asian monsoon response to global warming.

著者

Hiroaki UEDA E. Masatake HORI

出版者

The Association of Japanese Geographers

雑誌

地理学評論 (ISSN:13479555)

巻号頁・発行日

vol.79, no.12, pp.715-724, 2006-10-01 (Released:2008-12-25)

参考文献数

37

被引用文献数

1 1

---

Japan and neighboring regions experienced record-breaking hot weather during the 2004 summer. Two kinds of teleconnection patterns are considered to account for the anomalous anticyclone over these regions. One, originating from the western North Pacific (WNP), was responsible for the anomalous hot weather during the second half of June. The other, embedded in the mid-latitude Asian Jet, was discernible dúring early July. The Asian summer monsoon (ASM) was stronger than normal, which was consistent with the warmer Asian land surface in the pre-monsoon season. During the boreal spring, enhancement of convection occurred over the tropical Indian Ocean (IO) and WNP. These anomalous tropical heat sources are responsible for anticyclonic circulation extending over the Asian continent and resultant increase in the land surface temperature due to suppression of rainfall. The enhancement of thermal gradient between the Asian continent and the adjacent oceans are consistent with the strong ASM. An east-west asymmetric air-sea heat exchange across South china Sea is newly proposed to explain the connection between the ASM intensity and the localized convection to the east of the Philippines in June.

著者

Hiroaki UEDA

出版者

The Association of Japanese Geographers

雑誌

地理学評論 (ISSN:13479555)

巻号頁・発行日

vol.78, no.12, pp.825-841, 2005-10-01 (Released:2008-12-25)

参考文献数

58

被引用文献数

12 18

---

Observational evidence is presented to show an atmosphere-ocean coupled system in the maturing process of the Asian summer monsoon (ASM) and the western Pacific monsoon (WPM). The ASM and WPM are characterized by four abrupt seasonal changes that exhibit phase-locking features in the annual cycle. They correspond to the first transition of the ASM (mid May); the Indian monsoon onset (early June); the mature phase of ITCZ (mid June) to the east of Philippines and convection jump around 150°E (late July). The appearance of a warm pool, in excess of 29.0°C, is one of the key elements in understanding the sub-seasonal evolution of the ASM and WPM. Over the Indian Ocean, the seasonal increase of sea surface temperature (SST) follows the solar insolation and reduced evaporative cooling as well. In contrast, increase of SST over the subtropical western Pacific (SWP) lags behind those in the Indian Ocean by about one month. The heat flux analysis at the ocean surface in the SWP reveals that the delayed warming is attributed to reduced evaporative cooling, in relation to the weakening of the tropical easterlies, which is concurrent with the eastward expansion (_??_150°E) of the monsoon westerlies. These processes are also valid for interannual fluctuation; namely, the intensified ASM can induce warm SST anomalies over the SWP. Thus, these physical interpretations suggest further increase of the WPM predictability.

著者

Masamichi Ohba Hiroaki Ueda

出版者

(公社)日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.2, pp.176-179, 2006 (Released:2006-12-26)

参考文献数

16

被引用文献数

15 47

---

Interannual fluctuations of the convective activity around the Philippines are highly correlated with the east-west gradient of SST between the North Indian Ocean (NIO) and the western North Pacific (WNP). We conducted a set of experiments by use of an atmospheric general circulation model (AGCM) to assess the relative importance of the remote (NIO) versus in situ (WNP) SST anomalies in determining the WNP monsoon rainfall as ocean-to-atmosphere feedback. The solutions indicate that both in situ and remote SST anomalies regulate precipitation around the Philippines in the early summer. This result implies that the WNP monsoon rainfall is sensitive to the spatial distribution of the NIO SST anomalies as well as the in situ anomalies. These physical interpretations suggest further increase of the predictability in the WNP monsoon.