著者

Kohei Fukuda Kazuaki Yasunaga Ryo Oyama Akiyoshi Wada Atsushi Hamada Hironori Fudeyasu

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2020-019, (Released:2020-05-25)

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This study examined the diurnal cycles of brightness temperature (TB) and upper-level horizontal winds associated with tropical cyclones (TCs) over the western North Pacific basin, making use of data retrieved from geostationary-satellite (Himawari-8) observations that exhibited unprecedented temporal and spatial resolutions. The results of a spectral analysis revealed that diurnal cycles prevail in TB variations over the outer regions of TCs (300-500 km from the storm center). The dominance of the diurnal cycle was also found in variations in the radial wind (Vr) in intensive TCs, although there was no dominant cycle in tangential wind variation. In addition, coherence spectra demonstrated that the diurnal cycles of TB and Vr are significantly coherent in intensive TCs. The migration speed of TB and Vr anomalies exceeded the time-mean Vr, and it was speculated that diurnal cycle signals propagate (i.e., are not advected) toward the outer regions of TCs.

著者

Kohei Fukuda Kazuaki Yasunaga Ryo Oyama Akiyoshi Wada Atsushi Hamada Hironori Fudeyasu

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.16, pp.109-114, 2020 (Released:2020-07-01)

参考文献数

22

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This study examined the diurnal cycles of brightness temperature (TB) and upper-level horizontal winds associated with tropical cyclones (TCs) over the western North Pacific basin, making use of data retrieved from geostationary-satellite (Himawari-8) observations that exhibited unprecedented temporal and spatial resolutions. The results of a spectral analysis revealed that diurnal cycles prevail in TB variations over the outer regions of TCs (300-500 km from the storm center). The dominance of the diurnal cycle was also found in variations in the radial wind (Vr) in intensive TCs, although there was no dominant cycle in tangential wind variation. In addition, coherence spectra demonstrated that the diurnal cycles of TB and Vr are significantly coupled in intensive TCs. The migration speed of TB and Vr anomalies exceeded the time-mean Vr, and it was speculated that diurnal cycle signals propagate (i.e., are not advected) toward the outer regions of TCs.

著者

Kazuaki Yasunaga Atsushi Hamada Kazuaki Nishii

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.238-243, 2019 (Released:2019-11-30)

参考文献数

21

被引用文献数

2

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This study examines the factors responsible for the long-term changes of winter monsoonal flow around Japan in association with increasing precipitation trends in December along the coastal areas of Honshu (the main island of Japan) facing the Sea of Japan. The precipitation around the tropical eastern Indian Ocean and maritime continent has significantly increased in recent years. Thus, a packet of the stationary Rossby wave associated with the anomalous heating deflects the subtropical jet to the south over the eastern edge of the Eurasian continent. The deflection of the jet gives favorable conditions for the development of a low pressure trough in the lower level on the eastern side, leading to the formation of negative height anomalies near the surface around Japan.Although tropical precipitation also increases in November and January, the anomalous heating induces negative height anomalies and cyclonic circulations over the inland region of China and eastern offshore region of Japan (to the further west and east in comparison with those in December) in these months. As a result, monsoonal flow around Japan (and precipitation along the coastal areas of the Sea of Japan) shows no long-term trends in November or January.

著者

Kengo Arai Kazuaki Yasunaga

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.80-86, 2019 (Released:2019-04-12)

参考文献数

13

被引用文献数

1

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This study examines dominant precipitation patterns during winter in the north-central region (Hokuriku District) of Japan, based on empirical orthogonal functions (EOFs) analysis. The pattern of the first leading component is similar to that of the mean precipitation, and the second leading component shows a dipole structure in which positive and negative regions are separated by the coast line. This dipole pattern across the coast line is robust regardless of data stratifications for the EOF calculation. Composites reveal that maritime and inland precipitation is relatively enhanced before and after the passage of a mid-level trough, respectively. In the former case, the temperature is higher and westerly or southwesterly wind prevails, while northwesterly wind dominates in the latter case. It is suggested that interactions between cold air over the land and warm air over the ocean are essentially important to the distinct precipitation patterns; offshore winds wedge the inland cold air under the maritime warm air, and intensifies the precipitation over the ocean. On the other hand, the northwesterly monsoonal flow pushes the maritime warm air onto the inland cold air, and more precipitation is brought about around the mountain range.

著者

Kazuaki Yasunaga Atsushi Hamada Kazuaki Nishii

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2019-043, (Released:2019-11-06)

被引用文献数

2

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This study examines the factors responsible for the long-term changes of winter monsoonal flow around Japan in association with increasing precipitation trends in December along the coastal areas of Honhsu (the main island of Japan) facing the Sea of Japan. The precipitation around the tropical eastern Indian Ocean and maritime continent has significantly increased in recent years. Thus, a wave-packet of the stationary Rossby wave associated with the anomalous heating deflects the subtropical jet to the south over the eastern edge of the Eurasian continent. The deflection of the jet gives favorable conditions for the development of a low pressure trough in the lower level on the eastern side, leading to the formation of negative height anomalies near the surface around Japan.Although tropical precipitation also increases in November and January, the anomalous heating induces negative height anomalies and cyclonic circulations over the inland region of China and eastern offshore region of Japan (to the further west and east in comparison with those in December) in these months. As a result, monsoonal flow around Japan (and precipitation along the coastal areas of the Sea of Japan) shows no long-term trends in November or January.

著者

Kengo Arai Kazuaki Yasunaga

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2019-016, (Released:2019-03-26)

被引用文献数

1

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This study examines dominant precipitation patterns during winter in the north-central region (Hokuriku District) of Japan, based on empirical orthogonal functions (EOFs) analysis. The pattern of the first leading component is similar to that of the mean precipitation, and the second leading component shows a dipole structure in which positive and negative regions are separated by the coast line. This dipole pattern across the coast line is robust regardless of data stratifications for the EOF calculation. Composites reveal that maritime and inland precipitation is relatively enhanced before and after the passage of a mid-level trough, respectively. In the former case, the temperature is higher and westerly or southwesterly wind prevails, while northwesterly wind dominates in the latter case. It is suggested that interactions between cold air over the land and warm air over the ocean are essentially important to the distinct precipitation patterns; offshore winds wedge the inland cold air under the maritime warm air, and intensifies the precipitation over the ocean. On the other hand, the northwesterly monsoonal flow pushes the maritime warm air onto the inland cold air, and more precipitation is brought about around the mountain range.