著者

OSE Tomoaki ENDO Hirokazu TAKAYA Yuhei MAEDA Shuhei NAKAEGAWA Toshiyuki

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2022-032, (Released:2022-04-14)

被引用文献数

3

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Robust and uncertain sea-level pressure patterns over summertime East Asia in the future global warming projections and their causes are studied by applying the inter-model empirical orthogonal function (EOF) analysis to the multi-model experiments in the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and focusing common features with the previous CMIP5 analysis. The ensemble average and the first to third EOF modes associated with future pressure changes are similar to the corresponding ones from CMIP5. The first and second modes represent strengthened and weakened high pressure systems in subtropical and northern East Asia, respectively. The third mode is the reverse anomaly of the climatological pressure pattern over summertime East Asia, indicating weakened southerly monsoon winds. The second mode pattern makes positive contributions to almost all the CMIP6 future pressure changes, representing a robust future projection pattern. The robust mode is the result of surface warming over the northern continents and neighboring seas that is stronger than the global average. The first and third modes are considered to be uncertain (but major) patterns in the ensemble projections because the signs of their contributions to the future changes are dependent on the model used. Suppressed vertical motion over the equatorial (northern) Indian Ocean caused by the vertically stabilized atmosphere under the global warming scenario is the source of the first (third) mode, together with the counter vertical motion anomaly over the equatorial (northern) Pacific. The above characteristics of the modes are essentially similar to those identified in the CMIP5 analysis while different sea surface temperature anomalies are related to the secondary structures of the modes. Some uncertainties in the future projections can be attributed to the systematic differences in the model climatology of the present-day precipitation, which determines the distribution of the suppressed vertical motion under the future warmer climate.

著者

ENDO Hirokazu KITOH Akio MIZUTA Ryo OSE Tomoaki

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2021-073, (Released:2021-09-01)

被引用文献数

10

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Future changes in East Asian summer monsoon (EASM) precipitation and the associated atmospheric circulation changes are investigated based on ensemble projections with the 60-km mesh Meteorological Research Institute atmospheric general circulation model (MRI-AGCM60). The projections at the end of the twenty-first century under the Representative Concentration Pathway 8.5 (RCP8.5) scenario indicate an overall increase in EASM precipitation, but with large sub-seasonal and regional variations. In June, the Meiyu–Baiu rainband is projected to strengthen, with its eastern part (i.e., the Baiu rainband) shifted southward relative to its present-day position. This result is robust within the ensemble simulations. In July and August, the simulations consistently project a significant increase in precipitation over the northern East Asian continent and neighboring seas; however, there is a lack of consensus on the projection of the Meiyu–Baiu rainband in July. A small change in precipitation over the Pacific is another feature in August.  Sensitivity experiments with the MRI-AGCM60 reveal that the precipitation changes in early summer are dominated by the effects of sea surface temperature (SST) warming (i.e., uniform warming and the tropical pattern change), which induce an increase in atmospheric moisture and a strengthening and southward shift of the upper-level East Asian westerly jet (EAJ), especially over the Pacific. On the other hand, the influence of land warming and successive large SST warming in the extratropics is evident in the precipitation changes in late summer. These late summer effects oppose and exceed the early summer effects through changes in the EAJ and low-level monsoon winds. These results suggest that the competition between the opposing factors makes the signal of the Meiyu–Baiu rainband response smaller in July than in June, and thus there tends to be a larger spread among simulations regarding the future tendency of the rainband in July.

著者

OSE Tomoaki

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2019-018, (Released:2018-12-07)

被引用文献数

10

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Global warming experiments using three different 60 km-mesh atmospheric global circulation models are studied to characterize ensemble mean future changes in monthly East Asian precipitation for June to August. During the summer, wetting and drying effects due to changes in mean vertical motion play a key role in future precipitation changes, as does the “wet-get-wetter” effect due to increased moisture. The former processes are related adiabatically to the projected modification of 500 hPa horizontal atmospheric circulation, which is characterized by two cyclonic circulation anomalies extending over the eastern Eurasian Continent (C1) and the western North Pacific Ocean (C2) for each month. Over Japan, the western edge of C2 shifts from a region south of the Japanese Islands to northern Japan during June–August, representing a delayed northward movement or southward shift of the westerly jet over the western North Pacific in the future compared with the present-day climatology. Most regions of Japan lie within the northeasterly wind and associated downward motion zones of C2, leading to significant uncertainties in the future precipitation over Japan by the offset against the “wet-get-wetter” effect and possibly even a future decrease in precipitation. A wetter future climate is anticipated under weak subsidence or the upward vertical motion zone of C2, such as western Japan in August away from C2, and the Southwest Islands of Japan in June in the C2 southwesterly wind zone. Over the eastern Eurasian Continent, C1 is distributed mainly over northeastern China in June, central and southern China in July and August respectively. During these months, most of the eastern regions are located within the southwesterly-to-southeasterly wind zone of C1, indicating wet future conditions due to enhanced upward motion. This tendency drives a further increase in precipitation in future wetter East Asian climate via the “wet-get-wetter” effect and the increased evaporation.

著者

OSE Tomoaki TAKAYA Yuhei MAEDA Shuhei NAKAEGAWA Toshiyuki

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2020-047, (Released:2020-07-01)

被引用文献数

6

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The southerly surface wind index over the summertime East Asia (SWI) is strengthened in the future in the fifth phase of the Coupled Model Intercomparison Project (CMIP5). However, the differences among the models are much larger than the ensemble average. The empirical orthogonal function (EOF) analysis is applied to the future changes in the East Asian surface pressure pattern responsible for the SWI. The ensemble average and five EOF modes for the pressure patterns and the associated precipitation changes are identified, and their possible sources are examined. The CMIP5 ensemble mean change in the summertime Asia Pacific surface pressure pattern possesses the characteristics of the first to third modes. The first and second mode components contribute to the positive SWI in the future, but are cancelled mostly by the third mode component. The first mode is high surface pressure anomalies over low Asia Pacific sea surface temperature. The second mode is related to warm temperature anomalies over the Northern Hemisphere continents and the increased equatorial Pacific precipitation. The large model dependence of the SWI is created by the third mode, which represents the weak Pacific High in northern East Asia and is characterized with suppressed vertical motions over the northern Indian and Pacific oceans. The fourth mode is the Okhotsk High. The fifth mode represents the east–west contrast of the southern East Asian surface pressure anomalies and is associated with the Northern Hemisphere ocean temperatures. The fourth and fifth modes feature the mean projection using the 10 models reproducing an accurate present-day summertime East Asian climatology.  The mode-related suppressed vertical motions in global warming reflect the present-day vertical motion (i.e., precipitation) climatology; hence, the future increase/decrease in the SWI tends to be projected by models simulating the relatively small/large Asia Pacific monsoon precipitation over the tropical oceans, except near the mountains, in the present-day model climatology.