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

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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.

著者

関澤 偲温 中村 尚 小坂 優

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2018年大会

巻号頁・発行日

2018-03-14

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Variability of convective activity over the Maritime Continent (MC) influences climatic condition over East Asia via atmospheric teleconnections, through which SST variability such as ENSO is considered to provide seasonal predictability. In boreal winter, interannual variability of convection is centered around Indonesia and northern Australia, representing significant variability in the Australian summer monsoon (AUSM). Through an analysis of observational data, we show that interannual variability of austral summertime precipitation over northern Australia is hardly driven by tropical SST variability and is dominated by the internal variability of AUSM. Our analysis suggests that anomalously active AUSM sustains itself by inducing anomalous low-level westerlies over the eastern Indian Ocean and enhancing surface evaporation and moisture inflow into northern Australia. Anomalous AUSM activity is associated with distinct wavetrain pattern from the MC toward the extratropical North Pacific with dipolar pressure anomalies resembling the Western Pacific pattern. This teleconnection modulates the East Asian winter monsoon and exerts a significant impact on wintertime temperature and precipitation especially in Japan and Korea. This study reveals that interannual variability of the AUSM, which is unforced locally or remotely by tropical SST variability, substantially limits seasonal predictability in wintertime East Asia.