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[AAS05-P05] Estimation of impact of typhoon activity on accumulated rainfall in Japan area by using a large ensemble simulation
Keywords:typhoon activity, rainfall related to typhoon, ensemble simulation
Typhoon is accompanied with heavy rainfall and severe wind, which damages coastal areas including Japan. According to previous studies using satellite obsarvation, rainfall related to typhoon tends to become heavier as typhoon intensity increases. However, the impact of the seasonal typhoon activity on accumulated rainfall is not clear. This might be due to limitation in the number of samples in the presence of interannual variability (e.g., El Nino), as well as in the reliability of the observed TC intensity.
In our previous study using a large ensemble simulation with Nonhydrostatic ICosahedral Atmospheric Model (NICAM), intense cyclogenesis frequency varied among the ensemble members. The amplitude of the variation is comparable to that of the interannual variability. Given this variation, we evaluate the impact of seasonal typhoon activity on accumulated rainfall.
In order to evaluate the impact of seasonal typhoon activity on accumulated rainfall, we used output of a 64-member ensemble simulation with a global 14-kilometer mesh NICAM. The NICAM was run for June–October (5 months) between 2009 and 2019. In this study, we paid attention to Japan area. The Japan area was defined as the area within a 300-kilometer radius of each meteorological office of Japan Meteorological Agency. Typhoon activity was quantified by using accumulated cyclone energy (ACE). We decomposed 5-month accumulated rainfall on the Japan area into direct typhoon-related rainfall, indirect typhoon-related rainfall and typhoon-free rainfall. Direct typhoon-related rainfall was defined by rainfall within a 500-kilometer radius of the center of the typhoon. Indirect typhoon-related rainfall was defined as rainfall outside of 500-kilometer from the center of the typhoon when the typhoon was within the Japan area. Typhoon-free rainfall was defined as rainfall when typhoon was not within Japan area.
The result showed that direct/indirect typhoon-related rainfall positively correlated with ACE (R=0.89/R=0.64). Typhoon-free rainfall was negatively correlated with ACE (R=-0.45). The inverse relationship is possibly due to a decrease in typhoon days. As for spatial distribution, in the typhoon active members, an increase in the direct typhoon-related rainfall was seen over southwestern Japan compared with those in the typhoon inactive members, and an increase in the indirect typhoon-related rainfall was seen in the Pacific coastal region of Honshu, Shikoku and Kyushu. The differences between typhoon active and inactive members also appear in a cyclonic circulation to the southwest of Japan and an anticyclonic circulation to the southeast of Japan. These anomalies suggest difference in water vapor transport to the Japan area, leading to the change in the accumulated rainfall over the Japan area. These results indicate that accumulated rainfall in Japan area possibly increases as seasonal typhoon activity is higher.
In our previous study using a large ensemble simulation with Nonhydrostatic ICosahedral Atmospheric Model (NICAM), intense cyclogenesis frequency varied among the ensemble members. The amplitude of the variation is comparable to that of the interannual variability. Given this variation, we evaluate the impact of seasonal typhoon activity on accumulated rainfall.
In order to evaluate the impact of seasonal typhoon activity on accumulated rainfall, we used output of a 64-member ensemble simulation with a global 14-kilometer mesh NICAM. The NICAM was run for June–October (5 months) between 2009 and 2019. In this study, we paid attention to Japan area. The Japan area was defined as the area within a 300-kilometer radius of each meteorological office of Japan Meteorological Agency. Typhoon activity was quantified by using accumulated cyclone energy (ACE). We decomposed 5-month accumulated rainfall on the Japan area into direct typhoon-related rainfall, indirect typhoon-related rainfall and typhoon-free rainfall. Direct typhoon-related rainfall was defined by rainfall within a 500-kilometer radius of the center of the typhoon. Indirect typhoon-related rainfall was defined as rainfall outside of 500-kilometer from the center of the typhoon when the typhoon was within the Japan area. Typhoon-free rainfall was defined as rainfall when typhoon was not within Japan area.
The result showed that direct/indirect typhoon-related rainfall positively correlated with ACE (R=0.89/R=0.64). Typhoon-free rainfall was negatively correlated with ACE (R=-0.45). The inverse relationship is possibly due to a decrease in typhoon days. As for spatial distribution, in the typhoon active members, an increase in the direct typhoon-related rainfall was seen over southwestern Japan compared with those in the typhoon inactive members, and an increase in the indirect typhoon-related rainfall was seen in the Pacific coastal region of Honshu, Shikoku and Kyushu. The differences between typhoon active and inactive members also appear in a cyclonic circulation to the southwest of Japan and an anticyclonic circulation to the southeast of Japan. These anomalies suggest difference in water vapor transport to the Japan area, leading to the change in the accumulated rainfall over the Japan area. These results indicate that accumulated rainfall in Japan area possibly increases as seasonal typhoon activity is higher.