- 著者
- Yasumitsu Maejima Takemasa Miyoshi
- 出版者
- Meteorological Society of Japan
- 雑誌
- SOLA (ISSN:13496476)
- 巻号頁・発行日
- vol.16, pp.37-42, 2020 (Released:2020-02-23)
- 参考文献数
- 19
- 被引用文献数
- 4
This study aims to investigate the tradeoff between the computational time and forecast accuracy with different data assimilation (DA) windows of four-dimensional local ensemble transform Kalman filter (4D-LETKF) for a single-case severe rainfall event. We perform a series of Observing System Simulation Experiments (OSSEs) with 1-, 3-, 5- and 15-minute DA window in a severe rainstorm event in Kobe, Japan, on July 28, 2008, following the prior OSSEs by Maejima et al. (2019). Running 1-minute DA cycles showed the best forecast accuracy but with the highest computational cost. The computational cost could be reduced by taking a long DA window, but the forecast became less accurate even though the same number of observations were used. A significant gap was found between the 3-minute window and 5-minute window. With the 1- and 3-minute windows, the forecasts captured the intense rainfall, while with the 5-minute window or longer, the rainfall intensity was drastically underestimated. This single-case study suggests that 3-minute or shorter DA window be a promising method for a severe rainfall forecast, although more case studies are necessary to draw general conclusion.
- 著者
- Yasumitsu Maejima Takuya Kawabata Hiromu Seko Takemasa Miyoshi
- 出版者
- Meteorological Society of Japan
- 雑誌
- SOLA (ISSN:13496476)
- 巻号頁・発行日
- vol.18, pp.25-32, 2022 (Released:2022-03-07)
- 参考文献数
- 35
- 被引用文献数
- 6
This study investigates a potential impact of a rich phased array weather radar (PAWR) network covering Kyushu, Japan on numerical weather prediction (NWP) of the historic heavy rainfall event which caused a catastrophic disaster in southern Kumamoto on 4 July 2020. Perfect-model, identical-twin observing system simulation experiments (OSSEs) with 17 PAWRs are performed by the local ensemble transform Kalman filter (LETKF) with a regional NWP model known as the Scalable Computing for Advanced Library and Environment-Regional Model (SCALE-RM) at 1-km resolution. The nature run is generated by running the SCALE-RM initialized by the Japan Meteorological Agency (JMA) mesoscale model (MSM) analysis at 1800 JST 3 July 2020, showing sustained heavy rainfalls in southern Kumamoto on 4 July. Every 30-second synthetic reflectivity and radial winds are generated from the nature run at every model grid point below 20-km elevation within 60-km ranges from the 17 PAWRs. Two different control runs are generated, both failing to predict the heavy rainfalls in southern Kumamoto. In both cases, assimilating the PAWR data improves the heavy rainfall prediction mainly up to 1-hour lead time. The improvement decays gradually and is lost in about 3-hour lead time likely because the large-scale Baiu front dominates.
- 著者
- James Taylor Arata Amemiya Takumi Honda Yasumitsu Maejima Takemasa Miyoshi
- 出版者
- Meteorological Society of Japan
- 雑誌
- SOLA (ISSN:13496476)
- 巻号頁・発行日
- vol.17, pp.48-56, 2021 (Released:2021-03-23)
- 参考文献数
- 28
- 被引用文献数
- 6
The predictability of the July 2020 heavy rainfall event that saw record-breaking rainfall over Western Japan in July 2020 is examined with the near real-time SCALE-LETKF numerical modelling system in a low resolution 18-km configuration setting. Ensemble-mean 5-day rainfall total forecasts showed close agreement with Japanese Meteorological Agency 1-km precipitation analyses in relation to the large-scale distribution of rainfall and to location of heaviest rainfall over Kyushu. Onset and duration of rainfall at specific sites across Kyushu were also well predicted by the forecasts. However, the precise prediction of heavy rainfall, including over the worst-hit Kumamoto and Kagoshima prefectures, was severely underestimated. Examination of the atmospheric conditions at the time of the heavy rainfall from reanalysis datasets and ensemble member forecasts showed very high humidity over central Kyushu with strong transport of moisture from the southwest to central regions. In addition, strong low-level convergence was observed to the west of Kyushu in both reanalysis and best performing member forecasts during the time of heavy rainfall, suggesting a potential contributing factor to the record-breaking rainfall.
- 著者
- James Taylor Arata Amemiya Takumi Honda Yasumitsu Maejima Takemasa Miyoshi
- 出版者
- Meteorological Society of Japan
- 雑誌
- SOLA (ISSN:13496476)
- 巻号頁・発行日
- pp.2021-008, (Released:2021-02-09)
- 被引用文献数
- 6
The predictability of the July 2020 heavy rainfall event that saw record-breaking rainfall over Western Japan in July 2020 is examined with the near real-time SCALE-LETKF numerical modelling system in a low resolution 18-km configuration setting. Ensemble-mean 5-day rainfall total forecasts showed close agreement with Japanese Meteorological Agency 1-km precipitation analyses in relation to the large-scale distribution of rainfall and to location of heaviest rainfall over Kyushu. Onset and duration of rainfall at specific sites across Kyushu were also well predicted by the forecasts. However, the precise prediction of heavy rainfall, including over the worst-hit Kumamoto and Kagoshima prefectures, was severely underestimated. Examination of the atmospheric conditions at the time of the heavy rainfall from reanalysis datasets and ensemble member forecasts showed very high humidity over central Kyushu with strong transport of moisture from the southwest to central regions. In addition, strong low-level convergence was observed to the west of Kyushu in both reanalysis and best performing member forecasts during the time of heavy rainfall, suggesting a potential contributing factor to the record-breaking rainfall.
- 著者
- Yasumitsu Maejima Keita Iga Hiroshi Niino
- 出版者
- Meteorological Society of Japan
- 雑誌
- SOLA (ISSN:13496476)
- 巻号頁・発行日
- vol.2, pp.80-83, 2006 (Released:2006-06-29)
- 参考文献数
- 10
- 被引用文献数
- 2
Upper-tropospheric vortices having a horizontal wavelength of 300-400 km were observed on water vapor images of the Japanese geostationary satellite (MTSAT-1). Grid point values predicted by the Regional Spectral Model of the Japan Meteorological Agency show that the vortices were located along a zonal belt with strong cyclonic shear and horizontal convergence. A quasi-geostrophic linear stability analysis of the basic flow having horizontal and vertical shear shows that the fastest growing mode has a horizontal wavelength, a phase speed and a growth rate that reasonably agree with those of the satellite observation. The amplitude of the fastest growing mode is confined to a region having a meridional width of 2 degrees and a vertical depth of 2 km. An energy budget analysis shows that barotropic instability is the dominant generation mechanism for the growing mode.
- 著者
- Yasumitsu Maejima Masaru Kunii Takemasa Miyoshi
- 出版者
- (公社)日本気象学会
- 雑誌
- SOLA (ISSN:13496476)
- 巻号頁・発行日
- vol.13, pp.174-180, 2017 (Released:2017-09-27)
- 参考文献数
- 37
- 被引用文献数
- 14
This study aims to investigate the impacts of 30-second-update and 100-m-resolution data assimilation (DA) on a prediction of sudden local torrential rains caused by an isolated convective system in Kobe city on 11 September 2014. We perform a Local Ensemble Transform Kalman filter (LETKF) experiment with the Japan Meteorological Agency non-hydrostatic model (JMA-NHM) at 1-km and 100-m resolution using every-30-second radar reflectivity observed by the phased array weather radar (PAWR) at Osaka University. The 1-km-mesh experiment shows that 30-second-update PAWR DA has positive impacts on the analyses and forecasts. Moreover, the 100-m-mesh experiment shows significant advantages in representing the rainfall intensity and fine structure of the convective system. The promising results suggest that 30-second-update, 100-m-mesh DA have a great potential for predicting sudden local rain events.