文献一覧: Takemasa Miyoshi (著者)

7 0 0 0 OA Multi-Year Analysis Using the NICAM-LETKF Data Assimilation System

著者: Koji Terasaki Shunji Kotsuki Takemasa Miyoshi
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: vol.15, pp.41-46, 2019 (Released:2019-02-28)
参考文献数: 29
被引用文献数: 7

This study investigates the long-term stability of the global atmospheric data assimilation system, incorporating the Local Ensemble Transform Kalman Filter (LETKF) with the Nonhydrostatic ICosahedral Atmospheric Model (NICAM). The NICAM-LETKF system assimilates conventional observations, advanced microwave sounding unit–A (AMSU-A) radiances, and global satellite mapping of precipitation (GSMaP) data. The long-term stability of the data assimilation system can be investigated only by running an expensive long-term experiment. This study successfully performed a data assimilation experiment with more than 2 years of data, using the relaxation to prior spread (RTPS) method for covariance inflation. Analysis fields indicate a stable physical performance compared with the ERA-interim data for the entire experimental period.

2019-03-07 08:35:42
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5 0 0 0 OA Impact of the Window Length of Four-Dimensional Local Ensemble Transform Kalman Filter: A Case of Convective Rain Event

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.

2020-03-10 11:08:42
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4 0 0 0 OA A 1024-Member NICAM-LETKF Experiment for the July 2020 Heavy Rainfall Event

著者: Koji Terasaki Takemasa Miyoshi
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: vol.18A, no.Special_Edition, pp.8-14, 2022 (Released:2022-04-02)
参考文献数: 22
被引用文献数: 5

This study investigated the predictability and causes of the heavy rainfall event that brought severe disasters in Kyushu in July 2020 with a global numerical weather prediction system composed of the NICAM (non-hydrostatic icosahedral atmospheric model) and the LETKF (local ensemble transform Kalman filter). We performed ensemble data assimilation and forecast experiments using the NICAM-LETKF system with 1,024 members and 56-km horizontal resolution on the supercomputer Fugaku. The results showed that 1,024-member ensemble forecasts captured the probability of heavy rainfall in Kyushu about five days before it happens, although a 10-day-lead forecast is difficult. Ensemble-based lag-correlation analyses with the 1024-member ensemble showed very small sampling errors in the correlation patterns and showed that the moist air inflow in the lower troposphere associated with a low-pressure anomaly over the Baiu front was related to this heavy rainfall in Kyushu.

2022-04-09 22:27:03
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4 0 0 0 OA A 1024-Member NICAM-LETKF Experiment for the July 2020 Heavy Rainfall Event

著者: Koji Terasaki Takemasa Miyoshi
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: pp.18A-002, (Released:2022-02-08)
被引用文献数: 5

2022-02-25 21:42:08
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4 0 0 0 OA Improving the Observation Operator for the Phased Array Weather Radar in the SCALE-LETKF System

著者: Arata Amemiya Takumi Honda Takemasa Miyoshi
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: vol.16, pp.6-11, 2020 (Released:2020-01-28)
参考文献数: 18
被引用文献数: 7

The observation operator for the Phased Array Weather Radar in the SCALE-LETKF data assimilation system is revisited, and the impact of its improvement on the analyses and forecasts is examined. The observation operator provides a functional relationship between equivalent radar reflectivity factor (Ze) and hydrometeor mass density (W) of each precipitation particle category. The W–Ze relationship is obtained by a radar simulator. This study performs a radiation code calculation with the parameters regarding particle size distribution of graupel consistent with the cloud microphysics scheme in the SCALE model. The newly obtained observation operator provides much stronger sensitivity of graupel mixing ratio to observed Ze compared to the operator originally used in the model. To examine the impact on the SCALE-LETKF analyses and forecasts, an experiment on a 13 July 2013 heavy rain case is performed with the new observation operator and is compared with the previous study. The forecast initiated by the analysis using the new operator shows much more realistic evolution of Ze in the middle troposphere, where a large amount of graupel is located. The overestimation of forecast Ze is significantly alleviated by the new observational operator. The 30-minute forecast of surface precipitation rate is also improved.

2020-03-03 13:31:34
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4 0 0 0 OA Improving a Precipitation Forecast by Assimilating All-Sky Himawari-8 Satellite Radiances: A Case of Typhoon Malakas (2016)

著者: Takumi Honda Shohei Takino Takemasa Miyoshi
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: vol.15, pp.7-11, 2019 (Released:2019-01-19)
参考文献数: 23
被引用文献数: 7

Tropical cyclones (TCs) and associated heavy precipitation have large impacts in Japan. This study aims to find how data assimilation (DA) of every-10-minute all-sky Himawari-8 radiances could improve the quantitative precipitation forecast (QPF) for TC cases. As the first step, this study performs a single case study of Typhoon Malakas (2016) using a regional atmospheric model from the Scalable Computing for Advanced Library and Environment (SCALE) coupled with the local ensemble Kalman filter (LETKF). The results show that the all-sky Himawari-8 radiance DA at 6-km resolution improves the representation of Malakas and may provide more accurate deterministic and probabilistic precipitation forecasts if the horizontal localization scale is chosen appropriately.

2019-01-21 19:28:15
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4 0 0 0 OA The Impact of Additional Radiosonde Observations on the Analysis of Disturbances in the South China Sea during VPREX2010

著者: Miki Hattori Jun Matsumoto Shin-Ya Ogino Takeshi Enomoto 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.12, pp.75-79, 2016 (Released:2016-03-08)
参考文献数: 17
被引用文献数: 6

The impact of additional radiosonde observations during the Vietnam-Philippines Rainfall Experiment 2010 (VPREX2010) was investigated by performing observing system experiments using the local ensemble transform Kalman filter (LETKF) and the atmospheric general circulation model for the Earth Simulator (AFES). During the experimental period from 15 September to 15 October, 2010, a westward-propagating disturbance was developed in the South China Sea and caused heavy rainfall on the east coast of Vietnam and Hainan Island. By assimilating the additional radiosondes, significant increases in wind speed, temperature and specific humidity were detected in the lower troposphere around the disturbance. In addition, the analysis ensemble spread for meridional wind decreased by 5-25% across the Indochina Peninsula, Philippines Sea and western Pacific to the south of Japan. Moreover, winds became stronger around the disturbance due to the additional observations, and the ensemble spread for wind speed became larger. The results show that the disturbance in an early stage of development was not well detected in the South China Sea without the use of additional radiosonde observations. Therefore, it is suggested that continuous and intensive radiosonde observations in Vietnam and the Philippines are essential for the improvement of the objective analysis of such disturbances.

2016-03-14 11:00:59
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3 0 0 0 OA Observing System Simulation Experiments of a Rich Phased Array Weather Radar Network Covering Kyushu for the July 2020 Heavy Rainfall Event

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.

2022-03-10 23:17:39
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3 0 0 0 OA Predictability of the July 2018 Heavy Rain Event in Japan Associated with Typhoon Prapiroon and Southern Convective Disturbances

著者: Takumi Honda Takemasa Miyoshi
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: pp.2021-018, (Released:2021-04-23)
被引用文献数: 1

In July 2018, record-breaking heavy precipitation caused catastrophic disasters in west Japan. This study investigated the predictability of this precipitation event using a regional ensemble data assimilation system. A series of daily ensemble forecast experiments showed that the forecast ensemble spread during the heavy precipitation event increased in the forecasts initialized on July 1 and July 3. The first peak of the forecast ensemble spread was associated with the uncertain track forecast of Typhoon Prapiroon. Namely, about a half of the ensemble members predicted eastward recurvature of the typhoon, whereas the other members predicted that the typhoon stayed near China. The later peak was associated with the southern convective disturbances near the Ryukyu Islands. Composite analysis and ensemble-based correlations showed that more active convective activities corresponded to a stronger cyclonic circulation and pushed the main precipitation band northward. The results implied that Prapiroon and the southern convective disturbances played important roles in the July 2018 heavy rain event and largely contributed to its predictability.

2021-04-29 22:37:46
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3 0 0 0 OA Multi-year analysis using the NICAM-LETKF data assimilation system

著者: Koji Terasaki Shunji Kotsuki Takemasa Miyoshi
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: pp.2019-009, (Released:2019-01-31)
被引用文献数: 7

2019-03-22 09:37:12
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2 0 0 0 OA Predictability of the July 2018 Heavy Rain Event in Japan Associated with Typhoon Prapiroon and Southern Convective Disturbances

著者: Takumi Honda Takemasa Miyoshi
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: vol.17, pp.113-119, 2021 (Released:2021-06-01)
参考文献数: 38
被引用文献数: 1

In July 2018, record-breaking heavy precipitation caused catastrophic disasters in west Japan. This study investigated the predictability of this precipitation event using a regional ensemble data assimilation system. A series of daily ensemble forecast experiments showed that the forecast ensemble spread during the heavy precipitation event increased in the forecasts initialized on 1 July and 3 July. The first peak of the forecast ensemble spread was associated with the uncertain track forecast of Typhoon Prapiroon. Namely, about a half of the ensemble members predicted eastward recurvature of the typhoon, whereas the other members predicted that the typhoon stayed near China. The later peak was associated with the southern convective disturbances near the Ryukyu Islands. Composite analysis and ensemble-based correlations showed that more active convective activities corresponded to a stronger cyclonic circulation and pushed the main precipitation band northward. The results implied that Prapiroon and the southern convective disturbances played important roles in the July 2018 heavy rain event and largely contributed to its predictability.

2021-06-04 19:53:37
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2 0 0 0 OA Predictability of the July 2020 Heavy Rainfall with the SCALE-LETKF

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.

2021-03-29 18:56:14
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2 0 0 0 OA Predictability of the July 2020 Heavy Rainfall with the SCALE-LETKF

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

2021-02-18 21:28:04
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2 0 0 0 OA Improving the observation operator for the Phased Array Weather Radar in the SCALE-LETKF system

著者: Arata Amemiya Takumi Honda Takemasa Miyoshi
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: pp.2020-002, (Released:2019-12-28)
被引用文献数: 7

The observation operator for the Phased Array Weather Radar in the SCALE-LETKF data assimilation system is revisited, and the impact of its improvement on the analyses and forecasts is examined. The observation operator provides a functional relationship between equivalent radar reflectivity factor (Ze) and hydrometeor mass density (W) of each precipitation particle category. The W − Ze relationship is obtained by a radar simulator. This study performs a radiation code calculation with the parameters regarding particle size distribution of graupel consistent with the cloud microphysics scheme in the SCALE model. The newly obtained observation operator provides much stronger sensitivity of graupel mixing ratio to observed Ze compared to the operator originally used in the model. To examine the impact on the SCALE-LETKF analyses and forecasts, an experiment on a 13 July 2013 heavy rain case is performed with the new observation operator and is compared with the previous study. The forecast initiated by the analysis using the new operator shows much more realistic evolution of Ze in the middle troposphere, where a large amount of graupel is located. The overestimation of forecast Ze is significantly alleviated by the new observational operator. The 30-minute forecast of surface precipitation rate is also improved.

2020-01-06 15:41:18
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2 0 0 0 OA Using Observations near the Poles in the AFES-LETKF Data Assimilation System

著者: Akira Yamazaki Takeshi Enomoto Takemasa Miyoshi Akira Kuwano-Yoshida Nobumasa Komori
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.41-46, 2017 (Released:2017-03-25)
参考文献数: 26
被引用文献数: 6

The observation operators in the local ensemble transform Kalman filter (LETKF) were improved to enable use of observations in the vicinity of the poles in the data assimilation system composed of the atmospheric general circulation model for the Earth Simulator (AFES) and the LETKF. The improved observation operators allow to assimilate the observations located south (north) of southernmost (northernmost) Gaussian grid latitudes. An algorithm for searching the nearest observations from an analyzed grid for error covariance localization was also modified to efficiently assimilate observations near the poles.The new algorithms were incorporated into the LETKF, and the impacts of routine radiosonde observations at the South Pole during the periods of July 2012 and January 2013 were assessed. The radiosonde observations suppressed an artificial expansion of the analysis ensemble spread which occasionally caused numerical instability in the upper troposphere and the lower stratosphere over the Antarctic regions. The analysis was also improved in the Antarctic regions.

2017-03-27 22:50:09
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1 0 0 0 OA Predictability of Record-Breaking Rainfall in Japan in July 2018: Ensemble Forecast Experiments with the Near-Real-Time Global Atmospheric Data Assimilation System NEXRA

著者: Shunji Kotsuki Koji Terasaki Kaya Kanemaru Masaki Satoh Takuji Kubota Takemasa Miyoshi
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: vol.15A, pp.1-7, 2019 (Released:2019-01-26)
参考文献数: 25
被引用文献数: 26

This paper is the first publication presenting the predictability of the record-breaking rainfall in Japan in July 2018 (RJJ18), the severest flood-related disaster since 1982. Of the three successive precipitation stages in RJJ18, this study investigates synoptic-scale predictability of the third-stage precipitation using the near-real-time global atmospheric data assimilation system named NEXRA. With NEXRA, intense precipitation in western Japan on July 6 was well predicted 3 days in advance. Comparing forecasts at different initial times revealed that the predictability of the intense rains was tied to the generation of a low-pressure system in the middle of the frontal system over the Sea of Japan. Observation impact estimates showed that radiosondes in Kyusyu and off the east coast of China significantly reduced the forecast errors. Since the forecast errors grew more rapidly during RJJ18, data assimilation played a crucial role in improving the predictability.

2019-02-06 10:04:25
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1 0 0 0 OA 30-second-Update 100-m-Mesh Data Assimilation Experiments: A Sudden Local Rain Case in Kobe on 11 September 2014

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.

2017-09-30 21:42:37
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1 0 0 0 OA A Quality Control Algorithm for the Osaka Phased Array Weather Radar

著者: Juan J. Ruiz Takemasa Miyoshi Shinsuke Satoh Tomoo Ushio
出版者: (公社)日本気象学会
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: vol.11, pp.48-52, 2015 (Released:2015-04-28)
参考文献数: 20
被引用文献数: 3 8

This study develops and tests a quality control (QC) algorithm for reflectivity from the single polarization phased array weather radar (PAWR) in Osaka, with particular focus on clutter detection, in preparation for radar data assimilation into a high resolution numerical model. The QC algorithm employs a Bayesian classification that combines the information from different parameters based on reflectivity and radial velocity. To take advantage of PAWR's unique high temporal and vertical resolutions, a new parameter based on the temporal variability of reflectivity is included. In addition, clutter probability estimations from previous volume scans are also included. The newly developed QC algorithm performs properly in two events characterized by heavy convective precipitation and stratiform precipitation.

2015-04-29 07:17:35
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1 0 0 0 OA Local Ensemble Transform Kalman Filter Experiments with the Nonhydrostatic Icosahedral Atmospheric Model NICAM

著者: Koji Terasaki Masahiro Sawada 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.11, pp.23-26, 2015 (Released:2015-02-26)
参考文献数: 14
被引用文献数: 4 31

The Local Ensemble Transform Kalman Filter (LETKF) is implemented with the Non-hydrostatic Icosahedral Atmospheric Model (NICAM) to assimilate the real-world observation data. First, the NICAM-LETKF system was developed using grid conversions between the NICAM's icosahedral grid and LETKF's uniform longitude-latitude grid to take advantage of the existing codes of Miyoshi. The grid conversions require additional computations and may cause additional interpolation error. Therefore, the LETKF code is modified, so that the LETKF reads and writes the NICAM's icosahedral grid data directly. We call this new version ICO-LETKF. In this study, the two systems are tested and compared using real conventional observations. The results show that the ICO-LETKF successfully accelerates the computations and improves the analyses.

2015-03-02 11:44:41
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