Developing 2-way feedback nested-domain LETKF data assimilation system and application to high-resolution typhoon analyses and forecasts

2018 Fiscal Year Annual Research Report

• Project/Area Number: 17K14396
• Research Institution: Institute of Physical and Chemical Research
• Principal Investigator: Lien GuoYuan 国立研究開発法人理化学研究所, 計算科学研究センター, 特別研究員 (50744257)
• Project Period (FY): 2017-04-01 – 2019-03-31
• Keywords: データ同化 / 台風 / 気象学

Outline of Annual Research Achievements

This project ended in the middle of the second fiscal year because the principal investigator moved outside of Japan. During the one-year and four-month period of this project, the online nested-domain LETKF has been newly implemented in the SCALE-LETKF system. Combined with the existing online nested-domain function in the SCALE-RM model, the SCALE-LETKF has become capable of running both data assimilation cycles and extended ensemble forecasts with multiple nested domains in an online framework. The design is efficient in both the computational and human-effort aspects.
The data assimilation experiments with the September 2015 Kanto-Tohoku Heavy Rainfall case were conducted using this new online nesting function. Compared with the old offline downscaling experiment in Lien et al. (2017, SOLA), the online nested-domain experiment led to improved forecast skill, due to further performing data assimilation in the inner high-resolution domain and frequent coupling of the two domains in the model forecast steps.
The principal investigator also coauthored two papers by Honda et al. (2018a,b, MWR, JGR) for typhoon data assimilation studies using this SCALE-LETKF system.
All source code developed in this project is publicly available at https://github.com/gylien/scale-letkf, with an MIT license.
Due to early termination of this project, the 2-way feedback LETKF analysis with multiple nested domains is still under development. The principal investigator may be able to continue working on it and concluding the work in his next position.

Research Products

• [Presentation] Issues regarding maintaining ensemble spreads, balance, and high-resolution information in rapid-update-cycle radar data assimilation with the LETKF (2018)
  • Author(s): Guo-Yuan Lien, and Takemasa Miyoshi
  • Organizer: JpGU Meeting 2018, Chiba
  • Int'l Joint Research / Invited
• [Presentation] The computational aspect of the SCLAE-LETKF data assimilation system for rapid-update-cycle, high-resolution radar data assimilation (2018)
  • Author(s): Guo-Yuan Lien, Seiya Nishizawa, Ryuji Yoshida, Hisashi Yashiro, Tatiana Martsinkevich, Takumi Honda, Shigenori Otsuka, Takemasa Miyoshi, Hirofumi Tomita, and Yutaka Ishikawa
  • Organizer: JpGU Meeting 2018, Chiba
  • Int'l Joint Research / Invited
• [Remarks] SCALE-LETKF code repository on GitHub
  • URL: https://github.com/gylien/scale-letkf/