Introduction of water vapor balance method into variational assimilation scheme to solve the spin-down problem.

2022 Fiscal Year Final Research Report

• Project/Area Number: 19K23468
• Research Category: Grant-in-Aid for Research Activity Start-up
• Allocation Type: Multi-year Fund
• Review Section: 0204:Astronomy, earth and planetary science, and related fields
• Research Institution: Japan, Meteorological Research Institute
• Principal Investigator: Sawada Ken 気象庁気象研究所, 気象観測研究部, 主任研究官 (10847205)
• Project Period (FY): 2019-08-30 – 2023-03-31
• Keywords: 変分法データ同化 / 制約付き最適化 / 降水再現性

Outline of Final Research Achievements

This study attempts to solve the problem of over- (spin-down) or under- (spin-up) precipitation representation in the early stages of forecast, which is sometimes caused by conventional data assimilation systems, by introducing a mechanism to maintain water vapor balance among model variables, thereby producing high-quality initial data that are more consistent with observed data and forecast models. Compared to the conventional method, the new method, while approaching the observed data by decreasing the amount of water vapor and increasing the temperature on average in the lower and middle atmosphere, analyzes localized higher equivalent potential temperature regions in areas that may trigger precipitation events, and promotes smooth generation of convection that forms precipitation, thus improving the reproducibility of precipitation in the early forecast period.

Free Research Field

メソデータ同化

Academic Significance and Societal Importance of the Research Achievements

この研究で開発した手法は上下限がある相対湿度を変分法同化システムで同化する際に、簡便な制約条件付きの最適化問題の解法を応用したものであり、複雑な多自由度系での同化システムにおいて比較的簡便な方法でバランスの取れた品質の良い初期値が得られることが確かめられたことは学術的に有意義である。また、この手法により深刻な豪雨事例の予測が改善されることは防災・減災に直接的に関連するため、大きな社会的意義を持っている。