Elucidation of the mechanism of "warm rain" in urban atmosphere and optimization of numerical forecast models

2023 Fiscal Year Final Research Report

• Project/Area Number: 21H01163
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 17020:Atmospheric and hydrospheric sciences-related
• Research Institution: Nihon University (2022-2023); National Research Institute for Earth Science and Disaster Prevention (2021)
• Principal Investigator: MISUMI Ryohei 日本大学, 文理学部, 教授 (20414401)
• Co-Investigator(Kenkyū-buntansha): 橋本 明弘 気象庁気象研究所, 気象予報研究部, 室長 (20462525)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 降水システム / 雲物理 / 暖かい雨 / 雲粒

Outline of Final Research Achievements

It has been believed that precipitation through the warm rain process is less likely to occur in urban areas due to the abundance of aerosol particles. However, warm rain is often observed in Tokyo. The warm rain process in Tokyo was investigated through observations using Ka-band radar, a cloud droplet spectrometer, and numerical simulations. The results showed that large droplets formed through condensation process, and the droplets grew through collision coalescence with other particles. This process could occur when the cloud droplet number concentration was less than 1200 cm-3. An introduction of observation-based cloud droplet size distributions into the JMA nonhydrostatic model had a significant impact on the forecasting of warm stratiform rainfall through the increase of auto-conversion rate from cloud water to rain.

Free Research Field

気象学

Academic Significance and Societal Importance of the Research Achievements

東京上空におけるエアロゾル、雲凝結核、雲粒の数濃度のデータが学術論文を通して公表され、気象モデルの基礎となるデータが提供された。また、東京で起こる「暖かい雨」のメカニズムが明らかになり、この成果を通して「雨滴がどのようにして形成されるのか」について概念モデルが構築された。さらに雲粒粒径分布の仮定が、暖かい層状性降水の予報に影響を及ぼすことが分かり、数値予報モデルの高度化の方向性が示された。