[A-AS04] Extreme Events and Mesoscale Weather: Observations and Modeling

[AAS04-P03] Intensive Radiosonde Observations of Environmental Conditions on the Development of a Mesoscale Convective System in the Baiu Frontal Zone

*万田 敦昌¹、立花 義裕¹、中村 啓彦²、滝川 哲太郎³、仁科 文子²、茂木 耕作⁴、ジャオ ニン⁴、飯塚 聡⁵ (1.三重大学、2.鹿児島大学、3.長崎大学、4.海洋研究開発機構、5.防災科学技術研究所)

キーワード：豪雨、対流、水蒸気輸送、エントレインメント

Mesoscale convective systems (MCSs) that occur in the Baiu frontal zone (BFZ) can cause devastating flash floods during early summer in Japan; however, the environmental conditions necessary for their development require further investigation. High-frequency atmospheric soundings, conducted using multiple marine vessels in the East China Sea on 19 June 2022, captured the detailed environmental conditions pertaining to the development of an MCS within the BFZ. The MCS, which developed rapidly without any remarkable preceding synoptic or mesoscale disturbance in the mid- and upper troposphere, caused intense precipitation exceeding 100 mm/3 h. The MCS persisted for approximately 6 h, and it intensified when a moist southerly airflow near the sea surface moved toward a weak surface front and overlapped a southwesterly free-tropospheric moist airflow. These moist airflows were essential ingredients that determined the location, timing of initiation, and duration of the observed MCS. The moist airflow near the sea surface toward the weak surface front determined the area of nearly saturated conditional instability within the lower troposphere. The moist airflow in the free troposphere parallel to the front established the nearly saturated condition above the boundary layer, a feature inherent to the BFZ, and it played an important role in MCS development by minimizing the reduction in the buoyancy of air parcels. The results of this study suggest that nearly saturated free-tropospheric airflow plays an important role in the development of not only layer-lifting MCSs but also surface-based MCSs within the BFZ.