5:15 PM - 7:15 PM
[AAS10-P07] A numerical simulation of heavy rainfall in Akita, Japan, in mid-July 2023
★Invited Papers
Keywords:Baiu-Meiyu, heavy rainfall, Sea of Japan
On July 14 to 16, 2023, an extremely heavy rainfall event occurred in Akita prefecture (AP), Japan, which is located in a coastal reigion of the Sea of Japan (SOJ). Hirata and Kawamura (2014) showed that typhoons moving westward from the northwestern Pacific to Hainan Island induce heavy rainfall on central Japan's SOJ coast during the Baiu-Meiyu season. In this case, Typhoon Talim followed a similar path. To investigate the possible factors that caused heavy rainfall to AP, a numerical simulation was performed.
The numerical model used in this study is the Weather Research and Forecasting (WRF) model version 4.5.1. Two domains with horizontal resolutions of 9 km (D1) and 3 km (D2) were two-way nested. Initial and boundary conditions were obtained from NCEP-FNL and OISST data. The simulation period was 108-hours from 00 UTC on July 12 to 12 UTC on July 16, 2023. A comparison between the simulated precipitation and the radar-raingauge analyzed precipitation of the Japan Meteorological Agency confirmed that the precipitation distribution was successfully reproduced, although the precipitation amount was somewhat underestimated (Fig.1).
During the peak phase of extreme precipitation, the east-west pressure gradient between Typhoon Talim and the North Pacific subtropical high (NPSH) strengthened. As a result, a large amount of moisture was transported northward from the eastern periphery of Talim and the western periphery of the NPSH. In addtion, the north-south pressure gradient was enhanced between an extratropical cyclone in Eurasia and the NPSH, resulting in the formation of a vertically integrated moisture flux zone exceeding 1500 kg m-1 s-1 over the SOJ, and a large amount of moisture was intruded into AP. Furthermore, a convergence zone formed with the development of a mesoscale low off the coast of AP triggered active convection.
To investigate the inflow of moist air parcels from a Lagrangian perspective, a 70-hour backward trajectory analyses was conducted from 22 UTC on July 14 using RIP version 4.7 (Fig.2). Air parcels were initially placed at altitudes of 0.5 km and 1.5 km in the precipitation area near AP. Parcels originating from remote areas such as the western periphery of NPSH and the northeastern periphery of Typhoon Talim maintained abundant moisture and intruded into the precipitation area. On the other hand, parcels originating from the continent and entering the atmospheric boundary layer rapidly decreased in height and were moistened over the SOJ after 14 July, then intruded into the precipitation area.
These results suggest that the combined effect of the typhoon and the extratropical cyclone intruded abundant moisture from remote areas, and that the development of the mesoscale low off the coast of AP promoted the formation of a low-level convergence zone, resulting in the heavy rainfall. Since the topography of the Korean Peninsula may have affected the genesis and development process of the mesoscale low, we additionally performed a topography-modified experiment. Details will be presented later on.
The numerical model used in this study is the Weather Research and Forecasting (WRF) model version 4.5.1. Two domains with horizontal resolutions of 9 km (D1) and 3 km (D2) were two-way nested. Initial and boundary conditions were obtained from NCEP-FNL and OISST data. The simulation period was 108-hours from 00 UTC on July 12 to 12 UTC on July 16, 2023. A comparison between the simulated precipitation and the radar-raingauge analyzed precipitation of the Japan Meteorological Agency confirmed that the precipitation distribution was successfully reproduced, although the precipitation amount was somewhat underestimated (Fig.1).
During the peak phase of extreme precipitation, the east-west pressure gradient between Typhoon Talim and the North Pacific subtropical high (NPSH) strengthened. As a result, a large amount of moisture was transported northward from the eastern periphery of Talim and the western periphery of the NPSH. In addtion, the north-south pressure gradient was enhanced between an extratropical cyclone in Eurasia and the NPSH, resulting in the formation of a vertically integrated moisture flux zone exceeding 1500 kg m-1 s-1 over the SOJ, and a large amount of moisture was intruded into AP. Furthermore, a convergence zone formed with the development of a mesoscale low off the coast of AP triggered active convection.
To investigate the inflow of moist air parcels from a Lagrangian perspective, a 70-hour backward trajectory analyses was conducted from 22 UTC on July 14 using RIP version 4.7 (Fig.2). Air parcels were initially placed at altitudes of 0.5 km and 1.5 km in the precipitation area near AP. Parcels originating from remote areas such as the western periphery of NPSH and the northeastern periphery of Typhoon Talim maintained abundant moisture and intruded into the precipitation area. On the other hand, parcels originating from the continent and entering the atmospheric boundary layer rapidly decreased in height and were moistened over the SOJ after 14 July, then intruded into the precipitation area.
These results suggest that the combined effect of the typhoon and the extratropical cyclone intruded abundant moisture from remote areas, and that the development of the mesoscale low off the coast of AP promoted the formation of a low-level convergence zone, resulting in the heavy rainfall. Since the topography of the Korean Peninsula may have affected the genesis and development process of the mesoscale low, we additionally performed a topography-modified experiment. Details will be presented later on.