13:50 〜 14:15
[AAS03-01] 韓国、日本における2022年8月の記録的豪雨の発生に対するチベット高原の役割
★招待講演
キーワード：洪水、チベット高原、2022年8月、亜熱帯ジェット、熱帯対流圏界層
Record breaking precipitation occurred along a stationary front over Korea and Japan from 8 August 2022. A developed trough is also formed over Siberia north of the Sea of Japan, during this period. However, what is more closely associated with a rain band containing mesoscale convective systems is a low-level jet formed in the east of Tibetan Plateau (Fig. 1).
It is found that upper tropospheric subtropical jet over the Eurasian continent intensifies and shifts northward form 5 August. As a result, the interaction between the westerly jet and topography that is observed over the western slope of Tibetan Plateau, shifts to the eastern side of the Plateau. This induces upwelling over the leeside foothill region and decreases surface pressure in the east. Accordingly, meridional winds near the surface along the Tibetan Plateau converges over the low-surface pressure region. This induces very deep convective activity on the foothill, which moves eastward over Korea and Japan strengthened by the water vapor source over the Yellow Sea and Sea of Japan.
Further analysis suggests that very deep tropical convective activity penetrating near the TTL (Tropical Tropopause Layer) over the Indian Ocean-South China sea sector near the coastal regions may be responsible for the change in the subtropical jet by producing a large-scale meridional circulation that extends beyond the Tibetan Plateau.
It is also shown that this northward shift of tropical convection occurred in association with the BSISO (Boreal Summer Intraseasonal Oscillation) phenomenon. Such intraseasonal phenomenon alone, however, would not produce a record-breaking phenomenon. In fact, August 2022 is characterized by several extreme weather events such as intense drought in China and flooding in Pakistan. The strongest local Hadley circulation around the Tibetan Plateau since 1979 was also observed in August 2022, which may have contributed to the extreme precipitation event over Korea and Japan.
It is found that upper tropospheric subtropical jet over the Eurasian continent intensifies and shifts northward form 5 August. As a result, the interaction between the westerly jet and topography that is observed over the western slope of Tibetan Plateau, shifts to the eastern side of the Plateau. This induces upwelling over the leeside foothill region and decreases surface pressure in the east. Accordingly, meridional winds near the surface along the Tibetan Plateau converges over the low-surface pressure region. This induces very deep convective activity on the foothill, which moves eastward over Korea and Japan strengthened by the water vapor source over the Yellow Sea and Sea of Japan.
Further analysis suggests that very deep tropical convective activity penetrating near the TTL (Tropical Tropopause Layer) over the Indian Ocean-South China sea sector near the coastal regions may be responsible for the change in the subtropical jet by producing a large-scale meridional circulation that extends beyond the Tibetan Plateau.
It is also shown that this northward shift of tropical convection occurred in association with the BSISO (Boreal Summer Intraseasonal Oscillation) phenomenon. Such intraseasonal phenomenon alone, however, would not produce a record-breaking phenomenon. In fact, August 2022 is characterized by several extreme weather events such as intense drought in China and flooding in Pakistan. The strongest local Hadley circulation around the Tibetan Plateau since 1979 was also observed in August 2022, which may have contributed to the extreme precipitation event over Korea and Japan.