Causation of the heavy rainfall in Kyushu in early July 2020: A perspective of the depression that originated over the Tibetan Plateau

Heavy rain fell in Kyushu, Japan, in early July 2020, which caused huge life and economic losses. The present work reports that a Tibetan Plateau vortex (TPV) generated over the Tibetan Plateau transformed into a trough at the eastern edge of the Tibetan Plateau, and the trough continued to move eastward and was responsible for the heavy rainfall in Kyushu. Accordingly, the maintenance and eastward movement of the trough and the influencing mechanism of the trough on the rainfall in Kyushu are explored based on the final analysis data (FNL) from NCEP and the JRA-55 reanalysis from JMA. Diagnoses of the potential vorticity (PV) tendency equation indicate that the horizontal PV flux convergence east of the trough is the primary contributor to the eastward movement and maintenance of the trough. Furthermore, the trough is proved to have important effects on the moisture condition and the ascending motion around Kyushu. That is, the trough increases the moisture in Kyushu by intensifying the eastward moisture transportation to Kyushu; the positive vorticity and warm center, as well as the wind perturbation related to the trough, are in favor of stronger ascending motion in Kyushu. The findings in this work provide extended knowledge on the causation of rainfall in Japan, which is beneficial for further precipitation prediction.