Abstract
This study investigated the effect of large cities on wind systems over Kanto plain when heavy rainfall occurred in Tokyo, by using a meso-scale atmospheric model. Two types of land-use distribution, the actual land-use and virtual land-use where cities were converted to the forests, were prepared to simulate an actual heavy rainfall event. Also, a generalized heavy rainfall event was simulated by using the upper air observation of Tateno. The results indicated that the effect of large cities on wind systems over Kanto plain was trivial, however, the convergence area of wind was enhanced around the urban area. These led to new finding that cities changed wind around the urban area and developed convergence of wind. The generalized simulation did not reproduce the easterly wind from Kashima-nada which is important for the outbreak of the heavy rainfall event in Tokyo. The reason is explained by the fact that the easterly wind from Kashima-nada was originated from the pressure gradient around the Pacific Ocean. Since this easterly wind did not appear in the simulation without data assimilation, we come to the conclusion that this easterly wind developed with a process other than the sea breeze circulation or the heat island circulation.
