A NUMERICAL SIMULATION OF THE MESO-LOW FORMATION ON MEI-YU FRONT
Zhou Xiaoping Zhao Sixiong Zhang Baoyan (Institute of Atmospheric Physics, Academia Sinica)
The Mei-yu (called as Bai-U in Japan) is one of the important phenomena in middle and lower parts of the Changjiang (Yangtze) Valley in early summer. The Mei-yu front extending in west-east direction is nearly over the Changjiang Valley during this period A number of mesoseale cyclones frequently develop along the Meiyu front and sometimes bring very heavy rainfall. However, this kind of weather system is difficult to understand and to forecast, so further study is necessary to clarify the process of the mesoseale low along Mei-yu front. With this purpose, we have made some numerical experiments by using the fine mesh model to simulate the formation on mesoseale low in Mai-yu front. It is suggested that the development process of mesoseale low could be at least divided into two stages, that is, genesis stage and development stage. It is found that the wind-pressure fields give more influence than other meteorological elements such as moisture on the formation of the mesoseale low in the first stage especially.We have estimated the total amount of the latent heat released from 24 hr and 6 hr observation precipitation amount respectively. Only the latter was related with the mesoseale low formation. Also, we tested the sensitivity of the mesoseale model to the vertical distribution of convective heating and noticed that the vertical distribution of latent heat is important to determining the feedback to the large scale. We further noticed that the meso-low is sensitive only to the mesoseale moisture field in the second stage.