Review of the Researches on Changma and Future Observational Study(KORMEX)

Changma is the most important supplier of water resource in Korea. However, its interannual variation may cause either floods or droughts time to time in many regions of Korea. A number of studies on Changma have been done in many subjects, such as the on-set and retreat timing, duration of Changma, and its interannual variation, which may cause either wet or dry Changma, and the heavy rainfall phenomena associated with the Changma front. Also, the subjects covered the dynamical situation of Changma compared to that of Baiu and Mei-yu as a part of East Asian monsoon circulation, and relation between Changma and tropical Pacific sea-surface temperature (SST) through atmosphere-ocean interaction, etc. A numerical study is presented in this paper to check the teleconnection between the behavior of Changma front and the variation of tropical Pacific SST. The difference in the lower level streamfunction between theEl Nio event of 1987 and the La Nia event of 1988 illustrates that the cross-equatorial and westerly wind crossing over the India and Indo-China peninsula were weak during the summer of 1988 compared to 1987. This may cause the drought of 1988 in East Asia by reducing moisture supply from the Indian Ocean and the south-western Pacific. Even though there are numerous research activities on the Changma, our knowledge on the Changma is still limited to explain the mechanism of interannual variation of Changma and to provide a proper prediction of precipitation due to both geographical location of Korea and its complex topography. In collaboration with the international field observational projects, such as GAME and SCSMEX, the Korea Monsoon Experiment (KORMEX) has been planned by several scientists in Korea to improve our knowledge on the atmospheric circulation and water cycle related to the East Asian monsoon and to provide necessary information to predict both short- and long-term variation of rainfall during the Changma season.

Associations with the Interannual Variations of Onset and Withdrawal of the Changma

The associations of onset and withdrawal of the rainy season in South Korea (called Changma) have been examined. Composite studies showed that there are significant differences in circulations between extremely early and late onset (or withdrawals) not only over East Asia, but also over remote areas. The in situ significant differences include the upper-level jet over East Asia and the subtropical anticyclone over the western North Pacific at lower levels. The significant remote associations include the Indian monsoon and ENSO. The Indian summer monsoon is related to both onset and withdrawal of the Changma, while ENSO has a significant relation only to onset, but not to withdrawal. Key words Changma - Onset - Withdrawal - Interannual variation - Association This study was supported by the National Key Programme for Developing Basic Sciences (G1998040900, Part I), Brain Pool Program (Grant No. 991-5-8) funded by Korea Science and Engineering Foundation, and the Natural Hazard Prevention Research Project, one of the Critical Technology-21 Programs, funded by the Ministry of Science and Technology of Korea.