HUANG Ronghui1, CHEN Wen1 and ZHANG Renhe2
1. LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100080, China
2. Chinese Academy of Meteorological Sciences, Beijing 100081, China
Recent advances in the studies on the interaction between Asian monsoon and ENSO cycle are reviewed, especially the studies on the interaction between the East Asian winter and summer monsoons and ENSO cycle made by Chinese scholars are emphasized in this paper. Through the recent studies, Chinese scholars have proposed the East Asian summer monsoon system and the East Asian climate system affecting the interannual variability of this monsoon system and have revealed the responding features and processes of the East Asian winter and summer monsoon circulation anomalies and summer rainfall anomalies to ENSO cycle during its different stages. In recent years, the studies on the dynamical effect of East Asian monsoon on the thermal variability of the West Pacific warm pool and ENSO cycle have been greatly advanced. These studies not only demonstrated further that ENSO cycle originates from the tropical western Pacific but also pointed out that this dynamical effect may be through the impact on the atmospheric circulation and zonal wind anomalies over the tropical western Pacific, which can excite the oceanic Kelvin wave and Rossby waves in the equatorial Pacific. And it is also pointed in this paper that the warming phenomenon in the tropical central and eastern Pacific from the late 1970s of the 20th century may be one of the causes of the interdecadal variation of summer monsoon rainfall in East Asia. Besides, the scientific problems in the interaction between Asian monsoon and ENSO cycle, which should be studied further in the near future, are also pointed out in this paper.
Key words: Asian summer monsoon, Asian winter monsoon, ENSO cycle interacation
Asian monsoon and ENSO cycle are two important subsystems of the global climate system. As well known, monsoon is a kind of climatic phenomenon, in which dominant wind system changes with seasons. Many studies showed that Asian monsoon plays an important role in the global and regional climate variabilities (Yasunari, 1990; Ding, 1994; Huang and Fu, 1996b; Chang et al. 2000). Asian monsoon can bring a large amount of water vapor from the Pacific Ocean and the Indian Ocean to the mainland, as a consequence, a large amount of rainfall can be formed in the monsoon regions (Zhu, 1934; Tu and Huang, 1944; Huang et al., 1998; Huang et al., 1998). Because of the close relationship between monsoon and rainfall, monsoon variability influences economy, industry, agriculture and daily life of people in the monsoon regions, especially droughts and floods caused by monsoon may bring heavy economic losses in these regions. Every year of the 1980s and the 1990s, the climatic disasters caused the economic losses of about 200 billion RMB yuan, approximately 3%-6% of GDP of China, especially the extremely severe flood occurring in the summer of 1998 had caused the economic losses of about 260 RMB yuan in the Yangtze River Valley (Huang et al., 1998; Huang and Zhou, 2002).
Asian monsoon is a huge monsoon system including East and South Asian monsoon subsystems. Li and Yanai's (1996) investigation showed that the Asian summer and winter monsoons exhibit the characteristics of cycle in both the wind fields and temperature fields. And Chen et al. (2002) also pointed out that the East Asian summer and winter monsoons are a phenomenon of annual cycle in both the wind fields and rainfalls. In East Asia, there are many characteristic weather systems in different seasons, such as the Meiyu in China, the Changma in Korea and the Baiu in Japan in summer, persisting northwesterly winds and cold surges in winter. Moreover, the interannual and intraseasonal variabilities of East Asian monsoon are vary large, which can cause droughts and floods in the eastern part of China. Therefore, the different time-scale variabilities of East Asian monsoon have been an important scientific issue in China (Tao and Chen, 1987). Recently, studies on the interdecadal, interannual and intraseasonal variations and their causes, especially the physical mechanism of the interannual and intraseasonal variabilities of East Asian monsoon, have been greatly advanced. These recent studies on East Asian monsoon are systematically reviewed by Huang et al. (2003).
As another subsystem of the global climate system, ENSO cycle can be considered as the most important phenomenon in the tropical air-sea interaction. When an ENSO event occurs in the equatorial Pacific, severe climate anomalies will be caused in many regions of the world (Horel and Wallace, 1981; Rasmusson and Carpenter, 1982; Rasmusson and Wallace, 1983). Moreover, investigations have shown that ENSO cycle greatly influences South Asian monsoon (Mooley and Parthasarathy, 1983; Khandekar and Neralla, 1984). They found that a weak Asian summer monsoon tends to occur in an El Ni year. Similarly, ENSO event also has a large impact on the climate anomalies in East Asia (Wang, 1986; Fu and Teng, 1988; Huang and Wu, 1989).
Many studies showed that ENSO phenomenon is not only an event but also a cycle (Bjercknes, 1966; McCreay, 1983; Schopf and Suarez, 1988). Recently, the interaction between the Asian summer and winter monsoon cycle and ENSO cycle has become into an interesting scientific problem. The diagnostic and modeling studies have revealed that the Asian summer monsoon activities have a significant effect on the atmosphere/ocean coupled system in the equatorial Pacific (Yamagata and Matsumoto, 1989; Yasunari, 1990; Yasunari and Seki, 1992). Moreover, Li (1988,1990) pointed out that the strong East Asian winter monsoon activities play an important triggering effect on El Ni event. Because the study on the interaction between Asian winter and summer monsoon cycle and ENSO cycle is very important for the understanding of the physical mechanism of the formation of severe climatic disasters in China, recently, supported by the project “Research on the Formation Mechanism and Prediction Theory of Sever Climatic Disasters in China”, which has been started as the first batch of the National Key Program for Developing Basic Sciences, Chinese scholars made the deep research on the interactions between the East Asian summer and winter monsoon cycle and ENSO cycle. And many valuable advances have been achieved in the aspect. In order to summarize these progresses, the recent studies on the interaction between the Asian summer and winter monsoon cycle and ENSO cycle are systematically reviewed, especially the studies on East Asian monsoon made by Chinese scholars are emphasized in this paper.
II. THE EAST ASIAN MONSOON SYSTEM AND ITS INTERANNUAL VARIABILITY
In order to understand the interaction between East Asian monsoon and ENSO cycle, firstly, it is necessary to realize the components of the East Asian monsoon system and the causes of the interannual variability of this system. However, up to now, only the understanding of the components of the East Asian monsoon system has been a little clear, so the studies on the East Asian summer monsoon system cannot but reviewed in the section.
1. The East Asian Summer Monsoon System
It may be considered as an important progress in the study on Asian monsoon to realize the components of Asian monsoon circulation system. Krishnamurti (1982) proposed the Indian monsoon circulation system. Later on, Tao and Chen (1985) put forward the East Asian monsoon circulation system and pointed out that the East Asian summer monsoon circulation system includes: the monsoon trough over the South China Sea and the tropical western Pacific, the Indian SW monsoon flow, the cross-equatorial flow along the east to 100ºE, the western Pacific subtropical high and the tropical easterly flow, the disturbances in mid-latitudes, the Meiyu frontal zones, and the cold anticyclone in Australia.