A China-Japan Cooperative JICA Atmospheric Observing Network over the Tibetan Plateau (JICA/Tibet Project) : An Overviews (Special Issue on Japan-China Meteorological Disaster Reduction Corporation Research Center Project (JICA/Tibet Project))

Because of the importance of the impact of the Tibetan Plateau on atmospheric general circulations and climate across China, Asia, and even the world, Chinese and Japanese scientists jointly constructed an integrated atmospheric observing system, especially for the water vapor observation, across the Tibetan Plateau and its adjacent areas during the period of 2005–2009 under the JICA (Japan International Co-operation Agency) project (JICA/Tibet Project). The JICA/Tibet Project aims at understanding processes of the land-atmosphere interaction over the Tibetan Plateau and their impacts on the severe weather and climate over the Tibetan Plateau and the area to its east in the East Asian region. The project is designed in an attempt to alleviate impacts of meteorological disasters in these areas through improving the prediction skill. The implementation of the project has enhanced the capability of monitoring the Plateau atmosphere. The numerical forecast techniques are developed through assimilating observed data into the numerical model. Based on the investigation of observed surface energy balance, the land surface model is improved. It is found that the diurnal variation of precipitation over the Plateau is closely related with water vapor, and the latent heat release is a main factor a¤ecting the Plateau vortex. By analyzing observed seasonal features of the tropopause, the evidence of strong stratosphere and troposphere exchange over the Tibetan Plateau is provided. It reveals that the interannual variability of summer rainfall in East China corresponds to that of vegetation index over the Plateau. The crossing hemispheric circulations driven by the thermal and mechanical forcings of the Plateau play an important role in water vapor transports not only over East Asia, but also in the global scale. 1. Background and motivation The Tibetan Plateau sits in the subtropical area within 25 N–40 N, 74 E–104 E in the middle of Asia. It is the highest plateau in the world, with extremely complex terrains. The Plateau’s averaged elevation ranges between 4,000 m and 5,000 m Corresponding author: Renhe Zhang: Chinese Academy of Meteorological Sciences, No. 46 Zhong-GuanCun South Ave., Haidian District, Beijing 100081, China. E-mail: renhe@cams.cma.gov.cn 6 2012, Meteorological Society of Japan above sea level and thus is also called ‘the roof of the world’, or ‘the third pole’. The Plateau is bounded on the east by the Hengduan Mountains, with the Himalaya Range bordering the south and west, and the Kunlun Mountains the north. Most part of the Plateau sits in the southwest part of China, including the Xizang Autonomous Region, Qinghai Province, the west part of Sichuan Province, the southern part of Xinjiang Uygur Autonomous Region, and parts of Gansu Province and Yunnan Province. Geographically, it also covers part of Bhutan, Nepal, India, Pakistan, Afghanistan, Tajikistan, and Kyrgyzstan. The Plateau occupies an area of 2.5 million square kilometers, with 2.4 million square kilometers standing within the territory of the People’s Republic of China. The Tibetan Plateau is a huge piece of land jutting out of the earth surface, stretching up to the middle troposphere. As a result, the temperature, humidity, air pressure and other meteorological elements over the Plateau are noticeably di¤erent from the ones in the surrounding free atmosphere. In the boreal summer, the Plateau is an immense heat source in the middle troposphere, and a cold source in the boreal winter (Ye and Gao 1979). Its thermal and dynamical e¤ects cast a major impact on the formation and evolution of atmospheric circulations and climate across China, Asia, and even the world (Ye et al. 1957, 1998; Huang 1985; Yanai et al. 1992). The vortex formed up above the Plateau and its eastward moving can produce a critical e¤ect on the heavy rains occurred in the east part of China. For example, an extraordinary heavy rain that attacked North China in 1963, and an extraordinary flush flood that swept across the Yangtze River valley in 1954 were associated with the eastbound movement of vortexes stemmed from the Plateau (Tao and Ding 1981). The dynamic and thermal e¤ects of the Plateau play a key role in the water vapor transportation to the Yangtze River valley during the Meiyu period in China (Xu et al. 2002). The Plateau’s sensible heat driven air pump (SHAP) e¤ect not only sustains the summer monsoons in Asia, but also a¤ects global climate by inducing up a Rossby wave train (Wu et al. 1997). The e¤ects of the latent heat as well as the sensible heat were also identified recently. Fujinami and Yasunari (2001) investigated seasonal variations in cloud activity over the Plateau, reporting significant cloud activity in spring (March–April). Ueda et al. (2003) also demonstrated the importance of condensation heating in the heat balance during the pre-onset phase of the summer monsoon over the western Plateau. The first intensive in situ observations during early spring upon the Plateau were performed in April 2004 under the framework of the Coordinated Enhanced Observing Period (CEOP) (Koike 2004). Based on in situ and satellite observations, and numerical simulations, Taniguchi and Koike (2007) reported the importance of cumulus activity in terms of increases in atmospheric temperature in the upper troposphere, even in April. In the boreal winter, the change of the heat source across the Plateau may breed out abnormal zonal winds over the equatorial Pacific Ocean, which in turn may result in an abnormal sea surface temperature that would eventually a¤ect ENSO events (Chen et al. 2001). In recent years, China has witnessed a raised frequency of meteorological disasters (China Meteorological Administration 2007). China has been working hard to establish a well functioned meteorological observing network, in an attempt to meet the needs of disaster prevention and reduction. However, the operational meteorological stations in the west part of the country are noticeably lower in number, compared with the east part (Zhang 2006). The number of the meteorological stations sitting across the Tibetan plateau, a region that takes up about one fourth of the nation’s territory, is extremely out of proportion to the vast area it has covered, due to high elevation, tough natural environment and di‰cult observation. The scarcity of the observed data over such a vast area not only compromises the scientific research, but also questions the reliability and accuracy of predictions of high impact weather events across the Plateau and the area to its east, the Yangtze River and Yellow River valleys and other East Asian countries, in particular. Taking into account the importance of the Tibetan Plateau in studying and predicting the evolution of weather and climate in China and in East Asia as well, it is necessary to improve the capability and utility of the atmospheric watch across ‘the roof of the world’ and its adjacent areas, and enhance China’s capabilities in severe weather prediction and disaster prevention and reduction. Considering the importance of establishing an integrated atmospheric observing system on the Tibetan Plateau, the joint observation and research on the Tibetan atmosphere between Chinese and Japanese governments were defined as one of key cooperation topics in December 1999. In July 2002, the Chinese Academy of Meteorological Sciences 2 Journal of the Meteorological Society of Japan Vol. 90C