A China-Japan Cooperative JICA Atmospheric Observing Network over the Tibetan Plateau (JICA/Tibet Project): An Overviews

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1 Journal of the Meteorological Society of Japan, Vol. 90C, pp , doi: /jmsj.2012-c01 A China-Japan Cooperative JICA Atmospheric Observing Network over the Tibetan Plateau (JICA/Tibet Project): An Overviews Renhe ZHANG State Key Laboratory of Severe Weather (LaSW), Chinese Academy of Meteorological Sciences, Beijing, China Toshio KOIKE Department of Civil Engineering, the University of Tokyo, Tokyo, Japan Xiangde XU State Key Laboratory of Severe Weather (LaSW), Chinese Academy of Meteorological Sciences, Beijing, China Yaoming MA and Kun YANG Institute of the Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China (Manuscript received 1 April 2011, in final form 12 September 2011) Abstract 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 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. Corresponding author: Renhe Zhang: Chinese Academy of Meteorological Sciences, No. 46 Zhong-Guan- Cun South Ave., Haidian District, Beijing , China. renhe@cams.cma.gov.cn , Meteorological Society of Japan 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

2 2 Journal of the Meteorological Society of Japan Vol. 90C 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 In July 2002, the Chinese Academy of Meteorological Sciences

3 July 2012 R. ZHANG et al. 3 (CAMS) submitted a JICA (Japan International Co-operation Agency) project proposal to the Chinese Ministry of Science and Technology (MOST) on atmospheric monitoring over the Tibetan Plateau. The proposed collaboration included providing new observing equipment from JICA, especially GPS for water vapor observation, to set up an integrated meteorological observing network covering the Tibetan Plateau and its adjacent areas, on the basis of the existing equipment and facilities available for observation. Chinese side was responsible for the operation of the equipment and associated maintenance. Chinese and Japanese scientists worked jointly on observations, field experiments, and developments of the numerical weather prediction (NWP) model in a collaborative manner. Chinese side sent its research and operational personnel to study in Japan under the support of JICA. After reviewing by both MOST and JICA, the proposed project was endorsed by both Chinese and Japanese authorities concerned in September 2004 as an o - cial JICA project, which was named as China- Japan Meteorological Disaster Reduction Cooperation Research Center Project (hereafter referred to as JICA/Tibet Project). As a major international cooperation initiative launched by JICA in the area of meteorology, the JICA/Tibet Project started from August 2005 and ended in June Xu et al. (2008a) have reported the construction of the Plateau observing network. Here, after the finish of the project, the present paper introduces the implementation of the project as a whole, and especially the associated achievements. The objectives that the project was designed to achieve are depicted in Section 2, and implementation phases and equipment in Section 3. Section 4 gives the accomplishments made by the project, and concluding remarks are given in Section Objectives The JICA/Tibet Project was designed to establish a new generation of atmospheric observing network, especially for the water vapor observation, covering the Tibetan Plateau and its adjacent areas, to apply the achievements from observations to the meteorological operation, to understand the role of the Tibetan Plateau in the genesis of severe weather and climate, and to improve the NWP skill. To enhance the capability of monitoring the atmosphere over the Tibetan Plateau and its neighborhood in the east in a three-dimensional manner, the JICA/ Tibet Project aimed at establishing an integrated atmosphere observing network, improving both the quality and quantity of the meteorological data collected from said area; by e ectively utilizing the meteorological data collected from the Plateau in NWP models and developing a new generation of severe weather forecast and warning system, the project also aimed at enhancing operational capabilities of monitoring, predicting and assessment of severe weather and climate over the Plateau and the area to its east. Therefore, through enhancement of the regional operational meteorological forecast system, the losses caused by meteorological disasters were expected to be alleviated in the East Asian region, including China and Japan. The implementation of the JICA/Tibet Project provided the needed support for studying the impacts of the Tibetan Plateau on climate variabilities, and on high-impact weather events in the east low-lying areas, and in the world as well. The project has worked on the following major scientific issues: 1) the role of the unique topography and boundary layer structure of the Tibetan Plateau in shaping up a unique atmospheric heat source associated with hydrologic cycles, 2) the magnitudes of the energy and hydrologic cycles over the Tibetan Plateau in shaping up severe weather and climate in China as well as in East Asia, and 3) the convective systems over the Plateau and their impacts on droughts and floods in the East Asia region. The Observing System Research and Predictability Experiment (THORPEX) (Shapiro and Thorpe 2004), under the World Weather Research Programme (WWRP), initiated by the World Meteorological Organization (WMO) has a defined goal to improve weather forecast techniques through developing applicable observation methodologies and systems over sensitive areas. The Tibetan Plateau is a strong signal area for the possible flood-causing weathers in the east part of China, in particular, the Yangtze River valley. In this context, establishing an integrated atmospheric observing system covering the Plateau and its adjacent areas is a major scientific e ort to sort out the sensitive areas applicable to raise the capability in predicting severe weather in the eastern China, especially that causing floods across the Yangtze River valley. Severe weather forecast is extremely important to securing a smooth economic and social development, and to safeguarding people s lives and properties. Installing a range of modern observing equipment on the Tibetan Plateau and its adjacent areas makes an important part of China s climate observing

4 4 Journal of the Meteorological Society of Japan Vol. 90C system (Zhang and Xu 2008) that is under construction. Meanwhile, the application of achievements derived from the observational experiments in monitoring severe weather/climate and in improving NWP helps China raising its severe weather/climate watch and prediction capabilities. 3. Implementation phase and equipment The integrated atmospheric observing network established under the JICA/Tibet Project has mainly covered the southwest part of China in Xizang Autonomous Region, Yunnan Province and Sichuan Province, including some parts of Qinghai and Guizhou Provinces, Guangxi Zhuang Autonomous Region, and Chongqing municipality. In total the project was implemented over the region dealt with two autonomous regions, four provinces, and one municipality in southwestern China, covering the Tibetan Plateau and its neighborhood in the east, the upper reaches of Yangtze River valley. 3.1 Implementation phase The JICA/Tibet Project was implemented in a phased manner. Three phases were divided in the implementation period from December 2005 to June Phase I, running from December 2005 to September 2007, was designed to establish an observing system, and to develop the needed numerical prediction models; Phase II, from October 2007 to August 2008, focused on applications of the established observing system, and on improving the numerical prediction models; Phase III was staged to measure the performance of the observing system and numerical prediction models in the period of September 2008 June To improve the understanding of the impact of the Tibetan Plateau on East Asian summer monsoon and heavy rainfall process occurred in China, intensive observation periods (IOPs) were staged in 2008 in three separate time periods. The IOPs were designed with intensified upper air sounding activities from regular twice a day to 4 times a day. Period I (IOP1), from 24 February to 23 March 2008, focused on the observation of atmospheric activities over the Plateau and its adjacent areas prior to the onset of the East Asian summer monsoon, intending to understand the linkage of conditions of the Plateau atmosphere in late winter and early spring with the summer monsoon followed. Period II (IOP2), running from 20 April to 19 May 2008, was staged to understand the atmospheric activities before and after the onset of the East Asian summer monsoon, focusing on the role of the Plateau atmosphere in triggering up the onset of the East Asian summer monsoon. The last part of the IOP experiment, period III (IOP3), covering the period from 20 June to 19 July 2008, was made to observe features of atmosphere over the Tibetan Plateau during the flood season in the eastern China, in an attempt to understand their impacts on the rainfall in the flood season. 3.2 Equipment The integrated observing network established by the JICA/Tibet Project was mainly built on a range of existing facilities, including the meteorological observing network possessed by China Meteorological Administration (CMA), the Tibetan Plateau observing and experimental stations owned by the Institute of the Tibetan Plateau Research, the Chinese Academy of Sciences (ITP), GPS stations established by the State Bureau of Surveying and Mapping of China (SBSM), and observing sites equipped with the observing instruments provided by JICA. The aforementioned facilities were employed to establish the integrated observing network mainly composed of GPS water vapor observations, automatic weather stations (AWS), upper air soundings, wind profilers, and atmospheric planetary boundary layer (PBL) observing systems. The observing equipment employed in the JICA/Tibet Project and their geographic distributions are depicted as follows: a. GPS water vapor observing network The GPS water vapor observing network was composed of 26 GPS units. 24 units were those newly installed from JICA, and 2 were existing ones owned by SBSM. The geographical distribution of the units is presented in Fig. 1a. Among 26 GPS water vapor observing units, 9 were deployed in Xizang Autonomous Region, 7 in Yunnan Province, 7 in Sichuan Province, 1 in Guangxi Zhuang Autonomous Region, 1 in Guizhou Province, and 1 in Chongqing municipality. b. AWS observing network The AWS network was made up of 72 AWS units. Of them, 7 were unmanned AWS units newly installed from those provided by JICA, mainly distribute over the scarcely populated areas on the Plateau. CMA provided 58 units, and ITP 7 units. The geographical distribution of AWS is presented in Fig. 1b. Of the 72 AWS units, 27 sat in Xizang Autonomous Region, 10 in Yunnan Province, 11

5 July 2012 R. ZHANG et al. 5 Fig. 1. Geographical distributions of (a) GPS stations and (b) AWS stations utilized in the JICA/Tibet Project. Black and red dots represent the equipment provided by JICA and existing ones, respectively. The name and elevation (numeral in bracket; unit: m) for each GPS station are shown in (a). in Sichuan Province, 13 in Qinghai Province, 7 in Guangxi Zhuang Autonomous Region, 3 in Guizhou Province, and 1 in Chongqing municipality. c. Upper air sounding network The upper air sounding network had 19 sounding stations. In addition to 14 stations possessed by CMA, JICA contributed 5 GPS sounding stations. The geographical distribution of upper air sounding stations is shown in Fig. 2a. Of these Stations, 6 were distributed in Xizang Autonomous Region, 6 in Yunnan Province, and 7 in Sichuan Province. d. Other equipment In the observing network, 2 wind profilers, one from the JICA and one from CMA, were employed. One profiler was located in Xizang Autonomous Region, and another one in Yunnan Province.

6 6 Journal of the Meteorological Society of Japan Vol. 90C Fig. 2. Geographical distributions of (a) radiosounding stations provided by JICA (black dots) and existing ones (red dots), and of (b) wind profilers (five-pointed stars), PBL observing systems (circles) and the meteorological observing system for water surface (black dot). Black and red colors mark the equipment provided by JICA and existing ones, respectively. Numeral in bracket is the elevation for each station (unit: m). Meanwhile, 6 atmospheric PBL observing systems were applied in the network. JICA provided 4 units, CMA 1, and ITP 1, with 3 installed in Xizang Autonomous Region, 1 in Yunnan Province, and 2 in Sichuan Province respectively. In addition, JICA provided 1 set of the water surface meteorological observing system, which was installed on the Erhai Lake in Yunnan Province. The geographic distribution of these equipment is shown in Fig. 2b.

7 July 2012 R. ZHANG et al. 7 Table 1. Amount of equipment used in the atmospheric observing network of the JICA/Tibet Project provided by JICA, CMA, ITP and SBSM. Equipment type JICA CMA ITP SBSM Total GPS stations AWS stations Radiosounding stations Wind profiler PBL observing system Water surface observing system 1 1 Table 2. Amount of equipment used in the atmospheric observing network of the JICA/Tibet Project in each province (autonomous region or municipality) over the Tibetan Plateau and its adjacent areas. YN, SC, QH and GZ stand for Yunnan, Sichuan, Qinghai and Guizhou provinces, respectively; GX and XZ for Guangxi Zhuang and Xizang Autonomous Regions; and CQ for Chongqing municipality. Equipment type XZ YN SC QH GX GZ CQ Total GPS stations AWS stations Radiosounding stations Wind profiler PBL observing system Water surface observing system 1 1 All equipment employed in the integrated atmospheric observing network of the JICA/Tibet Project and their coming sources are given in Table 1, and in Table 2 their distributions in each Province (Autonomous Region or municipality) in the southwestern China. 4. Achievement highlights The establishment of an integrated atmospheric observing network under the JICA/Tibet Project has enhanced China s atmospheric monitoring capability over the Tibetan Plateau and its adjacent areas. It also improved China s capability of the operational warning and predicting of severe weathers across the Plateau and the east part of China. Noticeable progress has been achieved in research and its operational applications. 4.1 Operationalization of the observing network and database A platform has been established to function in transmission, processing and analysis of the observed data, and monitoring the integrated meteorological observing system over the Tibetan Plateau and its adjacent areas. Its operational application was realized and a real-time operational workflow was established. The observed real-time data were first received by four local centers at Provincial Meteorological Bureaus of Sichuan and Yunnan, and the Meteorological Bureaus of Guangxi Zhuang and Xizang Autonomous Regions, respectively. The received real-time observational data at the four local centers then were gathered at the Beijing Center at CAMS, where data processing, quality control, monitoring and distribution to users were conducted. The statistics show that the real-time data transmission rate has reached design target. By September 2007 at the end of Phase I for establishing the observing system, the receiving rate of the observed hourly data exceeded 90% from 26 GPS and 72 AWS units, including newly installed 24 GPS and 7 AWS units provided by JICA. The observational data from wind profilers, PBL observing systems and the meteorological observing

8 8 Journal of the Meteorological Society of Japan Vol. 90C Fig. 3. Correlation coe cients between the averaged total precipitable water observed by GPSs in the JICA/ Tibet Project and the precipitation lagged by 24 h in China in the period from 0000 UTC 10 January to 1200 UTC 2 February Shadings indicate correlation with significance level exceeding (from Xu 2009) system for water surface were continuously collected every 10 minutes. Quality control has been applied to all observed data. Utilizing the surface based in situ observations, e orts have been made to correct satellite data by applying the variational method (Weng and Xu 1999), resulting in a range of satellite remote sensing products involving soil moisture, snow cover, vegetation, cloud cover, rainfall, air temperature, and water vapor over the Tibetan Plateau. Therefore, the JICA/Tibet Project established a database containing not only surface based in situ observational data, but also satellite remote sensing products. The data produced by JICA/Tibet Project are archived at CAMS. Since the project joined the AMY (Asian Monsoon Years ) Program, all data are available publicly following the AMY Data Release Guidelines ( An operational platform for warning and predicting severe weathers In order to investigate the role of the data collected in the JICA/Tibet Project in severe weather in East China, the observed data were used in diagnosis and numerical modeling of the severe weather. During the implementation of the project, heavy snowstorms occurred in the southeastern China in the beginning of 2008 (Wen at al. 2009). To average the total precipitable water observed by the GPSs, its correlation coe cients with precipitation lagged by 24 h in China in January and February 2008 are shown in Fig. 3. It can be seen that more water vapor over the Tibetan Plateau corresponding to more precipitation lagged by 24 h in the belt area stretching from lower reaches of Yangtze River valley to the southwestern China (Xu 2009). The monitored water vapor over the Tibetan Plateau shows a strong precursor signal of the heavy snowstorms occurred in Southeast China. By utilizing the WRF-3DVAR system (Barker et al. 2004), Peng et al. (2009) made 48 h sensitivity forecast experiments for precipitation in January 2008 to test the role of the moisture, temperature and pressure observed by AWSs in the JICA/Tibet Project in improving the forecast of the snowstorms. As shown in Fig. 4, much weaker southeastern and much stronger southwestern centers of

9 July 2012 R. ZHANG et al. 9 Fig h forecast experiments initiated at 0000 UTC 25 January 2008 for accumulated 24 h precipitation ending at 0000 UTC January (a) is observation; (b) (d) are control run without data assimilation, data assimilation experiment with only one-cycle 3DVAR applying initial time, and data assimilation experiment with multi-cycle 3DVAR applying every hour from 1800 UTC 24 August to 0000 UTC 25 January 2008, respectively. (unit: mm) (from Peng et al. 2009) the 24 h accumulated precipitation than observations (Fig. 4a) can be found in control run without data assimilation (CNTR, Fig. 4b). In the data assimilation experiment with only one-cycle 3DVAR applying at initial time (DA-1, Fig. 4c), the southeastern center is less than 35 mm, which enhances to over 45 mm in the experiment with multi-cycle 3DVAR applying every hour (DA-2, Fig. 4d); the southwestern center reduces from over 45 mm in CNTR to less than 45 mm in DA-2. Meanwhile, the false center around 28.5 N, 108 E in both CNTR and DA-1 disappears in DA-2. Therefore, the results of DA-2 are much closer to the observations. The numerical experiments show that levels of forecasts have been noticeably raised when the data collected from observations are assimilated. The data assimilation techniques in NWP models and associated automated operational NWP system developed by utilizing real-time observational data over the Tibetan Plateau have found applications in operational forecasts, and applied in the operational platform. The JICA/Tibet Project has led to the establishment of the operational platform for warning and predicting severe weathers in East China. 4.3 Land surface processes The latent and sensible heat fluxes observed by the PBL tower at Linzhi in 2008 are shown in Fig. 5. We can see that the surface energy exchange is dominated by latent heat from mid-march to October in the rainy season, with averaged latent heat about 51 W m 2 and sensible heat 23 W m 2 from 11 March to 10 October. In the dry season from October to early March, sensible heat dominated the energy exchange with averaged sensible heat 27 W m 2 and latent heat 16 W m 2 from 11 October to 10 March. Yearly cumulated latent heat

10 10 Journal of the Meteorological Society of Japan Vol. 90C Fig. 5. Latent (upper panel) and sensible (lower panel) heat fluxes in 2008 observed by the PBL tower at Linzhi (29.46 N, E) (unit: W m 2 ) Fig. 6. Mean bias errors of the original and revised Noah model for the surface temperature (Tg ) (left), surface energy budget (Rnet ) (middle) and sensible heat flux (H ) (right) at three arid sites of Shiquanhe ( N, E) and Gaize ( N, E) in Xizang Autonomous Region, Audubon ( N, W) in Arizona of USA and one semi-arid site of Tongyu_G ( N, E) in Jilin Province during the daytime ( LT), calculated from 30-minute observations and simulations. Sensible heat flux was not observed at Shiquanhe and Gaize sites. is 1: J m 2, which is higher than yearly cumulated sensible heat (7: J m 2 ). The in situ observations were used to evaluate the revised Noah land surface model (LSM) (Yang et al. 2002) with an appropriate parameterization of the thermal roughness length (Chen et al. 2010a). Figure 6 shows that at the two Plateau sites (Shiquanhe and Gaize), the daytime surface tempera- ture (Tg ) is underestimated by 10 K on average in the original Noah model while they are much better simulated in the revised one. At the two lowland sites (Audubon and Tongyu-G), the daytime Tg is also simulated better in the revised one. The mean bias errors in modeling surface energy budget and sensible heat flux are simultaneously reduced in the revised model. The similar improvements to SiB2

11 July 2012 R. ZHANG et al. 11 (Sellers et al. 1996) were also demonstrated (Yang et al. 2009). The in situ observed micrometeorological data at Wenjiang in the period between January and March, 2008 were used to drive the Land Data Assimilation System developed at the University of Tokyo (LDASUT) (Yang et al. 2007). The consistency between LDASUT simulations and observations validates the capability of the LDASUT in reproducing accurate land surface energy budget (Lu et al. 2009). Boussetta et al. (2007) developed a coupled landatmosphere satellite data assimilation system as a new physical downscaling approach, by coupling the Advanced Regional Prediction System (ARPS) with the LDASUT. The ARPS produces forcing data for the LDASUT, and the LDASUT produces better initial surface conditions for the modelling system. This coupled system can take into account land surface heterogeneities through assimilating satellite data for a better precipitation prediction. The results of the system application to the Tibetan Plateau show significant improvement of simulation and prediction of soil moisture and rainfall at a meso-scale compared with a no assimilation regional atmospheric model simply nested from the global model. 4.4 Weather and climate over the Tibetan Plateau The generation processes of mesoscale convective systems (MCSs), which often cause heavy rainfall over the Sichuan Basin in China were investigated by using the JICA/Tibet intensive radio sonde observation data held in the 2008 monsoon season, the METEOSAT geostational satellite images and the numerical simulations using a weather research and forecast (WRF) model (Ueno et al. 2011). The MCS was generated under synoptic conditions of merging southwesterly low-level monsoon flows with a northerly midlatitude air mass following the trough in the leeward of the Tibetan Plateau. It was triggered in the evening by strengthening of the low-level wind convergences with horizontal shear between the southerly monsoon flow, with large convective available potential energy, and the northerly dry intrusion. A sudden increase in the northerly dry winds was confirmed by the sonde observation data in the western basin, and was related with the diurnal cycle of cloud activity over the Qinling Mountains. This study suggests the MCSs associated with heavy rainfall is caused and developed by the interaction between a synoptic Fig. 7. Scatter plots of hourly GPS water vapor anomalies (DPW, unit: mm) (a) against hourly rainfall frequency anomalies (DF, unit: %) and (b) against hourly rainfall amount anomalies (DP, unit: mm) for their diurnal cycles in summer (June August) of at Lhasa. (from Liang et al. 2010) scale atmospheric circulation pattern and the characteristic topography of the Sichuan Basin where the dry intrusion at the bottom is captured. Using the water vapor observed by GPS at Lhasa, the relationship of diurnal cycles between water vapor and precipitation is shown in Fig. 7 (Liang et al. 2010). It can be seen that the GPS water vapor is well positively correlated to both rainfall frequency and amount, with correlation coe cients being around The peak of the diurnal cycle of GPS water vapor appears at around 1600 UTC, about 2 hours earlier than those of rainfall frequency and amount appeared, indicating a significant e ect of the atmospheric water vapor on the rainfall frequency and amount. Using

12 12 Journal of the Meteorological Society of Japan Vol. 90C Fig. 8. Time-longitude section of the vertical integrated atmospheric heat source (hq 1 i) (shadings, unit: wm 2 ) and 500 hpa vertical vorticity averaged between 30 N and 33 N (isolines, unit: 10 5 s 1 ) for a vortex over the Tibetan Plateau in the period from 0600 UTC 25 June 2008 to 0000 UTC 26 June (from Li et al. 2011) CloudSat/CALIPSO data, Luo et al. (2011) found that deep convection in summer (June August) over the Tibetan Plateau is lower in cloud top height, less frequent and smaller in size than those over the southern slope of the Plateau and the southern Asian monsoon region. There is more deep convection at the daytime (i.e., early afternoon) than the nighttime (i.e., soon after midnight) over the Plateau. Over the southern slope of the Plateau there is more deep convection occurring during the nighttime, and over East Asia region the daytime and nighttime occurrences are about equal. The convective systems over the Plateau have much larger size in the nighttime than those in the daytime. The evolution mechanism of a vortex over the Tibetan Plateau in June 2008 was diagnosed (Li et al. 2011). From Fig. 8, we can see that the vertical integrated atmospheric heat source (hq 1 i) and the vorticity at 500 hpa moved eastwards with the center of the hq 1 i to the east of the vorticity center. The diagnosing the potential vorticity (PV) equation illustrates that the prominent factor which attributed to the eastward movement of the vortex is the vertical uneven distribution of the latent heating through producing positive PV tendencies to the east of the vortex center, revealing the dynamical role of the latent heat in the eastward movement of the vortex over the Tibetan Plateau. Based on the tropopause daily observation data at 14 sounding stations in , Zhou et al. (2010) found the annual mean heights of the tropical and polar tropopauses over the Tibetan Plateau are about km and km, respectively. The occurrence of the tropical tropopause is dominant in the warm season from May to October and the occurrence frequencies of the two types of tropopauses are roughly equal in other months. By using the radiosonde data collected in the three intensive observation periods in 2008, Chen et al. (2010b) found in IOP1 the overall bimodal tropopauses near the heights of 10 km and 17 km, respectively, and in both IOP2 and IOP3 a single tropopause near 17 km, which are in consistency with the statistics by Zhou et al. (2010). The bimodal tropopauses indicate frequent intrusions of the air from the troposphere to the stratosphere in the spring time over the Plateau, providing the evidence of strong stratosphere and troposphere exchange over the Tibetan Plateau. Taniguchi and Koike (2008) investigated seasonal variations in cloud activity observed by geostational satellites, an total precipitable water (TPW) by the Atmospheric Infrared Sounder (AIRS) aboard Aqua, and atmospheric instability (dq/dp) derived from Japanese 25-year Reanalysis Project (JRA-25), around (92.0 E, 31.5 N) over the eastern Tibetan Plateau. They identified an apparent seasonal progression comprising a first phase of frequent cloud activity (ACTIVE-I), a resting phase (REST), and a second phase of frequent cloud activity (ACTIVE-II). Tamura et al. (2010) found that the temperature in the upper troposphere over the Tibetan Plateau continues to increase even in the REST, and suggested dual atmospheric heating around the Tibetan Plateau during the onset phase of the Asian Summer Monsoon from late April to mid June on the basis of the heat budget analysis and numerical experiment. They showed that adiabatic warming plays an important role in warming the upper troposphere downward from the tropopause, while at the same time, surface heating warms upward from the land surface of the Tibetan Plateau. 4.5 Linkage of the Tibetan Plateau with East Asian and global climates By examine the correlation between the normalized di erence vegetation index (NDVI) over the

13 July 2012 R. ZHANG et al. 13 Fig. 9. Time series of the leading EOF mode for normalized rainfall in China (gray bars), normalized NDVI in the southern Tibetan Plateau (24 N 33 N, 75 E 105 E; black bars), and normalized rainfall in southeastern China (south of 27 N, east of 105 E; solid line) and in the area from the middle and lower reaches of Yangtze River valley to the Yellow River valley (30 N 35 N, 105 E 120 E; dashed line) in summer (June August). (from Zuo et al. 2011) Tibetan Plateau and the leading mode of the empirical orthogonal function (EOF) for the normalized summer (June August) rainfall over China, Zuo et al. (2011) found they are significantly correlated. As shown in Fig. 9, the time series of the leading EOF mode agrees well with the NDVI averaged over the southeastern Tibetan Plateau, which is positively correlated with the summer rainfall in the southeastern China and negatively with that in the area from the middle and lower reaches of Yangtze River valley to the Yellow River valley. In the interannual time scale, more vegetation over the southeastern Tibetan Plateau corresponds to more precipitation in the southeastern China and less precipitation in the area from the middle and lower reaches of Yangtze River valley to the Yellow River valley. By utilizing the radiosonde data from 12 meteorological stations with an averaged elevation of 3,560 m over the Tibetan Plateau and 16 stations in the same latitudes in the non-plateau region with the elevation below 300 m within the area to the east of 110 E in East China, Zhang and Zhou (2009) found that over the Plateau there appears not only a larger temperature drop in the lower stratosphere and upper troposphere, but also a larger temperature rise in the lower and middle troposphere, compared with the non-plateau region in East China. The larger ozone depletion over the Plateau may possibly make a major cause allowing the air temperature change over the Plateau di erent from that over the non-plateau region in East China (Zhou and Zhang 2005; Zhang and Zhou 2009). The role of the elevated high land of the Tibetan Plateau in the global water cycle was investigated by Xu et al. (2008b). As seen from Fig. 10, in summer (June August) the Tibetan Plateau exerts e ect on the general circulations in the global scale. The thermal and mechanical forcings of the Tibetan Plateau drive ascending motions over the Plateau and the circulations can cross south-north and east-west hemispheres respectively. The crossing hemispheric circulations driven by the thermal and mechanical forcings of the Tibetan Plateau play an important role in the water vapor transports not only over East Asia, but also in the global scale. 5. Concluding remarks To understand a range of key scientific issues, including the characteristics of atmospheric variations, water vapor transport, hydrologic cycle, and land-air interactions across the Tibetan Plateau and its adjacent areas, and to understand their impacts on the floods occurred in the East Asia region so as to raise the NWP model skill, Chinese and Japanese scientists jointly conducted an integrated atmosphere watch with emphasizing of the water vapor observation across the Tibetan Plateau and its adjacent areas during the period of under the JICA/Tibet Project. The project was designed to establish a three-dimensional atmospheric observing network across the Tibetan Plateau and

14 14 Journal of the Meteorological Society of Japan Vol. 90C Fig. 10. Climatological wind vectors and speeds (shadings, unit: ms 1 ) for the summer (June August) averaged in (a) in the meridional vertical cross section along 80 E 110 E and (b) in the latitudinal vertical cross section along 27.5 N 35 N. (from Xu et al. 2008b) its neighborhood in the east, in an attempt to collect the needed meteorological data on a long term basis and to alleviate the impacts caused by meteorological disasters in the East Asia region, including China and Japan. The project has established an integrated observing platform in this region, raised analyzing capabilities by utilizing observational data from both satellite remote sensing and surface based observations, developed NWP techniques by assimilating observed data into NWP model to predict severe weathers across the Plateau and Yangtze River valley, and improved the operational severe weather/climate monitoring, prediction, and assessment systems. The AWSs and GPS water vapor observing stations established by the JICA/Tibet Project have become part of the operational system run by CMA. The PBL boundary layer flux observation systems and wind profilers from the JICA/Tibet Project have been included as part of CMA s pilot stations. The establishment of the plateau-wide observing system is also practically important to the design and implementation of a range of major Chinese national projects, including the west development campaign, Qinghai- Xizang railway, south-to-north water diversion, and flood disaster prevention/control across the Yangtze River valley. It is also extremely important for regulating the water resources of the Yangtze River, making flood forecasts, enhancing the capacity building of major meteorological operations in the west part of the country, and improving meteorological authorities disaster prevention and reduction capability. Before the JICA/Tibet Project, China launched two Tibetan Plateau related scientific experiments in 1979 and 1997 respectively, mainly aiming at studying the large scale variation of the heat source across the Plateau and its ties with large scale atmospheric circulations, and land-air interactions in the Tibetan Plateau (Xu and Chen 2006). The second experiment conducted in 1997, named as TIPEX, was jointly implemented with the participation of both Chinese and Japanese scientists. The integrated atmospheric observing system of the JICA/ Tibet Project conducted this time has exceeded the previous two experiments in terms of the scope covered, the items observed, technical means applied, and instrument employed. It has collected much more data, GPS water vapor data in particular, in a systematic and reliable manner. Meanwhile, the JICA/Tibet Project pays close attention to the meteorological operations, focused more on the application of observational data and research achievements in operations, closely in line with constructions of meteorological operations for observation and prediction, and with the national needs for disaster prevention and reduction. Therefore, the JICA/Tibet Project has won the support and active participation of CMA and its operational departments concerned, which made the project a success in processes from the establishment of the project to the implementation, then to the construction, and further to the application of research achievements. The project makes a good example for the combined e orts of both research and operation. As it was pointed out in the final assessment report issued by the Japanese authorities in 2009 that the project is implemented not merely for the project s sake, and the achievements derived from the project have been utilized to the full. The project has rendered an important contribution to

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