Observation stations on the Tibetan Plateau (TP) are very sparse. Worse yet, very few stations are located in the central and vast western areas of the plateau due to complex topography including many glaciers and lakes. The scarcity of observational data from the field has had a severe impact on systemic research of regional climate change across the TP. In addition to the innate limitations of satellite data, other problems exist, such as a lack of temperature and wind data as well as low temporal resolution, etc. Therefore, developing a data assimilation system suitable to the TP and generating data that can be used for high-resolution regional reanalysis is very important to understanding the TP’s regional climate as well as climate change in general.
To solve this problem, research groups led by Deliang Chen, Earth Sciences professor at the University of Gothenburg and the CAS Center for Excellence in Tibetan Plateau Earth Sciences, and the late Fuqing Zhang, professor at Pennsylvania State University, work together to develop a data assimilation system for the TP. The system, which is based on the Weather Research and Forecasting (WRF) model and an ensemble Kalman filter (EnKF) data assimilation system, involves assimilating current sounding data into the WRF model driven by two datasets – the ERA-Interim and the newly released global reanalysis ERA5, both produced by the European Centre for Medium-range Weather Forecasts (ECMWF). Using this mechanism, the researchers achieved 30-km and 10-km grid spacing over the TP and surrounding areas. They subsequently evaluated regional reanalysis using independent sounding observations and satellite-based precipitation data for the summer of 2015. The results showed that the regional reanalysis was more responsive to changes in specific humidity and simulation of diurnal rainfall cycles across the TP. In balance, the system efficiently improved the downscaling simulation of precipitation intensity, distribution, and diurnal cycles across the TP.
In the near future, the researchers aim to further improve the regional reanalysis system, increase its resolution and complete analyses of several years of data, in order to accomplish further regional hydrological and ecological simulations.
Results of the research were published in the Journal of Advances in Modeling Earth Systems, with Ph.D. candidate Jie He as the first author. The research was funded by the China Scholarship Council; the National Science Foundation of the United States; the United States Department of Energy WACCEM; the Strategic Priority Research Program (PAN-TPE) of the Chinese Academy of Sciences; Sweden STINT, VR, the Gothenburg Chief Scientist Program; and the Korea Research Foundation.
