Zenith Tropospheric Delay from GPS Monitoring Climate Change of Chinese Mainland

We present results on long-term trends of precipitable water vapor over the Chinese mainland based on data from the crust monitor observation network of China (CMONOC), obtained during the period from 2002 to 2004. The correlation between GPS zenith tropospheric delay (ZTD) and radiosonde PWV amounts to 0.89, indicating that the variety of tropospheric zenith delay can reflect the change of precipitable water vapor. The good agreement also guarantees that the information provided by GPS will benefit the NWP models. According to the PWV results of CMONOC in 2004, the precipitable water vapor reaches maximum during July and August, and it countermarches minimum during January and February. The time series of GPS ZTD, which were derived continuously from 2002 to 2004, are used to analyze the change of precipitable water vapor in Chinese mainland. It shows that the general trend of GPS ZTD is diminishing from the south-east coastland to the north-west inland, which is in accordance with the distribution of Chinese annual amount of rainfall. The temporal distribution of GPS ZTD in the Chinese mainland is that the GPS ZTD reaches maximum in summer, and it reaches minimum in winter. The long term differences between the observational data sources require further study before GPS derived data become useful for climate studies.