The Global Climate Observing System (GCOS), supported by a number of international partners and the World Meteorological Organization (WMO), is establishing a reference climate observation network, the GCOS Reference Upper Air Network (GRUAN). Currently, this network comprises 30 reference sites worldwide, designed to detect long-term trends of key climate variables such as temperature and humidity in the upper atmosphere, thus providing a cornerstone to more reliable monitoring of signals of global and regional climate change. GRUAN observations are required to be of reference quality, with known biases removed and with an associated uncertainty value, based on thorough characterization of all sources of measurement.
In support of these goals, GNSS precipitable water (GNSS-PW) measurement has been included as a priority one measurement of the essential climate variable water vapor. In addition, a minimum of twice daily measurements (ideally hourly measurement) of PW are required as entrance to the GRUAN program. GNSS-PW is the primary means to accomplish this entrance requirement. The GNSS-PW program produces a nearly continuous reference measurement of PW and is therefore a substantial part of GRUAN.
GFZ contributes to GRUAN with its expertise in processing of ground-based GNSS network data to generate precise PW products. Since 2013, GFZ hosts a GRUAN central processing facility for the GNSS-PW. GFZ is responsible for the installation of GNSS hardware, data transfer, processing and archiving, derivation of GNSS PW products according to GRUAN requirements including PW uncertainty estimation, as well as for quality check and archiving of the GNSS-PW products. Currently half of the GRUAN sites are equipped with GNSS receivers. At the beginning of this year the data processing of GNSS-PW and its associated documentation has been GRUAN certified. GNSS-PW products including uncertainty estimation and results of selected validation studies are presented.
How to cite: Dick, G., Jones, J., Wang, J., Rannat, K., Wickert, J., Zus, F., Männel, B., Balidakis, K., and Wilgan, K.: GNSS-based Precipitable Water Vapor for the Global Climate Observing System, EMS Annual Meeting 2021, online, 6–10 Sep 2021, EMS2021-428, https://doi.org/10.5194/ems2021-428, 2021.
