The GCOS Reference Upper-Air Network is an international reference observing network of sites measuring ECVs above Earth's surface, designed to fill an important gap in the current global observing system. GRUAN measurements are providing long-term, high-quality climate data records from the surface, through the troposphere, and into the stratosphere.

These are being used to determine trends, constrain and calibrate data from more spatially‐comprehensive observing systems (including satellites and current radiosonde networks), and provide appropriate data for studying atmospheric processes. GRUAN is envisaged as a global network of eventually 30-40 stations of existing observational networks.

Find out more on the GRUAN website https://www.gruan.org/.