GCOS Reference Upper-Air Network (GRUAN): Justification, requirements, siting and instrumentation options - April 2007


World Meteorological Organization (WMO)

Last version

v1 (2007)






Shortcomings in the design and implementation of the current upper-air measurement network greatly limit the accuracy and detail of observations needed to specify how climate has varied and changed above the Earth’s surface. This deficit impacts our ability to accurately predict climate change, and hence has potentially serious consequences in areas of high relevance to society, such as water resource management, the health sector, energy management, transportation, financial infrastructure, and sustainable economic development. Foremost, the GCOS Reference Upper-Air Network (GRUAN), a network for atmospheric reference observations, is required to provide the foundation for long-term datasets that can be used to reliably monitor and detect emerging signals of global and regional climate change.

Specifically, the GCOS Reference Upper-Air Network is required to:

  • Provide long-term high quality climate records;
  • Constrain and calibrate data from more spatially-comprehensive global observing systems (including satellites and current radiosonde networks); and
  • Fully characterize the properties of the atmospheric column.

Essential characteristics of a successful GCOS Reference Upper-Air Network identified to date are:

  • Close coordination with the user community;
  • High-quality instrumentation;
  • Redundancy of measurements of climate variables at network sites;
  • Changes in the network managed in such a way that their non-climatic influences can be accurately adjusted for;
  • Real-time calibration and validation;
  • A strong lead centre managing the network in conjunction with station operators;
  • Archival of data and metadata, and easy, free access to these for bona fide research purposes;
  • Full adherence to the GCOS Climate Monitoring Principles;
  • Availability of complementary measurements from other networks in a collocation database, to enable cross-calibration.

Scientific evidence clearly shows that there is a pressing need to implement such a network. Equally, it is emphasized that the GCOS Reference Upper-Air Network would be part of a tiered system of networks to which both the GCOS Upper-Air Network (GUAN) and the WMO Global Observing System (GOS) are vital components.

This report outlines progress to date in establishing network requirements, in proposing a network architecture, and in identifying technological options. At the time of publication, the inception of the GCOS Reference Upper-Air Network remains a work in progress. Areas identified as requiring further work are outlined within the conclusions.