The GCOS Reference Upper-Air Network (GRUAN) GUIDE
World Meteorological Organization (WMO)
The GCOS Reference Upper‐Air Network (GRUAN) guide provides both mandatory operating requirements and guidelines on how to achieve the operating protocols specified in theGRUAN Manual(GCOS‐170). Mandatory operating protocols are distinguished by the words “must” or “shall” while guidelines are distinguished by the words “could” or “should”. The primary goals of GRUAN are to provide vertical profiles of reference measurements suitable for reliably detecting changes in global and regional climate on decadal time scales, initially for temperature, pressure and water vapour, with the aim of expanding to other Essential Climate Variables (ECVs), as resources permit, in liaison withother existing scientificnetworks. The measurements will provide a traceable reference standard for global satellite‐based measurements of atmospheric ECVs, will ensure that potential gaps in satellite measurement programmes do not invalidate the long‐term climate record, will be a reference standard for themeasurements made within the existing GCOS Upper‐Air Network (GUAN), and will provide data to fully characterize the properties of the atmospheric column.These goals have been agreed to by GCOS (Global Climate Observing System) and WMO (World Meteorological Organisation). The Guide defines the requirements for GRUAN site operations, including requirements on measurement uncertainty and long‐term stability of measurement time series. It establishes the philosophy under which GRUAN shall operate and informs current and future GRUAN sites of the expected modus operandi for GRUAN. This Guide recognizes that GRUAN is a heterogeneous network that includes sites from both the research community and the operational meteorological community. A GRUAN site may be a scientific observing site outside of the WMO operational Global Observing System, but the long‐term observational procedures are expected to follow the guidelines laid down in this Guide and in the GRUAN Manual whether it is primarily a scientific site or whether it is already part of the Global Observing System, and the WMO Manuals shall reference these practices. The mandatory practices required of GRUAN sites as detailed in this Guide and in the GRUAN Manual, reflect GRUAN’s primary goal of providing reference quality observations of the atmospheric column while accommodating the diverse capabilities of sites within the network. Relevant information from this Guide and from the GRUAN Manualis expected to be incorporated into the WMO Manual on the Global Observing System (WMO‐No. 544) and the Guide on the Global Observing System (WMO‐No. 488). Where possible, this Guide provides more in‐depth detail on specific methodologies, and these shall be appropriate for incorporation into, or referenced by, the WMO Guide to Meteorological Instruments and Methods of Observation (WMO‐No. 8). The GRUAN Manual and Guide are supported by a series of technical documents listed on the GRUAN website at www.gruan.org.