GCOS Upper-Air Network (GUAN)

A red balloon floats in a clear blue sky with a faint trail of an airplane visible on the right.

To serve specifically the needs of global climate applications, two networks of observing stations have been established as Global Climate Observing System (GCOS) Baseline Networks, mainly on the basis of existing GOS networks. These are:

the GCOS Surface Network (GSN) (1028 stations as of 01/01/2010)
the GCOS Upper-Air Network (GUAN) (169 stations as of 01/01/2010)

These networks form a minimum configuration required for global applications. Regional climatic needs can be much more extensive, and it is anticipated that such needs will be served by more dense networks on a regional basis, possibly with more extensive requirements for observing programmes and specifications.

The GCOS Upper-Air Network (GUAN) has been established mainly based on the existing Global Observing System (GOS) network and it forms a minimum configuration required for global applications for upper-air climate monitoring. The spacing of GUAN stations is set at 5 to 10 degrees latitude, sufficient to resolve synoptic-scale waves. The desired parameters are temperature, pressure (geopotential height), wind, and humidity (at least in the troposphere).

The detailed requirements of the GUAN are documented in the GCOS publication 144 - ‘GUIDE TO THE GCOS SURFACE NETWORK (GSN) AND GCOS UPPER-AIR NETWORK (GUAN)’, and is accessible from the WMO e-library.

Monthly monitoring statistics are provided by the ECMWF and additional monitoring products are available on the WMO Data Quality Monitoring System (WDQMS).

The following table is the 2023 summary for the GCOS Upper-Air Network (GUAN) monitoring against the GCOS minimum requirements (25 daily soundings to 30hPa per month) for each region, according to the monthly statistics provided by ECMWF. In brackets are the same statistics for 2011 to 2022. For 2013 to 2018 these are based on availability according to NCEP, and for 2011 to 2012 to NCEI.

Region	Number of GUAN stations (2023)	% meeting minimum GCOS requirements in 2023 (% for 2022, 2021, 2020, 2019, 2018, 2017, 2016, 2015, 2014, 2013, 2012 and 2011)
RA-I	23	43% (47%, 47%, 30%, 22%, 22%, 30%, 39%, 35%, 39%, 46%, 48%, 57%)
RA-II	38	84% (84%, 71%, 84%, 87%, 87%, 89%, 87%, 87%, 87%, 87%, 87%, 87%)
RA-III	18	56% (61%, 61%, 61%, 72%, 72%, 61%, 61%, 67%, 72%, 67%, 89%, 78%)
RA-IV	24	79% (92%, 96%, 96%, 96%, 92%, 92%, 87%, 79%, 83%, 75%, 83%, 87%)
RA-V	38	82% (82%’ 79%, 79%, 79%, 79%, 79%, 84%, 79%, 76%, 74%, 84%, 87%)
RA-VI	24	75% (83%, 87%, 87%, 92%, 87%, 87%, 87%, 87%, 87%, 83%, 92%, 87%)
Antarctica	12	67% (67%, 50%, 50%, 67%, 67%, 67%, 58%, 67%, 58%, 58%, 83%, 83%)