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Facilitating Access to Global Observing Systems Data and Information

Observing Requirements for the GSN

Stations in the GCOS Surface network (GSN) are to collect and manage data according to "best" practices, collect and provide detailed meta data, and report their data in both CLIMAT and SYNOP form on the GTS.

For a very good discussion of the requirements for GSN and GUAN data including accuracy and homogeneity, historical records, and national commitments to observations see the GCOS publication Guide to the GCOS Surface and  Upper-Air Networks: GSN and GUAN (Version 1.1) GCOS - 73 .

Required Variables for GSN Data

The historical and continuing operational variables that should be supplied, for as long a period of record as possible for the GSN stations are described in the above noted publication (GCOS-73) and are reproduced here.

Minimum Requirements:

  • Monthly means of daily maximum, minimum and mean temperature.
  • Monthly precipitation amounts.

Target Requirements (in addition to the minimum):

  • Temperature: monthly mean, minimum, and maximum.
  • Pressure: monthly mean values, station level and mean sea level.
  • Precipitation: number of days with precipitation.
  • Temperature: daily mean, minimum and maximum.
  • Daily precipitation amounts
  • Pressure: daily mean, station level and mean sea level.

If only monthly values are available, the number of days used in the calculation should be provided as a Minimum Requirement.

Updates of the complete daily data and supporting meta data for the GSN stations should be sent to the WDCs once national quality control procedures have been completed.

Length of Record

The minimum length of historical record for GSN data is 20 years and the target length is 50 years.

Best Practices for GSN Stations (Manual on the Global Observing System, WMO-No. 544, 2.10.3.17)

  • Long-term continuity should be provided for each GSN station. This requires the provision of the necessary resources, including well-trained staff, and keeping changes of location to a minimum.
  • In case of significant changes in sensor devices or station location, Members should provide for a sufficiently long period of overlap (at least one, but preferably two years) with dual operation of old and new systems to enable comparisons to be made and the identification of inhomogeneities and other measurement characteristics.
  • CLIMAT data should be provided in an accurate and timely manner. CLIMAT reports should be transmitted by the fifth day of the month but not later than the eighth day of the month.
  • Rigorous quality control should be exercised on the measurements and their message encoding. CLIMAT reports require quality control of the measurements themselves and their message encoding to ensure their accurate transmission to national, regional and world centres for their use. Quality control checks should be made on site and at a central location designed to detect equipment faults at the earliest stage possible. The Guide to Instruments and Methods of Observation (WMO No 8) provides the appropriate recommendations.
  • The site layout should follow the recommended form (Guide on the GOS, WMO No 488).
  • The site and instruments should be inspected regularly and maintained according to WMO recommended practices (Guide to Instruments and Methods of Observation (WMO No 8). As part of the maintenance, the necessary calibration practices should be traceable to the standards provide by the Guide.
  • A national plan should be developed to archive daily data and metadata pertaining to each climate station. Metadata should include data concerning a station's establishment, subsequent maintenance, and changes in exposure, instrumentation and staff. The data and metadata should be in its original form as well as in digital format.
  • Detailed metadata and historical climate data for each GSN station should be provided to the GSN Archive. Both data and metadata should be up-to-date.
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