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GCOS Upper Air Network (GUAN)
Performance Monitoring


The Global Climate Observing System (GCOS) was established in 1992 to ensure that the observations and information needed to address climate-related issues are taken and made available to all potential users. It is co-sponsored by the World Meteorological Organization (WMO), the Intergovernmental Oceanographic Commission (IOC) of UNESCO, the United Nations Environment Programme (UNEP) and the International Council for Science (ICSU).

GCOS does not directly make observations nor generate data products. Rather, its role is to stimulate, encourage, coordinate or otherwise facilitate making necessary observations by national or international organizations in support of their own requirements and other shared goals. GCOS provides an operational framework for integrating, and enhancing as needed, the observational systems of participating countries and organizations into a comprehensive system focused on requirements for climate studies. To do this, GCOS builds upon existing and developing observing systems such as the Global Ocean Observing System, the Global Terrestrial Observing System, and the Global Observing System and Global Atmospheric Watch of the World Meteorological Organization. The GCOS Upper air Network, or GUAN, is one of the GCOS atmospheric networks.

The principal aims of the GUAN include ensuring a relatively homogeneous distribution of upper air stations that meet specific record length and observation continuity requirements as outlined by GCOS, and to make available current and historical upper air data for climate research. To meet these aims, GCOS Monitoring, Analysis, Archive and Lead Centres have been established for the GUAN. The WMO and GCOS act on information provided by the GUAN Monitoring, Analysis and Lead Centres to feedback to contributing members to enhance network performance and encourage the provision of station data from the GUAN.

The Met Office, Hadley Centre of the UK, routinely monitor and quality control monthly CLIMAT TEMP radiosonde data and develop upper air datasets for use in climate research. The European Centre for Medium Range Weather Forecasts monitor the receipt and quality of daily TEMP data. The National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center (NCDC) update and quality control daily upper air data and historical metadata as part of this Health of the Networks project, and in support of the Integrated Global Radiosonde Archive. The World Data Center for Meteorology (WDC) holds the GUAN data archive.

Performance Indicators

Data Completeness
Completeness is computed as the percentage of reported observations at each mandatory level relative to the total number of possible sounding days in each data month. The 00 and 12 UTC standard reporting times are summarized separately. Soundings taken within 2 hours of the nominal reporting times are counted. Separate calculations are provided for each sounding parameter: geopotential height; temperature; dew point depression; wind speed; and wind direction. In addition, percent completeness is provided relative to those cases when all parameters were available at a given mandatory level as well as for cases where at least one parameter was available.

Data Quality
As a simple measure of data quality, parameter completeness percentages are calculated using both Level 1 (pre-QC) and Level 2 (post-QC) values. Level 1 data is nearly raw having been subject to minimal pre-processing that includes the removal of duplicates. Level 2 data has passed through a series of quality assurance algorithms, which remove suspect values. Any reduction in completeness between and Level 1 and Level 2 data would be a measure of data quality. A report on the quality assurance algorithms is forthcoming.

Report Descriptions

Station Listing
The Station Listing provides list of GCOS Upper Air Network stations including latitude, longitude, and elevation along with country and beginning and ending data months.

Station Inventory
The Station Inventory is generated either from the Station Listing or the GUAN Station Map and displays information for the most current year. The percentages are calculated as part of the IGRA processing system.

Station Graphs
Station Graphs are generated either from the Station Listing or the GUAN Station Map and allow the user to define period of record, observation hour, level, and element for a given station. The percentages are calculated as part of the IGRA processing system.

Data Availability and Source

Radiosonde Values
The source of GUAN station data is the Integrated Global Radiosonde Archive (IGRA). IGRA constitutes a compilation of eleven source datasets. The core of IGRA is formed by four datasets based on Global Telecommunication System (GTS) messages that were preprocessed at one of three different locations in the United States: the National Climatic Data Center (NCDC, 1963-1970 and 2000-present), the National Center for Atmospheric Research (NCAR, December 1970-1972), and the National Centers for Environmental Prediction (NCEP, 1973-October 1999). These datasets have nearly consecutive periods of record. Two additional sources include collections of GTS reports that were pre-processed at the Australian Bureau of Meteorology between 1990 and 1993 (Australian GTS) and at the All-Russian Institute for Hydrometeorological Information between 1998 and 2001 (Russian GTS). Another source with extensive spatial coverage is a dataset compiled by the United States Air Force that consists of both GTS reports and non-GTS data. With a period of record of 1946-1973 for stations included in IGRA, this dataset extends the records of many stations back in time from the 1960s to the 1950s or 1940s. The temporal completeness and vertical resolution of data at stations in the United States, Australia, Argentina, and South Korea is further enhanced by four country-specific sets of data that were archived before their transmission over the GTS and thus may contain levels and variables not found in the GTS reports.

For a variety of reasons, including differences in decoding practices, some messages transmitted over the GTS are decoded only at certain receiving centers and not at others. Thus, even though extensive duplication generally exists among the core, Australian, and Russian GTS data, the latter two sources occasionally supply soundings that are either not present or incomplete in the core data. Recent GUAN and IGRA data come only from GTS data decoded at NCDC.

GUAN Station Metadata
Historical station information comes primarily from two sources: the WMO publication Instruments and Observing Methods Report No. 50: Historical Changes in Radiosonde Instruments and Practices and NOAA Technical Memorandum ERL ARL-211: A Digitized Metadata Set of Global Upper-Air Station Histories by D. Gaffen. In addition, NCDC as the GUAN Lead Centre has contacted GCOS Focal Points within National Meteorological and Hydrologic Services to obtain more recent station history information where possible.

Metadata for GUAN sites is available from the Integrated Global Radiosonde Archive (IGRA) website at: IGRA Metadata.

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