The Operational Observing System for the GUAN

Data Flow Diagram

The GCOS Upper-air Network (GUAN) consists of 164 stations selected from the Global Observing System of the World Weather Watch. Criteria for choice of sites included homogeneity, a history of high quality observations, and an acceptable length of historical record.(GUAN Station List - Summary By Region) (GUAN Stations Map)

Data Flow Diagram for the GUAN

The data flow for the GUAN begins with national centers that collect and submit the data to the international system. International centers perform quality control on the data, prepare data products for users, and archive it for future users. Some of these international centers prepare routine reports on the performance of the system. The diagram below documents these activities and responsibilities.

National Collecting Centers for Upper Air Data

The National Center that operates the GUAN station is responsible for collecting the data according to "best practices" established by the AOPC. The best practices are as follows.

• long-term continuity;
• provision of detailed metadata;
• use of high altitude soundings (up to 5 hPa if possible);
• rigorous quality control at stations;
• back-up release in case of failure;
• co-location with atmospheric constituent measurements (e.g., GAW stations,)

The data collected by the network of GUAN stations are transmitted on the GTS in the form of upper-air reports (TEMP and CLIMAT TEMP). Stations are requested to make twice daily observations. Meta data supporting the observations are not transmitted on the GTS, but are made available to the final archives at a later date by the national collecting centers.

GUAN Monitoring Center

The European Centre for Medium-term Weather Forecasting (ECMWF) and the Hadley Centre have agreed to take on the responsibility of routine monitoring of daily TEMP and CLIMAT TEMP reports respectively.

The reports on TEMPs will include availability of messages and statistics on reports attaining certain critical levels of height (100 and 10 hPa) and of differences between observed values and model initial guess fields. The information from the Monitoring Center will include station performance indicators. Monitoring will include all GUAN stations.

The WMO Secretariat

The WMO Secretariat has two roles to play in the operation of the GCOS Upper Air Network. In the first role the Secretariat makes arrangements and encourages WMO Members to operate certain of their upper air stations according to the best practices developed by the AOPC and provide the data and supporting meta data to the international centers that operate the GUAN. When for any reason a GUAN Upper Air Station may be discontinued, the Secretariat tries to make alternative arrangements for a nearby station as a replacement.

The Secretariat also provides feedback to the National Meteorological Services who are providing data with persistent or common errors to request a resolution of the problem to improve data quality. The Secretariat acts on information provided the ECMWF based on monitoring of the upper air data quality and availability in the process of real time operational usage.

The GCOS Upper Air Analysis Centers

The Hadley Centre  in the UK and the National Climatic Data Center (NCDC) in the US cooperate to act as the GUAN Analysis Center GUAN AC) for the GCOS upper air data. These centers also cooperate with the ECMWF so that the quality control work done on the real time data flow by that center is taken into account in further processing, analysis, and improvement of the global GUAN data set. The GUAN AC provides an annual report on station performance including performance indicators.

The following diagram shows some of the tasks and QC operations carried out by these centers and the exchanges of data, meta data, and information.

In addition the NCDC in it's role as World Data Center A - Meteorology acts as a long term archive for the data and supporting meta data.

The GUAN Archive

The World Data Center A for Meteorology collocated with NCDC in Asheville, North Carolina will act as the archive for all GUAN data and station meta data. Data and meta data will be made available to users through the regular distribution facilities.

Quality Control of GUAN Observations and Feedback of Results

• Final quality control and bias removal of GUAN and other daily and monthly radiosonde data is planned within the Comprehensive Aerological Reference Data Set (CARDS) project at NOAA/NCDC, Asheville, North Carolina, USA. The results of the quality control of the data at the ECMWF and the Hadley Centre are provided for use in the final quality control as shown in the figure above.
• GCOS (through the chair of GCOS SC), The WMO Secretariat, and the ECMWF all provide feedback to operators of GUAN stations for correction of persistent problems with the upper-air observations. National operators are informed of the purposes and value of their contributions, and receive statistics on the performance of the GUAN stations to re-enforce the importance of continuing high quality observations.
• Where the performance of GUAN stations is consistently poor, GCOS will work with CBS and the relevant national meteorological service to identify the cause of the problem and identify possible solutions.

Data Management Principles for the GUAN

• Original data, quality-controlled data and bias-adjusted data (from any instrument or network) are all to be retained, along with flags indicating quality and source of data. (For radiosondes, these requirements apply to all stations, not just GUAN).
• Meta-data are also to be held in a readily accessible form in the appropriate archives.
• GUAN daily data and derived monthly statistics are held within CARDS at WDC-A Meteorology with a copy at WDC-B. NMSs whose daily radiosonde data are not in CARDS are requested to provide them. Temperature, humidity, wind and geo-potential height at standard and significant pressure levels are required.
• CARDS is being managed jointly by NCDC and the Hadley Centre of the UK Meteorological Office, which together may be regarded as fulfilling the role of a GCOS Upper Air Data Centre. The Hadley Centre also process monthly CLIMAT TEMP data 
• Derived data, based on the GUAN and the entire observing system (e.g. monthly averages of re-analyses at standard levels) are also to be available at WDCs A and B

Data Quality Information Flow from the Monitoring Centers

This flow provides quality information to the operators of GUAN stations experiencing problems with data quality and availability to allow them to correct the problems. The flow is also provided to the Secretariat in order that the WMO can provide assistance to the Members in resolving the more difficult problems.

Content:   Information on problems with the upper-air data on the GTS as detected by the GUAN Lead Center.
Format:    Statistical presentations and documents.
Frequency:    On a six monthly basis for GUAN stations with persistent problems
Availability:    Available to the WMO Secretariat, and the WMO Members operating the station in question.
Reason:    To provide the information necessary for WMO Members to solve problems with data availability and quality.

Upper-air Reports on the GTS

This data flow is the normal operational data flow for upper-air reports. The observations are made twice daily and inserted on the GTS as soon as possible after being made. CLIMAT TEMP reports are placed on the GTS monthly. The code forms used are available in the WMO Manual on the GTS.

Content:   Observations of atmospheric temperature, humidity, wind and geo-potential height at standard and significant pressure levels. 
Format:   The WMO Code Forms for Upper-air data.
Frequency:    Twice daily and monthly from upper-air stations where operational considerations permit.
Availability:    Freely available to all via the GTS
Reason:    To provide necessary data for operational weather forecasting and issuance of appropriate warnings.

Upper-air Reports and Supporting Meta Data

This data flow represents a delayed mode data flow from the national collecting centers (usually NMCs or NMHCs) to the Wolrd Data Centers for Meteorology. The data have been quality controlled and the necessary meta data provided to meet GUAN specifications have been gathered and included. The WDCs provide the final archive for the best available data sets for future users.

Content:   Observations of atmospheric temperature, humidity, wind and geo-potential height at standard and significant pressure levels and supporting meta data.
Format:   Formats are provided in the GUIDE to the GCOS Surface and Upper Air Networks: GSN and GUAN, Report GCOS - 73.
Frequency:    On an annual basis for new data. As soon as possible for historical data.
Availability:    Available to all at no more than the cost of reproduction from the World Data Centers.
Reason:    To provide a high quality data archive for future users of the GUAN data.

Data and Products from the Upper-air Analysis Centers

The Upper-air Analysis Centers provide upper-air analyses and products to users who are monitoring or conducting research into climate change. An example is the Intergovernmental Panel on Climate Change which is the main advisory body to the UN Framework Convention on Climate Change.

Content:   Analyses of climate related data including the GUAN upper-air data and evaluations of climate change and consequences.
Format:   Documents, statistical analyses, etc.
Frequency:    From monthly to annual and longer time periods.
Availability:    Available to various users by arrangement.
Reason:    To provide decision support data and information for the political and research processes.

QC Information, Bias Adjustments, etc

The archive center and the analysis center exchange information and revised data as a result of quality control to ensure the continued improvement of the GUAN database. For the monthly data, the procedures include analyzing the data; improving bias adjustments; creating global and regional monthly statistics; and developing and providing gridded products with reduced biases.

The Global Telecommunications System (GTS)

The GTS is the communications system operated by the World Weather Watch for the transmission of atmospheric, oceanographic, and terrestrial data for use in operational weather forecasting and for the distribution of data analyses and products.

Content:   Observations of atmospheric, oceanographic, and terrestrial data, data products, and data analyses for weather forecasting and the issuance of warning.
Format:   Code forms approved by the WMO Commission on Basic Systems and published in the Manual on the GTS.
Frequency:     Continuous broadcast.
Availability:    Available to all with physical access to the GTS or through arrangement with such GTS centers..
Reason:    To provide data, products, and analyses in operational time frames.