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Design Principles
- For climate change detection and calibration/validation, horizontal resolution should be sufficient to resolve synoptic-scale waves (wavenumber 6).
- Higher resolution is needed for other applications. Vertical resolution should be sufficient to monitor major variability in atmospheric structure.
- Ideally, radiosondes should ascend twice per day to monitor atmospheric variability, provide reliable monthly statistics, validate satellite retrievals, allow assessment of radiosonde instrument biases, and avoid biases which could arise through atmospheric tides.
- A single ascent per day is, though useful, a bare minimum. Measurements (from any instrument or network including MSU) must have low bias and high accuracy (Table 5.1)
Table 5.1 Upper-air data quality requirements.
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Maximum bias |
Maximum random error of individual observations |
|
Temperature |
0.1o C |
0.5o C |
| Moisture |
2% of climatology |
5% of climatology |
| Wind |
1 m/sec |
1 m/sec in lower troposphere; otherwise 2 m/sec. |
Other Observing Network Requirements
Every month at least one observation on each of at least 25 days should attain the minimum requirements below. The observing frequency (1 or 2 per day) in itself is not a criterion. The target requirement for observation frequency is 2 per day, in accordance with WWW regulations for radiosonde observations.
Minimum Requirements: • Temperature up to 100 hPa, humidity up to the tropopause, wind direction and speed up to 100 hPa.
Target Requirements: • Minimum requirements plus temperature and wind up to 5 hPa, 2 observations per day. |
Best practices for GUAN stations
(Manual on the Global Observing System, WMO-No. 544, 2.10.4.9)
- Long-term continuity should be provided for each GUAN station. This requires the provision of the necessary resources, including well-trained staff, and keeping changes of location to a minimum.
- Changes of bias caused by changes in instrumentation should be evaluated by a sufficient overlapping period of observation (perhaps, as much as a year) or by making use of the results of instrument intercomparisons made at designated test sites.
- Soundings should preferably be made twice a day and should reach as high as possible, noting the GCOS requirements for ascents up to a height of 5 hPa. Because climate data are needed in the stratosphere to monitor changes in the atmospheric circulation, composition and chemistry, every effort should be made to maintain soundings regularly up to a level as high as possible noting the above GCOS requirement
- CLIMAT TEMP data should be provided in an accurate and timely manner. CLIMAT TEMP 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 at each GUAN site. Periodic calibration, validation and maintenance of the equipment should be carried out to maintain the quality of the observations.
- Basic checks should be made before each sounding to ensure accurate data. Checks should also be made during and at the end of each sounding to assure corrections of incomplete soundings or errors before transmission.
- Back-up radiosondes should be released in cases of failure in order to maintain the record from the GUAN station.
- Detailed metadata should be provided. The batch identifier on the radiosondes should be logged for each flight, so that faulty batches can be identified and the data amended or eliminated from the climate records if necessary. Up-to-date records of metadata in a standard format should be provided to the GUAN Archive so that shifts in the data will not be mistaken for climate change. The metadata should include detailed information about the station such as location, elevation, operating instruments and their changes over time. Changes to operating and correction procedures should also be recorded. Both the corrected and uncorrected upper-air observation should be archived. Climate change studies require extremely high stability in the systematic errors of the radiosonde measurements.
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