The data quality monitoring practices are based on the assessment of the performance of observational systems against a set of targets defined for the three performance measures -availability, timeliness and quality - that are proposed in the Technical Guidelines for Regional WIGOS Centres on the WIGOS Data Quality Monitoring System (WMO, 2018) hereafter called WDQMS Guidance Document. The current version of the web tool provides only monitoring of availability and quality for land-based surface and upper-air observations.
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The monitoring of data availability is based on performance figures obtained from comparing the observations received from the network to those required and expected to be ingested into the WMO Information System (WIS) according to the schedule determined from OSCAR/Surface metadata. The Global Basic Observing Network (GBON) draft provisions are also used as reference for generating availability performance maps.
All targets regarding availability refer to the number of observations received by NWP centres from the network (Table 1). For each station, 6-hourly totals (section 4.1) and daily totals (section 4.2) are computed based on the quality monitoring information received from all the NWP Centres (section 5) and stored in WDQMS Database. This task is performed on a daily basis, so that availability information of the observing network is accessible in near-real time. It is worth noting that in WDQMS context “observations received” means the observations that were made available to the assimilation system of each NWP centre and are considered as a good proxy for the observations disseminated on the GTS.
OSCAR/Surface
For each station, the expected 6-hourly and daily totals (i.e. the number of observations the station should exchange internationally via GTS/WIS during the defined period) is extracted from OSCAR/surface and made available to be used as reference (Table 2). In this context, the schedule of observations is obtained for all the stations recorded in OSCAR/Surface that meet the following criteria: are declared operational or partially operational on the level of the GOS/RBSN affiliation; have an observation of the variable of interest; have the “international exchange” field set to “yes” (currently only for surface); are valid at the date of the defined period. For the upper-air, the schedule is obtained for all stations that are of station class Upper-air/Radiosonde. In case an observation has no deployment in OSCAR/Surface, a default schedule is assumed, which is of 3 hourly observations for surface and 2 daily observations for upper-air stations, one in each interval, the 00 and 12h interval. All the metadata used in WDQMS is updated daily, which means that any update on the station metadata recorded in OSCAR/surface will be reflected on the performance maps the next day.
The availability performance reports are generated by comparing the 6-hourly and daily totals against the respective expected values for each observed variable (Table 2). A performance report is generated individually for each NWP Centre and temporal interval. For the 6-hourly totals, four reports are generated daily for each of the NWP centres.
GBON
The availability is also compared against GBON requirements. According to the draft provisions the expected frequency of observations is: hourly for surface-based and 12-hourly for the upper-air observations. The availability performance reports based on GBON targets are generated by comparing the availability against the expected values calculated for the different periods using the frequency rules mentioned above. This means that for surface observations, the expected data is 6 and 24 observations for 6-hourly and daily reports, respectively. For upper-air observations, the GBON requirements are only applied to the daily reports with a total of 2 observations expected.
Table 1 - Availability
Definition | Number of observations per station as received by each NWP Centre during a defined period. |
Calculation | For each observed variable, the sum of all valid data is computed |
Valid data | Data not flagged as missing value |
Math expression | , where N is the total number of valid data for variable j. |
Table 2 - Availability performance
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Definition
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Number of observations per station as received by each NWP centre during a period divided by the number of expected for that period
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Calculation
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Total of received observations per observed variable calculated as described in Table 1 divided by the sum of all expected observations for the period.
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Expected data
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‘International exchange schedule’ and ‘observation schedule’ obtained from OSCAR/Surface database
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Math expression
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, where NValid is the maximum of Nj as described in Table 1 .