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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 the 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 the 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. Moreover the results are aggregated across NWP centres (section 5.2) to help reduce potential differences between the number of observations available on the GTS and the number of the observations seen by the individual assimilation systems.
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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 upper-air observations. The availability performance reports based on GBON targets are generated by comparing availability against 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 - AvailabilityAnchor Table1 Table1
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 | Nj, where N is the total number of valid data for variable j. |
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