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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
Definition | Number of observations per station as received by each NWP centre during a period divided by the number of expected for that period |
Calculation | Total of received observations per observed variable calculated as described in Table 1 divided by the sum of all expected observations for the period. |
Expected data | ‘International exchange schedule’ and ‘observation schedule’ obtained from OSCAR/Surface database |
Math expression | , where NValid is the maximum of Nj as described in Table 1 . |