The availability performance of the GBON-affiliated surface land stations is obtained by selecting “surface” under the GBON monitoring module. The maps display the availability performance against the GBON baseline requirements (hourly observations) for each station affiliated to GBON. Reporting performances for the selected period (i.e., 6-hourly, daily, or monthly) and variable (surface pressure, 2m temperature, 10m zonal wind, 10m meridional wind and 2m relative humidity), fall into one of four categories: compliant (green), reporting below requirements (orange and red), or not reporting at all (black). The values for the threshold are described in detail on the info icon for each category on the legend. The category in which a station is displayed on the map is determined by the data aggregation across centres, where the centre with the best availability performance is selected (i.e., the information will come from the centre with the highest total in the period). Clicking on the station dot shows a pop-up window with detailed information about the station data availability as provided by each of the NWP centres for the selected period. This pop-up contains links to a chart with the station availability statistics over time (“Time series”) and to the station metadata in OSCAR/Surface. Clicking on the former link will display a time series with the total number of received observations for the selected interval/variable as well as the number of expected observations according to GBON requirements (6, 24 and 24 times the number of days in the month for the 6-hourly, daily, and monthly periods, respectively).