The availability performance of the GBON upper-air land stations is obtained by selecting the “upper-air” option under the GBON monitoring module. The generated maps display the availability performance for each station against the GBON baseline requirements, which for the upper-air stations are 2 complete soundings per day (i.e., a radiosonde is deemed complete if it measures air temperature and horizontal wind up and above 100hPa and air humidity up to 100hPa). The availability maps highlight the differences in reporting performance: stations that are compliant are displayed is green, stations with availability issues in orange for the daily aggregation, and in orange and red for the monthly aggregations. Moreover, stations that did not receive observations in the selected period are shown in black. Each category's info icon on the legend includes a detailed description of the thresholds utilised for that category. The category in which a station is displayed on the maps (e.g., compliant) 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. In this pop-up there is a link to the station metadata in OSCAR/Surface as well as a link to a chart containing the station availability statistics over time. Clicking on this link (“Time series”) will display a time series with the total number of received observations during the selected interval as well as the number of expected observations according to GBON requirements (2 and 2 times the number of days in the month for the daily and monthly periods, respectively).