A first version of a comprehensive upper air network service back to 1905 on the Copernicus platform

Within the Copernicus Climate Change Service (C3S), several efforts have been initated for providing observation data via the Climate Data Store (CDS). We report on the InSitu Comprehensive Upper Air Network service which is under review for publication via the CDS.
Compared to existing repositories of historical radiosonde and PILOT balloon data, it introduces important novelties:
1) besides long-period records, it contains also short-period records, which are valuable for climate data assimilation efforts such as ERA5
2) homogeneity adjustments for temperature, humidity and wind for all records longer than a year.
3) observation+representativity error estimates derived from ERA5 reanalysis departure statistics
4) additional data and metadata that accompany observation data, such as departure statistics and instrumentation information that can be downloaded in structured form
5) a flexible and user friendly interface, based on that of gridded data from the CDS, that allows to download data in CSV or netCDF formats, suitable for both time series analysis (long single station records) but also reanalysis purposes (all observation records for a point in time). 

Existing challenges regarding the formats to be used and regarding a sensible structuring of the metadata will be discussed. We will also outline the future extension of the service to offer gridded products out of the station records.