Unified database of ozonesounding profiles

The unified database of ozonesounding profiles was obtained through the merging of three existing ozonesounding datasets, provided by the Southern Hemisphere Additional OZonesondes (SHADOZ), the Network for the Detection of Atmospheric Composition Change (NDACC), and the World Ozone and Ultraviolet Radiation Data Centre (WOUDC). Only a selected set of variables of interest, both data and metadata, were considered to build the unified dataset, due to the heterogeneous formats and varying levels of detail provided by each network, even when referring to measurements shared across different initiatives. These variables are listed in the following Table. Standard name Description Unit idstation The name of the station. N.A. location_latitude Latitude of station. deg location_longitude Longitude of station. deg lacation_height Height is defined as the altitude, elevation, or height of the defined platform + instrument above sea level. m date_of_observation Date when the ozonesonde was launched (in format yyyy-mm-dd hh:mm:ss with time zone). N.A. time Elapsed flight time since released. s pressure Atmospheric pressure of each level in Pascals. Pa geop_alt Geopotential height in meters. m temperature Air temperature in degrees Kelvin. K relative_humidity Relative humidity in 1. 1 wind_speed Wind speed in meters per seconds. m/s wind_direction Wind direction in degrees. deg latitude Observation latitude (during the flight). deg longitude Observation longitude (during the flight). deg altitude Height of sensor above local ground or sea surface. Positive values for above surface (e.g., sondes), negative for below (e.g., xbt). For visual observations, the height of the visual observing platform. m (a. s. l.) sample_temperature Temperature where sample is measured in degrees Kelvin. K o3_partial_pressure The level partial pressure of ozone in Pascals. Pa ozone_concentration The level mixing ratio of ozone in ppmv. ppmv ozone_partial_pressure_total_uncertainty Total uncertainty in the calculation of the ozone partial pressure as a composite of the individual uncertainty contribution. Uncertainties due to systematic bias are assumed as random and follow a random normal distribution. The uncertainty calculation also accounts for the increased uncertainty incurred by homogenizing the data record. Pa network Source network of the profile. N.A. type Station classification flag. N.A. filter_check Profile quality control flag. N.A. The dataset is organized into two main tables: unified_header, which contains metadata associated with each ozonesounding profile (idstation, date_of_observation, location_latitude, location_longitude, location_height, network, type, filter_check); unified_value, which includes the actual measurement data (idstation, date_of_observation, time, pressure, geop_alt, temperature, relative_humidity, wind_speed, wind_direction, latitude, longitude, altitude, sample_temperature, o3_partial_pressure, ozone_concentration, ozone_partial_pressure_total_uncertainty). To improve accessibility and performance, both tables are further subdivided into year-specific subtables, allowing for more efficient querying and data management across temporal ranges. Among the metadata variables included in the unified_header table, type and filter_check play a key role in characterizing the quality and coverage of the ozonesounding profiles. The type variable classifies each station based on the continuity of its time series: stations are grouped into Long Coverage (G), Medium Coverage (Y), or Short Coverage (R), depending on whether they provide at least one profile per month for at least 95% of the months in their time series, spanning: ≥20 years for Long Coverage, ≥10 and <20 years for Medium Coverage, <10 years for Short Coverage. The filter_check variable is a quality control flag ranging from 0 to 3, summarizing the results of three structural checks applied to each profile: completeness of monthly coverage (at least three ascents per month), vertical coverage (reaching at least 10 hPa), and vertical resolution (minimum one data point every 100 meters). A higher filter_check value indicates better compliance with these criteria and, consequently, higher data reliability. Furthermore, an algorithm was implemented able to merge the different datasets by handling their different features and duplicated profiles, i.e. profiles from different networks recorded within a 2-hour time window. In such cases, the profile that passes the greatest number of quality control (filter_check) tests is retained in the unified dataset. If multiple profiles meet the same number of quality control criteria, the selection is refined using additional indicators of dataset maturity, such as the availability of metadata, documentation, peer-reviewed publications, and especially the presence of measurement uncertainties associated with ozone concentration profiles. This last criterion is prioritized, as uncertainties are routinely provided in SHADOZ and, only for a limited number of profiles, in NDACC, while they are generally absent in WOUDC.