Twenty Years in the SHADOZ: Milestones in Tropical Ozonesonde Reprocessing and Uncertainties

Since 1998, the SHADOZ (Southern Hemisphere ADditional OZonesondes) project has archived electrochemical concentration cell (ECC) type ozone profiles from up to 14 stations in the tropics and subtropics. In that time, ozonesonde intercomparison campaigns and independent lab experiments have advanced reprocessing methods to improve overall data quality and homogeneity. This has motivated the SHADOZ community to homogenize their long-term ozone archive that contains an array of operating procedures, standard and non-standard sensing solution types, and changing ozonesonde/radiosonde systems. All these factors can cause discontinuities to appear in the ozone data records. A second major milestone has been to estimate the uncertainty of each ozone profile in the SHADOZ network. Based on community driven consensus, deriving ECC sensor uncertainties is an essential component of reprocessing. Here, we present an overview of reprocessing methods for homogenizing SHADOZ long-term ozone records and show the estimates of ozone profile and total column ozone (TCO) uncertainty. Profile uncertainties are generally within 15% and peak around the tropopause where ozone is a minimum and can approach the detection limit of the ECC sensor. Overall, TCO uncertainties are found to represent 5-6% of the column measurement. Reprocessing and uncertainty results are shown in the context of comparisons with satellite overpass data where ozonesonde uncertainties, in particular, will be an invaluable barometer for evaluating existing and future satellite ozone profile and column measurements. Reprocessed TCO ozone records have improved the agreement with reference satellite TCO to within ±5%.