First reprocessing of Southern Hemisphere ADditional OZonesondes (SHADOZ) profile records (1998-2015): 1. Methodology and evaluation

Electrochemical concentration cell ozonesonde measurements are an important source of highly resolved vertical profiles of ozone (O3) with long-term data records for deriving O3 trends, model development, satellite validation, and air quality studies. Ozonesonde stations employ a range of operational and data processing procedures, metadata reporting, and instrument changes that have resulted in inhomogeneities within individual station data records. A major milestone is the first reprocessing of seven Southern Hemisphere ADditional OZonesondes (SHADOZ) station ozonesonde records to account for errors and biases in operating/processing procedures. Ascension Island, Hanoi, Irene, Kuala Lumpur, La Réunion, Natal, and Watukosek station records all show an overall increase in O3 after reprocessing. Watukosek shows the largest increase of 9.0 ± 2.1 Dobson Units (DU) in total column O3; Irene and Hanoi show a 5.5 ± 2.5 DU increase, while remaining sites show statistically insignificant enhancements. Negligible to modest O3 enhancements are observed after reprocessing in the troposphere (up to 8%) and stratosphere (up to 6%), except at La Réunion for which the application of background currents reduces tropospheric O3 (-2.1 ± 1.3 DU). Inhomogeneities due to ozonesonde/solution-type changes at Ascension, Natal, and La Réunion are resolved with the application of transfer functions. Comparisons with EP-TOMS, Aura’s Ozone Monitoring Instrument and Microwave Limb Sounder (MLS) satellite O3 overpasses show an overall improvement in agreement after reprocessing. Most reprocessed data sets show a significant reduction in biases with MLS at the ozone maximum region (50-10 hPa). Changes in radiosonde/ozonesonde system and nonstandard solution types can account for remaining discrepancies observed at several sites when compared to satellites.