A Post-2013 Drop-off in Total Ozone at Half of Global Ozonesonde Stations: ECC Instrument Artifacts?

An international effort to improve ozonesonde data quality and to reevaluate historical records has made significant improvements in the accuracy of global network data. However, during 2013-2016, ozonesonde total column ozone (TCO; O) at 17 of 37 regularly reporting stations exhibited a sudden drop-off relative to satellite measurements. The ozonesonde TCO drop is 2-8 % compared to satellite and ground-based TCO, and 5-10 % or more compared to satellite stratospheric O profiles, compromising the use of recent data for trends, although they remain reliable for other uses. Hardware changes in the ozonesonde instrument appear to be a major factor in the O drop-off, but no single property of the ozonesonde explains the findings. The bias remains in recent data. Research to understand the drop-off is in progress; this letter is intended as a caution to users of the data. Our findings underscore the importance of regular ozonesonde data evaluation