Relative performance of three SAGE‐II data versions under high aerosol conditions based on comparisons with microwave and ozonesonde profiles measured at two NDSC sites

Abstract

Intercomparisons between SAGE‐II data versions 5.93, 5.96, and 6.1 with microwave ozone and ozonesonde measurements made at the NDSC primary station at Lauder, New Zealand, and with microwave measurements made at the NDSC complementary station at Table Mountain, California, are reported on here. The focus is on SAGE‐II measurement performance during the period when stratospheric aerosol levels were substantially elevated following the 1991 Mt. Pinatubo eruption. SAGE‐II ozone retrievals are potentially affected by aerosol levels and size distributions because extinction due to aerosol must be estimated and subtracted from the measured total extinction in the 600 nm ozone channel to determine the ozone amount; the microwave and ozonesonde comparison measurements are aerosol insensitive. Around 10–25 hPa, the newer algorithm versions retain a tendency toward extinction‐dependent bias previously reported for version 5.9; this dependence may be larger than previously indicated at moderately high aerosol levels. In the 30–40 hPa range, the extinction dependence of version 6.1 (and, usually, version 5.96) data is a few times less than that of version 5.93. Between about 30 and 80 hPa most points at moderately elevated aerosol extinctions are less affected than in version 5.93, and these are fewer and/or less affected in version 6.1 than in version 5.96. When aerosols are at background levels, the precisions of version 5.93 and 5.96 measurements are at least somewhat better, around 30 hPa, than the errors provided with the data. The errors provided with version 6.1 data are substantially smaller than in previous versions, and small enough that the experimental sensitivity was insufficient to draw conclusions regarding the actual precision in comparison to the error values.