Methods to homogenize ECC ozonesonde measurements across changes in sensing solution concentration or ozonesonde manufacturer
Other literature type
Schmidlin, Francis J.
Mercer, Jennifer L.
Smit, Herman G. J.
Johnson, Bryan J.
(issn: 1867-8548, eissn: 1867-8548)
From the mid 1990s to the late 2000s the consistency of electrochemical cell ozonesonde long term records has been compromised by differences in manufacturers, Science Pump and ENSCI, and differences in recommended sensor solution concentrations, 1.0 % potassium iodide (KI) and the one half dilution 0.5 %. To investigate these differences a number of organizations independently undertook comparisons of the various ozonesonde types and solution concentrations, resulting in 197 ozonesonde comparison profiles. The goal is to derive transfer functions to allow measurements outside of standard recommendations, for sensor composition and ozonesonde type, to be converted to a standard measurement and thus homogenize the data to the expected accuracy of 5 % (10 %) in the stratosphere (troposphere). Subsets of these data have been analyzed previously and intermediate transfer functions derived. Here all the comparison data are analyzed to compare: 1) differences in sensor solution composition for a single ozonesonde type, 2) differences in ozonesonde type for a single sensor solution composition and 3) the manufacturer’s recommendations of 1.0 % KI solution for Science Pump and 0.5 % KI for ENSCI. From the recommendations it is clear that ENSCI ozonesondes and 1.0 % KI solution result in higher amounts of ozone sensed. The results indicate that differences in solution composition and in ozonesonde type display little pressure dependence at pressures ≥ 30 hPa and thus the transfer function can be characterized as a simple ratio of the less sensitive to the more sensitive method. This ratio is 0.96 for both solution concentration and ozonesonde type. The ratios differ at pressures < 30 hPa such that OZ<sub>0.5 %</sub> / OZ<sub>1.0 %</sub> = 0.90 + 0.041 ● log<sub>10</sub>(p) and OZ<sub>ENSCI</sub> / OZ<sub>SciPmp</sub> = 0.764 + 0.133 ● log<sub>10</sub>(p). For the manufacturer recommended solution concentrations the dispersion of the ratio (SP-1.0/EN-0.5), while significant, is generally within 3 % and centered near 1.0, such that no changes are recommended. For stations which have used multiple ozonesonde types with solution concentrations different from the manufacturer’s recommendations, this work suggests that a reasonably homogeneous data set can be created if the quantitative relationships specified above are applied to the non-standard measurements. This result is illustrated here in an application to the Nairobi data set.