Stratospheric Aerosol and Gas Experiment II and ROCOZ‐A ozone profiles at Natal, Brazil: A basis for comparison with other satellite instruments

Abstract

We present the results of comparisons of satellite measurements of ozone from the Stratospheric Aerosol and Gas Experiment II (SAGE II) with in situ measurements from ROCOZ‐A and electrochemical concentration cell (ECC) ozonesondes at Natal, Brazil (5.9°S, 35.2°W), during the southern hemisphere autumn of 1985. Since data were collected over a region of low ozone variability, comparisons were made of the mean values of 14 SAGE II profiles with the mean values of 7 ROCOZ‐A and 7 ECC profiles, rather than of a more limited set of paired comparisons. The basic comparison presented here is ozone number density versus geometric altitude, the fundamental ozone measurement from SAGE II. Over the altitude region from 20 to 52 km SAGE II ozone densities averaged 0.4% lower than ROCOZ‐A. The average of the absolute values of the ozone density differences for the two instruments was 2.4% over these altitudes. Owing in large part to the number of profiles in the data sets, the 95% confidence limits for the ozone density differences in these comparisons averaged 3.5% from 20 to 52 km, a significant improvement over previous results. In terms of ozone mixing ratio versus geometric altitude from 20 to 52 km, SAGE II values had a difference of 3.4% from ROCOZ‐A (SAGE II higher), an average absolute difference of 3.8%, and an average of 4.7% for the 95% confidence limits. Differences between the ozone density and mixing ratio results are due to the auxiliary temperature and pressure values for the satellite and in situ instruments. The effects of pressure differences on the vertical positioning of the ozone profiles are not important for the altitude‐based comparisons of SAGE II and ROCOZ‐A. However, they become an important consideration in the comparisons of SAGE II with pressure‐based ozone measurements from other satellite instruments. The composite sets of ozone, temperature, and pressure values presented here form an excellent basis for comparisons with other satellite ozone measurements.