Ozone profiles in the high‐latitude stratosphere and lower mesosphere measured by the Improved Limb Atmospheric Spectrometer (ILAS)‐II: Comparison with other satellite sensors and ozonesondes

Abstract

A solar occultation sensor, the Improved Limb Atmospheric Spectrometer (ILAS)-II, measured 5890 vertical profiles of ozone concentrations in the stratosphere and lower mesosphere and of other species from January to October 2003. The measurement latitude coverage was 54–71°N and 64–88°S, which is similar to the coverage of ILAS (November 1996 to June 1997). One purpose of the ILAS-II measurements was to continue such high-latitude measurements of ozone and its related chemical species in order to help accurately determine their trends. The present paper assesses the quality of ozone data in the version 1.4 retrieval algorithm, through comparisons with results obtained from comprehensive ozonesonde measurements and four satellite-borne solar occultation sensors. In the Northern Hemisphere (NH), the ILAS-II ozone data agree with the other data within ±10% (in terms of the absolute difference divided by its mean value) at altitudes between 11 and 40 km, with the median coincident ILAS-II profiles being systematically up to 10% higher below 20 km and up to 10% lower between 21 and 40 km after screening possible suspicious retrievals. Above 41 km, the negative bias between the NH ILAS-II ozone data and the other data increases with increasing altitude and reaches 30% at 61–65 km. In the Southern Hemisphere, the ILAS-II ozone data agree with the other data within ±10% in the altitude range of 11–60 km, with the median coincident profiles being on average up to 10% higher below 20 km and up to 10% lower above 20 km. Considering the accuracy of the other data used for this comparative study, the version 1.4 ozone data are suitably used for quantitative analyses in the high-latitude stratosphere in both the Northern and Southern Hemisphere and in the lower mesosphere in the Southern Hemisphere

Intercomparison of ILAS-II version 1.4 and version 2 target parameters with MIPAS-Envisat measurements

“…16) was also found around 40 km. Such a result was reported by Sugita et al (2006), in which the data around 40 km revealed a negative bias of ≈0.6 ppmv compared to some satellite occultation measurements. An inclusion of transmittance correction method developed for the satellite sunrise measurement mode into the ILAS-II V2 retrieval algorithm successfully improved the ILAS-II V2 data of those species.…”

“…The ILAS-II V1.4 SH data did not reveal any degraded profiles as was found for the NH data Sugita et al, 2006). Since the transmittance correction was not applied to the satellite sunset mode, the differences in VMR between the two algorithm versions were due to the new tangent height registration and the trend correction method for the 100% signal part data (see Appendix A).…”

“…The simultaneous retrieval of the species presented below was made using all of the 44 spectral elements of the IR spectrometer. The first public release of the data was V1.4, including O 3 , HNO 3 , N 2 O, and CH 4 Irie et al, 2006;Sugita et al, 2006;Wetzel et al, 2006). As mentioned in Sect.…”

“…ILAS-II was designed to monitor vertical profiles of ozone and related minor species to study the ozone layer (Nakajima et al, 2006a). The first public release of the data was version 1.4 (V1.4), including O 3 , HNO 3 , N 2 O, and CH 4 Irie et al, 2006;Sugita et al, 2006;Wetzel et al, 2006). The validation studies showed that there were negative biases of the H 2 O, CH 4 , and O 3 data in the Northern Hemisphere (NH) measurements, although no major biases were found in the Southern Hemisphere (SH) measurements.…”

Past changes in the vertical distribution of ozone – Part 1: Measurement techniques, uncertainties and availability

“…Version 5.20 ILAS and version 1.4 ILAS-II ozone profiles were validated by comparing with various data sources (Sugita et al, 2002(Sugita et al, , 2006. These validations showed that ILAS ozone data agreed with other data sets within ±10 % with a few exceptions between 11 and 64 km (Table 1a, b).…”