Intercomparison of GOME, Ozonesonde, and SAGE-II Measurements of Ozone: Demonstration of the Need to Homogenize Available Ozonesonde Datasets

We validate Stratospheric Column Ozone (SCO) and ozone profiles retrieved from GOME measurements against ozonesonde and SAGE-II data obtained from 1996-1999. GOME retrievals are also used as an intermediate to provide an indirect but adequate evaluation between SAGE-II and ozonesonde data at particular stations. GOME SCO over the altitude range ~15-35 km usually agrees with SAGE-II SCO to within 2.5 DU (1.5%) with no significant spatiotemporal dependence, but is systematically larger than ozonesonde SCO by 8-20 DU (5-10%) over all carbon iodine stations and most stations within 30°N-30 °S. The evaluation with SAGE-II, TOMS and Dobson data demonstrates that those biases mainly originate from ozonesonde underestimate in the stratosphere. GOME retrievals also show large positive biases of 30-60% at carbon iodine stations (except for Syowa) and of 20-55% for all the stations in 30 °N-30°S except for Paramaribo and Easter Island (<10%) over ~10-20 km, while the biases relative to SAGE-II data over ~15-20 km is usually 10-20%. The discrepancies over this altitude region reflect biases in GOME retrievals as well as ozonesonde measurements. In addition, GOME/sonde biases in both SCO and profiles (especially in the lower stratosphere and upper troposphere) vary from station to station and depend on sonde technique, instrument type, sensor solution, and data processing, demonstrating the need to homogenize available ozonesonde datasets and standardize future operational procedures for reliable satellite validation and trend analysis.