The ozone distribution in the upper troposphere and lower stratosphere is needed in many geophysical applications. For example, it is needed in the quantification of cross-tropopause fluxes, tropospheric ozone, and radiative transfer calculations. Accurate estimates of ozone fields in the lowermost stratosphere and troposphere can provide better first guess profiles for retrievals of ozone from remote sensing instruments, and thus, improve our ability to extract information from satellite observations.

Global three-dimensional ozone fields are produced in the DAO by assimilating TOMS and SBUV observations into an ozone transport model. Satellite instrument ozone observations, including those by TOMS and SBUV instruments, have low vertical resolution in the upper troposphere and lower stratosphere. Consequently, the assimilated ozone field in this region will be sensitive to the choice of the assimilation method. We investigate the sensitivity of the assimilated ozone in this region to specification of error covariances and to data selection.