The impact of withholding observations from TOMS or SBUV instruments on the GEOS ozone data assimilation system

The Data Assimilation Office of NASA/Goddard will provide near-real-time global 3-dimensional ozone fields in support of instruments on NASA's Terra satellite. Ozone observations from Total Ozone Mapping Spectrometer (TOMS) and Solar Backscatter Ultraviolet (SBUV) instruments on board polar orbiting satellites are assimilated into an ozone transport and chemistry model. The assimilated observations are complementary; TOMS provides a global daily coverage of total column ozone, without profile information, while SBUV measures ozone profiles and total column ozone at nadir, only. We study the performance of the ozone assimilation system in the absence of observations from one of the instruments, TOMS or SBUV. The quality of analyzed ozone fields is evaluated using ozone measurements form TOMS, SBUV, Halogen Occultation Experiment (HALOE) and ozone sondes. Statistics of observed-minus-forecast residuals for the systems assimilating observations from one or both of TOMS and SBUV instruments are compared.