Chemical data assimilation: A case study of solar occultation data from the ATLAS 1 mission of the Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS)

A key advantage of using data assimilation is the propagation of information from data‐rich regions to data‐poor regions, which is particularly relevant to the use of solar occultation data such as from the Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS). For the first time, an in‐depth uncertainty analysis is included in a photochemical model‐data intercomparison including observation, representativeness, and theoretical uncertainty. Chemical data assimilation of solar occultation measurements can be used to reconstruct full diurnal cycles and to evaluate their chemical self‐consistency. This paper considers as an example the measurements made by the ATMOS instrument ATLAS 1 during March 1992 for a vertical profile in flow‐tracking coordinates at an equivalent potential vorticity (PV) latitude of 38°S. ATMOS was chosen because it simultaneously observes several species. This equivalent PV latitude was chosen as it was where ATMOS observed the atmosphere's composition over the largest range of altitudes. A single vertical profile was used so that the detailed diurnal information that the assimilation utilizes could be highlighted. There is generally good self‐consistency between the ATMOS ATLAS 1 observations of O 3 , NO, NO 2 , N 2 O 5 , HNO 3 , HO 2 NO 2 , HCN, ClONO 2 , HCl, H 2 O, CO, CO 2 , CH 4 , and N 2 O and between the observations and photochemical theory.