Geoscientific Instrumentation Methods and Data Systems A global historical ozone data set and signatures of El N no and the 11-yr solar cycle

Abstract

We present a vertically resolved (with pressure as the vertical coordinate) zonal mean monthly mean global ozone data set spanning the period 1900 to 2008, called HIS-TOZ.1.0. It is based on a new approach that combines information from an ensemble of chemistry climate model (CCM) simulations with historical total ozone information. 5 The CCM simulations incorporate important external drivers of stratospheric chemistry and dynamics (in particular solar and volcanic effects, greenhouse gases and ozone depleting substances, sea-surface temperatures, and the Quasi-Biennial Oscillation). The historical total ozone observations include ground-based measurements from the 1920s onward and satellite observations from 1970 to 1976. An off-line data assimi-10 lation approach (Ensemble Square Root Filter) is used to combine model simulations, observations, and information on the observation error. The period starting in 1979 was used for validation with existing ozone data sets and therefore only ground-based measurements were assimilated. Results demonstrate considerable skill from the CCM simulations alone. While the observations provide little additional skill at the full spatio-15 temporal resolution, they do increase the skill at lower spatio-temporal resolutions and specifically for total ozone. Analyses of HISTOZ.1.0 with respect to the effects of El N no/Southern Oscillation (ENSO) and of the 11 yr solar cycle on stratospheric ozone from 1934 to 1979 qualitatively confirm previous studies that focussed on the post-1979 period. However, a more pronounced effect of ENSO and slightly weaker effect of the 20 11 yr solar cycle are found in the earlier period. Several possible future improvements of HISTOZ.1.0 are discussed.