1Oeschger Centre, University of Bern, Switzerland
2Institute of Geography, University of Bern, Switzerland
3CSIRO Marine and Atmospheric Research, Aspendale, Australia
4Federal Office of Meteorology and Climatology MeteoSwiss, Zurich, Switzerland
5Climate and Environmental Physics, Physics Institute, University of Bern, Switzerland
6Bodeker Scientific, Alexandra, Central Otago, New Zealand
7Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado at Boulder, Boulder, Colorado, USA
8NOAA, Earth System Research Laboratory, Chemical Sciences Division, Boulder, Colorado, USA
9Physical-Meteorological Observatory Davos/World Radiation Center, Davos, Switzerland
10Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland
11CSCS, Lugano, Switzerland
Received: 21 Dec 2012 – Discussion started: 21 Mar 2013
Abstract. We present a vertically resolved zonal mean monthly mean global ozone data set spanning the period 1901 to 2007, called HISTOZ.1.0. It is based on a new approach that combines information from an ensemble of chemistry climate model (CCM) simulations with historical total column ozone information. 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 column ozone observations include ground-based measurements from the 1920s onward and satellite observations from 1970 to 1976. An off-line data assimilation approach 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. Assimilating observations provides additional skill for total column ozone. With respect to the vertical ozone distribution, assimilating observations increases on average the correlation with a reference data set, but does not decrease the mean squared error. Analyses of HISTOZ.1.0 with respect to the effects of El Niño–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. The ENSO signature exhibits a much clearer imprint of a change in strength of the Brewer–Dobson circulation compared to the post-1979 period. The imprint of the 11 yr solar cycle is slightly weaker in the earlier period. Furthermore, the total column ozone increase from the 1950s to around 1970 at northern mid-latitudes is briefly discussed. Indications for contributions of a tropospheric ozone increase, greenhouse gases, and changes in atmospheric circulation are found. Finally, the paper points at several possible future improvements of HISTOZ.1.0.
Revised: 14 Aug 2013 – Accepted: 16 Aug 2013 – Published: 30 Sep 2013
Brönnimann, S., Bhend, J., Franke, J., Flückiger, S., Fischer, A. M., Bleisch, R., Bodeker, G., Hassler, B., Rozanov, E., and Schraner, M.: A global historical ozone data set and prominent features of stratospheric variability prior to 1979, Atmos. Chem. Phys., 13, 9623-9639, doi:10.5194/acp-13-9623-2013, 2013.