AC&C/SPARC Ozone Database for CMIP5 - Hitop Version

The AC&C/SPARC ozone is provided on pressure levels between 1000-1hPa. For use in high-top models, an extrapolation of the dataset up to ~0.01 hPa or higher, may be required. The UK National Centre for Atmospheric Science (NCAS) has produced an updated/extended version of the SPARC ozone dataset. The following were done: (1) A multiple-linear regression is performed on the historical raw pressure-level data between 1000-1 hPa consistent with the Randal and Wu method used to construct the timeseries. The ozone is then represented as: O3(t) = a*SOL + b*EESC + seasonal_cycle + residuals. For consistency, the 11-yr solar cycle and EESC indices are identical to those used to prepare the original dataset. NOTE: the SOLAR index is a 180.5nm timeseries provided by Fei Wu at NCAR. (2) The seasonal cycle and residual fields are extrapolated and reduced above 1 hPa using O3(z)=O3(1hPa)*exp(-(z-z(1hPa))/H). Where H = 7 km. The seasonal cycle field is then used to provide a smooth climatology of ozone up to the model top. It has also been smoothed in latitude to the poles with a cosine function. (3) To minimize the 11-yr solar cycle and trend components in the mesosphere the a and b regression coefficients are extrapolated and reduced above 1 hPa twice as rapidly as the seasonal cycle, i.e. using the same method but with H = 3.5 km. (4) The full ozone timeseries is then reconstructed using the equation from (1). The ozone climatologies are not affected. (5) The standard SPARC ozone dataset which extends into the future does not include solar cycle variability post-2009. For production of a dataset extending into the future including an 11-yr ozone solar cycle, the solar regression index is used to build a future time series consistent with a repeating solar irradiance compiled by the UK Met Office and is modelled as a sinusoid with a period of 11 years, with mean and max-min values corresponding to solar cycle 23 (Gareth Jones, pers. comm.).