2018-02-06: Simultaneous assimilation of ozone profiles from multiple UV-VIS satellite instruments

Ozone profiles measured by two satellite instruments (GOME-2A and OMI) have been combined with a chemical transport model using data assimilation. The results give a better insight into the global spatial and temporal ozone distribution than either measurement or model results alone. Validation with independent measurements shows biases varying between -5% and +10% between the surface and 100 hPa, while between 100 and 10 hPa the biases vary between -3% and +3%.

A three-dimensional global ozone distribution has been derived from assimilation of ozone profiles that were observed by satellites. By simultaneous assimilation of ozone profiles retrieved from the nadir looking satellite instruments Global Ozone Monitoring Experiment 2 (GOME-2) and Ozone Monitoring Instrument (OMI), which measure the atmosphere at different times of the day, the quality of the derived atmospheric ozone field has been improved. The assimilation is using an extended Kalman filter in which chemical transport model TM5 has been used for the forecast. The combined assimilation of both GOME-2 and OMI improves upon the assimilation results of a single sensor. The new assimilation system has been demonstrated by processing 4 years of data from 2008 to 2011. Validation of the assimilation output by comparison with sondes shows that biases vary between -5 and +10% between the surface and 100 hPa. The biases for the combined assimilation vary between -3 and +3% in the region between 100 and 10 hPa where GOME-2 and OMI are most sensitive. This is a strong improvement compared to direct retrievals of ozone profiles from satellite observations.

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Validation of the model runs with ozone sondes for 20082011. (left) The median of the absolute difference in DU, (right) the median of the relative differences. Blue: model run without assimilation, green: model run with assimilation of GOME-2 only, yellow: run with assimilation of OMI only, red: assimilation of both GOME-2 and OMI. The error bars are plotted for the simultaneous assimilation only, and range from the 25 to the 75 % percentile.