On the quality of the ERA‐Interim ozone reanalyses: comparisons with satellite data

Abstract This article presents an assessment of the quality of the ERA‐Interim ozone analyses produced by the European Centre for Medium‐Range Weather Forecasts. Ozone retrievals from a number of satellite instruments and an ad hoc generated mean total column ozone (TCO) reference are used to assess the quality of the ERA‐Interim ozone analyses during the period from January 1989 to December 2008. The ERA‐Interim TCO is typically within ±5 DU (about ±3%) from the TCO reference, while showing up to 2% lower values than the Ozone Monitoring Instrument TCO between 50°S and 50°N. Comparisons with SAGE, HALOE and (UARS and Aura) MLS data show consistent results both in the Tropics and Extratropics, with mean residuals typically within ±5% around 5 hPa and within ±10% in the region of the ozone mixing ration maximum at 10 hPa. However, the comparisons with POAM II and III show mean relative residuals ranging from a few percent in summer to about –40% in winter at high latitudes, partly confirming the known problems of accurately modelling the ozone field during the polar night. Mean residuals of about +10% (but up to +20% at times) and within ±20% are found both in the Tropics and Extratropics for all instruments near 30 hPa and in the lower stratosphere around 65 hPa, respectively. The quality of the ERA‐Interim ozone analyses is also compared with that of ERA‐40. The study shows that, until December 1995, the ERA‐Interim ozone analyses are in better agreement with the independent observations than their ERA‐40 equivalent in the upper troposphere and lower stratosphere, but slightly degraded on average in the middle stratosphere. With the start of the assimilation of GOME ozone profiles (January 1996 –December 2002), the agreement between the independent data and the co‐located ERA‐Interim analyses improves and exceeds that calculated for ERA‐40 also in the middle stratosphere. Copyright © 2011 Royal Meteorological Society