Validation of Global Ozone Monitoring Experiment ozone profiles and evaluation of stratospheric transport in a global chemistry transport model

[1] This paper presents a validation of Global Ozone Monitoring Experiment (GOME) ozone (O-3) profiles which are used to evaluate stratospheric transport in the chemistry transport model (CTM) Tracer Model version 5 (TM5) using a linearized stratospheric O-3 chemistry scheme. A comparison of GOME O-3 profile measurements with independent O-3 sonde measurements at midlatitudes shows an excellent agreement. Differences are smaller than 5%, well within the uncertainty of the O-3 sonde measurements. Within the tropics, the GOME O-3 profile differences are larger, with a clear lower stratospheric negative O-3 bias with compensating positive biases in the troposphere and higher stratosphere. The TM5 model with linearized O-3 chemistry simulates realistic lower and middle stratospheric spatial and temporal O-3 variations on both short (daily) and long (seasonal) timescales. Model stratospheric O-3 is significantly overestimated in the extratropics and slightly underestimated in the tropics, as is also shown in a comparison with Total Ozone Mapping Spectrometer total O-3 column measurements. This model bias predominantly occurs in the lower stratosphere and is present throughout the year, albeit with seasonal variations: The bias is larger during local winter compared with local summer. The particular spatial and seasonal variations of the model bias suggest a too fast meridional stratospheric transport in TM5, which agrees with earlier found shortcomings of using winds from data assimilation systems. The model results are very sensitive to the data assimilation method in the numerical weather prediction that provides the model wind fields. A large reduction (up to 50% of the bias) in modeled lower stratospheric midlatitude O-3 was found when winds from four-dimensional instead of three-dimensional data assimilation were used. Previous work has shown that using different forecast periods was important for improving the age of air. Model results differed with different forecast periods (up to 3 days), although the effect was mainly confined to high-latitude lower stratospheric O-3. Apparently, using different forecast periods is more important for age-of-air calculations than for stratospheric O-3 calculations. A positive bias in the extratropical lower stratosphere of about 20% remained, possibly related to the lack of heterogeneous polar stratospheric O-3 destruction in TM5.