Based on the analysis of Sallee, et al. (2007) we use historical hydrographic profiles, combined with recent ARGO profiles, to obtain  an estimate of the mean geostrophic circulation in the Southern Ocean relative to 1500m. To this we add the sea-surface height anomaly from altimetry to reconstruct the time variable sea-level.

Using a 1500m level of zero motion implies that we neglect the mean barotropic flow and the mean baroclinic flow below 1500m. In order to assess the impact of this assumption we compared our mean dynamic  height field with the absolute mean dynamic height product developed by Rio et al. (2005). This latter product  mixes satellite data from GRACE and altimetry with in-situ data from SVP drifters, ARGO profiles and ship-based hydrographic data. Their mean field includes both barotropic and baroclinic components and is in very good agreement with ours. The Rio et al. (2005) product uses a different reference density, and when using the Rio et al. (2005) mean SSH our PF corresponds to a 0.6m contour, and our SAF to a 1.0m contour. We find that both products show the same large scale patterns and large stationary meanders of the ACC. Using the 1500m level of zero motion will reduce the steric height amplitude and slightly reduce the intensity of the cross-frontal gradients. However, it does not affect the position of the mean structure of the ACC fronts. We note that the variable part of the barotropic and the deep ACC baroclinic flow will be observed by altimetry. The Rio et al. (2005) product does not use in-situ profiles sampled after 2002. Given the substantial increase in the number of ARGO profiles in the Southern Ocean since 2002, we believe our mean field provides a better  representation of the finer scale structure of the Southern Ocean. A number of different contributions to error in SSH will induce movements in the SSH contour which do not represent a movement of the jet core, and are thus considered as errors of the method. The sum of these errors for this contour method is +/- 12cm, which corresponds to +/- 1.2 degrees of error in the latitudinal position.

This dataset has been analyzed to identify and monitor the position of the two main fronts of the ACC:

Abstract of Sallee, Speer, Morrow (2007) Response of the Antarctic Circumpolar Current to atmospheric variability, J. Climate, accepted.