Southern Ocean 4-D circulation from Argo float and altimeter data
Studies of temporal variability and eddy processes in the Southern Ocean depend on knowing the time-mean background circulation, which is not measured by altimetry and was not well- sampled in situ prior to the start of the Argo program. Accurately describing the circulation of the Antarctic Circumpolar Current (ACC) and detecting large-scale changes in its density structure during the last decade is key to understand the role of the Southern Ocean (SO) in the global climate system. The increasing array of Argo floats, in combination with satellite measurements, provides a new opportunity to assess this problem.
We present a new estimate of the mean and temporal upper ocean circulation, density (σ), temperature (T) and salinity (S) fields of the SO by combining in situ Argo float measurements and altimeter data. Eddy variability is estimated using sea surface height (SSH) anomaly maps and linear regression coefficients of SSH onto anomalies of T, S and σ as a function of position and depth. A substantial improvement of the signal to noise ratio is achieved; on average the anomaly variance is reduced by 40%. The removal of the altimeter signal from T, S and σ produces more stable and less noisy estimates of the mean fields of the Southern Ocean. The 4-D fields of T, S and σ show the highly filamented nature of the ACC in greater detail than in traditional spatially averaged climatologies, which tend to oversmooth fronts.