A Study Of The Antarctic Circumpolar Current In Streamfunction Space Based On Satellite Altimeter Data

The Antarctic Circumpolar Current (ACC) is an area of intense scientific interest due to its unique features and influences it has on the global climate system However, studies of the ACC are rare due to the lack of in situ observations. Based on a new streamfunction projection method, we combined the satellite remote sensing data with hydrographic observations and studied the ACC south of Australia. A robust description to the structure of the Subantarctic Front (SAF) was presented, and the temporal variation of the ACC structure and strength were further studied. Based on the work by Sun and Watts (2001), we extended the GEM (Geostrophic Empirical Mode) method into the sea surface height coordinate and studied the meso scale variation of the Antarctic Intermediate Water (AAIW). A frontal wave mechanism was proposed to explain the variation of the AAIW.The Absolute Dynamic Topography (ADT) product from AVISO is verified with two-year of continuous mooring observations south of Australia. Results show that ADT are able to capture the mesoscale processes in the ACC. Studies of the ACC jet structure in streamfunction space indicate that the jet does not correspond to a particular SSH value and it's affected strongly by the topography. The jet structures in the upstream and downstream of the SR3 line differ and exhibit obvious seasoanl and interannual variations, indicating the shortage of identifying the SAF with velocity jet. The double-branch structure proposed by Australian scientists is not a robust feature in the SAF. In contrast with the downstream, the seasonal mean path of the ACC at the SR3 line varies little. The ACC strength at the SR3 line has seasonal variation with semiannual period and it peaks in March and August. However, this seasonality varies at different longitude. The spatial difference reflects the topographic effects on the seasonality. On interannual time scale, the ACC at the SR3 line was strongest in 2000 and weakest in 1997. The interannual variation is stronger than the sesonal variation. The interannual variations in the upstream and downstream are similar to that at the SR3 line though the year with peak value differs. We also discussed the mechanism for the strengthening of the ACC in 2000, which appeared to be caused by the burst of the westerly wind in 1998 through the baroclinic adjustment.Based on the GEM developed by Sun and Watts (2001), we construct the H-GEM with satellite altimetry and hydrography. H-GEM for temperature and salinity captures more than 95% of the total variances. Comparison with in situ observations indicates H-GEM derived from Argo is an effective approach to reconstruct the three dimensional structure of the ACC from satellite altimetry.WOCE/SR3 transects are analyzed with an EOF technique in streamfunction space. Results show that the variation of the AAIW is related to the frontal wave in the SAF. We define the phase angle of the SAF at SR3 line as the index of the frontal wave, and there is more (less) AAIW descending across the SAF when the index is in positive (negative) phase. Spectral analysis to the frontal wave index shows the frontal wave is dominated by a period of around 130 days. The phase speed and wavelength of the frontal wave are 4cm/s and 450km respectively.