Variations of the Argentine Gyre Observed in the GRACE Time‐Variable Gravity and Ocean Altimetry Measurements

We investigate the nonseasonal and high‐frequency variations of the Argentine Gyre in the south Atlantic Ocean by analyzing the time‐variable gravity (TVG) measurements from the Gravity Recovery and Climate Experiment (GRACE) satellite mission in conjunction with the satellite ocean altimetry and two ocean general circulation model outputs (GLORYS2V4 and ECCO V4R3). We solve the empirical orthogonal functions (EOF) and complex EOF and find good agreement between TVG and altimetry observations, confirming the barotropic structure of the Argentine Gyre. In particular, the leading EOF modes of the overall up‐and‐down undulation in TVG and altimetry variations are found to be in pace temporally with the Antarctic Oscillation Index with correlation as high as 0.69 at zero time shift. Furthermore, the leading complex EOF mode signifies a counterclockwise dipole pattern of ~25‐day periodicity within the overall gyre with multiscale amplitude modulation. The fact that GRACE does observe these signals, while the de‐aliasing background ocean model fails to, ascertains that GRACE data have adequate sensitivity to allow the detection of TVG signals at spatial and temporal resolutions higher than practiced hitherto. The ~25‐day oscillation is well recovered in the GLORYS2V4 ocean general circulation model, but not in ECCO V4R3. Our study demonstrates that satellite‐observed TVG fields can be useful in studying oceanographic gyres, particularly the polar gyres, that are not well observed by altimetry and in situ data.This work is supported by Taiwan Ministry of Science and Technology grants 105-2811-M-001-031 and 106-2116-M-001-013 and by National Nature Science Foundation of China grants 41474019, 41504014, and 41704012