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Using ocean bottom pressure from the gravity recovery and climate experiment (GRACE) to estimate transport variability in the southern I ndian O cean
Author(s) -
Makowski Jessica K.,
Chambers Don P.,
Bonin Jennifer A.
Publication year - 2015
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2014jc010575
Subject(s) - circumpolar star , climatology , barotropic fluid , environmental science , longitude , atmospheric sciences , geology , oceanography , geodesy , latitude
Previous studies have suggested that ocean bottom pressure (OBP) from the Gravity Recovery and Climate Experiment (GRACE) can be used to measure the depth‐averaged, or barotropic, transport variability of the Antarctic Circumpolar Current (ACC). Here, we use GRACE OBP observations to calculate transport variability in a region of the southern Indian Ocean encompassing the major fronts of the ACC. We use a statistical analysis of a simulated GRACE‐like data set to determine the uncertainty of the estimated transport for the 2003.0–2013.0 time period. We find that when the transport is averaged over 60° of longitude, the uncertainty (one standard error) is close to 1 Sv (1 Sv = 10 6 m 3 s −1 ) for low‐pass filtered transport, which is significantly smaller than the signal and lower than previous studies have found. The interannual variability is correlated with the Southern Annual mode (SAM) (0.61), but more highly correlated with circumpolar zonally averaged winds between 45°S and 65°S (0.88). GRACE transport reflects significant changes in transport between 2007 and 2009 that is observed in the zonal wind variations but not in the SAM index. We also find a statistically significant trend in transport (−1.0 ± 0.4 Sv yr −1 , 90% confidence) that is correlated with a local deceleration in zonal winds related to an asymmetry in the SAM on multidecadal periods.