Abstract
The impact of assimilating global ocean bottom pressure (OBP)
information from the Gravity Recovery and Climate Experiment (GRACE)
gravity anomalies on the circulation estimate was investigated. For this
an estimate of the ocean circulation is being inferred by extending the
50-year-long German part of the Estimating the Circulation and Climate
of the Ocean (GECCO) ocean synthesis into recent years. The assimilation
system is an improved version of the previous GECCO optimization, which
now includes a sea ice model, has enhanced resolution on a truly global
domain including the Arctic Ocean. By analyzing differences to a
synthesis that additionally assimilated OBP, the GRACE data was found to
provide complementary information to standard ocean data sets including
satellite altimetry when assimilated. Although in principle standard
ocean data sets include the OBP information, the reason why this cannot
be extracted is the much larger prior errors for hydrographic and
altimeter data in comparison to OBP data owing to the fact that only the
former two need to include the unresolved eddy signal. The largest
impact of gravity data is found to be on the barotropic circulation,
particularly in the subtropical gyres and the polar latitudes. Remaining
differences between the simulated and observed OBP information are
associated with meridional stripes in the GRACE gravity maps and with
the leakage of terrestrial hydrological information into the ocean.
Additional differences close to the continental boundaries are related
to the self-attraction and loading, processes that are not included in
the models.
