Global Surface Geostrophic Ocean Currents Derived from Satellite Altimetry and GOCE Geoid

Abstract

The surface geostrophic currents (SGC) can be derived via the principle of geostrophy from the dynamic height of the ocean, or the deviation of the true, variable sea surface height with respect to the Earth's static geoid, both of which can be measured by geodetic means. Here we calculate the Mean Dynamic Topography (MDT) by subtracting the geoid height determined by the GOCE satellite mission from the Mean Sea Surface Topography (MSST) derived from multi-satellite ocean altimetry (T/P, Jason 1/2, ERS-1/2, GEOSAT). Results for SGC are compared with those obtained from a GRACE-based mean geoid, as well as with the mean circulation patterns from measurements done by in situ drifter buoys and from simulations of the ECCO Ocean General Circulation Model. We found GOCE-based geoid solution clearly leads to significant improvements in the spatial resolution of SGC globally except in the Equatorial band where special filtering may be needed, with current velocities and spatial patterns closest to the in situ measurements of currents, compared with the GRACE-based results or ECCO model simulations that give significantly weaker Values with lower spatial resolution.

Ocean Surface Geostrophic Circulation Climatology and Annual Variations Inferred from Satellite Altimetry and GOCE Gravity Data

“…The velocity map (cm/s) and the direction map for the annual mean climatology are presented in Fig. 1c, d. The results are in accordance with previous studies of the mean SGC (SÁ NCHEZ-REALES et al 2012;KNUDSEN et al 2011). The estimated velocities, Fig.…”

“…This corresponds to a potential resolving power of approximately 86 km for the geoid. SÁ NCHEZ-REALES et al (2012) showed that, because of the nature of the GOCE, this resolution is sufficient to resolve the mean geostrophic flow for middle-to-high latitudes, but not for the equator, which remains a noisy band for which some filtering is needed (described in the Sect. 5).…”

“…(1) can be readily expressed in the spectral domain (BINGHAM et al 2008, HUGHES andBINGHAM 2006). Although SÁ NCHEZ-REALES et al (2012), proved that GOCE data can resolve space scales as short as 86 km for middle-to-high latitudes, solving for circulation at low latitudes requires a high level of filtering. Therefore, Gaussian smoothing of 140 km of half-wave length was applied to both the ASL(t) and N to ensure homogenization of the length scales and remove omission errors in the geoid .…”

“…SÁ NCHEZ-REALES et al (2011, 2012, BINGHAM et al (2011) andKNUDSEN et al (2011) have recently proved the ability of GOCE to improve previous geodetic mean dynamic topography, and the corresponding benefits for ocean circulation studies.…”

Variation of Antarctic circumpolar current and its intensification in relation to the southern annular mode detected in the time-variable gravity signals by GRACE satellite

“…That is because the GRACE TVG data quantify large-scale mass redistributions referenced to the time-mean static geoid, in our case the time-mean "climatology" field. To study the latter would call for the determination of the ocean dynamic topography which in turn entails the ocean surface topography relative to the static geoid (for example from satellite altimetry observations) (e.g., Sánchez-Reales et al 2012;Feng et al 2013), work that is outside the scope of the present study.…”