Impact of the Gravity Field and Steady‐State Ocean Circulation Explorer (GOCE) mission on ocean circulation estimates: Volume fluxes in a climatological inverse model of the Atlantic

Abstract

Abstract. The Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) mission,by providing a precise estimate of the marine geoid height, will allow the determination of absolute geostrophic velocities at the surface of the ocean with unprecedented accuracy. The resulting impact on oceanic flux estimates is quantified within a climatological inverse model of the Atlantic in terms of reduction of uncertainties in volume transports. These uncertainty reductions are obtained by replacing the error spectrum of present-day geoid models by the error spectrum expected for the GOCE mission. The impact is large in the Circumpolar Current, with relative uncertainty reductions reaching 50% in the upper layers of the ocean, and 40% in the whole water column. It is also large in regions of sharp oceanic fronts like the Gulf Stream or the Brazil Current, with uncertainty reductions reaching 60% in the upper layers of the ocean. The reduction in transport uncertainties is large enough in absolute terms to have a significant impact on estimates of important climate processes like the rate of overturning in the Atlantic or the exchange of water between the Circumpolar Current and the South Atlantic. The impact of the Gravity Recovery and Climate Experiment (GRACE) mission, estimated within the same inverse model, is on average less than half the impact of GOCE because of the lower precision of this mission at small spatial scales. The fact that uncertainties in the baroclinic component of the velocity field limit the impact of GOCE at depths points to the need for precise in situ observations to complement gravity and altimetric observations.

Calculating the Ocean’s Mean Dynamic Topography from a Mean Sea Surface and a Geoid

“…Previously this space geodetic approach has been severely limited by the accuracy of global geoid models (Wunsch and Gaposchkin 1980;Stammer and Wunsch 1994;Tapley et al 1994;Losch and Schröter 2004). Recently, however, the Gravity Recovery and Climate Experiment (GRACE) mission has gone some way to overcoming this limitation by producing geoid models that represent an order of magnitude improvement in accuracy over previous satellite-based models (Tapley et al 2003(Tapley et al , 2005, while the forthcoming Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) mission promises to go even further with a target accuracy of l cm down to spatial scales of 100 km (LeGrand 2001).…”

Mean Dynamic Ocean Topography in the Southern Ocean from GRACE and GOCE and Multi-mission Altimeter Data

“…This concept was one of the basic motivations which led to the development and realization of the present gravity field satellite missions CHAMP, GRACE and GOCE (Balmino et al 1999). For the preparation of the GRACE (Gravity Recovery And Climate Experiment) and GOCE (Gravity field and steady-state Ocean Circulation Explorer) missions, a number of oceanographic simulation studies have been carried out, such as Le Grand (2001) and Schröter et al (2002). The studies demonstrated that the new satellite geoid models will allow the determination of geostrophic surface velocities with an accuracy of a few cm/s.…”

Bottom Topography as a Control Variable in an Ocean Model

“…These pseudo data are the natural choice because they are the only available observable physical property reflecting the three-dimensional, large-scale fluid flow (Wunsch and Stammer 1998). The uncertainties associated with existing absolute sea surface height data are still large because of geoid errors, but new gravity missions will reduce them by an order of magnitude (Ganachaud et al 1997;LeGrand 2001;Schröter et al 2002).…”