Satellite Gravity and the Geosphere Contributions to the Study of the Solid Earth and Its Fluid Envelopes (1997) / Chapter Skim
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4 OCEAN DYNAMICS AND HEAT FLUX
4 OCEAN DYNAMICS AND HEAT FLUX
Pages 35-46
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From page 35... ...
The state of the art of gravity modeling and existing satellite tracking is not likely to offer significant reductions in geoid error to improve oceanographic calculations at shorter wavelengths. In contrast, the satellite gravity missions will offer major improvement to degree 100 or greater (~400 km and shorter wavelength, with the exception of Me GPS scenario, which will not provide significant improvement for oceanographic purposes.
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From page 36... ...
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From page 37... ...
All missions except GPS will yield significant improvement in the static marine geoid. this problem very rigorously using Me accuracy of heat fluxes derived from inverse methods, and concluded that the JGM3 model coupled with altimetry did not reduce the uncertainty of the heat flux estimates, but that a more precise geoid could reduce uncertainties by as much as a factor of two in large data-sparse regions, such as the Antarctic Circumpolar Current (ACC)
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From page 38... ...
Longitude So ~30 60 90 120 150 180 210 80 ,...
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From page 39... ...
With the advent of any of the gravity missions, the situation reverses and the gravity error becomes insignificant for a range of resolutions of importance to oceanography. The geoid-error curves for SGG, SST, or SSI missions indicate they will provide at least an order of magnitude lower contribution than altimetry to the total error budget for the estimation of geostrophic currents on spatial scales greater than ~400 fan; the SST and SSI missions offer additional orders of magnitude improvement over SGG.
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From page 40... ...
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From page 41... ...
Such tracer measurements are limited in that they cannot resolve changes in ocean circulation but indicate the time it takes for a water mass to move along an unknown trajectory.) The second is that, when combined with altimetry from a mission such as TOPEX/Poseidon, gravity measurements will allow the separation of steric changes in sea level associated with changes in density from nonsteric changes.
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From page 43... ...
The accuracy versus spatial resolution comparison in Figure 4.3 shows that the SST and SSI missions are sufficiently accurate to measure annual and secular variations in this transport if the variations are assumed to be 10% or greater of the mean transport. Steric Changes Another way in which gravity measurements can contribute to improved understanding of ocean circulation is through their complementary relationship to altimetry and in situ measurements of temperature and salinity.
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From page 44... ...
They do not address the problem of separating the gravitational effects of different geophysical processes, however, which can be critical in determining how well a satellite gravity mission could constrain a specific process. The problem for oceanographic applications is best understood by noting that the most effective way to use the gravity data for oceanography will probably be to sum together the spherical harmonic geoid coeff~ cients to construct mass anomalies (equivalent to bottom pressure anomalies)
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From page 45... ...
Combining altimetry and gravity will allow separation of the timedependent stenc and nonsteric components of sea level. This separation will substantially increase the usefulness of sea level in testing ocean models and constraining ocean circulation through data assimilation.
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