The space-born geodetic temporal Mean Dynamic Topography (MDT) is
obtained from the difference of altimetric Mean Sea Surface (MSS) $h$
and the geoid height $N$. With the geostrophic surface currents
obtained from its gradient the MDT is an essential parameter when
discribing the ocean dynamics. Spectral consistency of $h$ and $N$
is crucial to minimize MDT errors. Usually, $h$ is globalized to
allows for a Spherical Harmonic (SH) analysis and small scales beyond
maximum degree and order (d/o) resolved in the geoid are cut-off.
However, the usual globalization causes ocean-land steps in $h-N$ and
spectral inconsistencies of $N$ and $h$ over land. To overcome both
issues a new methodology is proposed based on globalization of the MDT.
A Laplacian smoother with the coastal MDT values as boundary condition
is applied resulting in a flat surface over land and a continuous
ocean-land transition. The new methodology strongly reduces Gibbs
effects and the need to work with high resolution MDTs to minimize them.
Reduction of resolution is tested to reduce MDT uncertainties caused by
the commission error expected to increase whith decreasing scale.
Applying drifter data and a high resolution hydrodynamic ocean model it
is shown, that for the Gulf Stream and the Kuroshio geodetic MDTs
applying recent combined geoid models contain physical information up to
at least d/o 420 (48km spatial scale). Since for oceanic regions with
strong gradients in $N$ still inconsistencies between the geoid and
the MSS exist, it depends on application/region if a higher resolution
MDT is needed.