Geoscience Reference
In-Depth Information
et al.
2003
). The existing discrepancies may be further reduced if mass redistributions
in the global hydrosphere are added to the analysis. As demonstrated by Chen and
Wilson (
2005
) and Dobslaw et al. (
2010
), considering hydrological excitation can
lead to an reasonably good closure of the angular momentum budget for the annual
wobble.
Variations of length of day are primarily caused by the atmospheric wind term and
also slightly affected by surface pressure fluctuations, see Fig.
16
. Those small LOD
residuals that are void of the influence of AAM have been successfully compared to
oceanic bottom pressure and currents (Gross et al.
2004
) as well as to combined time
series of oceanic mass term and hydrological excitation (Chen et al.
2000
). The latter
study arrives at a particularly good agreement of modeled and observed excitation
at the seasonal cycle.
Even though a complete closure of the angular momentum budget at different
frequencies has hitherto been an elusive goal, relating Earth rotation parameters to
the output of geophysical models remains a valuable field in view of several issues. In
the first place, it allows assessing the quality of the applied models if observations of
nutation, polar motion and changes of length of day are used as a reference (Seitz and
Schuh
2010
). The presented excitation scheme is also a perfect tool for interpreting
time series of geodetic parameters with regard to distinct geophysical processes in
all subsystems of our planet. In this context, the investigation of Earth's reaction
to the manifold interactions between atmosphere, hydrosphere and solid Earth is
an intriguing task. And finally, via inversion of the observed rotation signal, it is
also possible to learn more about geophysically significant parameters and dynamic
processes within the system Earth (Seitz and Schuh
2010
). Such an approach is
regarded as a highly promising challenge for future research in the field of Earth
rotation.
Acknowledgments
The authors would like to thank Prof. A. Brzezi nski for his excellent review,
which helped to improve this part of the topic significantly and strengthened the major geophysical
discussion of each section. Innumerable comments on the style and writing were provided by D.
Salstein and are highly appreciated. The first author is particularly indebted to the Austrian Science
Fund (FWF) for supporting his work within project P20902-N10.
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