on the aggregate Earth system. In particular, we have performed an inverse solution, which
while preliminary, implies that there is a large contrast between lower and upper mantle
viscosity. It also indicates that a increase in Antarctica's ice mass is being somewhat offset
by a smaller decrease in the ice mass over Greenland. While these results must be viewed
as speculative, they are within the bounds of current estimates of mass balance over these
ice sheets.
The lack of support for the large viscosity contrast we obtain suggests that further
modeling improvements are warranted and inclusion of other contributing sources, like
continental water sequestering in reservoirs (e.g. Chao, 1988), are needed. Overall, utility
for an inverse modeling approach is demonstrated, where geodetic observations and
geophysical modeling relationships interplay. On-going field campaigns are likely to provide
additional constraints to help in the definition of post-glacial rebound and global hydrological
mass redistribution.
REFERENCES
Bentley, C.R. & M.B. Giovinetto, Mass Balance of Antarctica and Sea Level Change, Proc.
Int ConfRole of Polar Regions in Global Change, 481-488, Univ. Alaska, Fairbanks, 1991
Cartwright, D.E., and A.C. Edden, Corrected Tables of Tidal Harmonics, Geophys J R Astr
Soc, 33, 253-264, 1973.
Chao, B.F., Excitation of the Earth's Polar Motion due to Mass Variations in Major
Hydrological Reservoirs, J Geophys Res, 93 (B11), 13,811-13,819, 1988.
Chao, B.F., The Geoid and Earth Rotation, in Geoid and Its Geophysical Interpretations,
CRC Press, 285-298, 1993.
Cheng, M.K. et al., Temporal Variations in Low Degree Zonal Harmonics from Starlette
Orbit Analysis, Geophys Res Lett, 16 (5), 393-396, 1989.
Christodoulidis, D.C. et al., Observed Tidal Braking in the Earth/Moon/Sun System, J
Geophys Res, 93 (B6), 6216-6236, 1988.
Gegout, P. & A. Cazenave, Temporal Variations of the Earth's Gravity Field for 1985-1989
from Lageos, Geophys J Intl, 114, 347-359, 1993.
Giovinetto, M.B. and Zwally, J., An Assessment of Mass Budgets of Antarctica and
Greenland Using Accumulation Derived from Remotely Sensed Data in Areas of Dry
Snow, in press, 1995.
Gross, R.S., A Combination of Earth Orientation Data: Space93, IERS Annual Report,
Observatory of Paris, 1993.
Hedin, A.E., MSIS-86 Thermospheric Model, J Geophy Res, 92 (A5), 4649-4662, 1987.
Houghton, J. and L.G. Meira Filho, Intergovernmental Panel on Climate Change, in press,
WMO and UNEP Report, 1995
Ivins, E.R., et al., Deep Mantle Viscous Structure With Prior Estimate and Satellite
Constraint, J Geophys Res, 98 (B3), 4579-4609, 1993.
Jacobs, S.S., Is the Antarctic ice sheet growing?, Nature, 360, 29-33, 1992.
James, T.S. and E.R. Ivins, Present-day Antarctic Ice Mass Changes and Crustal Motion,
Geophys Res Lett, 22 (8), 973-976, 1995.
Kaula, Wm., Theol)' of Satellite Geodesy, Blaisdell, Waltham, MA, 1966.
Mitrovica, J.X., and W.R. Peltier, Present-Day Secular Variations in the Zonal Harmonics
of the Earth's Geopotential, J Geophys Res, 98 (B3), 4509-4526, 1993.
Nerem, R.S. et al., Expected Orbit Determination Performance for TOPEX/Poseidon, IEEE
Trans Geosci and Remote Sens, 31 (2), 1993.
Nerem, R.S. et al., Time Variations of the Earth's Gravity Field from Laser Ranging to
Lageos, Geophys Res Lett, 20 (7), 595-598, 1993b.
162
while preliminary, implies that there is a large contrast between lower and upper mantle
viscosity. It also indicates that a increase in Antarctica's ice mass is being somewhat offset
by a smaller decrease in the ice mass over Greenland. While these results must be viewed
as speculative, they are within the bounds of current estimates of mass balance over these
ice sheets.
The lack of support for the large viscosity contrast we obtain suggests that further
modeling improvements are warranted and inclusion of other contributing sources, like
continental water sequestering in reservoirs (e.g. Chao, 1988), are needed. Overall, utility
for an inverse modeling approach is demonstrated, where geodetic observations and
geophysical modeling relationships interplay. On-going field campaigns are likely to provide
additional constraints to help in the definition of post-glacial rebound and global hydrological
mass redistribution.
REFERENCES
Bentley, C.R. & M.B. Giovinetto, Mass Balance of Antarctica and Sea Level Change, Proc.
Int ConfRole of Polar Regions in Global Change, 481-488, Univ. Alaska, Fairbanks, 1991
Cartwright, D.E., and A.C. Edden, Corrected Tables of Tidal Harmonics, Geophys J R Astr
Soc, 33, 253-264, 1973.
Chao, B.F., Excitation of the Earth's Polar Motion due to Mass Variations in Major
Hydrological Reservoirs, J Geophys Res, 93 (B11), 13,811-13,819, 1988.
Chao, B.F., The Geoid and Earth Rotation, in Geoid and Its Geophysical Interpretations,
CRC Press, 285-298, 1993.
Cheng, M.K. et al., Temporal Variations in Low Degree Zonal Harmonics from Starlette
Orbit Analysis, Geophys Res Lett, 16 (5), 393-396, 1989.
Christodoulidis, D.C. et al., Observed Tidal Braking in the Earth/Moon/Sun System, J
Geophys Res, 93 (B6), 6216-6236, 1988.
Gegout, P. & A. Cazenave, Temporal Variations of the Earth's Gravity Field for 1985-1989
from Lageos, Geophys J Intl, 114, 347-359, 1993.
Giovinetto, M.B. and Zwally, J., An Assessment of Mass Budgets of Antarctica and
Greenland Using Accumulation Derived from Remotely Sensed Data in Areas of Dry
Snow, in press, 1995.
Gross, R.S., A Combination of Earth Orientation Data: Space93, IERS Annual Report,
Observatory of Paris, 1993.
Hedin, A.E., MSIS-86 Thermospheric Model, J Geophy Res, 92 (A5), 4649-4662, 1987.
Houghton, J. and L.G. Meira Filho, Intergovernmental Panel on Climate Change, in press,
WMO and UNEP Report, 1995
Ivins, E.R., et al., Deep Mantle Viscous Structure With Prior Estimate and Satellite
Constraint, J Geophys Res, 98 (B3), 4579-4609, 1993.
Jacobs, S.S., Is the Antarctic ice sheet growing?, Nature, 360, 29-33, 1992.
James, T.S. and E.R. Ivins, Present-day Antarctic Ice Mass Changes and Crustal Motion,
Geophys Res Lett, 22 (8), 973-976, 1995.
Kaula, Wm., Theol)' of Satellite Geodesy, Blaisdell, Waltham, MA, 1966.
Mitrovica, J.X., and W.R. Peltier, Present-Day Secular Variations in the Zonal Harmonics
of the Earth's Geopotential, J Geophys Res, 98 (B3), 4509-4526, 1993.
Nerem, R.S. et al., Expected Orbit Determination Performance for TOPEX/Poseidon, IEEE
Trans Geosci and Remote Sens, 31 (2), 1993.
Nerem, R.S. et al., Time Variations of the Earth's Gravity Field from Laser Ranging to
Lageos, Geophys Res Lett, 20 (7), 595-598, 1993b.
162