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1. Geocenter Solutions from Lageos 1/2 (Eanes) and Lageos 1 (Kar)

We have done a benchmark between Dr. Eanes' Lageos 1/2 geocenter series and Dr. Kar's Lageos 1 single satellite solutions. The agreements for X and Y components are pretty good, and the discrepancies on Z components are obviously large. The annual and semiannual fit to these two sets of solutions provide a quantitative comparison on them. Despite of the large difference on variablities for Z components, the phases for seasonal variations are nearly the same.

	  Table 1. Annual & Semiannual Fit to Two Solutions
	source                 Annual               Semiannual
	                  amp(mm) phase(deg)     amp(mm) phase(deg)
	Lageos 1/2	x  2.18      31.0 	  1.08    164.0 
	(Eanes)		y  3.20     150.5	  0.77    213.2 
			z  2.79      44.8	  0.38     12.6 
	Lageos-1	x  3.11      10.6         1.11     94.2 
	(Kar 87-95)	y  3.48     142.2         0.54    176.2 
			z  6.79      30.5         5.78    228.7 
	Lageos-1	x  2.79      26.9         1.08    104.9 
	(Kar 89-95)	y  3.19     141.2         0.98    146.6 
			z  9.17      37.3         5.92    234.0 
    Note: The phase is defined as following: 0 refers to 0h Jan 1,1992 
	  The geocenter vector is defined by Eanes' convention: from
	  TRF origin to the center of mass.

Figure 1. Comparison of two solutions. |<>| EPS format for downloading
Note: The EPS format has much higher resolution than the GIF you saw here.
2. Contributions from TOPEX/Poseidon

Using the sea surface deviations determined by TOPEX/Poseidon altimeter (cycle 2 - cycle 168), we estimate the geocenter variations under two assumptions, with and without steric correction. The steric sea level correction is based on a simplified thermal expansion model (Chen et. al. 1997) using the World Ocean Atlas 1994 (WOA-94). The Love number correction is not applied in the following plot.

Figure 2. Geocenters from Sea Level Variation |<>| EPS format for downloading
3. Contributions from Land Water

we apply a different approach to investigate the contributions from continental hydrological cycle using soil moisture and snow depth variations. The NCEP-NCAR Data Assimilation Syatem I (CDAS-1) provides nearly real-time monthly diagnostic fields of global soil moisture and snow depth. A preliminary estimation of geocenter variations induced by soil moisture and snow depth's fluctuations is shown on Figure 3.

Figure 3. Geocenters from Soil Moisture & Snow |<>| EPS format for downloading
4. Contributions from Surface Pressure

The surface pressure fields from NCEP-NCAR Climate Date Assimilation System I (CDAS-1) are applied to calculate the geocenter variations as a consequence of pressure variation. Two solutions representing inverted barometer and non-inverted barometer are derived. we have performed a benchmark using ECMWF and GEOS-1 surface pressure fields. No love numer correction applied yet.

Figure 4. Geocenters from Pressure Variations (IB) |<>| EPS format for downloading
Figure 5. Geocenters from Pressure Variations (Non-IB) |<>| EPS format for downloading

Email: cjl@maestro.geo.utexas.edu

Last updated: January 20, 1999