Overview
The CSR SLR Degree 2 products provide monthly estimates of Earth’s degree-2 spherical harmonic coefficients derived from Satellite Laser Ranging observations. They complement GRACE and GRACE-FO gravity solutions by supplying accurate information about the longest-wavelength components of the gravity field.
Earth’s Dynamic Oblateness
The degree-2, order-0 coefficient C(2,0) is associated with Earth’s flattening and is commonly described as Earth’s dynamic oblateness. It is also expressed as J2, with the relationship:
J2 = -C(2,0) × √5
The coefficient reflects differences in Earth’s principal moments of inertia and therefore responds to large-scale redistribution of mass within the Earth system.
Scientific Background
Satellite observations have documented a long-term decrease in J2 since 1979, while historical eclipse records indicate a similar trend over approximately 2,500 years. Glacial isostatic adjustment is the main cause of this secular change. Superimposed on that trend are variations associated with redistribution of ocean and ice mass [Cox and Chao, 2002; Dickey et al, 2002]. More recently, increased ice loss from Greenland and Antarctica appears to offset a growing portion of the long-term GIA signal [Cheng et al., 2013].
Available Products
| Product | Time Span | Description |
|---|---|---|
| Variations of C(2,0) | 1976 to present | Monthly variations of Earth’s dynamic oblateness [Cheng et al., 2013]. |
| Complete degree-2 harmonics | 2002 to present | Monthly C(2,0), C(2,1), S(2,1), C(2,2), and S(2,2) estimates [Cheng et al., 2011], using the same geophysical background fields as the latest GRACE RL06 processing, including the AOD models. |
Please consult the README and the individual file headers for additional details about the SLR observations and processing.
Download
Download the CSR SLR Degree 2 products, including the C(2,0) time series and complete monthly degree-2 spherical harmonic coefficients.
Contents: Monthly SLR-derived degree-2 spherical harmonic coefficients, documentation, and supporting files.
Processing
The estimates of C(2,0), C(2,1), S(2,1), C(2,2) and S(2,2) are obtained from the analysis of Satellite Laser Ranging observations of five geodetic satellites: LAGEOS-1 and 2, Starlette, Stella, and Ajisai.
The background gravity model used in the SLR analysis is consistent with the current GRACE Release-06 processing, including use of the same Atmosphere-Ocean De-aliasing model. The monthly mean of the AOD model, included in the file, is restored so that the monthly coefficients represent the full signal. These data are housed at the Center for Space Research at The University of Texas Austin.
Acknowledgement and Citation
When using these data, please acknowledge receiving the data from "http://grace.jpl.nasa.gov", and cite (depending on the product):
Cheng, M., J. C. Ries, and B. D. Tapley (2011), Variations of the Earth's figure axis from satellite laser ranging and GRACE, J. Geophys. Res., 116, B01409, doi:10.1029/2010JB000850.
Cheng, M., B. D. Tapley, and J. C. Ries (2013), Deceleration in the Earth's oblateness, J. Geophys. Res. Solid Earth, 118, 740-747, doi:10.1002/jgrb.50058.
Further References
C.M.Cox, B.F.Chao (2002), Detection of a Large-Scale Mass Redistribution in the Terrestrial System Since 1998, Science 297, p831.
J.O. Dickey et al (2002), Recent Earth Oblateness Variations: Unraveling Climate and Postglacial Rebound Effects, Science, p1975.