Earth’s low degree gravitational variations from space geodetic data€¦ · variations from...
Transcript of Earth’s low degree gravitational variations from space geodetic data€¦ · variations from...
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Earth’s low degree gravitational
variations from space geodetic data
18th International Workshop on Laser Ranging, 2013, Fujiyoshida
G. Bianco Agenzia Spaziale Italiana, CGS - Matera
V. Luceri e-GEOS S.p.A., ASI/CGS - Matera
C. Sciarretta e-GEOS S.p.A., Rome
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• The C21, S21 and C20 Stokes coefficients are related to the Earth’s
principal figure axis and oblateness
• The redistribution of the mass within the Earth system induces
changes in the Earth’s gravity field.
• Mass load variations induce excitations in the EOPs that are
proportional to those second-degree coefficients.
• SLR data are used to retrieve time series of direct estimates of low
degree geopotential coefficients
• Time series of 2-deg Stokes coefficients can be derived from the
EOP excitation functions (SLR and VLBI EOP in this study)
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All the SLR data available from 1983 to June 2013
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DC2,1 DS2,1 Full Time Series from SLR data
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DC2,1 and DS2,1 external comparison
CSR solution: Cheng, M. K., 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.
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DC2,0 Time Series from SLR data
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DC2,0 external comparison
CSR solution:
Cheng, M. K., 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.
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Polar motion and LOD
-2000
2004000
200400
6001983
1987
1991
1995
1999
2003
2007
2011
2014
X (mas) Y (mas) ASI/CGS
Ye
ars
1985
1990
1995
2000
2005
2010
1982 1986 1990 1994 1998 2002 2006 2010 2014-2
-1
0
1
2
3
4
Years
ms
D
ASI/CGS
LOD
• Surface mass load variations induce excitations in the EOPs
• The excitation functions are proportional to the C21, S21 and C20 coefficients
• Time series of excitation functions have been derived from the EOPs estimated at
ASI/CGS from SLR (LAGEOS 1-2) and VLBI data and available at IERS as
operational series
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SLR Polar motion & LOD excitations Polar Motion Excitation c1
-1,E-06
-5,E-07
0,E+00
5,E-07
1,E-06
1983 1987 1991 1995 1999 2003 2007 2011
SLR EOP - CGS
Wind (AAM) + Current (OAM)Polar Motion Excitation c2
-1,E-06
-5,E-07
0,E+00
5,E-07
1,E-06
1983 1987 1991 1995 1999 2003 2007 2011
SLR EOP - CGS
Wind (AAM) + Current (OAM)Polar Motion Excitation c3
-3,E-08
-2,E-08
-1,E-08
0,E+00
1,E-08
2,E-08
3,E-08
1983 1987 1991 1995 1999 2003 2007 2011
SLR EOP - CGS
Wind (AAM) + Current (OAM)
LOD Excitation c3
Polar Motion Excitation c2
Polar Motion Excitation c1
D. Salstein, aamf.ncep.reanalysis values, AER, IERS Special Bureau for the Atmosphere
R. Gross, ECCO_kf080.chi values, NASA/JPL, IERS Special Bureau for the Oceans
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DC21 from CGS SLR EOP
-4,E-10
-3,E-10
-2,E-10
-1,E-10
0,E+00
1,E-10
2,E-10
3,E-10
4,E-10
1993 1997 2001 2005 2009 2013
C21(EOP - 'Wind&'Current')
wind¤t
DC2,1 and DS2,1 from EOP
DS21 from CGS SLR EOP
-3,E-10
-2,E-10
-1,E-10
0,E+00
1,E-10
2,E-10
3,E-10
4,E-10
5,E-10
1993 1997 2001 2005 2009 2013
S21(EOP - 'Wind&Current')
wind¤t
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DC20 from CGS SLR EOP
-4,E-09
-3,E-09
-2,E-09
-1,E-09
0,E+00
1,E-09
2,E-09
3,E-09
4,E-09
1993 1997 2001 2005 2009 2013
C20(EOP - 'Wind&Current')
wind¤t
raw series
DC2,0 from EOP
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DS21 detrended
-2,E-10
-1,E-10
0,E+00
1,E-10
2,E-10
1992 1996 2000 2004 2008 2012
DC21 detrended
-2,E-10
-1,E-10
0,E+00
1,E-10
2,E-10
1992 1996 2000 2004 2008 2012
EOP SLR EOP VLBI
SLR DC2,1
DS2,1
Comparison
• The residual behavior of C21, S21 from SLR dynamics and from SLR & VLBI EOP excitation functions are similar.
• An annual frequency is clearly visible in all the terms, with more significant amplitude for S21 term.
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DC20 detrended
-6,E-10
-4,E-10
-2,E-10
0,E+00
2,E-10
4,E-10
6,E-10
1992 1996 2000 2004 2008 2012
DC2,0
EOP SLR EOP VLBI
SLR
Comparison
• The variations of C20 show similarities too, even if the interpretation of the direct comparison of the EOP derived series with the dynamics one is a bit more complicated: the LOD derived series, after the removal of the “motion” geophysical component, has been cleaned also from the low frequency terms (<1/4 y-1) and compared with the detrended C20 from SLR dynamics. Also in this case, a residual annual signature is visible in all the series.
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“Numerical” summary
Rate
(10-12)
Annual amp
(10-10)
Semi-annual amp
(10-10)
DC2,1 SLR -9.8 ± 0.6 0.25 ± 0.04 0.13 ± 0.04
DC2,1 EOP_SLR -9.0 ± 0.2 0.22 ± 0.01 0.07 ± 0.01
DC2,1 EOP_VLBI -9.1 ± 0.2 0.30 ± 0.02 0.06 ± 0.02
IERS conventions -3.3
DS2,1 SLR 0.7 ± 0.6 0.48 ± 0.05 0.11 ± 0.05
DS2,1 EOP_SLR 1.3 ± 0.2 0.71 ± 0.02 0.21 ± 0.02
DS2,1 EOP_VLBI 2.4 ± 0.2 0.77 ± 0.02 0.22 ± 0.02
IERS conventions 16.1
DC2,0 SLR 10.6 ± 1.2 1.15 ± 0.05 0.38 ± 0.05
DC2,0 EOP_SLR - 1.10 ± 0.05 1.01 ± 0.05
DC2,0 EOP_VLBI - 1.16 ± 0.05 0.99 ± 0.05
IERS conventions 11.6
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Variations of the figure axis C21 dyn SLR without annual and semiannual
-2.0E-10
-1.5E-10
-1.0E-10
-5.0E-11
0.0E+00
5.0E-11
1.0E-10
1.5E-10
2.0E-10
01/01/1993 01/01/1997 01/01/2001 01/01/2005 01/01/2009 01/01/2013
s21 dyn SLR without annual and semiannual
-2.0E-10
-1.5E-10
-1.0E-10
-5.0E-11
0.0E+00
5.0E-11
1.0E-10
1.5E-10
2.0E-10
01/01/1993 01/01/1997 01/01/2001 01/01/2005 01/01/2009 01/01/2013
DC2,1
DS2,1
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Figure from http://hpiers.obspm.fr
Mean pole since 1900