Don P. Chambers Don P. Chambers Center for Space Research Center for Space Research The University of Texas at Austin The University of Texas at Austin Understanding Sea-Level Rise and Variability Understanding Sea-Level Rise and Variability 6-9 June, 2006 6-9 June, 2006 Paris, France Paris, France The Potential to Estimate The Potential to Estimate Ocean Thermal Expansion by Ocean Thermal Expansion by Combining GRACE and Satellite Combining GRACE and Satellite Altimetry Altimetry
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The Potential to Estimate Ocean Thermal Expansion by Combining GRACE and Satellite Altimetry
The Potential to Estimate Ocean Thermal Expansion by Combining GRACE and Satellite Altimetry. Don P. Chambers Center for Space Research The University of Texas at Austin Understanding Sea-Level Rise and Variability 6-9 June, 2006 Paris, France. GOALS. - PowerPoint PPT Presentation
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Don P. ChambersDon P. ChambersCenter for Space ResearchCenter for Space Research
The University of Texas at AustinThe University of Texas at Austin
Understanding Sea-Level Rise and VariabilityUnderstanding Sea-Level Rise and Variability
6-9 June, 20066-9 June, 2006
Paris, FranceParis, France
The Potential to Estimate The Potential to Estimate Ocean Thermal Expansion by Ocean Thermal Expansion by
Combining GRACE and Satellite Combining GRACE and Satellite AltimetryAltimetry
GOALSGOALS
• Computing mean ocean mass component of sea level from GRACE
• Potential for combining with altimetry to determine long-term trend in steric sea level
» Steric SL = Altimeter SL - GRACE SL
• Sources of uncertainty in rate estimate for GRACE
» Glacial Isostatic Adjustment (GIA) correction
» Degree 1 gravity coefficients (geocenter)
» Interannual variations in ocean mass and a short record
Science GoalsMeasure time variable gravity field to detect changes in the water storage and movement from reservoir to another (e.g., from ice sheets to ocean)
MissionJoint NASA/German mission implemented by NASA and DLR (Deutschen Zentrum für Luft-und Raumfahrt) under the NASA Earth System Science Pathfinder Program.Science data processing by University of Texas Center for Space Research (UTCSR) and GeoForschungsZentrum (GFZ)
OrbitLaunched: March 17, 2002Regular Science Data: August, 2002Original Lifetime: 5 yearsRecently NASA/DLR extended mission through 2009
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GRACE ErrorsGRACE Errors
long wavelength short
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•GRACE project produces a set of global gravity coefficients (Clm, Slm) every month
•Can convert these to a time-series of monthly average water level (sea level) over a basin by
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ηba sin =QlΩba sinl,m
∑ W lmCΔClm +W lm
SΔSlm( )
Ql =aρE3ρW
2l +1( )1+ kl( )
Ocean kernel
•Ocean kernel designed to minimize error from GRACE noise AND aliasing of hydrology signals [Swenson and Wahr, JGR, 2002]
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• From CSR_RL01 GRACE coefficients
» Replacing C20 with values from SLR analysis and using seasonal model of C10, C11, and S11 terms (Chambers et al., GRL, 2004)
• Convert simulated water level changes into gravity field coefficients (to degree/order 180)
• Compute ocean mass with and without degree 1 terms
• Result: trend is 0.1 mm/year lower if degree 1 not used.
Greenland: 22.0 cm/m2 water mass lost per year (0.75 mm SL)
Antarctica: 4.1 cm/m2 water mass lost per year (0.75 mm SL)
Oceans: 1.5 mm/year increase in SL
Land: No change
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• We have limited knowledge of interannual variations in ocean mass
• Some evidence of ± 4-5 mm variations at ENSO periods
With 1-year smoothing
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Trend removed from Altimeter - TSL
• Simulate interannual ocean mass by scaling SOI to estimate from J. Willis in 1997-1998
» 55 yr. trend set to zero
• Estimate 95% confidence interval based on standard deviation of trends over 3-15 yr intervals
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Rate Uncertainty for Ocean Mass from Rate Uncertainty for Ocean Mass from GRACE with 3-years of ObservationsGRACE with 3-years of Observations
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Source Uncertainty (mm/year)
Formal 0.3
Knowledge of GIA correction 0.71
Knowledge of degree 1 rates 0.22
3-year period & ENSO-like variability 2.8
RSS (3-year rate)3 0.8
RSS (long-term)4 2.9
1 - from range of GIA corrections2 - doubled simulation estimate to be conservative; systematic!3 - without interannual uncertainty4 - all sources of trend uncertainty
• Why the big difference between in situ TSL and space-based estimates?
» Unknown error in one or more of the systems?
» Changes in deep ocean heat storage not measured by Argo floats?
Yearly averages, maximum GIA correction added to GRACE