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Toward closing the Toward closing the globally averaged sea globally averaged sea
level budget on seasonal level budget on seasonal to interannual time scalesto interannual time scales
Josh K. WillisJosh K. [email protected]@jpl.nasa.gov
Jet Propulsion LaboratoryJet Propulsion Laboratory
Don P. Chambers, R. Steven NeremDon P. Chambers, R. Steven Nerem
Co-Authors:Co-Authors:
OutlineOutline
• Motivation for assessing Motivation for assessing components of sea level risecomponents of sea level rise
• Assessing the recent sea level Assessing the recent sea level budgetbudget
• Remaining discrepanciesRemaining discrepancies
• The spurious cooling signalThe spurious cooling signal
How fast will sea level rise?How fast will sea level rise?
[Rahmstorf et al., 2007]
Tide Gauge Observations Satellite Observations
Climate Model Predictions(IPCC 3rd Assessment, 2001)
The Seasonal to Interannual The Seasonal to Interannual Sea Level BudgetSea Level Budget
from 2003 to 2007from 2003 to 2007
What causes What causes globally-averagedglobally-averagedsea level rise?sea level rise?
addition of freshwateraddition of heat
+ =
Total sea level rise
ArgoArgo JasonJasonGRACEGRACE
(roughly)
ArgArgoo
• Argo data Argo data onlyonly• All data with All data with knownknown pressures pressures
errors removed.errors removed.• Steric height computed from Steric height computed from
Argo Temp. & Sal.Argo Temp. & Sal.• Monthly objective maps of Monthly objective maps of
large scale steric variability.large scale steric variability.
Argo data distributionArgo data distributionMid 2003 is data sparse in Southern Hemisphere
1800 km zonal, 700 km meridional e-folding scale
Test of Mapping ProcedureTest of Mapping Procedure
RMS difference: 1.6
mm
• Jason data interpolated to time and Jason data interpolated to time and location of Argo profileslocation of Argo profiles
• Mapped using same mapping Mapped using same mapping proceduresprocedures
• Compared with full Jason time seriesCompared with full Jason time series
• Atmospheric and Ocean modelsAtmospheric and Ocean models• Adjustment for incompressibilityAdjustment for incompressibility• Degree 2, order 0 coefficients from Degree 2, order 0 coefficients from
SLRSLR• Monthly model of geocenterMonthly model of geocenter++
• GIA correctionGIA correction**
• Land maskLand mask• ± 66° latitude± 66° latitude
+ Swenson et al., JGR-Oceans, submitted.* Paulson et al., Geophys. J. Int., 2007
±± 0.2 mm/yr
±± 0.2 mm/yr
Mass exchange with high Mass exchange with high latitudeslatitudes
Difference between total ocean average and ± 66°± 66°
average
Very small interannual signal
JasonJason
• Jason data Jason data onlyonly• Standard corrections Standard corrections
applied (including IB)applied (including IB)• GIA +0.3 mm/yr GIA +0.3 mm/yr
[[Douglas and PeltierDouglas and Peltier, , 2002]2002]
The recent sea level budgetThe recent sea level budgetGlobal Mean Sea Level Global MSL, no seasonal
Total (Jason)
Steric (Argo)
Mass (GRACE)
Total (Jason)
Steric (Argo)
Mass (GRACE)
Sea Level BudgetSea Level Budget
AmplitudeAmplitude PhasePhase slopeslope
StericSteric 3.7 ± 0.8 mm 104° ± 13° -0.5 ± 0.5 mm/yr
MassMass 6.8 ± 0.6 mm 261° ± 5° 0.8 ± 0.8 mm/yr
SumSum 3.7 ± 1.0 mm 239° ± 16° 0.3 ± 0.9 mm/yr
AltimeteAltimeterr
3.2 ± 1.3 mm 250° ± 23° 3.6 ± 0.8 mm/yr
Seasonal cycles agree to within random error4-year trends have discrepancy larger than random error => systematic error remains!
The recent sea level budgetThe recent sea level budget
Global MSL, no seasonal cycle, no trend
RMS difference:
1.6 mm
Total (Jason)
Steric (Argo)
Mass (GRACE)
Removal of trend brings all three estimates into excellent agreement
The recent sea The recent sea level budgetlevel budget
4-year Trends in sea level
Jason
Jason-GRACE
Argo
General agreement is encouraging
But, difference in S. Hemisphere trends is concerning
The “rapid cooling” signalThe “rapid cooling” signal
Adapted from Lyman et al. (GRL, 2006)
~ 6 mm drop in thermosteric sea level
Most of the cooling was caused by two in situ data biases
ConclusionsConclusions
• Seasonal, intra- and interannual variations Seasonal, intra- and interannual variations in sea level can be explained as sum of in sea level can be explained as sum of steric and mass componentssteric and mass components
• Large discrepancy remains in 4-year trendLarge discrepancy remains in 4-year trend
• Rapid Ocean cooling was spuriousRapid Ocean cooling was spurious
• Global ocean observing systems are Global ocean observing systems are improving, but they are not yet complete!improving, but they are not yet complete!
ReferencesReferences
Willis, J. K., D. P. Chambers, and R. S. Nerem, “Closing Willis, J. K., D. P. Chambers, and R. S. Nerem, “Closing the Globally Averaged Sea Level Budget on Seasonal the Globally Averaged Sea Level Budget on Seasonal to Interannual Time Scales,” to Interannual Time Scales,” J. Geophys. Res.J. Geophys. Res., , submitted.submitted.
Lyman, J. M., J. K. Willis, and G. C. Johnson, 2006: Recent cooling of the Lyman, J. M., J. K. Willis, and G. C. Johnson, 2006: Recent cooling of the upper ocean. upper ocean. Geophysical Research LettersGeophysical Research Letters, , 3333, L18604, , L18604, doi:10.1029/2006GL027033. doi:10.1029/2006GL027033.
Willis, J. K., Lyman, J. M., G. C. Johnson, and J. Gilson (2007a), Correction to Willis, J. K., Lyman, J. M., G. C. Johnson, and J. Gilson (2007a), Correction to “Recent cooling in the upper ocean”, “Recent cooling in the upper ocean”, 3434, L16601, , L16601, doi:10.1029/2007GL030323..doi:10.1029/2007GL030323..
Willis, J. K., Lyman, J. M., G. C. Johnson, and J. Gilson (2007b), In Situ Data Willis, J. K., Lyman, J. M., G. C. Johnson, and J. Gilson (2007b), In Situ Data Biases and Recent Ocean Heat Content Variability, Biases and Recent Ocean Heat Content Variability, J. of Atmos. Oceanic J. of Atmos. Oceanic Technol.Technol., submitted, October, 2007., submitted, October, 2007.
Wijffels, S., J. K. Willis, C. Domingues, P. Barker, N. White, A. Gronell, K. Wijffels, S., J. K. Willis, C. Domingues, P. Barker, N. White, A. Gronell, K. Ridgway, and J. Church, “Changing eXpendable Bathythermograph Fall-Ridgway, and J. Church, “Changing eXpendable Bathythermograph Fall-rates and their Impact on Estimates of Thermosteric Sea Level Rise,” rates and their Impact on Estimates of Thermosteric Sea Level Rise,” J. J. Atmos. Oceanic Technol.Atmos. Oceanic Technol., in press., in press.
Paulson, A., S. Zhong, and J. Wahr, Inference of mantle viscosity from Paulson, A., S. Zhong, and J. Wahr, Inference of mantle viscosity from GRACE and relative sea level data, GRACE and relative sea level data, Geophys. J. Int.Geophys. J. Int. (in press), 2007. (in press), 2007.
Swenson, S. C., D. P. Chambers, and J. Wahr (2007), Estimating geocenter Swenson, S. C., D. P. Chambers, and J. Wahr (2007), Estimating geocenter variations from a combination of GRACE and ocean model output, variations from a combination of GRACE and ocean model output, J. J. Geophys. Res.Geophys. Res.. submitted.. submitted.