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globally averaged sea globally averaged sea level budget on seasonal level budget on seasonal to interannual time to interannual time scales scales Josh K. Willis Josh K. Willis [email protected] [email protected] Jet Propulsion Laboratory Jet Propulsion Laboratory Don P. Chambers, R. Steven Nerem Don P. Chambers, R. Steven Nerem Co-Authors: Co-Authors:

Toward closing the globally averaged sea level budget on seasonal to interannual time scales Josh K. Willis [email protected] Jet Propulsion

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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

MotivationMotivation

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)

Remaining Discrepancies Remaining Discrepancies in the Sea Level Budgetin the Sea Level Budget

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 Spurious Cooling the Spurious Cooling SignalSignal

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

3.4 mm/year

1.3 mm/year

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.