Thermosteric Effects on Long-Term Thermosteric Effects on Long-Term Global Sea Level ChangeGlobal Sea Level Change

Jianli Chen Jianli Chen

Center for Space Research, University of Texas at Austin, USACenter for Space Research, University of Texas at Austin, USA

http://www.csr.utexas.edu/personal/chenhttp://www.csr.utexas.edu/personal/chen

Email: chen@csr.utexas.edu Email: chen@csr.utexas.edu

2006 WPGM, July 24 - 27, Beijing, China OS35A-01 Wed. 16:45 2006 WPGM, July 24 - 27, Beijing, China OS35A-01 Wed. 16:45 PMPM

I sincerely apologize for being absent due to an unexpected urgency, and am grateful to Richard for his kind help. - Jianli Chen I sincerely apologize for being absent due to an unexpected urgency, and am grateful to Richard for his kind help. - Jianli Chen

What may cause sea level change?What may cause sea level change?

Warming of the ocean (thermal expansion)Warming of the ocean (thermal expansion) Salinity change (seawater density change)Salinity change (seawater density change) Ocean current (dynamic sea surface height)Ocean current (dynamic sea surface height) Polar ice sheet & glacial melting (water mass exchange)Polar ice sheet & glacial melting (water mass exchange) Ocean tide (solar & lunar gravitational force)Ocean tide (solar & lunar gravitational force) Pole tide (rotational deformation)Pole tide (rotational deformation) Terrestrial & atmospheric water storage changeTerrestrial & atmospheric water storage change Atmospheric pressure loading (inverted barometer)Atmospheric pressure loading (inverted barometer) Solid Earth deformation (uplift & subsidence)Solid Earth deformation (uplift & subsidence) ……

Steric ChangeSteric Change

Global Long-Term Sea Level Change RatesGlobal Long-Term Sea Level Change Rates

AVISO Merged Satellite AVISO Merged Satellite AltimetersAltimeters

World Ocean Atlas 2001 World Ocean Atlas 2001 (WOD01)(WOD01)

Observed Sea Level Rates (cm/year)

Steric Sea Level Rates (cm/year)

Global Mean Sea Level Change Using Merged Satellite Global Mean Sea Level Change Using Merged Satellite

Altimeters Measurements.Altimeters Measurements.

Thermal Steric Sea Level Changes Using Temperature Thermal Steric Sea Level Changes Using Temperature

& Salinity Data From the World Ocean Database 2001 & Salinity Data From the World Ocean Database 2001

& World Ocean Atlas 2001.& World Ocean Atlas 2001.

Non-steric Sea Level Changes From Terrestrial Water Non-steric Sea Level Changes From Terrestrial Water

Storage Change, Atmospheric Water Vapor Variation, Storage Change, Atmospheric Water Vapor Variation,

& Polar Ice Sheet Melting.& Polar Ice Sheet Melting.

ObjectivesObjectives

About Sea Level ChangeAbout Sea Level Change

Long-Term Sea level ChangeLong-Term Sea level Change

Thermal expansion & salinity changeThermal expansion & salinity change Polar ice sheet & glacial meltingPolar ice sheet & glacial melting Glacial isostatic adjustment (GIA)Glacial isostatic adjustment (GIA) Terrestrial water storage changeTerrestrial water storage change

Seasonal Sea Level ChangeSeasonal Sea Level Change

Thermal expansion & salinity changeThermal expansion & salinity change Terrestrial water storageTerrestrial water storage Atmospheric water vaporAtmospheric water vapor OthersOthers

Satellite Radar Altimeter Sea Level MeasurementsSatellite Radar Altimeter Sea Level Measurements

AVISO merged mean sea level anomalyAVISO merged mean sea level anomaly

TOPEX/Poseidon, Jason-1, ERS-1/2, EnvisatTOPEX/Poseidon, Jason-1, ERS-1/2, Envisat

October 1992 to August 2004October 1992 to August 2004

7-day intervals7-day intervals

1/3° x 1/3° Mercator grids1/3° x 1/3° Mercator grids

Data from 65° S to 65° N are included.Data from 65° S to 65° N are included.

Data and ProcessingData and Processing

World Ocean Database 2001 (WOD01)World Ocean Database 2001 (WOD01) Yearly temperature anomalyYearly temperature anomaly

1955 - 2003 , 1° x 1° grids1955 - 2003 , 1° x 1° grids

16 layers (0 - 700 m depth)16 layers (0 - 700 m depth)

Pentadal (5-year running) temperature anomalyPentadal (5-year running) temperature anomaly 1957 - 1996 , 1° x 1° grids1957 - 1996 , 1° x 1° grids

28 layers (0 - 3000 m depth)28 layers (0 - 3000 m depth)

World Ocean Atlas 2001 (WOA01)World Ocean Atlas 2001 (WOA01) Climatologies of temperature and salinity fieldsClimatologies of temperature and salinity fields

Jan, Feb, … Dec, 1° x 1° gridsJan, Feb, … Dec, 1° x 1° grids

24 layers (0 - 1500 m depth)24 layers (0 - 1500 m depth)

Data from 65° S to 65° N are included (for both WOD01 and WOA01)Data from 65° S to 65° N are included (for both WOD01 and WOA01)

Data and Processing Data and Processing (cont.)(cont.)

Terrestrial Water Storage Terrestrial Water Storage

Model 1: Model 1:

US Climate Prediction Center (CPC) Land Data Assimilation US Climate Prediction Center (CPC) Land Data Assimilation SystemSystem

Soil moisture and snow, monthly, Jan. 1980 - present, 1Soil moisture and snow, monthly, Jan. 1980 - present, 1 x 1 x 1 gridsgrids

Model 2:Model 2:

NASA Global Land Data Assimilation System (GLDAS)NASA Global Land Data Assimilation System (GLDAS) Soil moisture and snow, 3-hourly, Jan. 2001 - Dec. 2004, 1° x 1° gridsSoil moisture and snow, 3-hourly, Jan. 2001 - Dec. 2004, 1° x 1° grids

Atmospheric Water VaporAtmospheric Water Vapor

NCEP Reanalysis Surface Pressure dataNCEP Reanalysis Surface Pressure data Daily, Jan. 1993 - Aug. 2004 (same as altimeter data) Daily, Jan. 1993 - Aug. 2004 (same as altimeter data) Gaussian grids (~ 1.904° x 1.875° )Gaussian grids (~ 1.904° x 1.875° )

Data and Processing Data and Processing (cont.)(cont.)

Steric Sea Level ChangeSteric Sea Level Change

€

SSHsteric = −1

ρ 0

⋅ Δρ− h

0

∫ ⋅dz

= = (T, S, P) - (T, S, P) - 00

in which in which 00 is the mean density of sea water (1028 kg/m is the mean density of sea water (1028 kg/m33), and ), and is the density change as a is the density change as a

function of temperature (function of temperature (TT), salinity (), salinity (SS), and pressure (), and pressure (PP). The integral is from the ocean bottom ). The integral is from the ocean bottom to the sea surface (to the sea surface (h=0h=0). ). TT is from either yearly or pentadal temperature fields, is from either yearly or pentadal temperature fields, SS from the mean from the mean salinity of the WOD01 climatology, and salinity of the WOD01 climatology, and PP is computed from the mean depth of each layer. is computed from the mean depth of each layer. is is computed using the UNESCO (United Nations Educational, Scientific and Cultural Organization) computed using the UNESCO (United Nations Educational, Scientific and Cultural Organization) standard equations (Fofonoff and Millard 1983)standard equations (Fofonoff and Millard 1983)

Steric sea level change can be computed from seawater density change as,Steric sea level change can be computed from seawater density change as,

Global Water Mass Balance & Sea Level ChangeGlobal Water Mass Balance & Sea Level Change

Assuming the total water mass on the Earth surface is conserved, soAssuming the total water mass on the Earth surface is conserved, so

MMoceanocean + + MMland_waterland_water + + MMvaporvapor = 0 = 0

oror

MMoceanocean = - ( = - (MMland_waterland_water + + MMvaporvapor) )

So, non-steric global mean sea level (GMSL) change due to water mass exchange So, non-steric global mean sea level (GMSL) change due to water mass exchange between ocean and land/atmosphere can be computed as,between ocean and land/atmosphere can be computed as,

GMSLGMSLnon-stericnon-steric = = MMoceanocean/Ocean_Area /Ocean_Area

GMSLGMSLnon-stericnon-steric = - ( = - (MMland_waterland_water + + MMvaporvapor)/ /Ocean_Area )/ /Ocean_Area

Data and Processing Data and Processing (cont.)(cont.)

Assuming the total water mass on the Earth surface is conserved, soAssuming the total water mass on the Earth surface is conserved, so

GMSLGMSLaltimeteraltimeter = = GMSLGMSLstericsteric + + GMSLGMSLTWSTWS + + GMSLGMSLice_meltingice_melting + … + …

The big challenge is how to close the budget.The big challenge is how to close the budget.

GMSLGMSLaltimeteraltimeter = AVISO Mean Sea Level Anomaly= AVISO Mean Sea Level Anomaly

GMSLGMSLstericsteric = WOD01/WOA01= WOD01/WOA01

GMSLGMSLTWSTWS = CPC/NCEP= CPC/NCEP

GMSLGMSLice_meltingice_melting = GRACE (= GRACE (Gravity Recovery and Climate ExperimentGravity Recovery and Climate Experiment))

Long-Term Sea Level Change

AVISO merged altimeter estimate, 2.6 mm/year during 1993 -2004.AVISO merged altimeter estimate, 2.6 mm/year during 1993 -2004.

WOD01 steric effect, 1.2 mm/year during 1993 -2004, and 0.34-0.39 WOD01 steric effect, 1.2 mm/year during 1993 -2004, and 0.34-0.39

mm/year during last 50 years.mm/year during last 50 years.

GRACE observed polar ice sheet & mountain glacial melting.GRACE observed polar ice sheet & mountain glacial melting.

Interannual Sea Level ChangeInterannual Sea Level Change

AVISO merged altimeter estimateAVISO merged altimeter estimate

GLDAS terrestrial water storageGLDAS terrestrial water storage

NCEP water vaporNCEP water vapor

ResultsResults

Global Mean Sea Level (GMSL) Change From Satellite AltimetersGlobal Mean Sea Level (GMSL) Change From Satellite Altimeters

Long-Term Global Mean Sea Level Change From Altimeters & Steric EffectsLong-Term Global Mean Sea Level Change From Altimeters & Steric Effects

Steric Effects on Global Mean Sea Level Change From WOD01/WOA01Steric Effects on Global Mean Sea Level Change From WOD01/WOA01

The large bias of WOD98 estimated The large bias of WOD98 estimated

steric effects on global mean sea level steric effects on global mean sea level

change in 1997 & 1998 is apparently change in 1997 & 1998 is apparently

caused by poor data quality and caused by poor data quality and

incomplete data collection in WOD98. incomplete data collection in WOD98.

An algorithm error was later discovered An algorithm error was later discovered

and fixed in WOD01.and fixed in WOD01. Data Data

QualityQuality

Data CollectionData Collection

Interannual Global Mean Sea Level Change From CPC Terrestrial Interannual Global Mean Sea Level Change From CPC Terrestrial Water Storage & NCEP Water Vapor VariationsWater Storage & NCEP Water Vapor Variations

GRACE observed long-term ice melting:GRACE observed long-term ice melting:

Antarctic ice sheet ~ – 152 ± 80 kmAntarctic ice sheet ~ – 152 ± 80 km33/year [Velicogna & Wahr 2006, /year [Velicogna & Wahr 2006, ScienceScience]]

Greenland ice sheet ~ – 239 ± 23 kmGreenland ice sheet ~ – 239 ± 23 km33/year [Chen et al. 2006, /year [Chen et al. 2006, ScienceScience]]

Alaskan mountain glaciers ~ – 101 ± 22 kmAlaskan mountain glaciers ~ – 101 ± 22 km33/year [Chen et al. 2006, /year [Chen et al. 2006, EPSLEPSL]]

Polar Ice Sheet & Mountain Glacial Melting EffectsPolar Ice Sheet & Mountain Glacial Melting Effects

So, the total contribution of ice melting to the global ocean from Antarctica, So, the total contribution of ice melting to the global ocean from Antarctica,

Greenland, and Alaskan mountain glaciers is ~ – 492 kmGreenland, and Alaskan mountain glaciers is ~ – 492 km33/year, equivalent to /year, equivalent to

global sea level rise of ~ 1.33 mm/year.global sea level rise of ~ 1.33 mm/year.

About Long-Term and Interannual Sea Level ChangeLong-Term and Interannual Sea Level Change

Steric effect accounts for about half of the observed long-term sea Steric effect accounts for about half of the observed long-term sea

level rise during the period 1993-2004 (1.2 vs. 2.6 mm/year).level rise during the period 1993-2004 (1.2 vs. 2.6 mm/year).

Polar ice sheets & mountain glacial melting may cause sea level rise Polar ice sheets & mountain glacial melting may cause sea level rise

of ~ 1.3 mm/year (during the period 2002 - 2005).of ~ 1.3 mm/year (during the period 2002 - 2005).

Combined steric and ice melting effect may account for ~ 2.5 Combined steric and ice melting effect may account for ~ 2.5

mm/year, compared with 2.6 mm/year from satellite altimeters.mm/year, compared with 2.6 mm/year from satellite altimeters.

Steric and non-steric effects appear equally important in driving Steric and non-steric effects appear equally important in driving

the global sea level rise.the global sea level rise.

ConclusionsConclusions

About Long-Term and Interannual Sea Level ChangeLong-Term and Interannual Sea Level Change

There appears notable acceleration of steric global mean sea level rise There appears notable acceleration of steric global mean sea level rise

in the last 10 years as compared with the entire 50 years period, which in the last 10 years as compared with the entire 50 years period, which

can be associated with strong decadal variations.can be associated with strong decadal variations.

WOD01 estimated steric effects fail to show corresponding WOD01 estimated steric effects fail to show corresponding

interannual variability during the 1997/1998 El Nino event.interannual variability during the 1997/1998 El Nino event.

Terrestrial water storage and atmospheric water vapor do show Terrestrial water storage and atmospheric water vapor do show

strong interannual variability well correlated with altimeter strong interannual variability well correlated with altimeter

observations.observations.

Conclusions (cont.)Conclusions (cont.)

Thanks!Thanks!

Results presented here Results presented here are being published in,are being published in,

Chen, J.L., C.R. Wilson, B.D. Tapley, X.G. Hu, Thermosteric Effects on Interannual and Long-Term Chen, J.L., C.R. Wilson, B.D. Tapley, X.G. Hu, Thermosteric Effects on Interannual and Long-Term Global Mean Sea Level Change, J. Geodesy, DOI10.1007/s00190-006-0055-7, 2006 (in press).Global Mean Sea Level Change, J. Geodesy, DOI10.1007/s00190-006-0055-7, 2006 (in press).

Preprints are available (chen@csr.utexas.edu).Preprints are available (chen@csr.utexas.edu).