Ice mass loss in the polar regions of the Earth and mantle viscosity from GRACE data

Transcription

1 Ice mass loss in the polar regions of the Earth and mantle viscosity from GRACE data Valentina R. Barletta, Roberto Sabadini and Andrea Bordoni University of Milan Dip. di Scienze della Terra Ardito Desio

2 GRACE Products Level-2 data refers to monthly estimates of spherical harmonic coefficients of the Earth gravity field. Data products from all three centers are available, as follows: CSR (The University of Texas at Austin: Center for Space Research) release 01 release 02 (not openly available) GFZ (GeoForschungsZentrum Potsdam) release 03 JPL (Jet Propulsion Laboratory, California Istitute of Technology) release 02

3 Monthly Mass Grid from GRACE Tellus Site The CSR 01 data have their (2,0) coefficient from Cheng and Tapley, 2004 The CSR 01 needs correction for the pole tide and for long period tides Striping', an error source in the data due to unmodeled fast mass changes with periods lower than 1 month (tides, ocean, hydrology) that looks like near N-S stripes in monthly maps. Destriping Technique: Chambers, D.P.: Evaluation of New GRACE Time-Variable Gravity Data over the Ocean. Geophys. Res. Lett., in press, Acknowledgements: GRACE data were processed by D. P. Chambers, supported by the NASA Earth Science REASoN GRACE Project, and are available at

4 Test with GRACE Tellus mass grid Antarctica CSR G500 GFZ G500 JPL G Greenland CSR G500 GFZ G500 JPL G500 Mass in Gt Mass in Gt Diff = 70% -200 Diff = 65% Time in Month Time in Month Amazonia CSR G500 GFZ G500 JPL G Sahara CSR G500 GFZ G500 JPL G500 Mass in Gt Mass in Gt Diff = 20% -300 Diff = 45% Time in Month Time in Month

5 The suitable series: GFZ R03 GAB=Atmospheric and Oceanic Model The GFZ R03 after the correction prescribed (GFZ+GAB) are equivalent to the CSR R02 CSR 02 GFZ 03 GFZ+GAB 03

6 The Post Glacial Rebound " 2! " GRACE = "! ICE + "! PGR + "! H O +! Others "! GRACE = Mass Variation Seen by GRACE "! PGR = Modeled Mass Variation Produced by PGR "! H 2 O = Hydrology Cycle "! ICE = Ice Mass Variation "! " ICE $ "! GRACE #! PGR

7 Two Equivalent Processing Methods 1 Method a # ave % t (!," ) = & 3 2l k (% C( t) cos( m" ) + % S( t) sin( m" )) P (cos!) $ l m l m l m l m l 2 Method & " l m Cl m and Sl m ( t "! = ) '! $ # & % "!& t t (, ) d & R! a # ave 2l + 1 &(!,") = % l m + 3 k + 1 ( C& cos( m" ) S& sin( m" )) P (cos!) $ l m l m l m l # ' & =! &( %, $ ) d" R

8 The Averaging Function Simple Characteristic function of the Region R (",! ) = { 1 0 Inside the Region Outside the Region R (",! ) + Gaussian Filter r/2 = 250 Km r/2 = 500 Km r/2 = 750 Km Inner Region = R (",! ) $ # R( ",!) Outer Region = R (",! ) + # R( ",!)

9 Antarctica: Mass Variation seen by GRACE GFZ R G500 Linear (G500) Mass Mass in in Gt Gt/yr Time in Month

10 Antarctica: Mass Variation seen by GRACE GFZ R Tellus G500 G500 Linear (G500) Linear (Tellus G500) 147 Gt/yr 200 Mass in Gt Mass in Gt Gt/yr Time in Month

11 Antarctica: Mass Variation seen by GRACE GFZ R Int G500 Out G500 Linear (Out G500) Linear (In G500) 400 Mass in Gt Mass in Gt ±8 Gt/yr Time in Month

12 Antarctica: Mass Variation seen by GRACE CSR R Tellus G500 G500 Linear (G500) Linear (Tellus G500) 113 Gt/yr Mass in Mass in Gt ±7 Gt/yr Time in Month

13 Greenland: Mass Variation seen by GRACE GFZ R G500 Linear (G500) 100 Mass in Gt Mass in Gt Gt/yr Time in Month

14 Greenland: Mass Variation seen by GRACE GFZ R Tellus G500 G500 Linear (G500) Linear (Tellus G500) Mass in Gt Mass in Gt Gt/yr Time in Month -67 Gt/yr

15 Greenland: Mass Variation seen by GRACE GFZ R Int G500 Out G500 Linear (Out G500) Linear (In G500) 0 Mass in Gt Mass in Gt Upper Bound: -67±22 Gt/yr Time in Month Lower Bound: -88±36 Gt/yr

16 Greenland: Mass Variation seen by GRACE CSR R Upper Bound: -66±21 Gt/yr Tellus G500 G500 Linear (G500) Linear (Tellus G500) Mass in Gt Mass in Gt Gt/yr Time in Month Lower Bound : -79±27 Gt/yr

17 The Map of Mass Variation Trend Gaussian Filter Halfwidth = 500Km Water Equivalent in cm/yr

18 The Map of Mass Variation Trend Gaussian Filter Halfwidth = 400Km Water Equivalent in cm/yr

19 Details: Greenland and Antarctica Gaussian Filter Halfwidth = 250Km Water Equivalent in cm/yr Water Equivalent in cm/yr

20 Antarctica East and West Antarctica West GFZ! 43 Tellus GFZ! 123 Gt/yr Gt/yr Antarctica East GFZ! 26 Gt/yr Tellus GFZ! 24 Gt/yr

21 The Post Glacial Rebound Effects Geoid Variation in mm/yr

22 The Post Glacial Rebound Effects Water equivalent in cm/yr

23 The Post Glacial Rebound Effects Gaussian Filter Halfwidth = 500Km Water equivalent in cm/yr

24 The Earth Model Incompressible, Viscoelastic Maxwell Rheology Lithosphere Km Density 1024 Kg/m 3 Rigidity Pa Upper Mantle Lower Mantle 2221 Km Pa Core 3480 Km Kg/m 3 Upper Mantle Viscosity Pa s Lower Mantle Viscosity Pa s Tosi et al. 2005: Most Probable Upper-Lower Mantle Viscosity Pa s

25 The Deglaciation Process Ice Model: ICE 3G Sea Level Equation:! SL = # ICE " I + # Ocean "! SL +! ESL(t) I ESL(t) The Ice Model The Eustatic Sea Level! The Green Function The Convolution The subscript stands for the Region of the convolution! Geoid Variation: Standard: NoSL: Antarctica Only:! G # G = # All ICE " I + # O "! SL = " All! I ICE # G = " Antarctica! I

26 Changing The Deglaciation Process 100% 75% Antarctica Litho 80 Km Litho 121 Km Litho 200 Km 50% 25% 7% 8% 0% LOG of Upper-Low er M antle Viscosity (Pa s) 100% 75% Greenland Litho 80 Km Litho 121 Km Litho 200 Km 50% 25% 22% 7% 0% LOG of Upper-Low er M antle Viscosity (Pa s)

27 Changing The Lithosphere Thickness 80% 60% 40% Antarctica ICE 3G No Sea Level Antarctica Only 20% 0% 4% 7% LOG of Upper-Lower Mantle Viscosity (Pa s) 50% 40% 30% 20% 10% Greenland 15% 24% ICE 3G No Sea Level 0% LOG of Upper-Lower Mantle Viscosity (Pa s)

28 Changing The Mantle Viscosity E19 Pa s Antarctica 45 10E19 Pa s Greenland E20 Pa s 10E20 Pa s Mass Variation (Gt/yr) E21 Pa s Mass Variation (Gt/yr) E21 Pa s LOG of Lower Mantle Viscosity (Pa s) LOG of Lower Mantle Viscosity (Pa s) Upper Bound 280±10 Gt/yr Upper Bound 32±7 Gt/yr Lower Bound 66±6 Gt/yr Lower Bound 4 Gt/yr

29 Ice Mass Variation Antarctica GRACE Tellus GFZ Our best estimate GFZ PGR Min PGR Max +81±6-134±10 +4±14-211±18 GRACE Tellus CSR +47±13-168±10 CSR -13±13-228±17 In Gt/yr Greenland PGR Min PGR Max GRACE Tellus GFZ ±7 Our best estimate GFZ -71±22-99±29 Lower bound estimate GFZ -92±36-120±43 In Gt/yr

30 Ice Mass Variation Antarctica GRACE Tellus GFZ Our best estimate GFZ PGR Min PGR Max +81±6-134±10 +4±14-211±18-172±39 GRACE Tellus CSR +47±13-168±10 CSR -13±13-228±17 In Gt/yr Greenland PGR Min PGR Max GRACE Tellus GFZ ±7 Our best estimate GFZ -71±22-99±29 Lower bound estimate GFZ -92±36-120±43 In Gt/yr

31 Ice Mass Variation: Antarctica East and West Antarctica East GRACE Tellus GFZ PGR Min + 90 ± 4 PGR Max!14 ± 4 GFZ + 10 ± 4! 94 ± 7 In Gt/yr Antarctica West GRACE Tellus GFZ GFZ PGR Min! 6 PGR Max!103± 3! 4!101± 3 In Gt/yr

32 Ice Mass Variation: Antarctica East and West Antarctica East GRACE Tellus GFZ GFZ PGR Min + 90 ± 4 PGR Max!14 ± ± 4! 94 ± 7-54±57 In Gt/yr Antarctica West GRACE Tellus GFZ GFZ PGR Min! 6 PGR Max!103± 3! 4!101± 3 In Gt/yr

33 What Other Works Say GRACE CSR01 Velicogna & Wahr (2006) GRACE CSR01 Chen et al. (2006) GRACE LevelB1 Luthcke et al. (2006 ) GRACE Ramillien et al. (2006) SLR Tosi et al. (2005) Altimetry Zwally et al. (2005) Altimetry Rignot & Kanagaratnam (2006) -238±36-239±22-101±16-129±15-60±20 +11±3-224±41 Greenland Our estimate for Greenland -99±29 Antarctica West East Total GRACE CSR01 GRACE Chen et al. (2006) Ramillien et al. (2006) -77±14-107±23 +80±16 +67± Our estimate for Antarctica GRACE CSR01 SLR Velicogna & Wahr (2005) Tosi et al. (2005) -148± ± ±79-240±40-172±39 Altimetry Zwally et al. (2005) -47±4 +16±11-31±12