recent results from grace in greenland and antarctica

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Recent results from GRACE in Greenland and Antarctica Isabella Velicogna* and John Wahr** * ESS, University of California Irvine, Irvine CA ** Dept Of Physics and CIRES University of Colorado, Boulder CO

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Recent results from GRACE in Greenland and Antarctica. Isabella Velicogna* and John Wahr** * ESS, University of California Irvine, Irvine CA ** Dept Of Physics and CIRES University of Colorado, Boulder CO. Methods to estimate Ice Mass Variation: Remote Sensing Measurements: - PowerPoint PPT Presentation

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Page 1: Recent results from GRACE in Greenland and Antarctica

Recent results from GRACE in Greenland and Antarctica

Isabella Velicogna* and John Wahr**

* ESS, University of California Irvine, Irvine CA ** Dept Of Physics and CIRES University of Colorado, Boulder CO

Page 2: Recent results from GRACE in Greenland and Antarctica

Methods to estimate Ice Mass Variation:Methods to estimate Ice Mass Variation:

Remote Sensing Measurements:

- Snow input with respect to ice discharge (InSAR ), fluxes.

- Height of surface (radar, and laser altimetry), volume.

Problem: difficulty of monitoring the entire ice sheet, sparse data on accumulation (InSAR), ambiguity in density conversion (Altimetry).

- Mass variation (GRACE): comprehensive survey of the entire ice sheet,First direct measure of mass.

Models: Ice sheet modeling has many limitations that lead to underestimating ice mass rate (Alley et al., Science 2005).

Page 3: Recent results from GRACE in Greenland and Antarctica

Greenland

Page 4: Recent results from GRACE in Greenland and Antarctica

To estimate ice sheet change we need to account for:

-GRACE errors

-Measurements, processing and aliasing errors

-Contamination from other geophysical signals:

1- caused by signals outside Greenland

- continental hydrology outside Greenland (using GLDAS monthly global

water storage fields, and CPC).

- ocean mass variability using a JPL version of the ECCO general

circulation model.

2- from Greenland signals unrelated to snow and ice:

- error in atmospheric mass correction (<3% of GRACE variance)

- PGR signal.

We use two independent ice history models: ICE-5G and GREEN1

Best Estimate : 5 +/- 19 km3/yr

Page 5: Recent results from GRACE in Greenland and Antarctica

Trend, Apr 02-Jun07: -238 km3/yr

__ GRACE - hydrology leakage - PGR

Trend Apr 2002-Dec 2006: -238+/-36 km3/yr

Greenland Mass Variation From GRACE

Page 6: Recent results from GRACE in Greenland and Antarctica

NORTH GREENLAND

----Apr ‘02-Jun ‘07: -65/-18 km3/yr

SOUTH GREENLAND

----Apr ‘02-Jun ‘07: -164+/-24 km3/yr

Page 7: Recent results from GRACE in Greenland and Antarctica

Linear trend fit to same 33 months, between 4/2003 and 6/2006. km3/yr of ice.

CSR RL1: -254 CSR RL4: -256

JPL RL4 -119 GFZ RL4: N/A

GFZ RL3: -195

Goddard: -188

Total Greenland. PGR not removed.

Linear trend fit to same 30 months, between 2/2003 and 12/2005. km3/yr

CSR RL1: -214 CSR RL4: -230

JPL RL4 -99 GFZ RL4: -222

GFZ RL3: -185

Goddard: N/A

Page 8: Recent results from GRACE in Greenland and Antarctica

Helheim glacier.

Kangerdludssuaq glacier.

Page 9: Recent results from GRACE in Greenland and Antarctica

Elastic uplift of ∼35 mm in Kulusuk.

Khan et al GRL (2007)

Ku

Page 10: Recent results from GRACE in Greenland and Antarctica

ENVISAT2003-2005

(Davis, 2007)

Mass loss increased from 90 to 220

km^3/yr in 1996-2006

(Rignot & Kanagaratnam, 2006)

Melt area in Greenland increasing (K. Steffen)

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Ekström et al., Science 2006

Krabill et al., 2006

Watkins et al, 2006

Page 11: Recent results from GRACE in Greenland and Antarctica

Greenland mass balance

Page 12: Recent results from GRACE in Greenland and Antarctica

Antarctica

Page 13: Recent results from GRACE in Greenland and Antarctica

To estimate ice sheet change we need to account for:

-GRACE errors-Measurements, processing and aliasing errors

-Contamination from other geophysical signals:

1- caused by signals outside Antarctica

- continental hydrology outside Antarctica (using GLDAS monthly global

water storage fields).

- ocean mass variability (using a JPL version of the ECCO general

circulation model. (Negligible)

2- from Antarctic signals unrelated to snow and ice:

- error in atmospheric mass correction (~10 km3/yr)

- PGR: we use two independent ice history models: ICE-5G and IJ05

Best Estimate : the midpoint of this range. 192 +/- 79 km3/yr,

Page 14: Recent results from GRACE in Greenland and Antarctica

__ GRACE__ GRACE - hydrology leakage - PGR

---- Apr ‘02-Jun ‘07: -145 +/-80 km3/yr

Antarctica Ice mass Change

Page 15: Recent results from GRACE in Greenland and Antarctica

WAIS and EAIS Mass Variation From GRACE

WAIS (Apr ‘02-Jun ‘07) :-112+/-21 km3/yr EAIS (Apr ‘02-Jun ‘07) :-24+/-56 km3/yr

Page 16: Recent results from GRACE in Greenland and Antarctica

Linear trend fit to same 33 months, between 4/2003 and 6/2006. km3/yr

CSR RL1: -42 CSR RL4: -77

JPL RL3: -75 JPL RL4 -83

GFZ RL3: -48 GFZ RL4: N/A

Goddard: -28

West Antarctica. ICE-5 PGR model removed. PGR uncertainty: ±20 km3/yr.

Linear trend fit to same 30 months, between 2/2003 and 12/2005. km3/yr

CSR RL1: -86 CSR RL4: -118

JPL RL3: -110 JPL RL4 -115

GFZ RL3: -84 GFZ RL4: -121

Goddard: N/A

Page 17: Recent results from GRACE in Greenland and Antarctica

Linear trend fit to same 33 months, between 4/2003 and 6/2006. km3/yr

CSR RL1: 54 CSR RL4: 12

JPL RL3: -70 JPL RL4 -61

GFZ RL3: 120 GFZ RL4: N/A

Goddard: -3

East Antarctica. ICE-5 PGR model removed. PGR uncertainty: ±55 km3/yr.

Linear trend fit to same 30 months, between 2/2003 and 12/2005. km3/yr

CSR RL1: 46 CSR RL4: -14

JPL RL3: -61 JPL RL4 -76

GFZ RL3: 117 GFZ RL4: 3

Goddard: N/A

Page 18: Recent results from GRACE in Greenland and Antarctica

East/West dividing line

Page 19: Recent results from GRACE in Greenland and Antarctica

ICESat

Rignot et al. 2007

Harpold, Urban, & Schutz

Davis, 2006Watkins et al. 2006

Page 20: Recent results from GRACE in Greenland and Antarctica

Summary

- GRACE delivers mass estimates for the polar ice sheets.Strengths (relative to other techniques):

---GRACE samples the entire ice sheet, both the interior and the edges. It does not require interpolation between ground points.

---GRACE provides a direct observation of mass.

---GRACE has a dense enough (monthly) temporal sampling to allow separation between trends and seasonal terms.

Weaknesses:

---GRACE is more sensitive to PGR model errors than other techniques.

---GRACE cannot provide resolution below a few hundred km.

-- Greenland is losing mass significantly.

-- Mass loss increased significantly in the last few years(Grace observed timing is consistent with Kangerdlugssuaq and Helheim glaciers observed acceleration).

-- Antarctica appears to have lost significant mass between 2002 and 2007.

-- GRACE can help identify problems in other techniques.

-- COMBINING GRACE, InSAR and Altimetry we can improve interpretation of ice mass changes

Page 21: Recent results from GRACE in Greenland and Antarctica

Antarctica from range acceleration data

Preliminary plot of the trend in Greenland ice mass over 2002-2006 derived from analysis of range acceleration data

Watkins et al. 2006

Page 22: Recent results from GRACE in Greenland and Antarctica

Greenland Mass Variation From GRACE

Velicogna and Wahr, Nature 2006

SOUTH GREENLAND

----Apr ‘02-Apr ‘06: -161+/-24 km3/yr

---- Apr ‘02-Apr ‘04: -20+/-26 km3/yr

---- May‘04-Apr ‘06: -246+/-36 km3/yr

NORTH GREENLAND

----Apr ‘02-Apr ‘06: -83+/-18 km3/yr

Apr ‘02-Apr ‘04: -80+/-28 km3/yr

May‘04-Apr ‘06: -90+/-28 km3/yr

Page 23: Recent results from GRACE in Greenland and Antarctica

Greenland Mass Variation From GRACE

Velicogna and Wahr,Nature 2006

__ GRACE - hydrology leakage - PGR

Trend Apr 2002-Apr 2006: -248+/-36 km3/yr ~0.5+/-0.1 mm/yr sea level rise

Trend Apr 2002-Apr 2004: -104+/-54 km3/yr

Trend May 2004-Apr 2006: -342+/-66 km3/yr

Page 24: Recent results from GRACE in Greenland and Antarctica

Melt area in Greenland increasing (K. Steffen)

Red shows seasonal surface melt extent (slush and ponds of meltwater) for two extreme years. Surface melt has increased 16% between 1979 and 2002.

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Ekström et al., Science 2006 Krabill et al., 2006

Glacier changes 1996-2006(Rignot and Kanagaratnam, 2006)

-- Mass loss increased from 90 to 220 km^3/yr in 1996-2006.

-- 2/3 loss caused by glacier mechanics.

-- 1/3 caused by enhanced ice melt minus enhanced snowfall (Hanna et al., 2004).

Other evidence of changes of the Greenland Ice sheet

More snowfall ….(Johannessen et al., 2005) Accumulation 575 km3/yr

Page 25: Recent results from GRACE in Greenland and Antarctica

Secular trend from CSR Release 4

(de-striped). 4/02 –6/07. 300-km smoothing radius.

The same, but after removing a post-glacial-rebound model (ICE-5G).

Page 26: Recent results from GRACE in Greenland and Antarctica

Rate of ice volume change:

All Antarctica: -145 km3/yr

West Antarctica: -112 km3/yr

East Antarctica: -24 km3/yr

East/West dividing line

PGR uncertainty :

All Antarctica: ± 80 km3/yr

West Antarctica: ± 20km3/yr

East Antarctica: ± 55 km3/yr