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The Time-Variable Geoid Over North America from GRACE John Wahr, University of Colorado.

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Presentation on theme: "The Time-Variable Geoid Over North America from GRACE John Wahr, University of Colorado."— Presentation transcript:

1 The Time-Variable Geoid Over North America from GRACE John Wahr, University of Colorado

2 The are Legendre functions. The, are Stokes coefficients. GRACE provides monthly coefficients to degree and order 60 (or greater). Large scales (small l) are more accurate than small scales (large l). 85 monthly fields, between April, 2002 and July, 2009, are now available. Mission expected to end around GRACE

3 To map the linear trend, fit a trend to each Stokes coefficient, and put those trends in here WlWl harmonic coefficients of a Gaussian smoothing function I’ve chosen a 300-km radius for the smoothing function.

4 Uses monthly GRACE fields from the Center for Space Research at U Texas. Complete through degree and order = 60. Fit to April, 2002 – June, 2009.

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6 Questions: (1) Are these signals large enough to matter? (2) Is the 300-km smoothing masking out interesting signals? (3) Once GRACE is gone, will other data/models be able to give equivalent results?

7 Uses monthly GRACE fields from the Center for Space Research at U Texas. Complete through degree and order = 60. Fit to April, 2002 – June, Paulson et al (2007) PGR model has been removed. Implication: the PGR model seems to remove the PGR geoid signal to about mm/yr.

8 GRACE results (1)the signal in the southeastern US is not a true secular signal (probably true of most water storage signals). (2)the Alaskan glacier signal is closer to a secular signal,.

9 GRACEGLDAS/Noah Water Storage Model (Rodell et al 2004).

10 Secular Trend in Geoid From GLDAS/Noah Water Storage Model (Rodell et al 2004). unsmoothedsmoothed

11 The standard GRACE product has had atmospheric and oceanic models removed. What happens if those models are added back? Models added backNot added back

12 The standard GRACE product has had atmospheric and oceanic models removed. What happens if those models are added back? Models added backNot added back

13 Parts of Yellowstone are uplifting at up to several cm/yr. How large is the accompanying geoid change? Could GRACE see it? Yellowstone National Park

14 From Christine Puskas and Wu-Lung Chang at U Utah Suppose all of Yellowstone National Park is uplifting at 3 cm/yr. Suppose the uplift is not compensated, and that the density is 3 gm/cm 3. What would the geoid change look like?

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16 Could GRACE see it?

17 End


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