The Time-Variable Geoid Over North America from GRACE

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The Time-Variable Geoid Over North America from
GRACE

• John Wahr, University of Colorado

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GRACE

• 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 2013.

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To map the linear trend, fit a trend to each
Stokes coefficient, and put those trends in here
Wl
harmonic coefficients of a Gaussian smoothing
function
Ive chosen a 300-km radius for the smoothing
function.
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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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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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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?
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Implication the PGR model seems to remove the
PGR geoid signal to about 0.3-0.4 mm/yr .
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. Paulson et al (2007) PGR model has
been removed.
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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,.

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GRACE
GLDAS/Noah Water Storage Model (Rodell et al
2004).
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Secular Trend in Geoid From GLDAS/Noah Water
Storage Model (Rodell et al 2004).
unsmoothed
smoothed
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The standard GRACE product has had atmospheric
and oceanic models removed. What happens if
those models are added back?
Models added back
Not added back

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The standard GRACE product has had atmospheric
and oceanic models removed. What happens if
those models are added back?
Models added back
Not added back
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Yellowstone National Park
Parts of Yellowstone are uplifting at up to
several cm/yr. How large is the accompanying
geoid change? Could GRACE see it?
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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/cm3 .
What would the geoid change
look like?
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(No Transcript)
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Could GRACE see it?
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End