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Arctic Ocean Tides from GRACE Satellite Accelerations. Bryan Killett University of Colorado and CIRES, Boulder, CO, USA. TexPoint fonts used in EMF. Read the TexPoint manual before you delete this box.: A A A A A. The Tidal Potential V T. The Tidal Potential V T. The Tidal Potential V T. - PowerPoint PPT Presentation
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Arctic Ocean Tides from GRACE
Satellite Accelerations
Bryan KillettUniversity of Colorado and CIRES, Boulder,
CO, USA
The Tidal Potential VT
The Tidal Potential VT
The Tidal Potential VT
Tides for order m = 2
• ~12 hr periods.• “Semi-diurnal.”• Largest tides.
Adapted from Dr. Sylvain Paris
Tides for order m = 1
• ~24 hr periods.• “Diurnal.”• Medium tides.
Adapted from Dr. Sylvain Paris
Tides for order m = 0
Adapted from Dr. Sylvain Paris
Diurnal Tidal Spectrum
Adapted from Desai (1996)
GRACE
NASA/courtesy of nasaimages.org.
B A
MASCON
GRACE relative accel. due to a mascon directly
below satellitesRelative acceleration > 0
MASCON
GRACE relative accel. due to a mascon directly
below satellites
B A
MASCON
GRACE relative accel. due to a mascon directly
below satellites
B A
Relative acceleration < 0
MASCON
GRACE relative accel. due to a mascon directly
below satellites
B A
MASCON
GRACE relative accel. due to a mascon directly
below satellites
B A
Relative acceleration > 0
GRACE relative accel. due to a mascon not
below satellites
Motivation FES2004 is primarily based on TOPEX/Poseidon
data, which doesn’t extend north of 66°N. Thus, Arctic ocean tides aren’t well constrained by satellite altimetry.
The GRACE orbit goes up to 89°N. Relative acceleration values between the two
GRACE satellites are used to solve for “mass concentrations” (mascons) on Earth’s surface. The solution method allows each mascon’s mass to oscillate at tidal and seasonal frequencies, as well as changing linearly.
FES2004 effects have been subtracted from the acceleration values, so the amplitudes at tidal periods represent errors in FES 2004. The mass amplitudes are converted to equivalent “cm of water” amplitudes.
Inversion Details Smoothed residual acceleration values are
averaged at 5 second intervals when satellites are north of 50° N latitude.
7 million accelerations total over 7 years. A constant offset, secular trend and
amplitude/phase at seasonal and tidal periods are simultaneously solved for at each mascon.
Mascons are ~230km apart; 1200 mascons cover the area north of 50° N latitude.
Mascons are modeled as point masses for speed.
Tides are NOT Point Masses
Simulation Input – M2 Sine Coef.
Simulation Output – M2 Sine Coef.
Simulation Error – M2 Cos. Coef.
Simulation Input – K1 Sine Coef.
Simulation Output – K1 Sine Coef.
Simulation Error – K1 Cos. Coef.
Resolution Test
Inversion of Real GRACE Data
Non-tidal parameters
Non-tidal parameters
FES 2004 – M2 Amplitude
Residual M2 Amplitude
M2 – Diff. of Two 3.5yr Solutions
FES2004 M2 Deg90 Trunc. Error
Change in FES2004 M2 Amp.
FES 2004 – K1 Amplitude
Residual K1 Amplitude – 5 yrs
Residual K1 Amplitude – 7 yrs
K1 – Diff. of Two 3.5yr Solutions
FES2004 K1 Deg90 Trunc. Error
Change in FES2004 K1 Amp.
Original GRACE Power Spectrum
Noise Reduction for Accelerations Used in the
Inversion
Original GRACE Power Spectrum
Noise Reduction for Accelerations NOT Used in
the Inversion
Original FES2004 Power Spectrum
Conclusions GRACE-derived corrections are: large
where FES2004 is large, not generally larger north of 66°N, and much larger than truncation errors.
Conclusions GRACE-derived corrections are: large
where FES2004 is large, not generally larger north of 66°N, and much larger than truncation errors.
GRACE-derived corrections to FES2004 reduce the variance of accelerations not used in the inversion, so they can improve GRACE processing but can’t currently improve tide gauge predictions, probably due to short-scale effects that GRACE can’t resolve.
Conclusions GRACE-derived corrections are: large where
FES2004 is large, not generally larger north of 66°N, and much larger than truncation errors.
GRACE-derived corrections to FES2004 reduce the variance of accelerations not used in the inversion, so they can improve GRACE processing but can’t currently improve tide gauge predictions, probably due to short-scale effects that GRACE can’t resolve.
Two independent estimates agree on a ~1cm noise floor for the GRACE-derived corrections.
Conclusions GRACE-derived corrections are: large where
FES2004 is large, not generally larger north of 66°N, and much larger than truncation errors.
GRACE-derived corrections to FES2004 reduce the variance of accelerations not used in the inversion, so they can improve GRACE processing but can’t currently improve tide gauge predictions, probably due to short-scale effects that GRACE can’t resolve.
Two independent estimates agree on a ~1cm noise floor for the GRACE-derived corrections.
FES2004 amplitudes are too large in the oceans north of 50°N for the tides M2 , K1 , O1 , P1 .
