Arctic Ocean Tides from GRACE Satellite Accelerations Bryan Killett University of Colorado and CIRES, Boulder, CO, USA TexPoint fonts used in EMF. Read.

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 .