Estimation of steric sea level variations from combined GRACE and Jason-1 data

Yi-Shiang Li

Abstract

The GRACE (Gravity Recovery and Climate Experiment) space mission, launched in March 2002, consists of two low-orbiting spacecrafts linked by an inter-satellite microwave ranging system. GRACE measures spatio-temporal variations of the gravity field with an unprecedented resolution and precision. Launched in December 2001, Jason-1 is the successful follow-on to the pioneering TOPEX/POSEIDON ocean altimetry mission, which revolutionized our understanding of the dynamics of ocean circulation and global climate. Jason-1 mission satellite completes its primary three-year mission to measure the surface height of the worlds' oceans.

They estimate the mean steric sea level variations over the 60°S-60°N oceanic domain for the recent period (from August 2002 to April 2006), by combining sea level data from Jason-1 altimetry with time-variable gravity data from GRACE. In this study, they use that two different sets of GRACE geoid solutions (the GRGS EIGEN-GL04 and the GFZ EIGEN-GRACE04S products). So they exhibit of Jason-1 sea level minus GRACE ocean mass, and they observe amplitude and phase of those curves for those time spans. The inferred steric sea level curve exhibits an increasing trend during the last 3.5 yr (August 2002-April 2006), of the same order of magnitude as the 1993-2003 steric sea level trend computed with in situ hydrographic data.

Besides, they will analyze GRACE gravity field solutions, and they show those fields can be used to recover monthly changes in water storage, both on land and in the ocean, to accuracies of 1.5 cm of water thickness when smoothed over 1000 km. However, by applying the C20 coefficients of GRACE gravity field solutions, they can observe earth’s dynamic oblateness (J2) had been undergoing a decrease over the past 25 years. Therefore, these data of GRACE and Jason-1 can be used in some aspects, and they hope that these results will be calculated better. In the future, longer GRACE and Jason-1 time series will help reducing errors bars on trend estimates.

 

References

Lombard, A., Garcia, D., Ramillien, G., Cazenave, A., Biancale, R., Lemoine, J.M., Flechtner, F., Schmidt, R., Ishii, M., Estimation of steric sea level variations from combined GRACE and Jason-1 data; Earth and Planetary Science Letters 254(2007).

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