EGU2020-13258
https://doi.org/10.5194/egusphere-egu2020-13258
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Spherical and ellipsoidal surface mass change from GRACE time-variable gravity data

Michal Šprlák1, Khosro Ghobadi-Far2, Shin-Chan Han2, and Pavel Novák1
Michal Šprlák et al.
  • 1University of West Bohemia, Faculty of Applied Sciences, New Technologies for the Information Society, Plzeň, Czechia (michal.sprlak@gmail.com)
  • 2School of Engineering, Faculty of Engineering and Built Environment, University of Newcastle, University Drive, Callaghan, NSW 2308, Australia

The problem of estimating mass redistribution from temporal variations of the Earth’s gravity field, such as those observed by GRACE, is non-unique. By approximating the Earth’s surface by a sphere, surface mass change can be uniquely determined from time-variable gravity data. Conventionally, the spherical approach of Wahr et al. (1998) is employed for computing the surface mass change caused, for example, by terrestrial water and glaciers. The accuracy of the GRACE Level 2 time-variable gravity data has improved due to updated background geophysical models or enhanced data processing. Moreover, time series analysis of ∼15 years of GRACE observations allows for determining inter-annual and seasonal changes with a significantly higher accuracy than individual monthly fields. Thus, the improved time-variable gravity data might not tolerate the spherical approximation introduced by Wahr et al. (1998).

A spheroid (an ellipsoid of revolution) represents a closer approximation of the Earth than a sphere, particularly in polar regions. Motivated by this fact, we develop a rigorous method for determining surface mass change on a spheroid. Our mathematical treatment is fully ellipsoidal as we concisely use Jacobi ellipsoidal coordinates and exploit the corresponding series expansions of the gravitational potential and of the surface mass. We provide a unique one-to-one relationship between the ellipsoidal spectrum of the surface mass and the ellipsoidal spectrum of the gravitational potential. This ellipsoidal spectral formula is more general and embeds the spherical approach by Wahr et al. (1998) as a special case. We also quantify the differences between the spherical and ellipsoidal approximations numerically by calculating the surface mass change rate in Antarctica and Greenland.

 

References:

Wahr J, Molenaar M, Bryan F (1998) Time variability of the Earth’s gravity field: Hydrological and oceanic effects and their possible detection using GRACE. Journal of Geophysical Research: Solid Earth, 103(B12), 30205-30229.

How to cite: Šprlák, M., Ghobadi-Far, K., Han, S.-C., and Novák, P.: Spherical and ellipsoidal surface mass change from GRACE time-variable gravity data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13258, https://doi.org/10.5194/egusphere-egu2020-13258, 2020

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