11:30 〜 11:45
[G04-2-05] Determination of accuracy information for effective angular momentum functions derived from gravity field observations
Variations of Earth rotation are caused by the redistribution and motion of masses within the Earth system. Since 2002, the satellite mission GRACE observes variations of the Earth's gravity field which are caused by mass displacements. Therefore, time variable gravity field models can be used to determine effective angular momentum functions which describe mass-related excitation mechanisms of Earth rotation. By applying suitable filter techniques and masks, not only the integral mass effect on Earth rotation but also the mass effects of the oceans, continental hydrosphere and cryosphere can be studied. The effective angular momentum functions derived from gravity field observations suffer from uncertainties due to (1) the destriping and filtering of the GRACE data, (2) the separation of the individual contributions (leakage effect), (3) the reduction of glacial isostatic adjustment (GIA) and (4) an appropriate replacement of the Stokes coefficients C10, C11, S11 and C20.
In this study we will present a new method to reduce the leakage effect, and via closed loop analysis the impact on effective angular momentum functions is estimated. In order to reduce the GIA effect, different GIA models will be used and compared to evaluate the uncertainties. Due to the fact that the GRACE data processing is performed in the Earth's center-of-mass (CM) frame, the degree-1 Stokes coefficients are zero by definition. But processes at the Earth's surface and interior are referred to a coordinate system attached to the Earth's crust which moves relative to the CM. Therefore, external solutions for C10, C11 and S11 are used to investigate the impact on derived effective angular momentum functions. Due to the low sensitivity of the GRACE K-band measurements on the Earth's flattening the Stokes coefficient C20 obtained from GRACE data are inaccurate. Thus external solutions will be used for C20 to estimate the uncertainties of derived effective angular momentum functions.
In this study we will present a new method to reduce the leakage effect, and via closed loop analysis the impact on effective angular momentum functions is estimated. In order to reduce the GIA effect, different GIA models will be used and compared to evaluate the uncertainties. Due to the fact that the GRACE data processing is performed in the Earth's center-of-mass (CM) frame, the degree-1 Stokes coefficients are zero by definition. But processes at the Earth's surface and interior are referred to a coordinate system attached to the Earth's crust which moves relative to the CM. Therefore, external solutions for C10, C11 and S11 are used to investigate the impact on derived effective angular momentum functions. Due to the low sensitivity of the GRACE K-band measurements on the Earth's flattening the Stokes coefficient C20 obtained from GRACE data are inaccurate. Thus external solutions will be used for C20 to estimate the uncertainties of derived effective angular momentum functions.