GRACE Science Team Meeting

Session: B.1 - Multidisciplinary Science
(Convener: )

08:30-08:45 A Global Assessment of Accelerations in Surface Mass Transport
First Author: Xiaoping Wu
Co-Authors: M. B. Heflin
08:45-09:00 Impact of self-attraction and loading on Earth rotation
First Author: Katherine Quinn
Co-Authors: R. M. Ponte

Title: A Global Assessment of Accelerations in Surface Mass Transport
Presenter: Wu, Xiaoping
Co-Authors: M. B. Heflin

Abstract: Water mass transport in the Earth’s dynamic surface layer of atmosphere, cryosphere, and hydrosphere driven by various global change processes has complex spatiotemporal patterns. We determine global spatial patterns and regional mean values of accelerations in surface mass variations during the Gravity Recovery and Climate Experiment (GRACE) mission’s data span from 2002.2 to 2015.0. GRACE gravity data are combined with surface deformation from 607 Global Navigation Satellite System (GNSS) stations, and an ocean bottom pressure model in a global inversion to derive detrended surface mass density coefficient time series from n=1 to 60. The inverted degree-1 and degree-2 results are used to either validate or be combined with satellite laser ranging (SLR) C20 and other GRACE coefficients. The resulting full spectrum time series from data up to n=60 along with their full calibrated covariance matrices are further combined with loose a priori knowledge on mass variation regimes incorporating high-resolution geographic boundaries up to degree and order 180. Variance component estimations are also employed to calibrate the variance factors of the data and the a priori variation model.

While Greenland and West Antarctica have strong negative accelerations, Alaska and the Arctic Ocean show significant positive accelerations reversing earlier mass loss trends. No significant mass acceleration is found in the non-Arctic oceanic area during the nearly 13-year period. In addition, the accelerations are not constant in time with some regions showing considerable variability due to irregular interannual changes.

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Impact of self-attraction and loading on Earth rotation
Presenter: Quinn, Katherine
Co-Authors: R. M. Ponte

Abstract: The impact of self-attraction and loading (SAL) on Earth rotation has not been previously considered except at annual timescales. We estimate Earth rotation excitations generated by atmospheric, oceanic, and land hydrology surface mass variations and investigate the importance of including SAL over monthly to interannual timescales. We use land hydrology variability derived from GRACE RL-05 land mass grids as these include surface mass variations over Greenland and Antarctica and groundwater variations, which are not included in most land hydrology models. We assess SAL effects in comparison with simple mass balance effects where net mass exchanged with the atmosphere and land is distributed uniformly over the global ocean. For oceanic polar motion excitations, SAL impacts are important even though mass balance impact is minor except at the annual period. This is true of global (atmosphere+land+ocean) polar motion excitations as well, although the SAL impacts are smaller. When estimating length-of-day excitations, mass balance effects have a dominant impact, particularly for oceanic excitation. Although SAL can have a significant impact on estimated Earth rotation excitations, its consideration generally did not improve comparisons with geodetic observations. This result may change in the future as surface mass models and Earth rotation observations improve.

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