Impact of Selected Corrections in GRACE Mascon Data on Estimation of Polar Motion Excitation

Abstract:

Between 2002 and 2017, the Gravity Recovery and Climate Experiment (GRACE) mission provided temporal variations of the gravity field that have been used in a wide variety of studies, including observing changes in water resources around the world, determining changes in groundwater storage, monitoring floods and droughts, or analyzing ice mass changes in polar regions. In geodesy, a key application of GRACE mission data is an interpretation of changes in polar motion excitation due to variations in the Earth’s surficial fluids, especially in the continental hydrosphere. Such impacts are usually examined by computing hydrological polar motion excitation (Hydrological Angular Momentum, HAM).

The so-called GRACE Level-3 (L3) data delivers changes in terrestrial water storage (TWS) that can be used for computation of HAM. There are two methods of determining TWS from GRACE: from spherical harmonic coefficients of geopotential and directly from range-rate and acceleration measurements using mascon functions. However, mascon approach provides data of better quality than spherical harmonic method. In order to obtain the highest possible accuracy of TWS data, as well as to remove unwanted geophysical signals, a number of corrections were introduced in the L3 data, including GIA correction, geocenter correction and C₂₀ coefficient correction. Moreover, the newest mascon solution from Jet Propulsion Laboratory (JPL) improved separation of land and ocean mascons thanks to the use of the Coastal Resolution Improvement (CRI) filter.

The objective of this study is to assess the impact of corrections introduced by computing centers to mascon data on HAM determined. In particular, we test the influence on HAM trends, seasonal variations and non-seasonal changes. In addition, we examine the change in agreement between HAM and hydrological signal in geodetically observed excitation when the corrections are applied. To achieve these goals, we use mascon data provided by three GRACE data centers: Jet Propulsion Laboratory (JPL), Center for Space Research (CSR), and Goddard Space Flight Center (GSFC).