[G04-1] Earth rotation and geodynamics I

[G04-1-04] Hydrological excitation of polar motion by different representations of Earth's gravity field

^○Jolanta Nastula¹, Malgorzata Winska^{1, 2}, Waldemar Popinski³ (1.Space Research Centre Polish Academy of Sciences, Warsaw, Poland, 2.Warsaw University of Technology, Faculty of Civil Engineering, Warsaw, Poland, 3.Department of Methodology and Standards, Central Statistical Office, Warsaw, Poland)

The impact of continental hydrological loading from land water, snow and ice, on polar motion excitation, is difficult to estimate and is strongly needed for a full understanding of the excitation of polar motion. These global circulation of surface geophysical fluids induces Earth's gravity field changes.
Mass concentrations parameters and spherical harmonics have been widely used to model variations in planetary gravity fields. Variations in water storage on land affect the time dependent Earth's gravity field as well and can be estimated from Gravity Recovery and Climate Experiment (GRACE) satellite mission and hydrological models.
Firstly, the geographical patterns of terrestrial water storage (TWS) variations determined from GRACE data, as a global mascon solutions and from spherical harmonics coefficients, will be compared to each other and to TWS determined from Global Land Data Assimilation System (GLDAS) hydrological model.
Next, different estimations of hydrological excitation functions of polar motion (Hydrological Angular Momentum - HAM) will be investigated using either monthly TWS data, spherical harmonics as well as mascon parameters representations of Earth's gravity field derived from GRACE mission. Simultaneously, estimations of HAM from GLDAS hydrological model will be done.
Afterwards, we estimate the hydrological signal in geodetically-observed polar motion excitation as a residual by subtracting the atmospheric - AAM and oceanic - OAM contributions. Finally, the hydrological excitations are compared to these hydrological signal from the observed polar motion excitation series residuals.
In this study, linear trend, decadal, inter-annual, and seasonal variations of hydrological excitation functions of polar motion, determined from different representations of Earth's gravity field, are compared to each other. This way, a comparison of HAM estimation strategies from mass concentrations, harmonics coefficients and TWS changes will be investigated.