Geoid Height Changes over Türkiye: Insights from GRACE and GRACE-FO Spherical Harmonics

The Gravity Recovery and Climate Experiment (GRACE) and its Follow-On mission (GRACE-FO) have greatly improved our ability to monitor changes in Earth's mass distribution, providing unprecedented insights into variations in total water storage (TWS). These variations can be expressed as equivalent water thickness, and they can also be derived from other geopotential variations, such as changes in geoid height, gravity anomalies, or vertical displacements. Understanding these variations is essential for comprehending regional hydrology and solid Earth dynamics.

In this study, we use DDK2-filtered solutions from GRACE and GRACE-FO spherical harmonics to compute geoid height variations over the Türkiye region, based on roughly one hundred grid points. The trend in the geoid height changes for this region is approximately at the millimeter level. We also derive TWS time series from these DDK2-filtered spherical harmonics to compare the changes in geoid height with the corresponding equivalent water thickness values, aiming to explore the functional relationship and correlation coefficients between these two geopotential variations. In addition to time-domain analysis, we apply spectral analysis to examine the power spectrum of geoid height and TWS variations in the frequency-domain. This approach helps us understand the spatial and temporal diversity of geoid height changes across Türkiye and provides insights into their underlying patterns and trends. The preliminary results of this study offer an overview of geoid height changes in Türkiye and highlight the potential of GRACE and GRACE-FO data for monitoring mass redistribution on a regional scale.