Height Variations in the Mississippi River Basin From Daily Time-Varying Satellite Gravity Data and Hydrological Model.

The orthometric height variation is evident through changes in the geoid and surface vertical displacements. Hydrological mass change can induce variations in geoid height and surface deformation, consequently resulting in fluctuations in orthometric height. Studying the orthometric height variations in the Mississippi River Basin (MRB) caused by surface mass changes is crucial for understanding crustal uplift and ecological evolution. In this study, the superiority of daily solutions was demonstrated through comparison with the monthly solutions. Based on the Spherical Harmonic Function (SHF) and Green's Function (GF) methods, the orthometric height variations in the MRB were calculated by utilizing daily ITSG-Grace2018 solutions and a hydrological model. These results were then compared with the daily solutions obtained from 26 GPS stations within the study area. The results show that the spatial distribution of orthometric height variations in the MRB is uneven. Except for the western mountainous areas, which show an upward trend, the main trend is a decrease at a rate of 0.1 to 0.4 mm/yr. The average correlation coefficient between GPS solutions and the orthometric height variations calculated using SHF and GF is 0.71 and 0.72, respectively, indicating good consistency and hydrological loading was identified as a significant factor contributing to the orthometric height variations. After correcting GPS solutions with GLDAS, vertical tectonic motion rates were calculated at GPS stations. With the exception of a few GPS stations that were uplifted, most of the remaining GPS stations settled at a rate of 0.5 to 2.6 mm/yr.