Geopotential and Vertical Displacement Effects of Time-Variable Geophysical Processes on Chronometric Leveling

High-precision optical clock comparisons use gravitational redshift to determine geopotential differences and equivalent normal-height differences between stations, offering a new approach to height transfer and the realization of height reference systems. As optical clock uncertainties advance from the null to the null level, the effects of time-variable geophysical processes on chronometric leveling require further evaluation. In this study, available geopotential and vertical displacement products were used to assess solid Earth tides, ocean tide loading, atmospheric loading, hydrological loading, and non-tidal ocean loading. Using 32 candidate clock sites across China, we examined single-station effects, interstation differential effects, observation averaging, spatial coherence, and differences among ocean tide models. The results show that solid Earth tides are the dominant process, whereas ocean tide loading has a pronounced effect on links involving coastal or island sites. Interstation differencing reduces spatially coherent variations along short links, and observation averaging effectively reduces tidal effects. Environmental loading may nevertheless retain millimeter-level effects along cross-regional links after averaging. For centimeter-level measurements, priority should be given to solid Earth tides and to ocean tide loading along coastal links. For millimeter-level measurements, environmental loading, observation duration, and ocean tide model sensitivity should additionally be assessed for each link. These results provide a basis for controlling time-variable geophysical effects in wide-area chronometric leveling and developing future optical clock height measurement networks.