Non-tidal ocean loading signals of the North and Baltic Sea from terrestrial gravimetry, GNSS, and high-resolution modeling

Non-tidal ocean loading signals are known to be a significant source of geophysically induced noise in gravimetric and geodetic observations also far-away from the coast and especially during extreme events such as storm surges. Operational products suffer from a low temporal and spatial resolution and reveal only small amplitudes on continental stations. Dedicated high-resolution sea-level modelling of the North and Baltic Sea provides a largely improved prediction of non-tidal ocean loading signals. Superconducting gravimeter and GNSS observations on the small offshore island of Heligoland in the North Sea are used for a thorough evaluation of the model values revealing correlations of up to 0.9 and signal reductions of up to 50 % during a storm surge period of one month in Jan-Feb 2022. Additional continental superconducting gravimeter stations are used to assess the benefits from high-resolution modelling for an improved signal separation further away from the coast.