Understanding Baltic Sea loading

The Baltic Sea is a well-monitored semi-enclosed sea in northern Europe. The mass variations of the Baltic Sea are mostly due to atmospheric pressure changes and wind, which redistribute the water within the basin and also govern the so-called fill level, the amount of water exchange with the North Sea. The variation in the sea level can be abrupt and large, for example during storms. The variable load may cause significant effects - up to a centimeter in vertical component of GNSS - in geodetic measurements, especially near the coastline. 

We have studied the mass variations of the Baltic Sea to understand the varying load and its effect on different types of geodetic measurements. We have used tide gauge data to interpolate hourly surfaces for the whole basin as well as a numerical model for water heights. This data is convolved with Green’s functions to determine 3-D deformation, gravity, potential and tilt effects at two hundred stations around the Baltic. We show examples of the effect on different types of data, e.g. GNSS time series, absolute gravity measurements and time series of superconducting gravimeter. For example, up to 56 % of the east component in GNSS time series can be explained by the Baltic loading. The computed loading time series can be used for several purposes, e.g. for the studies of other error sources, to create stable time series and also to correct campaign measurements, which take place in varying conditions.