Barystatic and steric sea level variations in the Baltic Sea by GRACE/GRACE FO mascon solutions, satellite altimetry, and in situ measurements

Abstract

<p>The Baltic Sea is a semi-enclosed basin in northern Europe that is connected to the North Sea through the Danish Strait. We have deployed three datasets to study the barystatic and steric sea level changes in the basin. GRACE/GRACE FO mascon solutions of NASA Jet Propulsion Laboratory (JPL), CSR – University of Texas at Austin, and NASA Goddard Space Flight Center (GSFC) are used to examine the barystatic sea level in the Baltic Sea. Additionally, salinity and temperature at different depths have been monitored continuously in the basin since 1995, providing profiles to estimate the steric sea level variation.</p><p>Hydrological leakage is an inevitable factor of GRACE-derived barystatic time series in proximity of land-water transition zones, despite all efforts to minimize it. Thus, we also used the total sea level, measured by satellite altimetry, minus steric sea level as an independent measure to evaluate the barystatic sea level from mascon solutions. Satellite altimetry measurements of the basin are extensively processed and retracked, thanks to the BalticSEAL project. North Atlantic Oscillation index, a driver of sea level variation in the basin, is also compared to sea level components.</p><p>Multiresolution analysis of the maximal overlap discrete wavelet transform is deployed for temporal decomposition of the time series to annual, internannual, and decadal components. Despite overall agreement among mascon solutions on annual and internannual scales, there are notable differences in amplitudes and variations. The data provided by NASA-JPL shows the lowest root mean square (RMS) when it is compared to the total sea level acquired from satellite altimetry. The RMS is further reduced by 4% to 8% when steric sea level is added to three mascon solutions.</p>