Investigation of sea level variability in the Baltic Sea from tide gauge, satellite altimeter data, and model reanalysis

Abstract

The exploration of sea level variability from multiple satellite altimetry measurements in the Baltic Sea is yet to be performed due to the lack of reliable data, especially near the coast. In the present study, the number of available altimeter measurements was increased by 96% in coastal regions by replacing the radiometer wet troposphere correction with model-based correction. The satellite altimeter data show good agreement with monthly tide gauge data, with mean a root mean square difference (RMSD) of 3.4 cm and a mean correlation coefficient of 0.97 at 42 tide gauges in the Baltic Sea, and higher RMSD and lower correlation coefficient in the Gulf of Bothnian and the Danish Straits, respectively. Independent model reanalysis demonstrates similar performance at the sites. The collocated high-frequency tide gauge data and altimeter data demonstrate an RMSD of 8.86 cm and a bias of 6.63 cm at Stockholm, respectively. The tide gauge sea level variations in the Baltic Sea are highly correlated with the Hurrell North Atlantic oscillation (NAO) index at the decadal timescale. A decrease in the correlation coefficient of the tide gauge winter averaged sea level time series and the winter Hurrell NAO index has been observed on the decadal timescale in the last decade, especially during 2003 and 2005.