# Long-Term and Decadal Sea-Level Trends of the Baltic Sea Using Along-Track Satellite Altimetry
## 5 Results
### ASL and RSL Trends by Hourly TG Observations  
The long-term (1995-2022, 28 years) RSL and ASL trends were calculated using hourly data of \(DT_{obs}\) and \(DT_{TG}\) (VLM-corrected) based on Equation (6) (Section 2). The achieved RSL and ASL rates and their uncertainty from TG observations for the period 1995 to 2022 are listed in Table 3 and Figure 10.  
In general, the RSL varies within the magnitude of \(-2\) to 4.5 mm/yr, while the ASL rate spans from 2 to 5.4 mm/yr. Another notable characteristic is the spatial variance among the stations, mainly due to the VLM effect (cf. Figure 10 and Table 2). It is evident that the largest differences between RSL and ASL are observed at the northern stations, which tend to experience large VLM effects, for example, at stations Dirhami (0.49 vs. 3.58 mm/yr), Ristna (1.11 vs. 4.56 mm/yr), Marivken (0.44 vs. 4.9 mm/yr), Hanko (1.21 vs. 5.37 mm/yr), and Pori (\(-2.02\) vs. 5.41 mm/yr). Note the opposite trend sign for the (northernmost) Pori TG station, where the land uplift exceeds the sea-level rise. Note that the differences between the ASL and RSL rates (cf. Table 3, last column) are almost equal to the VLM  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**ID**} & \multirow{2}{*}{**Station**} & \multirow{2}{*}{**MDT [cm]**} & **ASL Trend** & **RSL Trend 1** & **ASL-RSL** \\  & & & **[mm/yr]** & **[mm/yr]** & **Difference [mm/yr]** \\ \hline
1 & Dirhami & 29.03 & \(3.58\pm 0.024\) & 0.49 & 3.09 \\
2 & Ristna & 26.87 & \(4.56\pm 0.012\) & 1.11 & 3.45 \\
3 & Ventspils & 23.73 & \(2.12\pm 0.014\) & 0.56 & 1.56 \\
4 & Ustka & 18.46 & \(2.36\pm 0.014\) & 2.22 & 0.14 \\
5 & Kolobrzeg & 18.10 & \(2.06\pm 0.014\) & 2.12 & \(-0.06\) \\
6 & Swinoujiscie & 15.29 & \(2.66\pm 0.014\) & 2.84 & \(-0.18\) \\
7 & Sassnitz & 10.66 & \(3.22\pm 0.010\) & 3.13 & 0.09 \\
8 & Rodvig & 10.55 & \(5.13\pm 0.011\) & 4.51 & 0.62 \\
9 & Simrishamn & 17.60 & \(3.55\pm 0.010\) & 2.66 & 0.89 \\
10 & Kungsholmsfort & 18.34 & \(4.81\pm 0.009\) & 3.45 & 1.36 \\
11 & Marviken & 19.57 & \(4.90\pm 0.009\) & 0.44 & 4.46 \\
12 & Hanko & 26.79 & \(5.37\pm 0.011\) & 1.21 & 4.16 \\
13 & Pori & 28.67 & \(5.41\pm 0.011\) & \(-2.02\) & 7.43 \\ \hline \hline \end{tabular}  
* Note that the RSL trend uncertainties are the same as for the corresponding ASL.  
\end{table}
Table 3: TG hourly data based on RSL and ASL estimates, their formal OLS-based uncertainties, and mean dynamic topography (MDT) of hourly TG observation [cm] for each station (during 1995-2022).  
at these locations (cf. Table 2, sixth column). This validates the reliability of our trend estimation methodology.  
Previous studies have also observed a decreasing RSL trend toward the north, whereas the ASL trend increased toward the south [29; 45; 46; 78]. Note that, in various studies, the trend estimates may differ due to the adoption of the time period examined, the source of measurement, the method of computation, and the exact locations of measurement. For instance, within the same region, [78] estimated an RSL within the approximate range of \(-8\) to \(1\) mm/yr. In the study by [45], a similar range of RSL trends was calculated using a TG and hydrodynamic model (HDM) for the period 1915 to 2014. The ASL trends varied from \(1\) to \(6\) mm/yr, a range similar to what was observed by [29] using gridded monthly SA and TG data. These results indicate that, despite the differences in time frames and the sources of sea-level data (such as TG, HDM, SA), the long-term sea-level trends calculated across these studies generally align. These studies also verify the importance of accounting for the VLM in sea-level trend studies. This prompts the question as to whether any major difference truly occurs between utilizing TG and SA data sources for sea-level trend estimations, and whether computing sea-level trends over shorter periods, like decades, yields comparable values. These questions are examined in the following sections.