Abstract
Sea-level variations in coastal areas can differ significantly from those in the nearby open ocean. Monitoring coastal sea-level variations is therefore crucial to understand how climate variability can affect the densely populated coastal regions of the globe. In this paper, we study the sea-level variability along the coast of Norway by means of in situ records, satellite altimetry data, and a network of eight hydrographic stations over a period spanning 16 years (from 2003 to 2018). At first, we evaluate the performance of the ALES-reprocessed coastal altimetry dataset by comparing it with the sea-level anomaly from tide gauges over a range of timescales, which include the long-term trend, the annual cycle and the detrended and deseasoned sea level anomaly. We find that coastal altimetry outperforms conventional altimetry products at most locations along the Norwegian coast. We later take advantage of the coastal altimetry dataset to perform a sea level budget along the Norwegian coast. We find that the thermosteric and the halosteric signals give a comparable contribution to the sea-level trend along the Norwegian coast, except for three, non-adjacent hydrographic stations, where salinity variations affect the sea-level trend more than temperature variations. We also find that the sea-level annual cycle is more affected by variations in temperature than in salinity, and that both temperature and salinity give a comparable contribution to the detrended and deseasoned sea-level along the entire Norwegian coast.
Highlights
Sea-level is considered a key indicator to monitor the earth’s energy imbalance and climate change (e.g., Oppenheimer et al., 2019; von Schuckmann et al, 2018)
The producers of ALES flag some of the data as unreliable. They recommend excluding observations that fall within a distance of 3 km from the coast and whose sea-level anomaly (SLA), significant wave height (SWH), and standard deviation exceed 2.5 m, m, and 0.2 m respectively. We have followed these recommendations with one exception: we have lowered the threshold on the sea-level anomaly from 2.5 to 1.5 m because this choice leads to a better agreement between the tide gauges and the ALES altimetry dataset between Måløy and Rørvik, along the west coast of Norway (Figure 1)
Over the following three years, the opposite situation has occurred. These results suggest that, coherent sea-level variability occurs along the Norwegian coast as seen from tide gauges, there are periods when it does not: during these periods, the sea-level variability is likely driven by local changes
Summary
Sea-level is considered a key indicator to monitor the earth’s energy imbalance and climate change (e.g., Oppenheimer et al., 2019; von Schuckmann et al, 2018). Several studies have found a clear improvement of the ALES-reprocessed satellite altimetry observations over conventional altimetry products in different areas of the World (e.g., Passaro et al., 2014, 2015, 2016, 2018, 2021), with the new algorithm providing estimates of the altimetry parameters in coastal areas with levels of accuracy typical of the open ocean (e.g., Passaro et al, 2014). We investigate how the ALES-reprocessed satellite altimetry dataset resolves sea-level along the coast of Norway compared to all the tide-gauge records available over the 16-year period between 2003 and 2018. We further use the ALES-reprocessed altimetry dataset in combination with a network of hydrographic stations along the coast of Norway to study the local sea-level budget, which is known to be challenging at the regional scale (e.g., Raj et al., 2020; Richter et al, 2012).
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