Day 4

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Paper title Investigating temporal variability in Arctic storm surges using SAR altimetry
  1. Inger Bij de Vaate TU Delft Speaker
  2. Cornelis Slobbe Geoscience and Remote Sensing, Delft University of Technology
  3. Martin Verlaan TU Delft / Deltares
Form of presentation Poster
  • A8. Ocean
    • A8.07 Oceanographic Change of the Arctic Ocean From Space
Abstract text Global warming has a pronounced effect on the frequency and intensity of storm surges in the Arctic Ocean. On the one hand, changes in atmospheric conditions cause more storms to be formed in the Arctic or elsewhere that may enter the Arctic (e.g. Day & Hodges, 2018; Sepp & Jaagus, 2011). On the other hand, the Arctic Ocean is becoming increasingly exposed to atmospheric forcing due to Arctic sea ice decline (ACIA 2005, Vermaire et al. 2013). Modelling studies show that the reduced sea ice extent provides greater fetch and wave action and as such allows higher storm surges to reach the shore (Overeem et al., 2011; Lintern et al., 2011). This may cause increased erosion (e.g., Barnhart et al. 2014) and pose increased risks to fragile Arctic ecosystems in low-lying areas (e.g., Kokelj et al. 2012). In addition, Arctic surges influence global water levels, therefore the impact may also be noticeable at lower latitudes.
However, little is known about the large-scale variability in Arctic surge water levels as the data availability is compromised by environmental conditions. Long water level records from tide gauges are limited to a few locations at the coast and the high-latitudes are poorly covered by satellite altimeters. Moreover, measurements of the Arctic water level by satellite altimeters is hampered by the presence of sea ice. Here, the usage of Synthetic Aperture Radar (SAR) altimeter data provides a solution. These altimeters have a higher along-track resolution than conventional altimeters, which allows to measure water levels from fractures in the sea ice (leads) (Zygmuntowska et al., 2013). However, the location of leads changes over time, and both the temporal and spatial resolutions of the resulting water level data are highly variable. In addition, a proper removal of the tidal signal is required in order to study surge water levels. This may be particularly problematic in the Arctic as the accuracy of global tide models is reduced in polar regions (e.g. Cancet et al., 2017; Lyard et al., 2021; Stammer et al., 2014). This is can for a part be attributed to the beforementioned constrains on data availability, as well as to the seasonal modulation of Arctic tides that is not considered in most global tide models.
In the presented study we aspired to overcome the identified issues and explore the opportunities provided by SAR altimetry in studying storm surge water levels in the Arctic. For this, data are used from two high-inclination missions that are equipped with a SAR altimeter: CryoSat-2 and Sentinel-3. A classification scheme is implemented to distinguish between measurements from sea ice and leads/ocean and data stacking is applied to deal with the restricted temporal and spatial resolution. The tidal signal is removed as much as possible by applying tidal corrections from a global tide model, as well as additional corrections derived from a residual tidal analysis including seasonal modulation of the major tidal constituents. To evaluate the approach, where possible, results are compared to water levels derived from nearby tide gauges. Implications of reduced accuracy in tidal corrections are identified by analyzing the results in the light of the level of tidal activity and seasonal modulation. Finally, temporal variations in surge water levels are linked to the seasonal sea ice cycle and interannual variations in sea ice extent.

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