Abstract
Variability of Sea-Surface Height (SSH) from ocean dynamic processes is an important component of sea-level change. In this study we dynamically downscale a present-day control simulation of a climate model to replicate sea-level variability in the Northwest European shelf seas. The simulation can reproduce many characteristics of sea-level variability exhibited in tide gauge and satellite altimeter observations. We examine the roles of lateral ocean boundary conditions and surface atmospheric forcings in determining the sea-level variability in the model interior using sensitivity experiments. Variability in the oceanic boundary conditions leads to uniform sea-level variations across the shelf. Atmospheric variability leads to spatial SSH variability with a greater mean amplitude. We separate the SSH variability into a uniform loading term (change in shelf volume with no change in distribution), and a spatial redistribution term (with no volume change). The shelf loading variance accounted for 80% of the shelf mean total variance, but this drops to ~ 60% around Scotland and in the southeast North Sea. We analyse our modelled variability to provide a useful context to coastal planners and managers. Our 200-year simulation allows the distribution of the unforced trends (over 4–21 year) of sea-level changes to be quantified. We found that the 95th percentile change over a 4-year period can lead to coastal sea-level changes of ~ 58 mm, which must be considered when using smooth sea level projections. We also found that simulated coastal SSH variations have long correlation length-scales, suggesting that observations of interannual sea-level variability from tide gauges are typically representative of > 200 km of the adjacent coast. This helps guide the use of tide gauge variability estimates.
Highlights
Relative sea-level change is one of the most important aspects of a changing climate
After showing how well our modelling system can reproduce interannual variability on the North West European Shelf Seas (NWS), we aim to investigate the behaviour of the modelled Sea-Surface Height (SSH) variability within the NWS and explore the relative roles of the variability associated with the ocean boundary conditions, and the atmosphere surface forcings
EN4 is relatively sparse on the NWS
Summary
Relative sea-level change is one of the most important aspects of a changing climate. Recent sea-level projections developed for the UK (Palmer et al 2018) suggested that for a given tide gauge, variability will dominate over the emission scenario uncertainty and model structural uncertainty for the decade (e.g., Newlyn, UK, Fig. 1) and will remain an important component throughout the twenty-first century. There are several components of SSH that can lead to variability, including steric sea-level change, mass convergence (manometric sea-level change, Gregory et al 2019) and the inverted barometer effect (Stammer and Hüttemann 2008). Each of these terms can vary on different time and space scales and have a different response to modes of climate variability—see Roberts et al (2016) for a review. Shelf exchange processes can mediate how tightly coupled these components are between the ocean and the adjacent shelf seas (e.g., Landerer et al 2007; Bingham and Hughes 2012; Chafik et al 2019)
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