Influence of ocean model horizontal resolution on the representation of
global annual-to-multidecadal coastal sea level variability
Abstract
Emerging high-resolution global ocean climate models are expected to
improve both hindcasts and forecasts of coastal sea level variability by
better resolving ocean turbulence and other small-scale phenomena. To
examine this hypothesis, we compare annual to multidecadal coastal sea
level variability over the 1993-2018 period, as observed by tide gauges
and as simulated by two identically-forced ocean models, at
$\sim$1$^{\circ}$ (LR) and
$\sim$0.1$^{\circ}$ (HR) horizontal
resolution. Differences between HR and LR, and misfits with tide gauges,
are spatially coherent at regional alongcoast scales. Resolution-related
improvements are largest in, and near, marginal seas. Near attached
western boundary currents, sea level variance is several times greater
in HR than LR, but correlations with observations may be reduced, due to
intrinsic ocean variability. Globally, in HR simulations, intrinsic
variability comprises from zero to over 80\% of coastal
sea level variance. Outside of eddy-rich regions, simulated coastal sea
level variability is generally damped relative to observations. We
hypothesize that weak coastal variability is related to large-scale,
remotely-forced, variability; in both HR and LR, tropical sea level
variance is underestimated by $\sim$50\%
relative to satellite altimetric observations. Similar coastal dynamical
regimes (e.g., attached western boundary currents) exhibit a consistent
sensitivity to horizontal resolution, suggesting that these findings are
generalizable to regions with limited coastal observations.