Sea Level Variability in the Coastal Ocean Induced by Atmospheric Forcing for the Period 1871-2012

Abstract:

Global mean sea level (GMSL) is the preferred proxy to assess changes in the ocean heat and freshwater content as it is less affected by internal variability that regional sea level (Cazenave and Nerem, 2004). However, what really matters for society is the variability of sea level at regional scales as the impact of sea level variations occur at those scales. Regional sea level (RSL) is not only affected by the same processes that GMSL (thermal expansion/contraction and water addition/removal) but also by the redistribution of mass. In particular, due to atmospheric forcing (i.e. atmospheric sea level pressure and wind stress) is the principal mechanism for the water redistribution in the ocean and accounts for a large fraction of the coastal sea level variance. In particular, it is the dominant mechanism for the variability in the subtidal to intraseasonal range (i.e. from days to months). This includes storm surge events, which are responsible for the largest damages in coastal regions. At frequencies from seasonal to interannual, its relevance is comparable to the steric contribution, specially at high and low latitudes (Fukumori et al. 1998). For the decadal to multidecadal range it is usually assumed that it has a secondary role, but this has not yet been studied in depth.

In this presentation we will show the results obtained from a new global simulation of atmospherically induced sea level variability for the period 1871-2012. This simulation uses the NOAA Twentieth Century Reanalysis (Compo et al., 2011) to force a global ocean barotropic model (TUGO, Carrère and Lyard, 2003). We will focus on the description of the impact of mass redistribution on coastal sea level variability at interannual to multidecadal scales and from a global perspective. We will also show how this mass redistribution can induce errors in GMSL trends and accelerations derived from tide gauge reconstructions.