Which part of the low-frequency sea-level variability is purely due to intrinsic ocean processes ?
Event: 2015 Ocean Surface Topography Science Team Meeting
Session: Science III: Large scale and global change ocean processes: the ocean's role in climate
Presentation type: Type Poster
Contribution: PDF file
The interannual (i.e. from 1.5 to 20 years) small-scale (< 6°) intrinsic sea-level variance that spontaneously emerges under purely seasonal forcing is very comparable to that obtained in fully-forced hindcasts (i.e. with interannual forcing). These scales, which are the main contributor to low-frequency intrinsic variability, may be isolated in the 22-year record of altimetric data using a spatio-temporal filtering as done in Fig. 1. This low-frequency intrinsic variability also has a substantial imprint at larger scales (> 12°) and on the Atlantic Meridional Overturning Circulation (Gregorio et al., 2015).
The ocean spontaneously generates erratic sea-level fluctuations in eddy-active regions up to decadal-to-multidecadal timescales. This ocean-only variability has an imprint on observed regional sea-level trends, especially in the ACC and in the WBC areas. The truncation of this very low-frequency intrinsic variability in the current 22-year altimeter dataset yields an uncertainty in observed sea-level trends ; this eddy-induced uncertainty is actually comparable (and should be added) to that estimated from the Coupled Model Intercomparison Project 5 (CMIP5) simulations with laminar ocean models.
Finally, the spatial structure of the observed sea-level variability modes in WBCs, which is well simulated by our model with or without low-frequency forcing, is shown to be shaped by oceanic intrinsic processes. The temporal evolution of these spatial modes may be triggered by the low-frequency atmospheric forcing when present, leading to a longer memory than in the purely seasonally-forced case.