Forced and chaotic interannual variability of regional sea level and its causes over 1993-2015
Event: 2020 Ocean Surface Topography Science Team Meeting (virtual)
Session: Science I: Climate data records for understanding the causes of global and regional sea level variability and change
Presentation type: Type Forum
Since the 1990s, satellite altimetry has become the main observing system for continuously measuring the sea level variations with a near global coverage, revealing a global mean sea level rise of 3.3 mm/yr since 1993 with large regional sea level variability. These measurements highlight complex structures especially for the western boundary currents or the Antarctic Circumpolar Current. A recent study shows that the chaotic ocean variability may mask atmospherically-forced regional sea level trends over 38% of the global ocean area from 1993 to 2015. The present study aims to complement this work in focusing on the interannual variability of regional sea level, which can show huge variations occurring in addition to the sea level trends. A global ¼° ocean/sea-ice 50-member ensemble simulation is considered to disentangle the imprints of the atmospheric forcing and the chaotic ocean variability on the interannual variability of regional sea level and its causes (i.e., steric sea level and manometric sea level contribution) over 1993-2015. First it is validated against observations. On the contrary to previous studies, we demonstrated that the forced signal has a signature for scales smaller than 3x3° and can be important in the western boundary current. The forced and chaotic interannual variability mainly have a steric origin except in coastal areas. However in the ACC, the chaotic variability is strong for both the steric and manometric contributions. Finally this study quantifies to what extent the chaotic variability explains the total interannual variability, questioning its detection and its characterisation.