Extreme Coastal Sea Level Events in the Tropical East Indian Ocean: the Role of Climate Variability

Tide gauge observations detected extreme sea level events along the coast of the tropical east Indian Ocean, with monthly mean anomalies of sea level rise exceeding 0.3m - 0.45m and sea level fall below -0.3m at some locations during some years of recent decades. Satellite altimetry data, ocean reanalysis product (e.g. ORAS4) and stand-alone OGCM experiments are able to capture most (but not all) of the events, although none of them is able to capture the full magnitude of interannual sea level variations observed by tide gauges. The OGCM experiments using HYCOM and ROMS, together with Large Ensemble Climate Model Experiments of the NCAR’s CESM1 and the Max-Planck Institute of Meteorology earth system model, are used to understand the causes for the extreme sea level anomalies. It is found that the most recent, extreme high sea level event results mainly from a combination of interannual and interdecadal climate variability over the tropical Indo-Pacific basin, which induced strong equatorial westerlies and thus the strong sea level rise along the eastern boundary of the tropical east Indian Ocean, with global sea level rise also has some contribution. By contrast, the extreme sea level lows are primarily caused by the interannual climate variability modes.