26 December 2014

Intensification of Decadal and Multi-Decadal Sea Level Variability in the Western Tropical Pacific during Recent Decades


Sea level in the western tropical Pacific has risen more rapidly than in other regions in the past 15 years or so.  During that time there has been a response of the climate system to increasing greenhouse gases as well as significant decadal variability associated with the Interdecadal Pacific Oscillation (IPO).  What are the contributions from each to the unusually large regional sea level rise?    Observations of sea level and surface winds are analyzed to documents observed changes.  These results are compared to analyses of an ocean-only model experiment driven by observed winds, an idealized atmosphere-only model run with observed SSTs and a uniform tropical warming, an experiment with an additional warming added to the tropical Indian Ocean to mimic the global warming signal there, and two additional atmospheric model experiments run with global SSTs and with time-varying tropical SSTs.  Analysis of these experiments shows recent faster sea level rise in the western tropical Pacific is due to a combination of the transition of the IPO from positive to negative in the late 1990s that increased Pacific trade wind strength, and a faster warming of the Indian Ocean from increasing greenhouse gases that also contributed to stronger trades.  Consequently, more water piled up faster in the western Pacific to produce the observed  rapid regional increases of sea level there.

W. Han
Han, W, GA Meehl, MA Alexander, T Yamagata, D Yuan, M Ishii, P Pegion, J Zheng, BD Hamlington, X- Quan, and RR Leben.  2013.  "Intensification of decadal and multi-decadal sea level variability in the western tropical Pacific during recent decades."  Climate Dynamics 43: 1357-1379, doi:10.1007/s00382-013-1951-1.