Title: Two case studies of regional sea level changes: 1. Connection between ocean circulation and sea level; 2. Forced changes vs. internal variability
Venue: Room 412, College of Physical and Environmental Oceanography, Laoshan Campus
Time: 10:30am, 2015.06.18
Speaker: Dr. ZHANG Xuebin
Affiliation: CSIRO Oceans and Atmosphere Flagship, Australia
Abstract:
In this seminar talk, I am going to present two recent case studies of regional sea level changes. In the first case (published by Clim. Dyn., DOI:10.1007/s00382-013-1902-x), we examined the projected changes of subtropical gyre circulation and sea level changes in the Pacific based on CMIP3 and CMIP5 models, and identified connection between them. In particular, we identified an asymmetric features of projected subtropical gyre circulation changes and associated sea level changes between the North and South Pacific. Poleward expansion of subtropical gyres is projected in the upper ocean for both N & S Pacific. Contrastingly, the subtropical gyre circulation is projected to spin down by about 20% in the subsurface N Pacific, while S Pacific subtropical gyre is projected to strengthen by about 25% and expand poleward in the subsurface to at least 2000m. This asymmetrical distribution is directly related to changes of T & S, forced by surface heat and freshwater fluxes, and surface wind stress changes.
In the second case (published by Nature Climate Change, DOI: 10.1038/NCLIMATE2397), we examined the forced climate change signals vs. natural variability in CMIP5 climate models, and determined the time when the forced signals exceeds and thus emerges from natural climate variability for both regional sea level and sea surface temperature. Three regional sea level projection products which have increasing complexity in terms of included processes are examined to reveal contributions from ocean dynamics, thermal expansion and land ice melting. We found the Time of Emergence for total sea level is substantially earlier than that for surface air temperature and exhibits little dependence on the emission scenarios, which means that our society will face detectable sea level change and its potential impacts earlier than surface air warming.
Bio:
Dr. Xuebin Zhang is a Senior Research Scientist of CSIRO Sea-level Team in the Oceans and Atmosphere Flagship. His general research interests includes ocean and climate change, sea-level rise, climate variability, ocean dynamics and climate modelling. He has been actively involved in the Pacific Climate Change Science Program (PCCSP), to study sea level change from global climate models with a focus on the regional distribution of sea-level rise and its underlying physical mechanisms. He is currently leading a CSIRO Ocean Downscaling Strategic Project to dynamically downscale future climate change signals with a near-global eddy-resolving OGCM. Before joining CSIRO, he had been studying and working at University of Washington, NOAA/Pacific Marine Environmental Laboratory (Seattle, Washington) and Scripps Institution of Oceanography (San Diego, California), mainly focusing on ENSO and tropical ocean dynamics by applying both in-situ data analysis and numerical modelling.
