Understanding climate
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Seminar talk: Remote influence of the tropical Pacific variability on Arctic climate in coupled model simulations

Speaker on this seminar is Yu Kosaka from RCAST, University of Tokyo



Decadal modulations of global mean surface temperature (GMST) increase is associated with the Pacific decadal variability (PDV), as highlighted by the recent slowdown event of surface global warming. Quantification of this PDV influence on GMST is therefore crucial for global warming attribution. A multimodel analysis reveals large inter-model diversity in surface air temperature anomalies at high latitudes of the Northern and Southern Hemispheres in association with PDV. This is related to recent attribution studies of the early-20th century rapid Arctic warming which highlight the PDV influence. Thus, understanding the mechanism of the Pacific-Arctic climate linkage and the cause of its inter-model diversity is important for attributions of both GMST and Arctic warming.


We examine influence mechanism of the tropical Pacific variability on the Arctic through numerical experiments with GFDL CM2.1. Both on interannual and decadal timescales, tropical Pacific warming induces surface and tropospheric warming and sea ice reduction in the Arctic. This Arctic warming, when scaled to a unit increase of tropical Pacific SST, is much stronger on decadal than interannual timescales. On both timescales, the warming is amplified in the lower troposphere, and peaks in boreal winter. Our energy budget analysis reveals that underlying mechanism of the Arctic warming differs drastically between the two timescales. On interannual timescales, intensified atmospheric energy transport from mid-latitudes and adiabatic warming due to anomalous descent play the leading role, while radiation and surface turbulent heat flux anomalies act as damping. On decadal timescales, by contrast, significant sea ice decrease is induced by year-to-year accumulation of those surface heat flux and radiation anomalies. The resultant enhancement of heat release from the ocean, which peaks in winter, plays the leading role in decadal Arctic warming, while atmospheric meridional heat transport anomalies become secondary to the energy budget. There is an additional contribution from ocean heat flux increase from the North Atlantic on decadal timescales.


Yu Kosaka
Yu Kosaka

Short biography:

Research interests: Climate variability, air-sea interactions, teleconnections, attributions


Ph.D. at the University of Tokyo in 2007

Postdoc at the University of Tokyo for 2007-2009 and International Pacific Research Center, University of Hawaii, for 2009-2012

Project Scientist at Scripps Institution of Oceanography, University of California San Diego, for 2012-2014

Associate Professor at RCAST, the University of Tokyo since 2014


Arranged date for the seminar talk: Sep 20, 2019