1A.2 Stratospheric Variability Contributed to and Sustained the Recent Hiatus in Eurasian Winter Warming

Monday, 23 January 2017: 11:15 AM
605 (Washington State Convention Center )
Chaim I. Garfinkel, Hebrew University, Jerusalem, Israel; and S. W. Son, K. Song, V. Aquila, and L. D. Oman

The recently-ended hiatus in global-mean surface temperature warming was characterized
 by (and in part due to) a pronounced Eurasian winter cooling trend. While changing SSTs
 can largely account for the hiatus in other seasons and in other regions, they cannot explain the midwinter cooling over Eurasia and the cause(s) for this cooling is unclear.

Here, we show that much of the observed hiatus in Eurasian warming was associated with a recent

 trend towards weakened stratospheric polar vortices. Specifically, by calculating the change
 in Eurasian surface air temperature associated with a given vortex weakening on a range
of timescales and for several data sources, we demonstrate that the recent trend towards
weakened polar vortices reduced the anticipated Eurasian warming due to increasing greenhouse gas concentrations. Those model integrations whose stratospheric vortex evolution
closely matches that in reanalysis data also simulate a hiatus quantitatively similar to that
observed. While it is unclear whether the recent weakening of the midwinter stratospheric
polar vortex was forced, a properly configured model can simulate substantial deviations
of the polar stratosphere on decadal timescales and hence such hiatus events, implying that
similar decadal hiatus events may recur despite the multi-decadal warming trend forced by
 greenhouse gas increases.

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