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Arctic Sea Ice Loss Effects Paper Looks Much Like The New SST Pattern That Developed In 2013

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https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL077325

Fast Response of the Tropics to an Abrupt Loss of Arctic Sea Ice via Ocean Dynamics

Whereas previous modeling studies have examined the equilibrium coupled climate response to projected Arctic sea ice loss, we have investigated aspects of the transient adjustment to an abrupt loss of Arctic sea ice, with a particular focus on the tropics and the role of ocean dynamics. To study the relative roles of dynamical versus thermodynamic air‐sea interaction, we conducted identical sets of experiments with CCSM4 in the full‐depth ocean model (FOM) and slab ocean model (SOM) configurations. The SOM response is dominated by a quasi‐steady interhemispheric SST contrast (warming in the NH and little change in the SH), accompanied by a northward shift of the ITCZ and Hadley Circulation. The FOM response is more complex, with distinctive patterns that evolve over time. The tropical SST response is characterized by a distinct equatorial Pacific maximum, which develops within approximately 20 years, accompanied by an equatorward intensification of the ITCZ and Hadley Circulation. These structures amplify with time and are in marked contrast to the SOM response. A heat budget analysis for the upper 100 m of the eastern equatorial Pacific indicates the importance of anomalous vertical advection, which is tied to a monotonic warming at depth (below 200 m). Although further diagnostics and experiments are needed to understand the origins of this subsurface warming, it appears to be qualitatively consistent with the adjustment of the global thermohaline circulation to a density perturbation in the North Atlantic, in this case induced by a freshening and warming of the subpolar gyre due to sea ice melt.

In addition to distinctive tropical responses, FOM and SOM also exhibit some differences in their NH midlatitude atmospheric circulation responses. In particular, FOM shows an increase in lower tropospheric westerlies over the North Pacific, a response that strengthens over time. This aspect is very weak and shifted poleward in SOM compared to FOM. In addition, SOM shows reduced westerlies farther south, a feature that is lacking in FOM. These distinctions in the midlatitude circulation responses between FOM and SOM, apparent even within the first 25 years, can be traced to differences in their tropical Pacific SST responses and affect the precipitation response along the west coast of North America among other regions.

In summary, the coupled ocean‐atmosphere response to an abrupt loss of Arctic sea ice is rapidly (within 20–30 years) and markedly modified by dynamical ocean processes. To what extent our results depend on the particular model used and the experimental design remains to be ascertained.

 

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