Sensitivity of Stratospheric Circulation Response to Different Geographic Locations of the Arctic Sea Ice Loss

The impact of future Arctic sea ice loss on the stratospheric circulation is investigated using the Whole Atmosphere Community Climate Model (WACCM), a state-of-the-art chemistry climate model. Two 161-year simulations are conducted: one with a repeating seasonal cycle of Arctic sea ice for the late twentieth century (1980-99), taken from the fully-coupled WACCM historical run; the other with Arctic sea ice for the late twenty-first century (2080-99), obtained from the fully-coupled WACCM RCP8.5 run. In agreement with previous studies, the stratospheric polar vortex weakens in winter but strengthens in spring in response to Arctic sea ice loss.

To examine the impact of different geographic locations of sea ice loss on the stratospheric circulation, two additional experiments are performed: one with ice loss confined to the central Arctic, and one with ice loss confined to the marginal ice zones. Interestingly, the polar vortex weakens in response to ice loss in the central Arctic, but strengthens in both seasons in response to ice loss in the marginal ice zones. Thus the stratospheric circulation response to the combined pattern of sea ice loss can be understood as a consequence of largely canceling effects from these two regions. This highlights that different geographic locations of Arctic sea ice loss have different impacts on the stratospheric circulation. Particularly, the forced wave response to sea ice loss in some specific locations (e.g., North-western Pacific) can easily interfere with the climatological planetary waves. Therefore these places are the sensitive spots for upward wave propagation from the troposphere to the stratosphere.