[A-AS06] Atmospheric (Stratosphere-troposphere) Processes And their Role in Climate

[AAS06-P09] Impacts of the Arctic sea-ice loss on the middle atmosphere

*Shosuke Mori¹, Yasunobu Miyoshi² (1.Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University, 2.Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University)

Sea ice extent in the Arctic has been decreasing in recent decades. It has been reported that the Arctic sea-ice loss affects the planetary wave activity propagating from the troposphere to the stratosphere, thereby influencing the general circulation in the stratosphere such as weakening of the polar night jet (polar vortex). In this study, we examined the effect of the Arctic sea-ice loss on the middle atmosphere by performing two general circulation model experiments. We used GAIA model (T42L90) with the model top of 100 km height. The control run (CNTL) was conducted under climatological SST and sea-ice extent (1980-1990s). On the other hand, the sea-ice loss experiment (NICE) used climatological SST and the reduced Arctic sea-ice extent (2016-2020). This means that the lower boundary conditions in the NICE is identical to those in the CNTL except for the Arctic sea-ice extent. We performed 100-year integrations for CNTL and NICE experiments. By comparing the results of these two experiments, we investigate the effect of the Arctic sea-ice loss on the middle atmosphere. Our results showed that the Arctic sea-ice loss induced weakening of the westerly wind in the stratosphere and mesosphere at high latitudes, warming in the Arctic stratosphere and cooling in the Arctic mesosphere in the first of January. In addition, the planetary wave activity propagating from the troposphere to the lower stratosphere is modulated by the Arctic sea-ice loss. For example, in the NICE experiment, the upward propagation and amplitude of planetary wave with zonal wavenumber of 1 is enhanced in December, and those with zonal wavenumber 2 is enhanced in January. On the other hand, in the upper stratosphere and mesosphere, the increase of the planetary wave with zonal wavenumber of 1 and 2 in the NICE experiment is found. These enhancements of the planetary wave activity are closely related with the weakening of the westerly wind at high latitudes in the NICE experiment. In addition, we will discuss the meridional propagation of the planetary wave, and wave forcing in the middle atmosphere.