[A-AS10] Stratosphere-troposphere (Atmospheric) Processes And their Role in Climate

[AAS10-08] Large-scale atmospheric response to anomalies in the sea surface temperatures and sea ice in the 2021-22 winter

★Invited Papers

*Kazuaki Nishii¹, Bunmei Taguchi², Hisashi Nakamura³, Yvan J Orsolini⁴ (1.Graduate School of Bioresources, Mie University, 2.Faculty of Sustainable Design, University of Toyama, 3.Research Center for Advanced Science and Technology, The University of Tokyo, 4.Climate and Environmental Research Institute (NILU))

Keywords:PDO, blocking, Okhotsk Sea ice, stratospheric vortex intensification

The 2021-22 winter was characterized by cooling of the Arctic stratosphere particularly around the late winter, extremely warm sea surface temperatures (SST) in the North Pacific associated with the negative phase of the Pacific Decadal Oscillation (PDO), and reduction of sea ice in the Sea of Okhotsk. We investigated the large-scale atmospheric responses to observed anomalies in the SST and sea ice in this winter through ensemble time-slice experiments of an atmospheric general circulation model (AGCM). An anticyclonic response to the observed anomalies in the extratropical SSTs and sea ice was found over the western North Pacific in the troposphere in February 2022, which is consistent with observed anticyclonic anomaly there. In the polar stratosphere, a cooling response was found in association with weakening of upward planetary wave propagation into the stratosphere. This is again consistent with the observation. Further experiments suggest that each of anomalies in the extratropical North Pacific SSTs, extratropical North Atlantic SSTs, and sea ice in the sea of Okhotsk may contribute to the tropospheric anticyclonic anomaly over the western North Pacific and cooling in the polar stratosphere. In contrast, significant responses consistent with the observation in the extratropical troposphere and stratosphere were not obtained in response to the observed tropical SST anomalies.