講演情報
[ACG68-P08]Atmospheric response to winter sea ice extent in the Sea of Okhotsk
*栗原 德人1、山根 省三1 (1.同志社大学)
キーワード：
オホーツク海、大気大循環モデル、テレコネクション
The Sea of Okhotsk is the southernmost region in the Northern Hemisphere where sea ice appears during winter. The sea ice extent in the Sea of Okhotsk is known to exhibit a long-term decreasing trend associated with global warming. Many studies with observational data have clarified the relationship between the sea ice extent and the atmospheric circulation in the Northern Hemisphere. However, it is not easy to determine from these results whether a causal relationship or feedback exists between the two. Honda et al. (1996, 1999) conducted numerical experiments using a relatively low-resolution atmospheric general circulation model (AGCM), and shown that the sea ice extent has a significant impact on the atmospheric circulation in the North Pacific. Further investigation is needed to examine the effects on the development of extratropical cyclones and storm track activity using a higher-resolution AGCM.
This study investigated the impact of sea ice extent in the Sea of Okhotsk on atmospheric circulation using monthly mean sea ice data from COBE-SST3, monthly mean atmospheric data from JRA-3Q (Japanese Reanalysis for Three Quarters of a Century), and numerical experiments with an AGCM called AFES. We selected years with large and small sea ice extent during January-March from the period of 1971-2024, and analyzed the differences in the composite atmospheric fields for these years. Numerical experiments were conducted with a horizontal grid spacing of approximately 1 degree and 60 vertical layers under two conditions: the Sea of Okhotsk covered by 0.5 m thick sea ice from January to March, and the Sea of Okhotsk without sea ice cover. For each condition, three numerical integrations with different initial conditions were performed from July 1st to April 1st two years later. The atmospheric response to sea ice extent was investigated based on the ensemble mean fields averaged over January to March obtained from these calculations.
The circulation patterns associated with the extent of sea ice in the Sea of Okhotsk, obtained from both observational data analysis and numerical experiments, resembled the Pacific/North America (PNA) teleconnection pattern. The wave activity flux in the circulation patterns derived from observational data analysis indicated the propagation of quasi-stationary waves northward from the central North Pacific. On the other hand, the wave activity flux in the circulation patterns from the numerical experiments showed propagation northward from the Sea of Okhotsk and eastward from the vicinity of Japan toward the Aleutian Islands, North America, and the North Atlantic. These results suggest that changes in the extent of sea ice in the Sea of Okhotsk contribute to the formation of circulation patterns similar to the PNA.
This study investigated the impact of sea ice extent in the Sea of Okhotsk on atmospheric circulation using monthly mean sea ice data from COBE-SST3, monthly mean atmospheric data from JRA-3Q (Japanese Reanalysis for Three Quarters of a Century), and numerical experiments with an AGCM called AFES. We selected years with large and small sea ice extent during January-March from the period of 1971-2024, and analyzed the differences in the composite atmospheric fields for these years. Numerical experiments were conducted with a horizontal grid spacing of approximately 1 degree and 60 vertical layers under two conditions: the Sea of Okhotsk covered by 0.5 m thick sea ice from January to March, and the Sea of Okhotsk without sea ice cover. For each condition, three numerical integrations with different initial conditions were performed from July 1st to April 1st two years later. The atmospheric response to sea ice extent was investigated based on the ensemble mean fields averaged over January to March obtained from these calculations.
The circulation patterns associated with the extent of sea ice in the Sea of Okhotsk, obtained from both observational data analysis and numerical experiments, resembled the Pacific/North America (PNA) teleconnection pattern. The wave activity flux in the circulation patterns derived from observational data analysis indicated the propagation of quasi-stationary waves northward from the central North Pacific. On the other hand, the wave activity flux in the circulation patterns from the numerical experiments showed propagation northward from the Sea of Okhotsk and eastward from the vicinity of Japan toward the Aleutian Islands, North America, and the North Atlantic. These results suggest that changes in the extent of sea ice in the Sea of Okhotsk contribute to the formation of circulation patterns similar to the PNA.