1:45 PM - 3:15 PM
[ACG30-P11] Circum-Western Canada pattern in boreal summer excited by the Boundary Current Synchronization
Keywords:Boundary Current Synchronization, extreme weather, teleconnection, air-sea interaction
The Kuroshio Current and the Gulf Stream are separated by about 10,000 km across the continent. However, the sea surface temperatures along the Kuroshio Current and the Gulf Stream synchronize via the westerly jet stream, which is referred to as the Boundary Current Synchronization (BCS). BCS brings extreme heat waves and other extreme weather events to metropolitan areas in the mid-latitudes of the Northern Hemisphere, including Japan. However, the mechanism has not been investigated in detail.
In this study, we define the “Circum-Western Canada (CWC) pattern” as an atmospheric variability closely related to the BCS index, and investigate the impact of the BCS on extreme weather in the mid-latitudes of the Northern Hemisphere. We define the CWC index using a reference region with a large regression and correlation coefficients of geopotential height at 200hPa on the BCS index. The Empirical Orthogonal Function analysis shows that the CWC pattern is the predominant mode in the western half of the Northern Hemisphere. The regression map of geopotential height at 200hPa on the Arctic Oscillation (AO) index and that on the CWC index exhibit similar features, which suggests that the CWC index is also in close relation to the AO index defined by the surface pressure. The regression map of precipitation and 2m-air temperature on the CWC index show that CWC explains 2m-air temperature pattern in July 1994, July 2018 and July 2022 and precipitation pattern in July 1994 and July 2018. The results of a pacemaker experiment, in which sea surface temperatures in the Kuroshio Current and the Gulf Stream is relaxed to a different control run, indicate that BCS can actively excite the CWC pattern.
In this study, we define the “Circum-Western Canada (CWC) pattern” as an atmospheric variability closely related to the BCS index, and investigate the impact of the BCS on extreme weather in the mid-latitudes of the Northern Hemisphere. We define the CWC index using a reference region with a large regression and correlation coefficients of geopotential height at 200hPa on the BCS index. The Empirical Orthogonal Function analysis shows that the CWC pattern is the predominant mode in the western half of the Northern Hemisphere. The regression map of geopotential height at 200hPa on the Arctic Oscillation (AO) index and that on the CWC index exhibit similar features, which suggests that the CWC index is also in close relation to the AO index defined by the surface pressure. The regression map of precipitation and 2m-air temperature on the CWC index show that CWC explains 2m-air temperature pattern in July 1994, July 2018 and July 2022 and precipitation pattern in July 1994 and July 2018. The results of a pacemaker experiment, in which sea surface temperatures in the Kuroshio Current and the Gulf Stream is relaxed to a different control run, indicate that BCS can actively excite the CWC pattern.