5:15 PM - 6:45 PM
[AAS10-P02] Characteristics of planetary-wave packet propagation during a minor SSW event in early January 2024 and its impact on the troposphere
Keywords: Sudden stratospheric warming, Planetary-wave packet propagation, Three-dimensional wave activity flux, Extremely low temperatures on the North American continent
Observational features of atmospheric fields during January 2024 are investigated by the use of the Japanese Reanalysis for Three Quarters of a Century (JRA-3Q, Kosaka et al. 2024), on the basis of the three-dimensional wave activity flux (3D-flux-W, Kinoshita and Sato 2013; Sato et al. 2013; Harada et al. 2019).
In mid-January 2024, a major SSW occurred in the Northern Hemisphere stratosphere. It was preceded by another warming in early January. This is classified as a minor SSW according to the WMO definition. However, the warming over several days reached 60 K at 10 hPa and nearly 70 K at 5 hPa. On the other hand, below 10 hPa, there was little westerly deceleration of the zonal mean zonal wind, but rather occurred westerly acceleration.
Eliassen-Palm (EP) flux analysis of planetary-scale wave packets showed that upward propagation of planetary-scale wave packets with zonal wavenumber 1 (WN1) was dominant in early January, while divergence near the stratopause and downward propagation in the stratosphere of planetary-scale wave packets with WN2 and WN3 were clearly seen in the second half of early January. These features are considered to be associated with the westerly acceleration in the upper stratosphere and the reason why the SSW could not develop to a major one. Further analysis using 3D-flux-W shows that the downward propagation of planetary-scale wave packets in the stratosphere is concentrated in the 60-120°W longitude region, which strengthened the upper tropospheric trough over the North American continent, and in mid-January 2024, the North American continent experienced extremely low temperatures due to a high-pressure system migrating southward accompanied by cold air in the lower troposphere. The enhancement of the upper tropospheric trough simultaneously leads to a cooling of its lower region. Therefore, the downward propagation of planetary-scale wave packets from the stratosphere to the upper troposphere described above may have contributed to the onset of the extreme cold wave on the North American continent.
In mid-January 2024, a major SSW occurred in the Northern Hemisphere stratosphere. It was preceded by another warming in early January. This is classified as a minor SSW according to the WMO definition. However, the warming over several days reached 60 K at 10 hPa and nearly 70 K at 5 hPa. On the other hand, below 10 hPa, there was little westerly deceleration of the zonal mean zonal wind, but rather occurred westerly acceleration.
Eliassen-Palm (EP) flux analysis of planetary-scale wave packets showed that upward propagation of planetary-scale wave packets with zonal wavenumber 1 (WN1) was dominant in early January, while divergence near the stratopause and downward propagation in the stratosphere of planetary-scale wave packets with WN2 and WN3 were clearly seen in the second half of early January. These features are considered to be associated with the westerly acceleration in the upper stratosphere and the reason why the SSW could not develop to a major one. Further analysis using 3D-flux-W shows that the downward propagation of planetary-scale wave packets in the stratosphere is concentrated in the 60-120°W longitude region, which strengthened the upper tropospheric trough over the North American continent, and in mid-January 2024, the North American continent experienced extremely low temperatures due to a high-pressure system migrating southward accompanied by cold air in the lower troposphere. The enhancement of the upper tropospheric trough simultaneously leads to a cooling of its lower region. Therefore, the downward propagation of planetary-scale wave packets from the stratosphere to the upper troposphere described above may have contributed to the onset of the extreme cold wave on the North American continent.