Limited Surface Impacts of the January Sudden Stratospheric Warming
Sudden stratospheric warmings (SSWs) are typically followed by cold and stormy weather throughout Europe and United States, and warm temperatures in Northern Canada. Such a pattern was observed following the Jan 5, 2021 SSW. By performing unique experiments with the CESM2(WACCM6) subseasonal prediction system, we showed that the SSW itself had a limited impact on surface weather in the four weeks following the event. We found no evidence that the event itself, nor the polar vortex stretching and wave reflection, caused or otherwise influenced the record cold in North America in February 2021. We showed that when the SSW was removed, the surface weather pattern during weeks 3-4 after the forecast was very similar to that with the SSW. Similarly, we showed that it’s primarily the tropospheric atmospheric state that was responsible for the record-breaking North American cold temperatures in February 2021.
We have shown that a subseasonal prediction system experiments, particularly those with scrambling the initial conditions of different aspects of the atmosphere, can be valuable for assessing the causes and impacts of individual events.
In this study, we find, that the 2021 SSW was not likely responsible for the cold weather over Eurasia and warm temperatures in North America in the weeks following the event. This pattern would have occurred even if the SSW did not occur. Experiments with the CESM2 (WACCM6) prediction system show that the record-breaking North American cold temperatures in February 2021 are also not attributable to the SSW, but rather to the tropospheric state.