[Seminar] Dr. Kanghyun Song

Stratospheric-Tropospheric interaction and its application: Stratospheric sudden warming events

Stratospheric sudden warming (SSW) events are one of the most remarkable examples of subseasonal variability in the boreal-winter stratosphere. These events are driven by vertically-propagating planetary-scale waves from the upper troposphere, but also significantly impact on the tropospheric circulation through stratosphere-troposphere dynamical coupling. The downward influence is often maintained for up to two months in the northern extratropics. The SSW events also exhibit pronounced interannual variability, related to El Niño-Southern Oscillation (ENSO) in the troposphere and quasi-biennial oscillation (QBO) in the stratosphere. The SSW events occur more favorably during El Niño and easterly-phase QBO winters. Due to the long-lasting impact on the troposphere and the relationship with the interannual variability, the SSW events have been regarded as an important source for subseasonal-to-seasonal (S2S) prediction in the northern extratropics. In the numerical weather prediction models, the tropospheric prediction skills are improved during the winters accompanying SSW events. For the better prediction on the S2S timescale, the improved prediction of SSW events should be needed during the winter.