| Summary: | A series of reforecast experiments by using the ensemble prediction system of the Meteorological Research Institute is conducted to investigate the predictability and occurrence mechanism of a stratospheric sudden warming event in January 2009, which is a typical polar vortex-splitting event. The polar vortex splitting is predicted for forecasts initialized after 8 days before the warming peak. It is found that in the failed forecast, the upward propagating planetary waves from the troposphere are reflected by the polar night jet and propagate downward into the troposphere. Thus, this study indicates that the propagating property of planetary waves in the stratosphere would be another important control factor for the occurrence of the polar vortex-splitting event. A series of reforecast experiments by using the ensemble prediction system of the Meteorological Research Institute is conducted to investigate the predictability and occurrence mechanism of a stratospheric sudden warming event in January 2009, which is a typical polar vortex-splitting event. The polar vortex splitting is predicted for forecasts initialized after 8 days before the warming peak. It is found that in the failed forecast, the upward propagating planetary waves from the troposphere are reflected by the polar night jet and propagate downward into the troposphere. Thus, this study indicates that the propagating property of planetary waves in the stratosphere would be another important control factor for the occurrence of the polar vortex-splitting event.
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