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Arctic Influence on the Eastern Asian Cold Surge Forecast: A Case Study of January 2016
戴国锟
复旦大学
An extreme cold surge impacted eastern Asia during 21-25 January 2016, which resulted in extensive damage to eastern Asian countries. Synoptic diagnoses have shown that the southward movement of the north Siberian anticyclone to the Ural Mountains is the key process for the cold surge. Moreover, operational forecasts from the European Centre for Medium-Range Weather Forecasts show that this event could be forecasted nine days before its onset. Further diagnostic analysis of the control forecasts reveals that large uncertainties in Arctic may be the reason for cold surge forecast failure. This failure occurs because the north Siberian anticyclone is not strong enough due to the erroneous eddy vorticity forcing (EVF) induced by the uncertainty in Arctic initial conditions; thus, the anticyclone cannot be guided southward to the Ural Mountains when the anticyclone comes from Caspian Sea. Finally, numerical experiments are conducted with the OpenIFS model to verify the influence of the Arctic. Numerical results show that integration with the ERA5 initial conditions could capture the cold surge nine days in advance, while integration with the ERA-Interim initial conditions cannot. The largest differences between these two initial conditions are in polar regions. A sensitivity experiment with modified Arctic initial conditions shows improved cold surge forecast skill. This improvement may be due to the north Siberian anticyclone with accurate EVF induced by the improved initial conditions in Arctic, which is sufficiently strong to be guided southward when an anticyclone comes from the Caspian Sea. This result highlights the importance of the Arctic initial conditions in the forecast of eastern Asian cold surges.