Arctic Influence on the Eastern Asian Cold Surge Forecast: A Case Study of January 2016

Abstract

AbstractAn extreme cold surge during 21–25 January 2016 resulted in extensive damage to eastern Asian countries. Synoptic diagnoses show that the southward movement of the north Siberian anomalous anticyclone to the midlatitudes was the key process for the cold surge. Operational forecasts from the European Centre for Medium‐Range Weather Forecasts show that this event could be captured in the control forecast started on 12 January. Further diagnosis shows that the control forecast started on 11 January missed it, possibly due to uncertainties in the Arctic because the north Siberian anomalous anticyclone is not strong enough due to the erroneous eddy vorticity forcing (EVF) induced by the Arctic initial conditions uncertainty. Therefore, the north Siberian anomalous anticyclone cannot move southward to midlatitude when another anomalous anticyclone comes from the Caspian Sea. Finally, numerical experiments are conducted with the Open Integrated Forecasting System model to verify the role of the Arctic initial conditions. Numerical results show that integration with the ERA5 initial conditions could capture the cold surge in the forecast starting on 12 January, while integration with the ERA‐Interim initial conditions could not. Sensitivity experiments with modified Arctic initial conditions show an improved cold surge forecast skill. This improvement may be due to the north Siberian anomalous anticyclone, which is sufficiently strong to move southward when the anomalous anticyclone comes from the Caspian Sea, with accurate EVF induced by the improved initial conditions in the Arctic. This result highlights the importance of the Arctic initial conditions in this eastern Asian cold surge forecast.