Influence of Arctic Sea-ice Concentration on Extended-range Forecasting of Cold Events in East Asia

Abstract

Utilizing the Community Atmosphere Model, version 4, the influence of Arctic sea-ice concentration (SIC) on the extended-range prediction of three simulated cold events (CEs) in East Asia is investigated. Numerical results show that the Arctic SIC is crucial for the extended-range prediction of CEs in East Asia. The conditional nonlinear optimal perturbation approach is adopted to identify the optimal Arctic SIC perturbations with the largest influence on CE prediction on the extended-range time scale. It shows that the optimal SIC perturbations are more inclined to weaken the CEs and cause large prediction errors in the fourth pentad, as compared with random SIC perturbations under the same constraint. Further diagnosis reveals that the optimal SIC perturbations first modulate the local temperature through the diabatic process, and then influence the remote temperature by horizontal advection and vertical convection terms. Consequently, the optimal SIC perturbations trigger a warming center in East Asia through the propagation of Rossby wave trains, leading to the largest prediction uncertainty of the CEs in the fourth pentad. These results may provide scientific support for targeted observation of Arctic SIC to improve the extended-range CE prediction skill.

摘要

本文利用通用大气模式(CAM4),研究了北极海冰密集度(SIC)对东亚冷事件延伸期预报的影响。数值结果显示,北极SIC对东亚冷事件的延伸期预报至关重要。采用条件非线性最优扰动方法,计算得到了对东亚冷事件延伸期预报影响最大的北极SIC扰动模态。研究结果表明,相较于具有特定空间结构的SIC扰动,相同约束下空间上随机的SIC扰动对东亚冷事件的影响较小。进一步的诊断揭示,最优SIC扰动首先通过非绝热过程调节局地温度,随后通过水平平流和垂直对流过程影响东亚气温。因此,通过Rossby波列的传播,北极最优SIC扰动在东亚形成一个暖中心,引起第四侯冷事件的预报不确定性。这些结果可为北极地区海冰的目标观测及提高冷事件延伸期预报技巧提供科学支持。