Dynamics and Predictability of Troposphere-Stratosphere Dynamical Coupling during Stratospheric Sudden Warming Events

本文利用日本气象厅（JMA）提供的1个月集合预报资料和长期全球分析资料，以及基于大气环流模式和日本气象厅（JMA）业务数值预报模式的一系列数值试验，对平流层突然变暖（SSW）事件中平流层-对流层动力耦合的动力学和可预测性进行了研究。时间演变相当简单的热带风暴的发生，如2001年12月的热带风暴，可至少提前2周预测。这种ssw的可预测周期至少比对流层环流的可预测周期长两倍。在ssw发生期间，对ssw预报初始条件的敏感性变得非常高。对流层阻塞对SSW前兆事件的重要性得到了统计证实。预报实验还表明，与初始条件所规定的阻塞相关的对流层环流异常实际上导致了随后的SSW。平流层环流对指定异常的强度有非线性响应。纬向风异常的纬向-平均纬向风异常的向下迁移最多可提前1周预测。向下迁移是由E-P通量辐合与纬向波数（WN） 2行星波从对流层向上传播引起的。wn2分量的传播特性在很大程度上取决于高纬度对流层顶附近纬向平均风的廓线。时间演变相对复杂的南风，如2004年1月的南风，可预测周期最多为9天。冬季平流层环模变率变大时，平流层环模的预报能力有提高的趋势。

In this study, we obtained the following results on the dynamics and the predictability of the stratosphere-troposphere dynamical coupling during stratospheric sudden warming (SSW) events by examining 1-month ensemble forecast dataset provided from the Japan Meteorological Agency (JMA) and long-term global analysis datasets as well as performing a series of numerical experiments based on atmospheric general circulation models and the operational numerical weather forecast model of the JMA :1.The occurrence of SSWs with rather simple time evolution, such as a SSW in December 2001, is predictable at least 2 weeks in advance. The predictable period of such SSWs is at least two times longer than that of the tropospheric circulation.2.Sensitivity to the initial condition for the forecast of SSWs becomes very high during the onset period of the SSWs.3.The importance of the tropospheric blocking for the precursory event of the SSW is statistically confirmed. Prediction experiments also indicate that the tropospheric circulation anomaly associated with the blocking specified for the initial condition actually causes the subsequent SSW. The stratospheric circulation nonlinearly responds to the magnitude of the specified anomaly.4.The downward migration of the zonal-mean zonal wind anomaly after the SSW is predictable at most 1 week in advance. The downward migration is caused by the E-P flux convergence associated with zonal wavenumber (WN) 2 planetary waves propagating upward from the troposphere. The propagating property of WN 2 components strongly depends on the profile of the zonal-mean zonal wind around the tropopause region in high latitudes.5.Predictable period of SSWs with relatively complicated time evolution such as a SSW in January 2004 is at most 9 days.6.Forecast skill of the stratospheric annular mode tends to be improved for winter seasons when the variability of the stratospheric annular mode becomes large.