基于平流层大气质量环流的北半球中纬度地区冬季地面气温次季节尺度预测方法研究

Cold air outbreak (CAO) events are the most frequently occurring severe weather phenomena for Northern Hemisphere (NH) mid-latitudes in winter. Improving the predictability of CAOs at sub-seasonal range can increase our chance to plan ahead and devise an optimal strategy to minimize the adverse impacts of CAOs on the socioeconomic well being of the modern society. The sub-seasonal forecast skill sources for winter temperature include the dominant sub-seasonal variability in the tropics and the comparatively low frequency signals at the sea surface and land surface, and in the stratosphere. However, neither of them is perfect in providing the timing and spatial information of individual CAOs. For instance, the low frequency signals can only indicate monthly or seasonal mean temperature. Thus, new forecast skill sources at sub-seasonal range are needed. Recently, the PI and her colleagues put forward a prototype hybrid (dynamical-statistical) paradigm for sub-seasonal forecasts of continental-scale CAOs in the mid-latitudes based on the 2-week variability of the stratospheric meridional mass circulation in the extratropics. In the proposed work, a systematic evaluation of the sub-seasonal predictability of all kinds of key features of stratospheric mass circulation will be conducted and systematic error correction schemes will be designed to strengthen the dynamical component. Meanwhile, the statistical relationship of the stratospheric mass circulation variability with the temporal-spatial variations of surface air temperature in mid-latitudes as well as the underlying mechanism will be investigated in order to refine the statistical component of the prototype paradigm. Finally, an operational hybrid model for real-time sub-seasonal forecasts of wintertime surface air temperature in NH mid-latitudes will be built, which is expected to open up a new opportunity to sub-seasonal forecasts of surface air temperature.

寒潮及其伴随的极端低温是北半球中纬地区冬季最为频繁、影响范围最广的天气气候灾害。丰富其次季节尺度预报因子、提高其次季节尺度预测水平对防灾减灾工作的决策部署具有重要意义和显著价值。目前，地面气温次季节尺度预测的技巧来源主要包括热带季节内振荡模态以及海表、地表和平流层的缓变信号，但均存在一定局限（如：缓变信号只能用于时段平均气温的预测）。申请人近期研究提出了利用平流层大气质量输送快信号（主导周期为2周）的次季节尺度可预测性、通过动力－统计相结合的方法对逐个寒潮事件进行次季节预测的可能。项目拟从理论研究和应用实践两方面，系统考查平流层大气质量环流关键特征的次季节尺度可预测性，深入研究平流层大气质量环流变率与北半球冬季气温的可能联系及其物理机制，旨在建立以平流层大气质量环流变率为基础、以北半球中纬地区冬季低温灾害次季节尺度预测为目标的动力－统计预测模型，为气温的次季节尺度预测提供新思路和新方法。

寒潮及其伴随的极端低温是北半球中纬地区冬季最为频繁、影响范围最广的天气气候灾害。丰富其次季节尺度预报因子、提高其次季节尺度预测水平对防灾减灾工作的决策部署具有重要意义和显著价值。然而在当前气象预报业务中，次季节预测是“无缝隙预报”的难点。目前地面气温次季节尺度预测的技巧来源主要包括热带季节内振荡模态以及海表、地表和平流层的缓变信号，但均存在一定局限（如：缓变信号只能用于时段平均气温的预测）。申请人近期研究提出了利用平流层大气质量输送快信号的次季节尺度可预测性、通过动力－统计相结合的方法对逐个寒潮事件进行次季节预测的可能。..本项目从理论研究和应用实践两方面，系统考查平流层大气质量环流关键特征的次季节尺度可预测性，深入研究平流层大气质量环流变率与北半球冬季气温的可能联系及其物理机制，旨在建立以平流层大气质量环流变率为基础、以北半球中纬地区冬季低温灾害次季节尺度预测为目标的动力－统计预测模型。主要成果有：（1）通过平流层爆发性增温、平流层大气质量环流关键指数次季节尺度预测的多模式评估，证明了平流层快变信号具有延伸期可预报性；（2）基于全球等熵大气质量环流框架揭示了北半球冬季平流层大气质量环流与中纬度地区地面气温次季节尺度变化的联系及其复杂多样性，并揭示了其可能机制；同时也厘清了平流层极涡不同尺度变率（北半球环状模、爆发性增温、平流层大气质量环流）的物理联系；（3）成功搭建以平流层大气质量环流变率为基础、以北半球中纬地区冬季低温灾害次季节尺度预测为目标的预测模型，建设了实时预报平台，开展了北半球中纬度地区冬季地面气温次季节尺度预测试验（amccao.com），对大陆尺度低温异常事件预测效果良好，大部分事件可提前20-30天预测准确。..本项目的顺利完成为提高北半球冬季寒潮低温事件的次季节预测水平提供了新的思路和途径，同时在学术上，为深化平流层变化机理和向下影响研究，做出了贡献。