海温主模态对我国北方季风区初夏和盛夏旱涝影响的不稳定性研究

The climate of monsoon region in North China (MRNC) is very complicated, which is mainly affected by the atmospheric circulation both in the tropical and the extra tropical regions for its special location – in the mid-high latitudes of East Asia and in the north edge of East Asian summer monsoon. And the forecasting skills of climate model are not as satisfactory as possible in the MRNC. So it is difficult to predict its climate there. Sea surface temperature anomalies (SSTA) are the main signals of climate prediction. But the globe warming has led to an inter-decadal change in the relationship between these signals and regional climate. This makes it harder to predict the climate in the MRNC. Thus, strengthen the study on the instability of the influence of the main SST modes on the summer drought and flood over the MRNC is helpful to improve climate prediction. But it's worth noting that there is an obvious seasonal variation of summer climate variability in the MRNC. So it is necessary to distinguish the early summer and late summer. Firstly, Based on the latest and complete observational data and climate model data, this project will study the multi-time-scale and multi-space-scale change characteristics of the early- and late- summer precipitation over the MRNC under globe warming. Then the analysis will be performed on the seasonal feature and the instability of the relationship between the different time-scale precipitation over MRNC and the main SST modes. And we will focus on the reasons and mechanisms of the instability of the inter-annual relationship. Finally, a new prediction model for the prediction of the different time-scale of the early- and late- summer precipitation over MRNC will be built based on the combination of the dynamics methods and the statistics methods，which may be helpful for the short-term climate prediction of the summer drought and flood over the MRNC.

我国北方季风区受热带、副热带及中高纬气候系统的综合影响，气候复杂性和预测难度较大，模式预测技巧也较低。海温等下垫面异常是气候预测的主要信号，但气候变暖导致了这些信号与区域气候之间年际关系发生了年代际变化，进而加大了预测的难度。因此，加强海温主模态对我国北方季风区夏季降水影响的不稳定性研究，有助于提高气候预测的理论和预测水平。我国北方季风区夏季气候变率季节内差异突出，必需区别初夏和盛夏。本项目利用最新的、完整的历史资料和数值模式结果，分别研究北方季风区初夏和盛夏降水的型态及其时、空尺度在全球变暖背景下的变化特征，在此基础上，利用数理诊断方法和动力模式技术相结合的途径，重点揭示不同尺度降水与海温主模态之间关系的季节特征、不稳定性及其物理机制，深化我国北方季风区降水变异成因和变化的科学认识，进而针对北方季风区分别构建初夏和盛夏不同尺度降水的动力统计预测模型，为提高短期气候预测准确率提供科学依据。

我国北方季风区夏季旱涝异常成因复杂，动力模式和业务发布的夏季降水预测技巧均较低。因此，有必要加强北方季风区夏季降水异常机理及预测方法研究。本项目以海温主模态对北方季风区夏季旱涝影响机理和预测方法为主要目标，四年来开展了以下工作：一、全球变暖背景下北方季风区夏季降水时空变化特征；二、海温主模态对北方季风区夏季降水的影响、不稳定性及其物理机制；三、评估模式技巧，有针对性地构建夏季降水的预测模型。该项目的研究成果为我国北方季风区夏季降水预测研究提供新视角、新途径。围绕预期的研究目标，项目发表学术论文24篇，其中SCI收录10篇。研究发现华北雨季开始早晚与春、夏季热带印度洋、赤道中东太平洋海温关系显著且稳定，当热带中东太平洋和热带印度洋暖异常时，东亚夏季风偏弱，华北雨季开始偏晚；20世纪70年代以来，华北盛夏降水与赤道东太平洋海温年际关系显著增强；东北夏季降水具有季节内、年际和年代际变化等多时间尺度特征，初夏和盛夏降水的年际、年代际变化规律存在明显的差异，二者年际变化相互独立，而年代际变化趋势相反，形成条件也存在明显差异；20世纪60年代初期开始，东北盛夏降水与春季热带印度洋海温存在稳定的显著正相关；三大洋冬春季海温演变是东北盛夏降水年际变率的主要驱动因子，构建海温驱动经验预测模型，预测技巧显著高于五个国内外先进气候模式和集合预测结果；利用时间尺度分离方法，结合CFSv2模式的多变量预测信号，构建了东北盛夏降水的动力-统计预测模型。将项目的研究成果，应用于2020-2022年的全国汛期预测，连续三年准确地预测了华北雨季开始时间和雨量异常特征、及东北地区夏季降水异常，取得了良好的预测效果，为提高我国防灾减灾能力提供了技术支撑。相关研究成果获得中国气象局3项气象科技成果登记。其中“基于动力统计相结合的中国汛期降水多模式集合预测新理论与新方法”被评为十三五以来气象科技成果“优秀”等级。