东亚-太平洋遥相关和欧亚遥相关对江淮持续性极端降水的影响机理

Existing studies on extreme precipitation paid more attention to intensity, frequency and climate change characteristics, with duration and mechanisms less focused. Atmospheric teleconnection can trigger long-lived circulation anomalies and further result in persistent weather anomalies. Accordingly, this study aims to reveal a key issue that on synoptic to sub-monthly scales, how the East Asia-Pacific teleconnection and Euro-Asia teleconnection induce persistent precipitation extremes (PPEs) in the Yangtze-Huai River Valley (YHRV). From the perspective of atmospheric energy budgets, influences of each teleconnection on key circulation systems and corresponding mechanisms for PPEs would be analyzed during the period dominated by each single teleconnection; teleconnection-induced precursors with lead time of 1-2 weeks would be traced, with much emphasis on their migrating routines and growth mechanism. Cases witnessing two joint teleconnections would also be identified to illustrate the interaction between these two teleconnections. Impacts of such interactions on the duration and intensity of PPEs are further highlighted by comparing with the situation of single teleconnection. Pertinent results would be of great help in deepening the understanding of mechanisms for PPEs in the YRV. Derived conclusions would lay a scientific foundation for improving forecasting accuracy of PPEs and lengthening forecasting lead time.

目前的极端降水研究重视强度、频次及气候变化特征，对持续时长和发生机理关注较少。大气遥相关能造成持久的大尺度环流异常进而引发持续性异常天气。鉴于此，本研究旨在揭示：在天气尺度-月内尺度上，东亚-太平洋遥相关和欧亚遥相关对江淮持续性极端降水的影响机理。基于大气能量学的诊断，分别讨论东亚-太平洋遥相关和欧亚遥相关独立维持时段内，遥相关对关键环流系统发展演变的影响和造成持续性极端降水的原因；揭示与各遥相关相联系的时效为1-2周的前兆环流信号的移动路径和发展过程。进一步分析两种遥相关共存的背景下，二者之间的相互作用过程；并与单一遥相关情形对比，阐明两遥相关相互作用对江淮持续性极端降水的强度和持续时间的影响。相应成果将有助于加深对江淮持续性极端降水发生机理的认识，为提高持续性极端降水的预报准确率和延长预报时效奠定科学基础。

目前关于极端降水的研究多关注强度及频次，对持续时长关注较少。极端降水的持续性与大气环流的持续异常有关，大气遥相关是造成持久的大尺度环流异常的重要的天气型。本研究旨在揭示在天气尺度-月内尺度上，东亚-太平洋遥相关和欧亚遥相关对江淮持续性极端降水的影响机理；提取与各遥相关相联系的时效为1-2周的前兆环流信号并描述其发展规律；进一步对比单一遥相关维持条件下和多种遥相关共存条件下，江淮持续性极端降水强度和持续时间的异同，并阐明其原因；.经过三年的研究，本项目：1）发展了单一遥相关和多遥相关影响下的持续性极端降水事件识别方法，建立了相应的事件库。2）揭示了不同遥相关配置影响江淮持续性极端降水的关键动力-热力过程，确认了东亚-太平洋遥相关是导致江淮持续性极端降水发生的直接因子，其他遥相关通过激发关键扰动并触发波流相互作用使得东亚太平洋遥相关维持时间更长，利于延长极端降水的持续时间；3）前兆环流信号时效大概为一周，这是由于东亚太平洋遥相关主要受到准双周振荡调制。准确刻画了各关键系统在该尺度上的发展、移动、维持和消亡规律及各阶段对极端降水的影响。.项目成果将为预报员提前研判此类高影响天气提供准确的、可用的预报着眼点。部分成果已被国家气象中心中长期预报科所采纳，结合神经网络方法，建立了一套基于历史相似度的针对持续性极端降水的预报方法，已投入业务试运行。大气遥相关-持续性极端降水的事件识别方案被国家气候中心采纳，用以建立相应的监测系统。