亚非夏季风区大气遥相关与青藏高原热源的相互作用

The position and intensity of Afro-Asian summer monsoon rainband motivate in-phase variations of large-scale drought and flood pattern. An in-depth understanding about variability of Afro-Asian summer monsoon rainband would benefit not only for our country but also for the entire Afro-Asia domain in help developing policy of disaster precautions and mitigations. Existing studies have placed primary emphasis on external forcing related to sea surface temperature anomalies on Afro-Asian monsoon precipitation, and it is now clear that the transition of Afro-Asian summer monsoon from inactive to active regime around 1995 was dynamically ascribed to an atmospheric teleconnection triggered by the Atlantic Multi-decadal Oscillation (AMO). However, as a key relay node along the propagating route of this teleconnection, the role of Tibetan Plateau and its impacts related to thermal anomalies on the maintenance and propagation of the teleconnection pattern remain unclear; meanwhile, whether and how the decadal to inter-decadal advance/retreat of the Afro-Asian summer monsoon rainband influenced observed warming and wetting tendency atop the Plateau warrants further explorations. To this end, based on dynamic theory for atmospheric teleconnections, this project will employ in-situ station observations, reanalysis and satellite observations to analyze spatiotemporal variations of Tibetan Plateau heat source, and reveal the interaction process between thermal anomalies of Tibetan Plateau and the AMO-triggered teleconnection with the Afro-Asian summer monsoon system. Relevant conclusions hold great promise to provide new clues for seasonal-to-decadal forecast of Afro-Asian summer monsoon rainband, and provide novel insights into the reason for observed warming-wetting tendency for climate above the Plateau.

亚非夏季风雨带的位置和强度异常使亚非季风区旱涝灾害呈现同步性。深入理解亚非夏季风雨带的变化规律，不仅为我国也为整个亚-非地区的防灾减灾提供科学支撑。现有研究多侧重于海洋热力异常强迫对亚非夏季风降水的影响，揭示了亚非夏季风在1995年后的由弱转强与北大西洋多年代际振荡（AMO）激发的大气遥相关传播有关。然而，青藏高原作为这支大气遥相关传播路径中的关键节点，其热力异常如何影响该遥相关的维持和传播进而调制亚非夏季风雨带的进退尚不明确；同时，亚非夏季风雨带的年代际进退是否对高原变暖变湿的特征起到重要贡献也亟待探索。鉴于此，本项目拟利用观测资料、再分析资料和卫星资料等，运用大气遥相关动力理论，分析高原热源时空变化特征，讨论并揭示高原热力异常与亚非夏季风区AMO-北半球大气遥相关在年代际尺度上的相互作用过程。相关结论将为亚非夏季风雨带的气候预测提供新的线索，为解释近十几年来高原的暖湿化倾向提供新视角。

青藏高原热力异常是影响区域和全球大气环流异常的主要驱动力之一。青藏高原作为亚非夏季风区大气遥相关路径中位于南亚和东亚子系统的关键节点，其热力异常对亚非夏季风区大气遥相关的影响，尚且关注较少。亚非夏季风增强是否对高原暖湿化起到影响作用也尚待解答。本研究旨在揭示青藏高原热源的时空变化特征及年代际变化等观测事实；在明确亚非夏季风区大气遥相关的传播路径的基础上，揭示在年代际时间尺度上，青藏高原热力强迫对亚非夏季风降水的关键大气遥相关型的影响；进一步分析亚非夏季风增强变化对青藏高原暖湿化的影响及成因；阐明亚非夏季风区大气遥相关与青藏高原热源的相互作用。.经过三年的研究，本项目：1）计算得到了近四十年青藏高原热源的时间序列；揭示了青藏高原夏季地表热源存在年代际和年际时间尺度上均存在高原东部与西部反相变化特征；高原西部地表感热通量指数表征出更为明显的年代际特征，高原东部地表潜热通量指数则表现出年际变化特征。2）明确了影响亚非夏季风年代际降水的AMO-北半球遥相关的传播路径，揭示了青藏高原热力强迫（高原西部地表感热）本身能激发对流层高层的气旋-反气旋波列，阐明了在年代际时间尺度上，高原西部地表感热与AMO反位相（同位相）变化对亚非夏季风区对流层高层AMO-北半球大气遥相关的传播起到了叠加（减弱）的影响。3）基于气候模式长期模拟实验数据评估了未来亚非夏季风的增强使得青藏高原气候向着更暖和更湿变化，并浅析了成因。.项目取得的成果加深了青藏高原热力强迫对北半球遥相关调制作用的认识，为理解全球大气遥相关与青藏高原热源的关系提供了新的着眼点。有助于认识青藏高原与亚非夏季风的相互影响，并为亚非夏季风雨带进退的预测提供新的视角。