| 摘要: |
| 众多古气候记录的分析表明：轨道尺度气候变化下我国北方地区的季风降水变化显著，该现象的理解对于深入认识东亚夏季风降水的长期演变模态具有重要意义。本文基于瞬变古气候模拟的分析发现：在轨道尺度气候变化下，东亚夏季风降水的变化中心位于季风区北边界附近的半干旱区，是季风环流整体性演变及季风区北边界摆动的综合作用结果。东亚夏季风降水的轨道尺度演变模态与古气候记录的指示相一致，但与当前观测记录给出的以年际尺度变化为主的模态显著不同，说明东亚夏季风降水对气候变化的响应与气候变化的时间尺度有关。进一步的分析表明：轨道尺度气候变化下东亚夏季风北方降水的响应幅度取决于气候变化的驱动因素，其中轨道辐射的影响最为显著。 |
| 关键词: 东亚夏季风 北方季风降水 环流 北边界 轨道尺度 |
| DOI：10.7515/JEE222010 |
| CSTR：32259.14.JEE222010 |
| 分类号: |
| 基金项目:国家自然科学基金项目（41630527，41776017） |
| 英文基金项目:National Natural Science Foundation of China (41630527, 41776017) |
|
| Northern China dominating orbital-scale variation of East Asian summer monsoon rainfall |
|
CHENG Jun, ZHANG Jintong, LIU Yitao, TAN Liangcheng
|
|
1. School of Marine Sciences, Nanjing University of Information Science & Technology, Nanjing 210044, China
2. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
|
| Abstract: |
| Background, aim, and scope East Asian summer monsoon (EASM) is a dominant regional circulation system over East Asia, its intensity determines the local rainfall and ecosystem. Numerous paleoclimate records indicated a robust ecosystem and monsoon rainfall variations over northern China under orbital-scale climate variations, which is quite different with the modern observations. How to understand the robust orbital-scale variation of northern China monsoon rainfall is crucial to the identification of long-term variation mode of East Asian summer monsoon rainfall. Materials and methods Modern observation of rainfall used in this work is GPCP (Global Precipitation Climatology Project) version 2.3 with spatial resolution of 2.5°×2.5° from 1979 to 2021. Rainfall and wind component of JRA55 (Japanese 55-year Reanalysis) is also used here to identify their coherent mode under EASM variation. The paleoclimate simulation used here is TraCE, which is integrated with fully-coupled general circulation model of NCAR CCSM3 with T31 resolution (3.75°×3.75°) and forced with real external factors such as orbital insolation, greenhouse gases (CO2), ice sheet over the past 2.1 ka. The calculations of EASM component are all based on the summer mean (June to August). EASM circulation index is defined as the regional averaged meridional wind of 850 hPa over 110°—120°E, 27°—37°N. Northern China monsoon rainfall index is defined as the regional averaged summer rainfall over 100°—120°E, 37°—45°N. Northern boundary of EASM is defined as the latitude where 850 hPa meridional wind switching from southerly to northerly, whose result is similar with that defined by seasonal rainfall changes. EASM northern boundary index is defined as the averaged latitude within the longitude band of 110°—120°E. Results Paleoclimate simulation indicates the orbital-scale variation center of EASM rainfall locates at northern China, the result of stable coherent variation of entire EASM circulation and northern boundary, which is totally different with the modern observation. The entirely variation of EASM circulation is driven by the robust changes of adjacent land-ocean thermal contrast under orbital scale climate changes. Based on TraCE simulation, the relative contribution from each external forcing factor is different, orbital insolation dominated the past evolution of northern China monsoon rainfall since LGM. Discussion The proxy-based reconstruction of monsoon rainfall is crucial to understand the past evolutions of EASM, its scheme is traditionally derived from the observed pattern. The scale-depended responding patterns of EASM rainfall proposed here coincides with the geological records, and invokes the necessary notice to the paleomonsoon rainfall reconstruction. Furthermore, the responding pattern of EASM rainfall under orbital-scale climate changes is also related with the forcing factor of climate changes, orbital insolation is the key components among all forcing factors that dominated rainfall changes of EASM since LGM. In addition, the northern-China-centered rainfall changes of EASM is similar under solo forcing of CO2 changes since LGM, that proposes the long-term responding pattern of EASM rainfall under future stronger warming may center around northern China too. Conclusions Combining the proxy records and the model simulations, we propose that the long-term variation center of EASM rainfall locates around its northern boundary, which is significantly different from the result as shown in short-term-variation dominated observation. Recommendations and perspectives The scale-depended responding pattern of EASM rainfall variation is not only crucial to understand its modern and past changes, also is important to a better rainfall reconstruction with monsoon-related geological records. |
| Key words: EASM northern China monsoon rainfall circulation northern boundary orbital scale |
