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| 蒙古高原地形对亚洲季风气候影响的模拟研究 | |
| 其他题名 | Numerical simulation of the topographic effect of the Mongolian Plateau on Asian monsoon climate |
| 沙莹莹 | |
| 出版年 | 2016 |
| 学位类型 | 博士 |
| 导师 | 安芷生 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 气象观测和数值模拟研究均表明，青藏高原大地形对现代亚洲季风—干旱气候系统的形成有显著的加强作用，甚至会影响到全球尺度的气候变化。因此，青藏高原气候效应一直是气候动力学领域的热点问题。由于青藏高原规模巨大，大多数理论研究都重点关注高原主体地形的影响，青藏高原主体被认为是引发构造尺度亚洲气候形成演化的主要因素。然而，除青藏高原大地形外，中小尺度地形对季风对流活动中心、爆发时间以及内陆干旱形势也可能有重要作用，而不仅仅影响局地气候变化。蒙古高原位于青藏高原东北部，面积约为2500×700 km，平均海拔高度1500-2000 m，其水平尺度和高度均远小于青藏高原主体。作为地处北半球西风带核心区的中尺度山脉地形，对对流层低层西风具有非常明显的阻碍作用，这种强迫绕流效应对亚洲气候的可能影响目前尚不清楚。基于此，本研究聚焦于蒙古高原小地形，重点评估其对亚洲季风气候的可能影响。首先利用现代再分析资料简要分析蒙古高原区域的绕流状况及其与下游东亚气候变化的联系。然后通过大气环流模式有无地形的数值试验，深入评估蒙古高原地形对亚洲季风气候系统的影响，并与青藏高原大地形进行对比，在此基础上探讨蒙古高原气候效应的物理机制。最后建立耦合海气模式的对比试验，分析高原地形对海表温度的影响以及海表温度对气候的反馈作用。本论文的主要结论如下：\n（1）蒙古高原冬季的纬向风绕流在高原西南侧为东风而西北部、北部和东部均为西风，经向风绕流分量在蒙古高原西北部为南风而高原东部以及东亚地区为北风。高原东部40°-50°N，110°-125°E为西北风绕流的高值区。蒙古高原东部绕流指数与冬季东亚地区低层气温以及降水的相关关系表现为：东亚地区气温和降水与高原东部的纬向风绕流指数为负相关，而与经向风绕流指数为正相关。相关关系表明，蒙古高原东部的西北风绕流越强，则东亚地区冬季温度越低、降水越少，反映了东亚冬季气候与蒙古地区绕流的密切关系。\n（2）模拟试验表明，蒙古高原对西伯利亚高压的形成和加强至关重要。蒙古高原的出现使冬季亚洲地区的大陆性高压位置明显北移。除西伯利亚高压外，位于北太平洋的阿留申低压也得到加强。蒙古高原对东亚冬季风的加强有重要贡献，冬季时加强的偏北风从东亚较高纬度一直延伸至东亚南部沿海，东亚地区对流层低层温度也显著降低。东亚冬季风的加强同时受青藏高原的影响，但蒙古高原的作用更加显著。夏季时，蒙古高原对亚洲40°N以北地区贡献较大，使蒙古高原东部地区出现偏东风异常且降水增多。亚洲夏季风和干旱区的加强受青藏高原和蒙古高原的共同影响，但青藏高原的作用更大。\n（3）蒙古高原对东亚冬季风的显著加强与其地形的动力绕流密切相关。冬季强的西风气流在经过蒙古高原时产生沿地形走向的流动。在高原西侧表现为偏南风绕流而高原东侧为偏北风绕流。偏南风将低纬暖空气带到较高纬度使局地温度升高加强平均脊，而高原下游的偏北风将高纬度干冷空气带到东亚地区使东亚大槽加深，同时东亚地区温度显著降低。这种温度平流引起的温度变化还影响影响大气准定常行星波的槽脊结构和强度。中高层长波槽脊的加强反过来使大气低层的西伯利亚高压和阿留申低压加强，东亚冬季风也进一步加强。\n（4）青藏和蒙古高原的出现使海表温度发生了显著的变化。冬季时北太平洋中高纬度地区以及东亚沿海海域海表温度降低，而热带西太平洋和印度洋海温升高。太平洋海表温度变化受青藏和蒙古高原的共同影响但印度洋主要受青藏高原的影响。夏季海温变化幅度小于冬季。北太平洋高纬度海域以及阿拉伯海的海表温度降低而整个太平洋西部和孟加拉湾海温升高。\n（5）考虑海洋反馈作用后，蒙古高原对东亚冬季风的加强作用仍占主导地位。冬季海洋的反馈作用比较弱，海表温度的变化使蒙古高原对东亚冬季风的加强作用有所减弱，表现为负反馈作用，但并不显著。夏季亚洲夏季风和内陆干旱的加强主要受青藏高原的影响，海洋起正反馈作用。海洋反馈使蒙古高原对亚洲夏季风的加强作用有所提高，但作用较小，其主要表现在对40°N以北局地降水增加和偏东风异常的正反馈作用上。 |
| 英文摘要 | The Tibetan Plateau (TP) is widely recognized to have significantly influenced the formation of the modern monsoon-arid climate over Asia, and even global climate change, by meteorological observations and numerical simulations. Due to the huge size, most studies are mainly focused on the climate effect of the main TP, and the uplift of the main TP is often linked to the evolution of Asian climate on the tectonic scale. However, the meso- and small-scale mountains around the main TP may also play a potential role on the Asian climate. The Mongolia Plateau (MP), which is located to the northeast of the main TP, is much lower and smaller, with an area of 2500 × 700 km and averaged altitude of 1500-2000 m. As a meso-scale topography located in the core zone of the Northern Hemisphere westerly wind belt, it strongly blocks the westerly wind in the lower troposphere. However, the effect of such forced bypassing flows on Asian climate gets little attention so far. Thus, in this study, we focused on the topography of the Mongolian plateau and evaluated its possible influence on the Asian monsoon climate. The reanalysis data was first used to calculate the spatial-temporal structure of modern bypassing flows around the Mongolian Plateau and its relationship with the climate variation over East Asia. Then the numerical experiments with/without mountains were conducted to analyze the topographic effect of the MP on Asian monsoon climate in details. The relative contributions between the MP and the main TP were analyzed and compared. Finally, coupled ocean-atmosphere model experiments were conducted in order to examine the response of sea surface temperature (SST) to the topography and also its feedback on climate. The main results are summarized as follows:\n(1) The bypassing zonal wind in winter is easterly to the southwestern MP and westerly over the northwestern, northern and eastern MP. The bypassing meridional wind is southerly wind to the western MP and intense northerly to the eastern MP. The region of 40°-50°N，110°-125°E to the eastern MP is characterized with strong northwesterly bypassing flows. The low-level East Asian temperature and precipitation in winter are negatively correlated with the zonal bypassing flow index while positively correlated with the meridional bypassing flow index to the eastern MP. When the northwesterly bypassing flows get stronger, it becomes colder and drier over East Asia, indicating the close relationship between the East Asian climate in winter and the MP-induced bypassing flows. \n(2) Numerical simulations show that the MP is essential to the formation and strengthening of the Siberian High (SiH). The continental high pressure system in winter moves remarkably to higher latitudes with the appearace of the MP. Besides the SiH, the Aleutian Low (AlL) is also intensified. The MP significantly contributes to the intensification of the East Asian winter monsoon. The strengthened northerly wind blowing from higher latitudes extends to the southern coast of East Asia. The air temperature at lower troposphere over the whole East Asia also decreases significantly in winter. The intensification of the East Asian winter monsoon is ascribed to both the TP and MP, but the effect of the MP is more significant. In summer, the MP strengthens the precipitation and brings easterly wind to the regions north of 40°N in Asia. The increase in the Asian summer monsoon and aridity is mainly resulted from the TP.\n(3) The MP-induced strengthening of the East Asian winter monsoon is closely related to its bypassing flows around the topography. Acting as a mechanical barrier to the westerly flows in winter, the MP blocks the westerly so that the westerly wind turns northward over the upwind region and then turns back to the south over the downwind region. The induced southerly wind over upwind region brings warm air to northwest MP and intensifies the mean Asian ridge. The northerly wind anomaly over downwind regions brings cold air to east MP and thus deepens the East Asian trough. Therefore, the changed thermal structure significantly modifies the upper-level quasi-stationary planetary wave pattern. The upper level wave changes can then intensify the SiH, AlL and the East Asian winter monsoon.\n (4) The SST changes significantly with the uplift of the TP and MP. The temperature over the middle-, high-latitudes of the North Pacific and the eastern coast of Asia is reduced in winter. But the SST over the tropical West Pacific and Indian Ocean is slightly increased. The SST anomalies over the North and West Pacific are contributed both to the TP and MP while the warm of the Indian Ocean is linked to the TP. The amplitude of the SST change in summer is lower than in winter. With the TP and MP, the high-latitudes of the North Pacific and the Arabian Sea are colder in summer while the West Pacific and the Bay of Bengal are warmer.\n (5) When considering the SST feedback to the plateau-induced climate response, the MP still plays a dominant role to the East Asian winter monsoon. The effect of the SST in winter is weak. It slightly reduces the MP-caused strengthening of the East Asian winter monsoon, but the decrease is not significant. The SST feedback intensifies the-TP induced strengthening of the Asian summer monsoon and inland aridity. The SST feedback to the MP-induced climate change in summer is mainly over the local regions north of the 40°N in Asia, where the precipitation is increased and the easterly wind becomes stronger. |
| 中文关键词 | 亚洲季风 ; 蒙古高原 ; 青藏高原 ; 绕流 ; 数值模拟 |
| 英文关键词 | Asian monsoon Mongolian Plateau Tibetan Plateau bypassing flow numerical modeling |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 环境科学 |
| 来源机构 | 中国科学院地球环境研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287667 |
| 推荐引用方式 GB/T 7714 | 沙莹莹. 蒙古高原地形对亚洲季风气候影响的模拟研究[D]. 中国科学院大学,2016. |
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