Knowledge Resource Center for Ecological Environment in Arid Area
| 青藏高原地形气候效应的耦合模式模拟研究 | |
| 其他题名 | Simulation of the climatic effect of the Tibetan Plateau topography using a coupled general circulation model |
| 苏宝煌 | |
| 出版年 | 2018 |
| 学位类型 | 博士 |
| 导师 | 白艳 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 新生代（距今约65 Ma）以来，全球气候和环境发生了巨大变化。青藏高原隆升作为新生代最重大的地质构造事件之一，一直被认为是长时间尺度气候变化的重要驱动因素，研究青藏高原地形的气候效应是理解新生代气候演变历史及机制的关键环节。本文以研究青藏高原地形的气候效应作为研究主线，利用新一代通用地球系统模式（CESM），开展多组不同气候边界条件下青藏高原地形的海气耦合模式试验，集中探讨青藏高原地形对欧亚内陆干旱、热盐环流、热带气旋生成环境和潜在生成频率以及厄尔尼诺—南方涛动（ENSO）变率的影响。主要结论如下：1、揭示了青藏高原地形和海洋反馈影响欧亚内陆干旱的主要热力和动力过程。现代边界条件下有、无青藏高原试验结果显示，青藏高原地形造成欧亚大陆干旱和湿润区之间发生了显著转变，其中，欧亚大陆副热带干旱区面积总体减小，这主要源于扩展的干旱区小于增加的湿润区，这与亚洲地质记录定性一致，表明青藏高原地形在亚洲干旱—季风环境格局演化中扮演了重要角色。进一步研究揭示，青藏高原地形主要通过影响降水，而后依次通过改变相对湿度、近地面气温和风速等因子来引起欧亚干旱环境变化。对比耦合模式和大气环流模式试验显示，相对于青藏高原地形的直接气候作用，海洋反馈对干燥度变化的影响较弱。2、阐明了冷室和暖室边界条件下青藏高原地形对热盐环流影响的主要机制。在现代冷室气候背景下，随着青藏高原隆升，北大西洋和太平洋大气环流发生显著变化，一方面通过北大西洋水汽辐散增加使得海表净淡水通量减少，另一方面通过改变风驱动的海冰动力过程引起北大西洋海冰范围收缩，导致海—气交界面潜热和感热损失加强，两方面变化共同造成海水总密度通量增加，从而触发北大西洋经向翻转环流（AMOC）加强。与此同时，青藏高原地形引起亚洲及其西北太平洋边缘海的季风环流加强、与之相联系的降水和径流增加，导致北太平洋海表总密度通量减少，触发北太平洋经向翻转环流（PMOC）减弱。而后，AMOC增强和PMOC减弱进一步触发了海洋与大气间的正反馈过程，最终导致北半球最强的热盐环流下沉中心从北太平洋转移至北大西洋。在二氧化碳浓度增加的暖室气候背景下，青藏高原地形主要通过改变北太平洋和大西洋的大气环流来实现海盆间的淡水再分配，导致AMOC与PMOC间的跷跷板变化，而风驱动的海冰反馈过程则几乎消失。上述模拟结果与一些深海沉积记录所揭示的热盐环流在晚始新世—早渐新世发生变化的现象定性一致，暗示青藏高原隆升是构造尺度上热盐环流演化的关键因素。3、评估了青藏高原地形对热带气旋生成环境和气旋潜在生成指数的影响。在冷室气候条件下，青藏高原地形有利于西北太平洋热带气旋的生成，抑制北印度洋和中东太平洋热带气旋的生成。其中，大尺度热带气旋生成环境影响因子对前者的相对贡献由大到小依次为相对湿度、垂直风切变、低层涡度、潜在强度，而对后者的贡献由主到次为垂直风切变、潜在强度、相对湿度、低层涡度。与冷室气候情景相比，暖室气候背景下青藏高原地形的气候效应总体偏弱，使得北半球大尺度热带气旋生成环境因子和气旋生成潜势强度对青藏高原地形的响应幅度整体偏小。4、提出青藏高原地形直接影响ENSO变率并调制轨道驱动的ENSO变率。在现代气候条件下，青藏高原地形使得赤道太平洋信风加强且经向宽度变窄，导致太平洋纬向温度梯度加大，ENSO变率减小、周期变短且分布不规则。在改变了轨道参数的间冰期边界条件下，青藏高原地形和轨道强迫的联合调制作用使得ENSO变率减小，而无青藏高原地形时轨道强迫导致ENSO变率增加，表明ENSO变率对轨道强迫引起入射太阳辐射量变化的响应依赖于青藏高原地形边界条件，这对于古ENSO研究具有借鉴意义。 |
| 英文摘要 | Global climate and environments have experienced a series of fundamental reorganization since the Cenozoic (~65 million years ago). As one of the most significant geological tectonic events during the Cenozoic, the Tibetan Plateau (TP) uplift has long been considered as an important driving force for the long-term climate change. Therefore, studying the climatic effect induced by the TP topography is crucial to understand the history and mechanism of the climate change during the Cenozoic. To explore the potential linkage between the Cenozoic climate changes and the TP uplift, we performed several sets of numerical experiments with and without TP under different boundary conditions by adopting a fully coupled atmosphere–ocean model namely, the Community Earth System Model. Special attention has been given to the response of the Eurasian inland drought, the thermohaline circulation, tropical cyclone genesis environment and potential genesis frequency, and the El Ni?o–Southern Oscillation (ENSO) variability to the TP topography. The main conclusions are summarized as follows.(1) The thermal and dynamical processes for the impact of the TP topography and oceanic feedback on the formation of dryness in Eurasia inland are revealed. Numerical experiments with and without TP under modern boundary conditions demonstrate that the TP topography causes a significant transition between the arid and humid regions over the Eurasian continent and leads to an overall decrease in the subtropical arid areas due to the expanded arid areas being less than the increased wet areas. The above results agree qualitatively with several lines of geological evidence, implying that the TP uplift plays an important role in the formation of the Asian paleoenvironmental patterns. In addition, a quantitative diagnostic analysis based on the aridity index indicates that the TP topography affects the Eurasian inland drought primarily through precipitation and then the relative humidity, the near-surface air temperature, and the near-surface wind speed. Comparisons between the coupled and atmospheric model experiments show that, relative to the direct effect of the TP topography, the influence of oceanic feedback on the formation of the Eurasian arid environment is weak.(2) The main mechanisms responsible for the changes of the thermohaline circulation in response to the TP uplift under both the cold-house and hot-house boundary conditions are illustrated. Under the cold-house boundary conditions, the atmospheric circulation over the North Atlantic and the Pacific Ocean has undergone a significant modification accompanying with the TP uplift. On one hand, the sea surface net freshwater flux decreases due to the anomalous water vapor divergence; on the other hand, the latent and sensible heat loss increases because of the shrinkage of sea-ice coverage in association with the weakened wind-driven sea-ice dynamical process over the North Atlantic; both of them cause an initial intensification of the North Atlantic meridional overturning circulation (AMOC). Meanwhile, the TP topography induces the intensification of the East Asian monsoon circulation and associated freshwater flux and runoff over the marginal seas of Asia and the northwestern Pacific, which gives rise to the initial slowdown of the Pacific meridional overturning circulation (PMOC). Then, both the strengthening of the AMOC and weakening of the PMOC could further trigger the positive ocean–atmosphere feedback processes, which eventually lead to the switch of the deep water formation location from the North Pacific to Atlantic. Under the hot-house boundary conditions with increased atmospheric carbon dioxide concentrations, however, the TP topography modulates this seesaw changes between the AMOC and PMOC primarily through altering the atmospheric circulation over the North Pacific and the Atlantic to redistribute the freshwater flux between the two basins, while the role of the wind-driven sea-ice feedback processes almost disappears. These results imply that the uplift of the TP could have been a potential driver for the reorganization of the PMOC–AMOC between the Late Eocene and Early Oligocene, as was evidenced by many geologic records.(3) The impact of the TP topography on the large-scale tropical cyclone formation environment and tropical cyclone genesis potential index (GPI) are investigated. Under the cold-house boundary conditions, the TP topography is conducive to the increase of the GPI in the northwestern Pacific, while it is not beneficial to the tropical cyclone genesis in the northern Indian Ocean and the Middle-East Pacific. Among the large-scale environmental factors contributing to the former changes, the relative humidity is the most important, which is followed successively by vertical wind shear, low-level vorticity, and potential intensity; the factors contributing to the latter changes, in order from high to low, are vertical wind shear, potential strength, relative humidity, and low-level vorticity. Compared to the cold-house boundary conditions, the climatic effects of the TP topography under the background of the hot-house boundary conditions are generally weaker, leading to an overall weakened magnitude of the response of large-scale environmental parameters in association with tropical cyclone formation and GPI in the Northern Hemisphere to the TP topography.(4) TP topography exerts a direct impact on the modern ENSO variability and modulates the orbitally induced ENSO variability. In the context of the modern boundary conditions and in response to the TP uplift, the equatorial Pacific trade winds are enhanced in intensity and narrowed in meridional width, which results in an increase in the zonal temperature gradient over the tropical Pacific Ocean and a decrease in the ENSO variability with a shorter period and a more irregular frequency spectrum distribution. Under the interglacial boundary conditions with the modification of orbital parameters, the orbital forcing induced ENSO variability decreases in the simulation with the topography of the TP, but increases in the simulation without the TP topography. This indicates that the responses of the ENSO variability to changes in the incoming solar radiation due to orbital forcing rely on the TP topography boundary conditions, which has important implications for the paleo-ENSO research communities. |
| 中文关键词 | 青藏高原 ; 亚洲内陆干旱 ; 热盐环流 ; 热带气旋 ; 厄尔尼诺—南方涛动 |
| 英文关键词 | Tibetan Plateau Asian inland drought Thermohaline circulation Tropical cyclone ENSO |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 气象学 |
| 来源机构 | 中国科学院大气物理研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/288065 |
| 推荐引用方式 GB/T 7714 | 苏宝煌. 青藏高原地形气候效应的耦合模式模拟研究[D]. 中国科学院大学,2018. |
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