Knowledge Resource Center for Ecological Environment in Arid Area
| 东北亚气候过渡带夏季降水年际和年代际变化及其成因研究 | |
| 其他题名 | Interannual and interdecadal variation of summer rainfall over the climate transition zone of Northeast Asia and its possible causes |
| 朴金玲 | |
| 出版年 | 2018 |
| 学位类型 | 博士 |
| 导师 | 陈文 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 东北亚气候过渡带地处中高纬度之间，位于东亚季风区的北边缘位置。该地区主要被干旱和半干旱带所覆盖，包含多种多样的生态系统，包括森林，草原，农田和沙漠等。作为生态脆弱带和农牧业交错带，该地区对气候变化尤为敏感，复杂的气候变化可以对农业生产，经济和社会发展等造成深远的影响。由于该地区的年总降水量少，年际变率大，降水的变化可以显著影响生态系统的稳定性，如植被的覆盖面积，草原荒漠化和湖泊面积的收缩等。同时，作为影响干旱发展的重要因子之一，降水的持续减少还会使得干旱问题进一步发展，严重危害该地区的农牧业发展以及社会生活等。鉴于降水变化对该地区持续性发展的重要性，本文从年际和年代际的角度分析了降水的演变特征，包括相应的大气环流异常和水汽输送通道的改变等。主要的研究成果如下：（1）东北亚气候过渡带与西伯利亚水汽收支的对比分析：夏季东北亚气候过渡带和西伯利亚之间的降水变化呈现偶极子的模态，且主要与欧亚大陆上空的遥相关波列有关。由于水汽输送是影响降水的主要因子之一，因此对比分析了这两个地区的水汽收支状况。结果显示，在年循环的尺度上，蒸发对这两个地区降水的贡献最大。而在年际变化的尺度上，水汽辐合是影响降水变化的主导因子。基于水汽输送的重要性，进一步将其分解为与平均流有关的定常分量和与气旋活动有关的瞬变分量。在年循环的尺度上，定常和瞬变水汽输送共同主导这两个地区总的水汽收支。然而在年际变化的尺度上，定常水汽输送是影响总的水汽收支的主导因子，瞬变水汽输送的作用较小。边界水汽输送的分析显示，经向和纬向水汽输送联合控制总的定常水汽输送。而瞬变水汽输送主要依赖于西边界和南边界水汽输送，并且具有与定常分量相近的量级，这进一步表明了在年循环的尺度上，定常和瞬变水汽输送对总的水汽收支的重要性。此外，通过合成分析的方法，分别讨论了与东北亚气候过渡带和西伯利亚干湿年有关的定常和瞬变水汽输送环流。 （2）五月北大西洋涛动和后期夏季降水的关系：在年际变化的尺度上，夏季东北亚气候过渡带降水与前期五月的北大西洋涛动（NAO）显著相关。但是二者的关系并不稳定，在70年代末以前二者之间没有显著的关联，而在70年代末以后，二者的关系显著加强。对比研究发现，70年代末以前与五月NAO有关的大气环流异常局限在北大西洋区域，这种异常仅仅可以持续到六月份。而70年代末之后，与五月NAO有关的大气环流异常与典型的北极涛动（AO）的模态类似，并且该信号一直可以持续到七月份，从而影响到七月份的降水。进一步的研究发现，极地-欧亚大陆型（POL）是连结五月NAO与七月降水的重要桥梁。在70年代末以后，五月NAO与七月POL的关系显著加强，从而显著加强了与夏季降水的联系。至于五月NAO与七月POL关系的年代际加强，可能与70年代末北半球极涡的年代际收缩有关。（3）90年代末降水的年代际减少：东北亚气候过渡带的夏季降水在90年代末发生了一次明显的年代际减少，减少的降水量大概为气候态降水的18.2%。90年代末以后，地表温度和蒸散强度明显地增加，而土壤湿度异常降低。同时，植被覆盖率也表现为明显减弱的趋势。这些因子的异常变化，均反映了干旱问题的加剧。为了进一步验证干旱的发展，这里主要利用三种干旱指数（标准化降水指数，标准化的降水蒸散指数以及自校正的帕尔默干旱指数）来表征干旱的演变。结果显示，这三个干旱指数均在90年代末发生了明显的年代际减少，这说明90年代末伴随着降水的年代际变化，该地区的干旱问题也呈现进一步恶化的趋势。同时降水蒸散指数和降水指数的差异场显示，此次干旱的发展除了受到降水减少的影响之外，温度的升高也是影响因子之一。通过对比90年代末前后大气环流的异常，可发现此次降水的年代际变化主要与出现在欧亚大陆上空的遥相关波列有关，该波列从欧洲西部向东传播至东北亚地区。模式实验的结果表明，北大西洋海温的异常增暖可以触发该波列的产生，进而导致东北亚气候过渡带降水出现年代际的减少。（4）与90年代末降水年代际变化有关的水汽输送的分析： 90年代末以后，东北亚气候过渡带500百帕的垂直速度出现了明显的下沉运动，伴随着水汽辐散的加强，有利于降水出现年代际的减少。通过计算，在年代际的尺度上，降水与500百帕垂直运动以及水汽辐合均是显著相关的，通过了90%的信度检验。这表明，除了垂直运动的作用外，水汽辐合也是此次降水年代际减少的影响因子之一。进一步的分析显示，在90年代末以前，东北亚气候过渡带被异常的气旋性水汽输送环流控制，此时与西风带和东亚季风有关的水汽输送较强，将水汽从东北亚的西部和南部输送至东北亚气候过渡带，有利于水汽辐合；而90年代末以后，反气旋性的水汽输送环流出现在东北亚气候过渡带，这种情况下西风和西南风水汽输送明显减弱，导致东北亚气候过渡带出现异常的水汽辐散。此外，边界水汽输送的分析显示，在90年代末以前，经向水汽输送主导总的水汽收支的演变，而90年代末以后，纬向和经向水汽输送均是主要的影响因子。进一步的分析表明，与扰动风场有关的水汽输送分量主导了90年代末东北亚气候过渡带水汽输送环流的演变。 |
| 英文摘要 | The climate transition zone of Northeast Asia (CTNA) is located between the middle and the high latitudes, the marginal areas of the East Asian monsoon. It is mainly covered by arid and semi-arid climate zones, thus including diverse ecosystems such as forests, grasslands, farmlands and deserts. As an ecological fragile zone and agro-pastoral region, CTNA is very vulnerable to climate change. The complicated climate change can exert profound influence on agricultural production, animal husbandry, economic and social development. The annual total precipitation here is relatively low, but has a large interannual variability. The precipitation variation is significantly associated with the stability of the ecosystems, in regard to the vegetation cover, grassland desertification, the lake shrinkage and so on. On the other hand, as a key factor for the drought formation, the reduced precipitation can worsen the drought problem, seriously threatening the agricultural development and social life. Due to the importance of precipitation variation on the sustainable development of the Northeast Asia, this paper investigates the basic features of the precipitation change on interannual and inter-decadal scale, along with the responsible atmospheric circulation and water vapor transport. The main conclusions are listed as follows:1. The comparison of the moisture budget between CTNA and Siberia: In summer, there is a dipole pattern in summer precipitation between CTNA and Siberia, which is related to the teleconnection pattern over the Eurasian continent. As the water vapor transport is a key influencing factor for precipitation, it is further compared the moisture budget over the two regions. It shows that on annual scale, evaporation plays an important role on precipitation over the two regions. However, on interannual scale, moisture convergence contributes most to precipitation variation. Due to the importance of water vapor transport, it is further separated into two parts: the stationary component associated with the mean flow and the transient component related to the cyclone activities. On annual scale, the moisture budget over the two regions is subject to the combined effects of both the stationary and transient water vapor transport. On interannual scale, the stationary component is the dominant factor for the net moisture convergence, instead of the transient component. According to the analysis of boundary moisture transport, both the zonal and meridional water vapor transport play important roles on the net stationary moisture convergence. On the other hand, the transient moisture convergence mainly depends on the west and south boundary water vapor transport. The magnitude of the transient moisture convergence is close to that of the stationary one, further confirming the dominant roles of the stationary and transient components on the net moisture budget on annual scale. Besides, it is further investigated with the composite analysis the responsible stationary and transient moisture circulation for the wet and dry years over CTNA and Siberia. 2. The relationship between the North Atlantic Oscillation (NAO) in May and the early summer precipitation: On interannual time scale, there exists a significant relationship between the May NAO and summer precipitation over CTNA. However, this relationship is not stable, with weak correlation coefficients before the late 1970s, but strong and significant ones after the late 1970s. Before the late 1970s, the May NAO-related atmospheric circulation anomalies are confined to the North Atlantic, which can only persist into the following June. In contrast, after the late 1970s, the May NAO-related atmospheric circulations bear resemblance to the typical Arctic Oscillation (AO), and can continue through July, thus impacting the July precipitation over the Northeast Asia. Further analysis imply that the Polar/Eurasia pattern (POL) might be a contributing factor for bridging the May NAO and July precipitation. After the late 1970s, the connection between the May NAO and July POL strengthens sharply, leading to the strong May NAO-July precipitation relationship. Besides, the interdecadal contraction of the circumpolar vortex seems to contribute to the enhanced relationship between the May NAO and the July POL.3. The interdecadal decrease of summer rainfall in the late 1990s: The summer rainfall over CTNA experienced an interdecadal decrease around the late 1990s, with the reduced amount approaching 18.2% of the climatological mean. After the late 1990s, the surface air temperature and evapotranspiration increased significantly, with the decrease of the soil moisture. Besides, the vegetation cover also presents negative anomalies. The anomalies of these factors all reflect the development of the drought problem over CTNA. To further confirm the worsening drought condition here, three drought indices (the standardized precipitation index (SPI), the standardized precipitation evapotranspiration index (SPEI) and the self-calibrating Palmer drought severity index (sc-PDSI)) are employed to represent the drought evolution. The three indices all show interdecadal decrease in the late 1990s, which indicates that with the interdecadal decrease of summer rainfall, the drought condition over CTNA also underwent an interdecadal development. Besides, the differences between SPEI and SPI imply that the drought development is not only caused by the reduced precipitation, but also the rising temperature. By comparing the differences of atmospheric circulations between before and after the late 1990s, it is suggested that the interdecadal decrease of summer rainfall is mainly associated with the teleconnection over the Eurasian continent, which propagates from the West Europe to Northeast Asia. The model experiments imply that the warming sea surface temperature over the North Atlantic mighty excite the teleconnection pattern, thus leading to the interdecadal decrease of summer rainfall over CTNA. 4. The water vapor transport related to the interdecadal variation of summer rainfall around the late 1990s: After the late 1990s, the vertical velocity at 500hPa shows an anomalous downward movement, along with the strengthening of the moisture divergence, which is in favor of the rainfall decrease. By calculation, on interdecadal scale, precipitation is closely related to the vertical velocity at 500hPa and moisture convergence, which is significant at the 90% confidence level. This demonstrates that, the moisture convergence can exert influence on the interdecadal decrease of summer rainfall, in addition to the anomalous vertical movement. Further analysis show that, before the late 1990s, an anomalous cyclone moisture circulation covers CTNA. On this occasion, the water vapor transport related to the westerlies and East Asian monsoon gets stronger, bringing in water vapor from the western and southern parts of Northeast Asia, thus causing anomalous moisture convergence. After the late 1990s, an anomalous anticyclone moisture circulation appears over CTNA, with the weakening water vapor transport associated with the westerlies and East Asian monsoon, leading to anomalous moisture divergence. Besides, analysis on the boundary moisture transport indicate that, the meridional water vapor transport dominates the net moisture budget before the late 1990s, but the meridional together with zonal after the late 1990s. Besides, it is implied that the water vapor transport in association with the disturbance wind dominates the net moisture convergence variation after the late 1990s. |
| 中文关键词 | 东北亚气候过渡带 ; 水汽收支 ; 降水变化 ; 年际和年代际变化 |
| 英文关键词 | climate transition zone of Northeast Asia moisture budget precipitation change interannual and interdecadal variation |
| 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/2XILL650/288063 |
| 推荐引用方式 GB/T 7714 | 朴金玲. 东北亚气候过渡带夏季降水年际和年代际变化及其成因研究[D]. 中国科学院大学,2018. |
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