The Qinghai-Xizang (Tibet) Plateau has a profound influence on atmospheric circulation patterns on all time and space scales. This report constitutes a short summary of work being performed at the Lanzhou Institute of Plateau Atmospheric Physics of the Academia Sinica. A short discussion of the climatic characteristics of the plateau is followed by a description of the main features of annual and diurnal cycles in pressure and circulation patterns.
The southeastern Tibetan Plateau is one of the predominant summer rainfall regions in the world and is also the crucial water vapor channel of the Asian summer monsoon. The rainfall variability in the region influences not only the local communities but also downstream communities in East Asia. However, previous studies have exhibited large rainfall biases in this region in state‐of‐the‐art climate models. Understanding the observed rainfall variability provides an opportunity to identify the origin of model biases and to lay a foundation for improving model performance. In this study, the interannual variability of the summer precipitation (May–September) over the southeastern Tibetan Plateau was investigated based on National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis monthly mean data from 1979 to 2010. The associated atmospheric circulation anomalies of the southeastern Tibetan Plateau summer precipitation (SET_PR) display a North Atlantic Ocean‐Europe‐Asia teleconnection pattern, indicating a possible role of the Atlantic climate in the SET_PR. Further studies have revealed that the Atlantic sea surface temperature (SST) anomalies have the greatest influence on the SET_PR via the Rossby wave response, whereas the SST anomalies in the Indo‐Pacific have less of an influence on the SET_PR because their main impacts are confined to the western North Pacific subtropical high and the monsoonal circulation there. This paper also documents the detailed spatial pattern of the atmospheric circulation anomalies associated with the SET_PR and Atlantic SST year‐to‐year variability.
In this study, the relationship between the East Asian winter monsoon (EAWM) and the Arctic oscillation (AO) and El Niño southern oscillation (ENSO) are reanalysed using long‐term reanalysis data. The AO and ENSO influence the EAWM by means of a significant inter‐decadal oscillation with a periodicity of approximately 60 years. When the linkage between the AO and EAWM is strengthened (weakened), the ENSO has a weakened (strengthened) relationship with the EAWM. The AO and ENSO alternately affect the EAWM for approximately 30 years. Furthermore, an analysis is completed regarding the possible mechanism of the inter‐decadal relationship between the EAWM and ENSO, as well as the AO. Such an inter‐decadal relationship could be due to the phase transition of the Pacific multi‐decadal oscillation (PMO). When the PMO is positive, sea surface temperatures (SSTs) in the Bering Strait and Alaska Current region are warmer than average, which results in a decrease in the East Asian trough and an increase in the Aleutian low and northeastern Pacific vertical wave activity flux. In this case, the vertical wave activity flux propagates upward and is reflected in the polar vortex, which significantly strengthens the relationship between the Asia‐Pacific climate and AO. Simultaneously, during the positive phase of the PMO, the increase in the SST in the eastern South Pacific is stronger than in the west, which leads to a weakening of the east–west temperature gradient and southern oscillation. Thus, the relationship between the ENSO and Asia‐Pacific region is significantly weakened and vice versa. The results of this study deepen the understanding of the Asia‐Pacific climate and may improve the inter‐decadal prediction of the Asia‐Pacific regional climate in the future.
The El Niño‐Southern Oscillation (ENSO) has an intimate relationship with Asian summer monsoon precipitation. Previous study pointed out that the most recent 2015–2016 El Niño event is tied with the 1997–1998 and 1982–1983 El Niño events as the strongest event since 1950, which may result in catastrophe in Asian monsoon region. Therefore, in this article, we mainly focus on the anomalous precipitation pattern in the Pan‐Asian monsoon region during MJJ 2016 and its impact factors. Results show that the summer precipitation anomalies display a meridional tripole pattern from north to south in the Pan‐Asian monsoon region during 2016. This pattern indicates that the anomalous increased rainfall is located over the middle–lower reaches of the Yangtze River valley–East China Sea (ECS) and the tropical eastern Indian Ocean–western Maritime Continent, while the anomalous decreased rainfall is located over the South China Sea (SCS)–Philippine Sea. Results suggest that the preceding winter and spring ENSO and the simultaneous summer Maritime Continent sea surface temperature (SST) are the primary impact factors of the pattern of tripole precipitation anomalies in the Pan‐Asian monsoon region during MJJ 2016. The preceding ENSO can intensify the western North Pacific subtropical high (WPSH), which results in the anomalous decrease in precipitation over the Indo‐China Peninsula–Philippine Sea. Meanwhile, more moisture is transported from the northwestern flank of WPSH to the Yangtze River valley–ESC to increase rainfall. In the ENSO decaying summer, the Maritime Continent SST anomalous warming induces an anomalous convergence in situ, which increases the local precipitation. Later, this warming can intensify the WPSH through the local meridional circulation. The north Indian Ocean SST, including Arabian Sea and Bay of Bengal, also has a high relationship with tripole precipitation pattern, but it cannot induce this tripole rainfall pattern, which establishes the linkage through the extending WPSH.
Twenty‐one climate models from Coupled Model Intercomparison Project Phase 3 (CMIP3) and thirty‐one models from the project's Phase 5 (CMIP5) were used to evaluate model reproducibility in assessing interannual variability of summer precipitation in Pan‐Asian monsoon region. The results show that both the multi‐model ensemble means of the best eight models and of the thirty‐one CMIP5 models are more skilful than those of the CMIP3 models in simulating the climatological pattern and the dominant mode of summer precipitation in Pan‐Asian monsoon region. CMIP5 models show improved skill in representing the main characteristic of the first mode of summer precipitation in Pan‐Asian monsoon region, which is a meridional tripole pattern from north to south occurring east of the 80°E region. That is, owing to the improved El Niño–Southern Oscillation (ENSO) pattern and the relationship between Antarctic oscillation in the southern Pacific Ocean (AAOSP) and ENSO, the first dominant mode of summer precipitation in Pan‐Asian monsoon region are captured by CMIP5 models, which indicates that these models are more skilful in simulating the air–sea interaction of the Southern Hemisphere.
The Shangri-La County of the Yunnan Province, SW China, is an economically and ecologically important area. This is especially true for Jiantang that is famous for the Napahai, Bitahai and Shudu Lake wetlands. However, continuing development has threatened the wetland ecosystems and the associated biodiversity in these areas. To better document such changes in land use and their effect on the ecosystem, land use was mapped using a time series of satellite images acquired in 1974, 1993, 2000 and 2012. The results of this survey suggest that forest cover first decreased and then increased. The most obvious changes occurred in cultivated and developed land types, each expanding 1.6× and 17.6×, respectively. Population growth, and previous large-scale deforestation, converting cropland to forest and grassland project, and tourism development were the main socio-economic driving forces. It was also apparent that the rapid development of the tourism industry played a key role in the land-use change, especially after 2000. These data suggest that some regulation to the region's tourism industry and implementation of a sustainable land management policy should be considered to ensure preservation of the Jiantang wetlands.
Downloaded by [113.183.67.87] at 21:25 21 June 2016The internal modes of the North Pacific can lead to climatic oscillations through ocean-atmosphere interactions and induce global climate responses. The best example is the Pacific Decadal Oscillation, but this fails to explain many climate phenomena. Here, another multidecadal variability over the North Pacific is described, found by analyzing reconstructed data covering the past 140 years. It is named the Pacific Multidecadal Oscillation (PMO), with anomalously high/low SSTs over the northeastern Pacific, and a quasi-60-year cycle. Related to this low-frequency variability of SST, the global mean temperature and precipitation present significant interdecadal differences. More importantly, the PMO index leads the global mean surface air temperature and SST by one to three years. The Arctic Oscillation pattern and atmospheric circulations are shown to change substantially with the transition of the PMO mode from positive to negative phases. This multidecadal oscillation improves the prospect for a long-term forecast of the global warming trend, since the PMO bears a remarkable relationship with global temperature. 研究表明北太平洋海洋内部模态能够通过海气相互作用导致气候系统振荡和全球气候 响应。最好的例子就是太平洋年代际振荡(PDO) ,但是以往的研究中发现很多气候年 代际变化现象用 PDO 没法给与很好的解释。本研究通过分析过去 140 年的资料发现北 太平洋区域另外一个多年代际振荡模态,并将其定义为太平洋多年代际振荡(以下简称 PMO) ,其表现为北太平洋白令海峡以南和阿拉斯加湾流区域海表面温度存在 60 年左 右周期的异常偏高或者异常偏低。随着海温这一低频振荡的发生,全球气温、降水都表 现出显著的年代际异常。更重要的是,PMO 超前全球气温 2-3 年和海温 3-7 年发生转 变。与此同时,北极涛动形态和大气环流随着 PMO 正负位相的转变也发生改变。由于 PMO 与全球温度有着很好的关系, 因此 PMO 的发现对全球变暖趋势长时间尺度预报的 改进有着重要作用。
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