Influence of Icelandic Low pressure on winter precipitation variability over northern part of Indo-Pak Region

Several studies demonstrate that North Atlantic Oscillation (NAO) has dominant influence on the variability of climate over Southwest Asia. We deconstruct the NAO into its two components, the Azores High and the Icelandic Low. Regional circulations are influenced by changes not only in the pressure but also the positions of the Azores High and the Icelandic Low. The results presented in this paper exhibit that significantly great portions of interannual variance of winter precipitation over Indo-Pak Region (consists of Northeast Pakistan and Northwest India) can be explained by including the contributions of the Icelandic Low pressure in addition to ENSO and AO. This contribution also explains the physical mechanisms to establish the relationships between the COA and regional climate by examining composite maps of large-scale circulation fields using NCEP/NCAR reanalysis data.     

中更新世全球最大冰期与中国沙漠扩张

位于青藏高原和西北干旱区交界带的沙沟黄土剖面, 详细记录了0.8 Ma BP以来东亚季风系统和沙漠演化的历史. L6黄土层中, 中值粒径和砂粒含量表明当时冬季风极端强盛, 沙漠大规模扩张, 其范围仅次于末次冰期最盛期. 在0.6～0.7 Ma BP以前(即深海氧同位素MIS16阶段), 北半球高纬度大陆冰盖大规模扩展, 全球冰量达到最大, 并且西伯利亚冰盖的扩展, 还使得西伯利亚高压增强; 同时, 青藏高原上也发育了最大规模的冰川, 从而强化了西风和东亚冬季风. 其结果造成了中国季风边缘区的沙漠扩张. 虽然全球冰量和青藏高原是影响沙漠演化的重要因素, 但在不同的时段其机制可能有所不同, 也不能忽略其它因素的影响.     

青藏高原地面辐射对中国东部夏季降水影响的数值试验

利用CAM5模式设计敏感性试验,研究了中国东部夏季降水对青藏高原地面辐射异常变化的响应和可能的物理机制。试验结果表明：当高原北部、中部等区域夏季地面辐射减小,中国东部夏季降水整体上增多,但南部、东部沿海区域降水异常减少。青藏高原地面辐射的变化,对青藏高压、西太平洋副热带高压和季风等天气系统具有一定影响,进而影响中国东部地区的夏季降水。当青藏高原地面辐射减小,青藏高压中心位置偏西,强度减弱;东亚季风和南亚季风强度增大,中国东部大部分地区850 hPa风场强度增强;西太平洋副热带高压位置偏东,强度减弱,中国南部、东部沿海区域夏季降水受其影响而减少,但华中、华北、东北等地夏季降水整体上增多。故中国东部夏季降水异常变化与青藏高原地面辐射之间具有显著的相关关系。     

http://www.sciencedirect.com/science/article/pii/S167498711400036X

Global warming and climate change is one of the most extensively researched and discussed topical issues affecting the environment.Although there are enough historical evidence to support the theory that climate change is a natural phenomenon,many research scientists are widely in agreement that the increase in temperature in the 20 th century is anthropologically related.The associated effects are the variability of rainfall and cyclonic patterns that are being observed globally.In Southeast Asia the link between global warming and the seasonal atmospheric flow during the monsoon seasons shows varying degree of fuzziness.This study investigates the impact of climate change on the seasonality of monsoon Asia and its effect on the variability of monsoon rainfall in Southeast Asia.The comparison of decadal variation of precipitation and temperature anomalies before the 1970 s found general increases which were mostly varying.But beyond the 1970 s,global precipitation anomalous showed increases that almost corresponded with increases in global temperature anomalies for the same period.There are frequent changes and a shift westward of the Indian summer monsoon.Although precipitation is observed to be 70%below normal levels,in some areas the topography affects the intensity of rainfall.These shifting phenomenon of other monsoon season in the region are impacting on the variability of rainfall and the onset of monsoons in Southeast Asia and is predicted to delay for 15 days the onset of the monsoon in the future.The variability of monsoon rainfall in the SEA region is observed to be decadal and the frequency and intensity of intermittent flooding of some areas during the monsoon season have serious consequences on the human,financial,infrastructure and food security of the region.     

全球大气季节内振荡对长江流域持续暴雨影响的研究进展

在引证论述大气季节内振荡(ISO)对暴雨(强降水)重要作用的基础上,概括性地回顾影响长江流域持续暴雨的大气ISO基本特征及其形成机制的主要成果。重点针对全球热带内外不同时间尺度的大气ISO的空间变化和年际变化与长江流域持续暴雨之间联系的研究工作进行总结评述,较为完整地总结长江流域夏季降水季节内变化的气候特征和全球不同空间和时间尺度的ISO对东亚副热带地区持续暴雨影响的已有认识,并结合2个半球的ISO与长江流域持续暴雨关系的研究现状,对未来暴雨(强降水)与不同时尺度ISO相互作用及其在10～30 d延伸期预报中的应用中有价值的科学问题和研究热点进行探讨,以期强调南半球ISO变化在全球和东亚副热带气候系统中的重要地位,提高夏季长江流域持续暴雨10～30 d延伸期预报和旱涝气候预测准确率。     

Estimation of shortening between the Siberian and Indian Plates since the Early Cretaceous

A comparative study of the amount of latitudinal shift of the Siberian Plate, the Lhasa Block, the Himalayan Block and the Indian Plate using palaeomagnetic data shows that the Himalayan Block belongs to the Indian Plate. The Neo-Tethys Ocean, which separated the Himalayan and Lhasa Blocks, opened to its greatest width of 31.9° in latitude in the Early Cretaceous. The extent of shortening of the latitudinal distance between the Siberian and Indian Plates amounts to 58.2° since the Early Cretaceous. It was found that after the determination of the greatest width of Neo-Tethys Ocean, the latitudinal shortening of the crust between the Indian and Siberian Plates reached 26.3°, or about 2760 km. On the basis of the palaeomagnetic data obtained from the Qaidam Block, the latitudinal shortening between the Himalayan and Qaidam Blocks reached 50.2° since the Early Cretaceous. It was concluded that over the past 50 Ma, since the Early Cretaceous, the latitudinal shift of the southern blocks or plates was larger than that of the northern ones, and that shortening between the Qaidam and Himalayan blocks was greater than the shortening between the Qaidam Block and the Siberian Plate. This differential latitudinal movement is the main cause of convergence, resulting in the compression and uplift of the Qinghai–Tibetan Plateau.     

第四纪时期东亚季风变化的动力机制

本文作者主张：古气候演化的动力机制研究应从动力因子和动力过程两个方面人手。通过对比东亚冬季风、夏季风、印度季风及全球冰量变化的时间特征和频率特征,我们得到以下认识：1）大致在过去0.8Ma这个时段,东亚冬、夏季风基本上具同相位、同周期的互为消长演化特征;2）东南季风演化具0.1Ma的主导周期,而印度季风变化则以较短周期为主;3）东亚冬、夏季风与全球冰量变化在时间范畴上可作很好的对比,尤其是这三者均含有主导性的0.1Ma周期。在此基础上,本文提出东亚季风演化的“全球冰量驱动模式”,并初步讨论了东亚季风变化对全球冰量变化响应的动力过程。     

青藏高原南部冰芯记录与大气环流的关系*

通过念青唐古拉峰拉弄冰川垭口处(30°24'30″N, 90°34'12″E;海拔5850m)长度为29.5m的冰芯记录,恢复了1952~1998年间大气降水δD和净积累量的时间变化序列。上述两组序列与NCEP/NCAR气候资料的相关分析表明:δD和净积累量与中亚冬季的气压、南亚和青藏高原冬季、夏季的位势高度关系密切。中亚地区冬季气压的升高以及冬、夏季南亚和青藏高原位势高度的异常增强了印度夏季风,导致了念青唐古拉峰地区20世纪80年代以来降水量的增多和降水中δD值的降低。根据念青唐古拉冰芯δD和净积累量记录及其与亚洲地区大气环流的关系,可以通过青藏高原南部较长的冰芯记录来恢复过去该地区大气环流变化的历史。     

Resource potential of one of Earth's final remaining frontiers: the Siberian Platform

The Siberian Platform, covering a vast area of East Siberia (Russian Federation), represents one of the largest underexplored regions in Asia. Previous expeditions and regional surveys in the twentieth century, however, suggest that the Siberian Platform and adjacent orogenic belts hold significant potential for large undiscovered gold, copper, diamond and industrial mineral deposits, along with extensive oil and gas fields. The remoteness of the region, its inhospitable winter climate, and a major lack of modern infrastructure and mining methods have long hampered exploration in this area. These factors, along with the additional investment required and political uncertainties involved with operating in Russia, have deterred many international mining companies from considering the Siberian Platform as a viable region for exploration and mining. However, as mining industry paradigms change into a green, battery metals‐driven commodity sector, and modern mining methods are developed, increasing efficiency at a lower cost, the significant undiscovered mineral potential of the Siberian Platform could elevate the region to the forefront of mineral exploration and mining in the future.     

Linking moisture and near-surface wind with winter temperature to reveal the Holocene climate evolution in arid Xinjiang region of China

An increasing number of palaeo-climatic records have been reported to identify the Holocene climate history in the arid Xinjiang region of northwest China. However, few studies have fully considered the internal linkages within the regional climate system, which may limit our understanding of the forcing mechanisms of Holocene climate change in this region. Here, we systematically consider three major issues of the moisture/precipitation, temperature and near-surface wind relevant to the Holocene climate history of Xinjiang. First, despite there still has debated for the Holocene moisture evolution in this region, more climatic reconstructions from lake sediments, loess, sand-dunes and peats support a long-term regional wetting trend. Second, temperature records from ice cores, peats and stalagmites demonstrate a long-term winter warming trend during the Holocene in middle- to high-latitudes of Asia. Third, recent studies of aeolian sedimentary sequences reveal that the near-surface winds in winter gradually weakened during the Holocene, whereas the winter mid-latitude Westerlies strengthened in the Tienshan Mountains. Based on this evidence, in the arid Xinjiang region we propose an early to middle Holocene relatively cold and dry interval, with strong near-surface winds; and a warmer, wetter interval with weaker near-surface winds in the middle to late Holocene during winter. Additionally, we develop a conceptual model to explain the pattern of Holocene climate changes in this region. From the early to the late Holocene, the increasing atmospheric CO₂ content and winter insolation, and the shrinking of high-latitude continental ice-sheets, resulted in increasing winter temperatures in middle to high latitudes in the Northern Hemisphere. Subsequently, the increased winter temperature strengthened the winter mid-latitude Westerlies and weakened the Siberian high-pressure system, which caused an increase in winter precipitation and a decrease in near-surface wind strength. This scenario is strongly supported by evidence from geological records, climate simulation results, and modern reanalysis data. Our hypothesis highlights the important contribution of winter temperature in driving the Holocene climatic evolution of the arid Xinjiang region, and it implies that the socio-economic development and water resources security of this region will face serious challenges presented by the increasing winter temperature in the future.     

青藏高原陆表特征与中国夏季降水的关系研究

利用青藏高原72个站逐日积雪、冻土观测资料,AVHRR归一化植被指数（NDVI）和全国550个站逐日降水资料,分析了青藏高原陆表特征与中国夏季降水的关系。结果表明,我国夏季降水在华北和东北南部,长江中下游和华南地区降水空间一致性较好,相邻站点间降水变化趋势近似。华南、长江中下游和淮河降水呈增加趋势,其中长江中下游每10年增加37 mm,但华北降水呈减少趋势。华南、长江中下游和华北对高原积雪、冻土和植被的变化均较为敏感,而淮河仅对高原植被变化较为敏感。利用高原积雪、冻土和植被建立了代表高原地表特征的变化序列,其对长江中下游、淮河、华北夏季降水均有较好指示意义,与夏季降水的相关系数由南到北表现为"负-正-负"的分布特征。最后,提出一种高原陆表状况影响中国夏季降水的概念模型：高原冬春积雪偏多（少）、冬季冻土偏厚（薄）、春季植被偏多（少）会使得夏季高原地区土壤湿度偏大（小）,高原地表感热偏弱（强）,从而使得南亚高压和西太副高偏弱（强）,南海季风偏弱（强）,长江流域降水偏多（少）,华南和华北地区降水偏少（多）。     

A 500 yr speleothem-derived reconstruction of late autumn–winter precipitation, northeast Turkey

A verified instrumental calibration of annually resolved δ¹⁸O for a stalagmite from Gümü?hane in northeast Turkey is presented and cross-validated using a ‘leave-one-out’ technique. The amount of late autumn to winter precipitation is negatively correlated with stalagmite δ¹⁸O between AD 1938 and 2004. The observed relationship is extrapolated back to ~ AD 1500 leading to the first long winter precipitation reconstruction for this region. Modern day October to January precipitation is linked to pressure fields in Western Russia. Anomalously lower reconstructed rainfall is recorded in AD 1540–1560 at which time higher pressure over the Caspian Sea region is inferred.     

兴都库什山及伊朗高原抬升对南亚季风-中亚干旱气候演化影响的模拟研究

新生代以来青藏高原大地形及其周围边缘地形的构造抬升对亚洲气候演化有着深远而复杂的影响。目前的气候代用指标表明南亚季风的开始可以追溯到始新世, 随后在早中新世和晚中新世经历了显著的加强过程。同时, 构造地质证据表明兴都库什山脉和伊朗高原的隆升可能开始于10~12 Ma。兴都库什山脉和伊朗高原作为南亚季风和中亚干旱区之间的天然地理屏障, 其对南亚季风和中亚干旱区气候演化和分异是否有一定的影响, 目前尚未可知。本研究利用高分辨率的大气环流模式系统性评估了兴都库什山脉和伊朗高原对南亚和中亚气候的影响。结果表明, 兴都库什和伊朗高原对南亚季风的加强和中亚干旱区降水的抑制均有贡献。相较而言, 兴都库什山脉对南亚季风的加强和向北扩张起主导作用。兴都库什山脉引起的南亚夏季降水增量达到兴都库什和伊朗高原共同作用的65.6 %。兴都库什山脉抬升后, 南亚地区15° N以北, 尤其是印度半岛中部和西北部夏季降水均显著增加, 阿拉伯海对流层低层的西南风和印度西北部偏南风显著加强。伊朗高原对中亚干旱区的干旱化作用更强, 并以冬季变化为主导。伊朗高原引起的中亚地区冬季降水减少量占兴都库什和伊朗高原共同作用的71.4 %。伊朗高原抬升后, 中亚地区冬季的盛行西风显著减弱, 从而导致降水显著减少。本研究的数值模拟试验表明, 地质记录揭示的南亚季风在晚中新世的加强可能与兴都库什山脉和伊朗高原在该阶段的抬升密切相关。

     

全新世南亚高压南北移动及其与亚洲夏季风降水的关系

南亚高压是亚洲夏季风系统的重要组成部分,它的强度及位置变化对亚洲夏季风降水有非常重要的影响,对其变化特征和物理机制的研究可以加深对亚洲夏季风演化的认识。论文利用一个海-气耦合模式（KCM）,在轨道参数的强迫下模拟了全新世以来（9.5~0 ka B.P.）的气候变化,分析了全新世南亚高压的南北移动特征,并探讨其与亚洲夏季风降水的关系。研究发现,全新世以来南亚高压持续向南移动,同时也反映了对流层上层西风逐渐向南扩张,响应逐渐减少的夏季太阳辐射。早全新世南亚高压偏北主要是由于夏季太阳辐射增加导致伊朗高原感热加热加强。南亚高压的南北移动与亚洲夏季风降水有显著的关系,它与东亚季风区北部和印度季风区降水呈正相关关系,而与东亚季风区南部和西南季风区降水呈负相关关系。偏北的南亚高压在东亚北部上空产生异常反气旋,有利于对流层低层空气辐合上升,降水增加,此外异常反气旋还可以加强西太副高,使得输送到东亚北部的水汽增加。南亚高压偏北时还会在中低纬地区产生异常东风带,减弱了来自孟加拉湾的水汽输入,从而使得东亚南部和西南季风区降水减少。偏北的南亚高压还在阿拉伯海上空产生异常气旋,有利于印度夏季风降水的增加。南亚高压的南北振荡可以部分解释相同轨道强迫下亚洲夏季风降水出现显著空间差异的原因。

     

末次冰盛期和全新世中期东亚地区水汽输送的模拟研究

利用国际古气候模拟比较计划最新第3阶段中9个气候模式针对末次冰盛期、13个气候模式针对全新世中期的数值试验数据,集中研究了这两个时期东亚地区的水汽输送变化。结果表明,相对于工业革命前期,末次冰盛期东亚地区冬季异常水汽输送主要来自跨赤道气流和西北太平洋,东亚大陆沿岸及其临近海域为主要的水汽异常辐合区,对应冬季净降水量增加,异常辐散区主要位于热带海洋和西北太平洋,净降水量减少;夏季,东亚地区异常水汽输送通量以辐散为主,大部分地区净降水量减少,对应东亚夏季风减弱。全新世中期东亚地区冬季水汽输送变化较弱,东南部及临近海域和赤道中太平洋为异常辐散区,不利于冬季净降水;夏季异常水汽输送分别来自热带中西太平洋广阔洋面和西北太平洋异常反气旋式环流西南侧,东亚大陆大部分地区为水汽异常辐合区,夏季净降水量增加,对应东亚夏季风增强。两个时期外强迫驱动下的经向温度梯度、海陆热力对比和大气含水量变化是上述冬、夏季东亚水汽输送异常的主因。

     

东亚冬、夏古季风变化的相位差及热带太平洋在季风变化中的驱动作用

斋堂黄土剖面古气候记录表明：１)冬、夏季风在千年尺度上的变化存在相位差;２)冬、夏季风记录在变化趋势上具有互为消长的关系,而在变化幅度和频率方面则有明显的差异。这表明,冬、夏季风在千年尺度上的变化是分别由不同的因素和过程所控制。我们提出热带太平洋海气相互作用系统在东亚季风变化过程中起着直接的驱动作用。     

北极海冰对长江流域主汛期降雨的影响

针对极地冰雪显著影响中低纬气候的事实,利用1979-2017年长江流域116站降水资料和美国国家冰雪数据中心海冰资料,通过奇异值分解等统计学方法,研究北极海冰对长江流域主汛期降水的影响及可能的机制,结果表明:冬春季节,巴伦支海和鄂霍次克海海冰面积偏多、波佛特海海冰面积偏少时,主汛期长江上中游干流、汉江上游和雅砻江降水偏多;北极群岛、楚科奇海和拉普捷夫海以北海域海冰面积偏多时,主汛期两湖水系降水偏多,嘉陵江上游、汉江上游降水偏少;反之亦然。可能的机制为冬春季关键区海冰变化通过影响湍流热通量引发大气能量波动,这种波动以大气波列形式向东亚传播,影响东亚地区夏季的大气环流和水汽输送,从而间接影响长江流域主汛期降水。应用多元回归法,以关键区海冰面积作为预测因子建立4个流域内主汛期降水趋势预测模型,模型对预报区降水的定量预测有明显的波动,但对预报区总体的降水趋势有较好的预测效果。     

四川盆地降水日变化特征分析和个例模拟

利用台站观测降水资料,分析四川盆地及周边地区降水分布和日变化特征,得到以下结论:四川地区降水存在2个高值中心,均位于盆地周围的山地;盆地降水"夜雨"特征明显;川西高原降水峰值以午夜前降水量的贡献为主;盆中与盆地西南边缘山地的降水峰值由夜间降水量与降水频率共同作用;盆地东北边缘的山地是午前降水频率与后半夜的降水量均有贡献。其次,结合WRF模式的数值试验,对2008年9月23～24日发生在盆地的夜间暴雨过程进行模拟研究和综合分析。结果表明WRF模式较好地模拟了此次天气过程降水的空间分布和日变化规律,通过分析模拟的环流场与温湿场发现,夜雨的形成与大尺度环流场的影响和地形强迫关系密切。     

Dominant impact of South Asian low heat on summer monsoon rainfall over Central India

Although previous literature have considered Southern Oscillation Index (SOI), Indian Dipole, and SST as the major teleconnection patterns to explain the variability of summer monsoon rainfall over India. South Asia low pressure and Indian Ocean high are the centers of action that dominates atmospheric circulations in Indian continent. This paper examines the possible impact of South Asian low pressure distribution on the variability of summer monsoon rainfall of India using centers of action approach. Our analysis demonstrates that the explanation of summer monsoon rainfall variability over Central India is improved significantly if the SOI is replaced by South Asian low heat. This contribution also explains the physical mechanisms to establish the relationships between the South Asian low heat and regional climate by examining composite maps of large-scale circulation fields using NCEP/NCAR Reanalysis data.     

The relationship between the isotopic content of precipitation and the precipitation amount in tropical regions

General circulation models (GCMs) fitted with stable isotope schemes are widely used to interpret the isotope–climate relationship. However, previous studies have found that the spatiotemporal isotope/precipitation correlation simulated by GCMs is stronger and more widespread than the observed value. To understand the reason for this failure, we investigated the factors influencing the empirically well-known isotope/precipitation relationship, or precipitation amount effect, in the tropics using newly obtained daily precipitation isotope monitoring data over Asia. As in previous studies, we found an apparent correlation between the long-term monthly mean isotopic content and the corresponding precipitation amount (local precipitation) observed at sub-tropical island stations. Furthermore, on a monthly timescale, the isotopic variability of precipitation for these stations was more clearly related to the regional precipitation amount than to local precipitation. This correlation of isotopic content with the regional precipitation amount was observed at the equatorial (Maritime Continent) stations. For these stations, isotope/local precipitation relationships only appeared over longer timescales, with different regression line slopes at each station. However, at the coastal stations, there was a strong linear relationship between the monthly mean isotopic content and corresponding regional precipitation, and regression line slopes were spatially uniform. For the two sub-tropical terrestrial (Indochina Peninsula) stations, the isotopic minimum appeared without any relationship to rainfall amount but usually occurred at the leeward station during the rainy season. These results suggest that the isotopic variations of precipitation did not depend on the ’local’ rain-out history but on the rain-out process in the surrounding region. However, local rainfall events were associated not only with large-scale disturbances but also with regional circulation. Thus, the scale difference of controlling factors between local rainfall amount and isotopic value results in the weakening of the rainfall amount effect at the observation site and in the discrepancy between GCM simulations and observations. This finding suggests that regional precipitation–isotope relationships should be compared with GCM results. Additionally, because the isotope signal reflects the rain-out history at a regional scale, evaluation of the isotopic field using isotopic GCMs will be useful not only to reconstruct paleoclimate conditions but also to examine how GCMs can reproduce real atmospheric circulation over the tropics.