Primary study on pattern of general circulation of atmosphere before uplift of the Tibetan Plateau in eastern Asia

The Tibetan Plateau is a key factor for the pattern of the general circulation of the atmosphere (GCA) in eastern Asia. The pattern of the GCA after the uplift of the plateau is well known, while the pattern of the GCA before the uplift of the plateau is lack of direct evidences. Based on the knowability of desert, a section recording wind directions across the Cretaceous northern hemisphere mid-low latitude desert belt is measured and the pattern of the GCA in the Cretaceous is revealed. The result shows that the eastern Asia was really controlled by the planetary circulation before the uplift of the plateau, i.e. westerlies in the north and northeast trades in the south. The convert belt between westerlies and trades had drifted northwards and southwards. The possibility of existence of paleo-monsoon is also dealt with and a possibly imposed paleo-monsoon is suggested.     

‘Thailand was a desert' during the mid‐Cretaceous: Equatorward shift of the subtropical high‐pressure belt indicated by eolian deposits (Phu Thok Formation) in the Khorat Basin,northeastern Thailand

The Tibetan Plateau is a key factor in controlling the present‐day climate and atmospheric circulation pattern in Asia. The pattern of atmospheric circulation after the uplift of the plateau is well known, whereas direct evidence is lacking regarding the nature of the circulation pattern prior to the uplift. The distribution of desert directly reflects the position of the subtropical high‐pressure belt, and the prevailing surface‐wind pattern recorded in desert deposits reveals the position of its divergence axis. Cretaceous eolian sandstone of the Phu Thok Formation is extensively exposed in the northern Khorat Basin, northeastern Thailand. We conducted a sedimentological study on this formation to reconstruct temporal changes in the latitude of the subtropical high‐pressure belt in low‐latitude Asia during the Cretaceous. Spatio‐temporal changes in the paleo‐wind directions recorded in the Phu Thok Formation reveal that the Khorat Basin mainly belonged to the northeast trade wind belt and subtropical high‐pressure belt was situated to the north of the Khorat Basin during the initial stages of deposition, shifted southward to immediately above the basin during the main phase of deposition, and then shifted northward again to the north of the basin during the final stages of deposition. The paleomagnetic polarity sequence obtained for the Phu Thok Formation comprises three zones of normal polarity and two of reversed polarity, correlating to chrons M1n to C34n of the geomagnetic polarity time scale. This result suggests that the Phu Thok Formation is mid‐Cretaceous in age (from c. 126 Ma to c. 99–93 Ma), similar to the age of eolian sandstone in the Sichuan Basin, southern China (the Jiaguan Formation). These results, in combination with paleo‐wind direction data, suggest the development of low‐latitude desert and an equatorward shift of the subtropical high‐pressure belt (relative to the present‐day) in Asia during the mid‐Cretaceous.     

A study of the atmospheric circulation between equator and 60oN during the winter and summer seasons

Summary The mean zonal and meridional wind components and the mean mass circulation in different latitudes are discussed in relation to previous studies. Divergence and vertical motion are calculated for various latitude belts. There is evidence for a strong tropical Hadley cell with a temperate latitude indirect circulation during the winter season. During summer, the northern Hadley cell is weaker and displaced poleward; a circulation in the opposite sense appears in equatorial latitudes.The regional patterns of divergence and vertical motion appear related particularly to the position of the subtropical high pressure cells. Subsidence and lower-layer divergence are characteristic of the eastern flanks of the subtropical anticyclones, while the opposite pattern prevails on its western flanks. These longitudinal contrasts appear particularly pronounced during the summer season. The three-dimensional flow pattern in the tropics is illustrated by selected trajectories for the winter and summer seasons.     

祁连山东北缘黄土磁组构记录的古风向重建

近年来,利用黄土磁化率各向异性/磁组构（AMS）研究古风向变化被广泛应用.在对祁连山东北缘厚755 m的中路黄土剖面岩石磁学和磁组构研究的基础上,恢复了该区14 Ma以来古风向变化序列.磁组构指示的古风向表明,在14～078 Ma期间,本区的地面主导风向为NW-SE;从078 Ma开始,地面主导风向逐渐向NE-SW过渡;至05 Ma时,该区地面主导风稳定为NE-SW向.对青藏高原隆升的研究显示,在12～08 Ma期间青藏高原发生过称为“昆黄运动”的大规模隆起.结合我们对主导风向变化驱动因子的分析表明,祁连山东北缘近地面主导风向的第一次转变很可能是同时期青藏高原构造强烈隆升对大气环流影响产生的环境后果.     

青藏高原春季积雪在南海夏季风爆发过程中的作用

本文应用欧洲中期预报中心（ECMWF,European Centre for Medium\|Range Weather Forecasts—ERA\|40）资料和美国国家环境预测中心和国家大气研究中心(NCEP/NCAR, National Centers for Environmental Prediction/National Center for Atmospheric Research)资料,研究了青藏高原雪深变化对南海夏季风爆发的影响和ENSO对青藏高原降雪的影响.结果表明：（1）ECMWF的雪深资料是可信的,可以用来研究青藏高原雪深变化对南海夏季风爆发的影响;（2）青藏高原的积雪异常影响到500 hPa以上的温度异常和印度洋与大陆间的气温对比,一方面使上层的南亚高压移动速度发生变化,另一方面也影响到低层大气的运动和东西向风异常,在青藏高原少雪年,东印度洋产生西风异常和一个气旋对,而在青藏高原多雪年,东印度洋产生东风异常和一个反气旋对;（3）ENSO与青藏高原春季积雪关系密切.东太平洋SST正异常时,东印度洋和南海气压偏高,从而导致该区海陆经向压强梯度增强和西风异常.另外,此时青藏高原北部气压偏高,北风偏强,副热带锋面增强,同时,印度洋的SST偏高,为青藏高原降雪提供了水汽保障,这些都有利于青藏高原的降雪.     

Teleconnection between the Indian summer monsoon onset and the Meiyu over the Yangtze River Valley

Based on the Indian and Chinese precipitation data and the NCEP-NCAR reanalysis circulation data, the relationship between the Indian summer monsoon (ISM) onset and the Meiyu over the Yangtze River Valley has been discussed by the methods of correlation analysis and composite analysis. The results show that the date of ISM onset over Kerala in the southwestern coast of the Indian Peninsula is about two weeks earlier than the beginning of the Meiyu over the Yangtze River Valley. After the outbreak of ISM, the teleconnection mode sets up from the western coast of India via the Bay of Bengal (BOB) to the Yangtze River Valley and southern Japan. It is different both in time and space from the telecon- nection mode which is from the northwest of India via the Tibetan Plateau to northern China. The for- mer mode is defined as the "south" teleconnection of the Asian summer monsoon, forming in the pe- riod of ISM onset; while the latter mode is called the "north" teleconnection, mainly occurring in the Asian monsoon culminant period. During the process of the "south" teleconnection’s formation, the Asian monsoon circulation has experienced a series of important changes: ISM onset, the northward movement of the south Asia high (SAH), the onset vortex occurrence, the eastward extension of the stronger tropical westerly belt, and the northeastward jump of the western Pacific subtropical high (WPSH), etc. Consequently, since ISM sets up over Kerala, the whole Asian continent is covered by the upper SAH after about two weeks, while in the mid- and lower troposphere, a strong wind belt forms from the Arabian Sea via the southern India, BOB and the South China Sea (SCS), then along the western flank of WPSH, to the Yangtze River Valley and southern Japan. With the northward moving of the subtropical jet streams, the upper westerly jet stream and the low level jet have been coupled ver- tically over east Asia, while the Yangtze River Valley happens to locate in the ascending motion area between the upper jet stream and the low level jet, i.e. right of the entrance of the upper jet stream and left of the low level jet. Such a structure of the vertical circulation can trigger the Meiyu onset over the Yangtze River Valley.     

一次切断低压诱发的暖区深对流与异常副热带锋及其平流层-对流层交换

采用Cloudsat/CPR云雷达,FY2C/TBB亮温,Aura/MLS大气成分等卫星遥感资料,结合ECMWF气象分析资料和HYSPLIT4轨迹模式,研究了2009年6月一次东亚切断低压的暖区深对流和异常副热带锋面的结构和演变.分析表明,由于低压切断前的旧槽背景,在低涡的近成熟期,内部冷、暖锋降水偏弱,边沿的高空副热带锋面异常发展到对流层底部,低空西南暖湿水汽在副热带锋前聚集,形成千公里长的暖区深对流降水带.随着该锋面的快速东移,副热带锋区进入原暖区雨带,锋区热力间接次级环流的强上升支,加强了锋下冷侧（原暖湿区）的深对流,但该锋面阻挡了来自暖侧的水汽补充,降水结束.该异常副热带锋区还发生了强烈的平流层-对流层相互交换,在高空急流出口区的下方,平流层1.5PVU等位涡线向下入侵可达5.5 km（约500 hPa）处,锋下向上的深对流注入可达10 km,在入侵-注入混合区,臭氧和水汽的散点图上出现了二者浓度双高和双低的特殊气团.     

一类西太平洋副热带高压双脊线过程维持机制初探

本文通过对1979~2005年5~10月发生在西太平洋地区的156个副热带高压双脊线过程进行统计分析,发现87.82%的双脊线过程的出现是因为南侧新生一脊线,而且有明显的“季节锁相”,即其发生频数在7月中旬至9月中旬有两个峰值.历年过程中最典型的“南生南存型”双脊线过程的合成分析表明该类双脊线过程形成、维持和消失与副高南侧外围东风波系统自东南向西北传播发展密切相关.500 hPa距平环流演变显示北侧脊线的减弱消失符合气候规律,东风波槽前的异常气旋仅影响副高北侧脊线位置;而东风波槽后的异常反气旋性环流有利于南侧脊线异常发展与维持,造成该类双脊线过程结束后副高异常偏南.进一步分析发现,东风波和西太平洋副热带高压的相互作用改变了副高区域垂直运动分布.这一方面改变了经向风的分布,使500 hPa副高南侧脊线区域地转涡度平流项发展;另一方面引起非绝热加热垂直分布不均匀,在两脊线之间诱生一异常气旋性环流,在南侧脊线区生成异常反气旋环流.因此,东风波与西太平洋副热带高压的相互作用可能会造成副高的不连续南退,这对副高预报有一定预示作用.     

地球自转与北半球中纬度地面温度的年代际关系及其可能物理过程分析

利用地球日长（LOD）资料和美国环境预报中心/国家大气研究中心（NCEP/NCAR）的气象要素资料,统计分析发现1962-2010年LOD的变化和北半球中纬度地面温度均存在明显的十年以上的波动周期.相关分析、合成分析等统计方法均检测到LOD与中纬度地面温度的显著负相关关系,当地球自转速率加快时,北半球中纬度地面增温;反之,中纬度地面降温.小波功率谱和交叉谱分析则确定二者的相互关系属于准20年周期尺度上的年代际变化联系,并且LOD的变化超前于地面温度的变化大概3~4年.平均而言,LOD的变化可带来中纬度地面温度0.2℃的降温（或增温）.通过对大气相对角动量、纬向风场、海平面气压场的年代际合成分析,揭示了LOD与地面温度的年代际联系形成的具体物理过程.当地球自转加速时,北半球高低纬度经向温差梯度减弱,热带地区向极地扩展,造成北半球中纬度地区地面增温;地球自转减速时段相反,经向温差梯度增强,热带地区向赤道收缩,中纬度地区地面降温.     

A magnetotelluric study of the Damara Belt in Namibia: 1. Regional scale conductivity anomalies

The Namibian margin is dominated by the late Proterozoic to early Cambrian fold belts of the Damara Orogen, which wrap around and separate the Congo and Kalahari Cratons. This mosaic of relatively ‘soft’ fold belts and ‘hard’ cratons apparently controlled the path for the opening of the South Atlantic in the early Cretaceous. The continents split along the coast-parallel fold belts of the Damara Orogen while the inland fold belt (Damara Belt) was effected by extension and widespread igneous intrusion but never developed to the rift stage. This paper is concerned with the interpretation of magnetotelluric (MT) data along a 200 km NW-SE profile across the Damara Belt in NW Namibia. The regional, two-dimensional electrical resistivity model and the induction vector data exhibit three distinctive zones: (i) a generally very resistive upper crust which is typical for the granites and metasediments of the Damara Belt, (ii) two subvertical conductors in upper to mid-crustal levels which correlate with major tectonic zone boundaries and (iii) a highly conductive middle to lower crust in the southern part of the profile. The geometry of the conductive structures could reflect a regional shear system in which upper crustal listric faults pass into a detachment zone in the middle crust. We interpret the high electrical conductivity in terms of graphite (or other forms of mineralization) enrichment along the shear planes. This zone of crustal weakness may have originated in Pre-Damara times and had probably experienced several episodes of crustal reactivation before the intrusion of basaltic dike swarms during the Cretaceous rifting and magmatism associated with the opening of the South Atlantic.     

蒙古-贝加尔裂谷区地壳应变场及其地球动力学涵义

蒙古-贝加尔地区是现今构造最活跃的大陆地区之一,其地壳构造运动及变形对我们理解大陆动力学问题具有重要的科学意义.基于融合的这一区域的GPS速度场,本文计算了该区应变率场和应变能变化率场.结果显示,蒙古褶皱带以南区域表现为NNE-SSW方向的压缩状态,主压应变率约为-2.0×10^-9/a,剪应变及面膨胀均较弱,表明蒙古褶皱带比较稳定.贝加尔裂谷整体处于拉张状态且伴有较强的剪应变和面膨胀,暗示可能有多种机制控制裂谷的张裂过程.蒙古高原西部有两条高应变率的构造带,结合深部存在地幔热柱等证据,我们认为这两条构造带及所围限的区域共同构成Amurian板块的西部边界—一条弥散变形的边界带.蒙古-贝加尔地区剪应变分布与0~40 km的地震活动性基本一致,表明该地区形变在地壳尺度耦合程度较高.地幔对流拖曳力场与主应变轴方向及应变率场的一致性表明,地幔对流可能是蒙古—贝加尔地区区域构造动力学过程主要控制因素之一.     

Relationship between equatorial pressure oscillations and tropical cyclones landing over China

With daily reanalysis data by NCEP/NCAR and data of tropical cyclones landing over China from 1949 to 2005, the variation of low-frequency oscillations of equatorial pressure and their relationship with tropical cyclones landing over China in the summer half of the years (June through October) are studied for the 57 years, using spectral analysis and correlation analysis. The results show that the summertime equatorial pressure is mainly of periodic oscillations of 5―7 days and 10―30 days and the interannual variation of the intensity of its quasi-biweekly oscillation is significantly positive correlation with the number of tropical cyclones landing over China. The quasi-biweekly oscillation is filtered from daily equatorial pressure in May―November over the 57 years with inverse wavelet transform and the probability for tropical cyclones landing on coastal China within four days before and after the oscillatory valleys of quasi-biweekly pressure at the equator is 59.7% and 73.0% for June to October and July to September respectively. The model of atmospheric circulation for quasi-biweekly oscillatory valleys of equatorial pressure in association with or without tropical cyclones landing over China in July―September is set up with the composite analysis method. When the valleys are associated with (without) landfall, zonal (meridional) circulation prevails in the mid and high latitudes of the Eastern Hemisphere, the high pressure ridge is weak (strong) near the Sea of Okhotsk, the westerly zone is northward (southward), the subtropical high is westward (eastward) in location and strong (weak) in intensity, the cross-equatorial flow is strong (weak) in southeast Asia, Southwest Monsoon is strong (weak) and stronger (weaker) while in the valleys of pressure, being favorable (unfavorable) for tropical cyclones landing over China. The atmospheric circulation model for oscillatory valleys of biweekly equatorial pressure in association with (without) tropical cyclones landing over China, which can reflect the difference of atmospheric circulation between them, is beneficial to medium-term forecasts of tropical cyclones landing over China.     

Quaternary Tectonic Deformation in Front Area of the Tianjingshan Fault Zone and Analysis of Its Genesis

Through detailed field mapping, the tectonic deformation in the front area of the Tianjingshan fault zone is discussed in this paper. The result shows that there are two Quaternary thrust (oblique) fault-fold belts, namely: the Miaoshan and Hongjianshan fault-fold belts, in the front area of the south wall's strike-slip movement of the Tianjingshan fault zone. The Hejiakouzi Quaternary anticline, which is a part of the Miaoshan fault-fold belt, is mainly discussed. It is pointed out that the fold began to grow in the middle part near Hejiakouzi in the mid-late stage of middle Pleistocene epoch and then gradually developed towards the ends in late Quaternary. Based on the Cenozoic structural features, the genesis of the Miaoshan and Hongjianshan fault-fold belts and the kinematic relation they bear with the Tianjingshan fault zone are analyzed.     

The westerly fluctuation and water vapor transport over the Qilian-Heihe valley

The westerly fluctuation and the atmospheric water vapor transport over the Qilian-Heihe valley are analyzed and the results show that, in the water vapor transport stream field from Jun to September, this valley is in the westerly stream and the water vapor comes from westerlies water transport via the Black Sea and the Caspian Sea. The net water vapor transport is less net import and different from most areas of the northwest China. The interannual changes in water vapor transport over the valley arise from the westerly fluctuation, and have a positive relationship to the interannual changes in westerly wind speed. The cold air actions from the Mongol low pressure are the primary system that controls the westerly water vapor transport. Its action chain is that, the Mongol low pressure is strengthened → the circulation meridionality will be increased → the cold air will move southwards → the westerly will be stronger → the wind convergence of direction and speed will be stronger → the water vapor convergence transport will be increased → the local water vapor content will be increased. The interannual changes in atmospheric water vapor transport over the valley rely mainly on the convergence transport, but the effect of advection transport is less. The interannual changes of strong or weak westerly affect mainly the convergence transport, and then make the atmospheric water vapor net transport increase or decrease over the Qilian-Heihe valley.     

张北地震地下流体异常场的研究

对比研究了张北M_S 6. 2和MS5. 6地震前地下流体异常时空演化特征。结合二次地震前的地震活动图像及其迁移规律, 二次地震所产生的地表宏观裂度与地震的震源机制解, 研究结果认为: 地下流体趋势异常空间分布受区域构造格局控制; 短期异常具有重复性, 可能受震源机制影响; 短期异常的强度、临震异常形态的差异性以及地震宏观破裂的差异性与地震强度和交替活动的构造有关; M_S 5. 6地震应为M_S 6. 2地震后该地区能量的进一步释放, 并且是NE向构造带与近EW向构造带交替活动的结果; 二次地震前的短期异常主要沿着近EW向张家口-渤海构造带分布, 可能说明近EW 向张家口-渤海构造带活动水平高于N E向山西构造带。     

The westerly fluctuation and water vapor transport over the Qilian-Heihe valley

The westerly fluctuation and the atmospheric water vapor transport over the Qilian-Heihe valley are analyzed and the results show that, in the water vapor transport stream field from Jun to September, this valley is in the westerly stream and the water vapor comes from westerlies water transport via the Black Sea and the Caspian Sea. The net water vapor transport is less net import and different from most areas of the northwest China. The interannual changes in water vapor transport over the valley arise from the westerly fluctuation, and have a positive relationship to the interannual changes in westerly wind speed. The cold air actions from the Mongol low pressure are the primary system that controls the westerly water vapor transport. Its action chain is that, the Mongol low pressure is strengthened → the circulation meridionality will be increased → the cold air will move southwards → the westerly will be stronger → the wind convergence of direction and speed will be stronger → the water vapor convergence transport will be increased → the local water vapor content will be increased. The interannual changes in atmospheric water vapor transport over the valley rely mainly on the convergence transport, but the effect of advection transport is less. The interannual changes of strong or weak westerly affect mainly the convergence transport, and then make the atmospheric water vapor net transport increase or decrease over the Qilian-Heihe valley.     

鄂尔多斯块体北缘中强以上地震活动特征分析

从阴山地震带6.0级以上地震周期性规律等角度,着重研究了该区域中强以上地震活动特征。阴山地震带6.0级以上强震自公元849年以来,具有百年尺度的周期性特征,1900年之后进入第五活跃期,且当前应变处于较高状态,未来几年内该地震带发生6级以上地震可能性较大。临河—乌海—巴彦浩特地区是7.0级地震的主体空区。ML5.0以上地震具有以东经110°为轴东西对跳特征,东经110°以西地区是新一轮中等以上地震活动的主体区域。1970年以来,发生的6次5.9级以上地震前,均存在ML4.0级以上地震空区或条带。2000年1月1日至2011年9月30日,阴山地震带逐渐形成两条明显的ML4.0级以上地震条带,条带交汇部位所在临河—乌海地区可能是未来发生强震的区域。     

长江中游砂山沉积物磁组构特征及其指示的古风场

本文通过对新发现的江西九江新港砂山剖面沉积物磁化率各向异性测量和磁化率椭球体主轴的统计分析,揭示了该风成砂剖面磁组构参数在不同层位的变化特征,获得了古风向特征及其演变规律.(1)整个时期内该区的主导风向为NW-SE和NNW-SSE向,但在不同时期风向和风力强度又有所不同,变化最为剧烈的时期是砂2层,风向发生了根本性的改变,由原来的NW-SE为主,变为NE-SW向为主,且该阶段沉积环境相对比较稳定;(2)砂2、砂5、砂6层具有较大P、F、L和较小的q值,说明在其形成时气候最为寒冷,冬季风的风力最强、风速比较稳定,这与野外观察到的在这几层中大型板状斜层理发育,砂层粒度较粗,黏土含量较少的结果一致;(3)晚更新世末期长江中游的风成沙丘广泛发育,表明该时段是长江中下游地区气候最干冷、风力作用最强的时期,有着与北方沙漠—黄土区相类似的气候环境;(4)研究表明,AMS主轴的等面积赤平投影法和玫瑰花图,可以用来分析古风向的变化规律,是一种简易有效的方法.     

前冬南半球环状模对春季华南降水的影响及其机理

利用相关、合成、奇异值分解等统计诊断和数值模拟方法,分析了前冬(12—2月)南半球环状模(SAM)对春季(3—5月)中国华南降水的可能影响及其机理.诊断分析的结果表明,前冬南半球环状模与春季华南降水存在显著的负相关关系,也即前冬SAM偏强(弱),对应春季华南降水偏少(多).为了探讨这种南半球中高纬信号影响滞后一个季节的华南降水的物理机制,需要考虑下垫面海洋的桥梁作用.诊断分析的结果表明,当前冬SAM偏强时,南半球中高纬海洋的潜热释放受到海表风速影响发生变化,导致30°S—45°S海温偏高, 45°S—70°S海温偏低,并且异常的海温信号可以持续到次年春季.这种前冬SAM偏强时的春季海温异常信号,对应着春季西北太平洋副热带高压位置偏东且强度偏弱,西北太平洋上盛行异常气旋式环流,华南地区上空对流层低层有异常东北风和风场辐散,西南水汽输送较常年减弱,为春季降水偏少提供了有利的条件.前冬SAM偏弱时,南半球中高纬的海温异常及其引起的华南区域大气环流异常相反,有利于华南降水偏多.利用CAM3进行海温敏感性试验,也证明了上述南半球中高纬海温异常对应的环流异常.模拟结果表明,SAM偏强时的海温异常,对应着华南上空对流层低层的东北风异常、风场辐散、以及下沉运动,不利于华南降水生成;SAM偏弱时的海温异常,对应的环流异常相反,有利于华南降水增多,验证了资料诊断的结论.综上,在前冬SAM影响春季华南降水的过程中,体现了海气耦合桥的作用,即:海洋储存了冬季SAM的异常信号并在春季释放,通过影响春季大气环流,进一步影响华南春季降水.因此,前冬SAM为华南春季降水预测提供了一个有意义的前期信号.