青藏高原单点陆面过程模拟试验

利用青藏铁路北麓河试验2002年6月的大气资料作为陆面模式的强迫场, 研究陆面过程模式(NCAR/LSM)在高原地区的模拟能力. 模拟结果表明, 在观测资料的强迫下, NCAR/LSM能够较好地模拟出地表特征量的变化趋势. 在LSM模式中青藏高原地区的地表植被类型描述与实况存在较大差异, 根据实际地表特征, 我们定义北麓河地区草原植被覆盖度为0.6, 叶冠高度为0.15, 位移高度为0.10. 通过对比试验发现, 修正模式参数后, 模拟的地面气温和地表温度日变化更接近于观测值, 对温度峰值模拟有较好改善. 地面通量模拟也有一定改善. 所以, 修正LSM模式中高原地区的地表及植被描述参数, 可以有效地提高陆面过程模式在青藏高原地区的模拟性能.     

基于微波亮温及集合Kalman滤波的土壤湿度同化方案

基于集合Kalman滤波及SCE-UA(shuffled complex evolution)算法发展了能够直接同化微波亮温的土壤湿度同化方案. 该方案以陆面过程模式CLM 3.0中的土壤水模型作为预报算子, 以辐射传输模型作为观测算子. 整个同化过程分为参数优化和土壤湿度同化两个阶段, 利用SCE-UA算法优化辐射传输模型中难以确定的植被光学厚度参数和地表粗糙度参数, 并利用优化参数作为观测算子的模型参数进行同化. 通过人工理想试验表明该同化方案可以明显改善表层土壤湿度的模拟精度, 并且对深层土壤湿度的模拟也有一定程度的改善; 利用AMSR-E亮温(10.65 GHz垂直极化)所进行的实际同化试验表明顶层(0~10 cm)土壤湿度同化结果与观测的均方根误差(RMSE)由模拟的0.05052减小到0.03355, 相对减小了33.6%, 而较深层(10~50 cm)平均减小了20.9%. 这些同化试验显示该同化方案的合理性.     

基于卫星遥感资料的中国区域土壤湿度EnKF数据同化

土壤湿度在陆气相互作用过程中扮演着重要的角色,是气候、水文、农业、林业等研究中重要的地球物理参数之一.土壤湿度影响地面蒸散,径流、地表反射率、地表发射率以及地表感热和潜热通量,从而对气候有重要影响,它对大气的影响在全球尺度上仅次于海面温度,在陆地尺度其影响甚至超过海面温度.本文介绍了基于EnKF及陆面过程模型的中国区域陆面土壤湿度同化系统（CLSMDAS,China Land Soil Moisture Data Assimilation System）,以及该系统应用于中国区域陆面土壤湿度同化试验的结果.CLSMDAS包括以下几个部分：1）陆面模式采用美国国家大气研究中心NCAR的陆面过程模型Community Land Model Version3.0（简写为CLM3.0）;2）大气驱动场数据中的降水和地面入射太阳辐射数据来自FY2静止气象卫星每小时产品;3）陆面数据同化方法采用EnKF（Ensemble Kalman Filter）同化方法;4）观测数据包括AMSR-E卫星反演土壤湿度产品以及地面土壤湿度观测资料.利用CLSMDAS对2006年6~9月的土壤湿度同化试验结果的分析表明：陆面模式模拟和同化结果都能比较合理地反映出土壤湿度时空分布,同化的土壤湿度分布与2006年8月重庆、四川发生建国以来最严重的夏伏旱有非常好的对应关系,与发生在9月的湖北东部、广西南部等地的干旱区也有非常好的对应关系.     

基于集合四维变分方法PODEn4DVar的GRACE陆地水储量同化：方法与验证

地球重力场季节和年际变化主要来源于地球表层大气、海洋和陆地各系统间水的质量交换,由GRACE重力卫星探测地球重力场变化所反映陆地水储量的改变主要来自降雨、土壤蒸发蒸腾、河流输运以及向地下深层的渗透等过程．本研究利用陆面过程模式CLM3．5以及基于本征正交分解的集合四维变分同化方法PODEn4DVar,构建能够同化GRACE卫星重力场的陆面水文同化系统LDAS．G,实现对地球重力场所反映的大尺度陆地水储量变化在时间及垂直方向各分量的分解,并对垂直方向的水文变量进行同化,从而更好地估计陆面水循环要素变化并实现其监测．利用LDAS．G同化系统进行理想试验以及针对中国区域所进行的同化试验表明该同化系统能够改善对陆面水文要素变化的模拟,对大尺度陆面水文循环监测研究具有重要意义．     

沙漠陆面过程参数化与模拟

沙漠地区植被稀疏、干旱少雨,其陆面物理过程具有与全球其它地区显著不同的特点.本文利用巴丹吉林沙漠观测资料,分析和计算了地表反照率、比辐射率、粗糙度和土壤热容量、热传导系数等关键陆面过程参数,建立了适合于沙漠地区的陆面过程模式DLSM (Desert Land Surface Model),并与NOAH陆面过程模式的模拟结果和观测资料进行了比较.结果表明:巴丹吉林沙漠地表反照率为0.273,比辐射率为0.950,地表粗糙度为1.55×10-3 m,土壤热容量和热扩散系数分别为1.08×106 J·m-3·K-1和3.34×10-7 m2·s.辐射传输、感热输送和土壤热传导过程是影响沙漠地区地表能量平衡的主要物理过程.通过对这三种过程的准确模拟检验,DLSM能够较准确地模拟巴丹吉林沙漠地气能量交换特征;短波辐射、长波辐射和感热通量的模拟结果与观测值间的标准差分别为7.98,6.14,33.9 W·m-2,与NOAH陆面过程模式的7.98,7.72,46.6 W·m-2的结果接近.地表反照率是沙漠地区最重要的陆面过程参数,地表反照率增大5%,向上短波辐射通量随之增加5%,感热通量则减小2.8%.本文研究结果对丰富陆面过程参数化方案,改进全球陆面过程模式、气候模式具有参考意义.     

北京大学陆面过程模式PKULM(Peking University Land Model)介绍及检验

陆面过程模式是气候模式和天气模式的核心组成部分之一.在土壤-植被-大气耦合模式(Soil-Plant-Atmosphere Model, SPAM)的基础上,发展了新一代北京大学陆面过程模式PKULM(Peking University Land Model).本文首先介绍了PKULM的辐射传输、湍流输送、光合作用、土壤水热输送等过程的参数化方案;采用隐式迭代计算框架,发展并应用了一个快速的线性方程组求解算法,提高了模式计算稳定性;提出并使用了二分搜索算法计算气孔阻抗,避免了CLM(Community Land Model)等使用的迭代方法在干旱区不稳定的情况,提高了模式的适用性;采用水势为基础的土壤水分扩散方程,使模式能够模拟土壤饱和区的水分输送过程,为进一步与水文过程模式耦合奠定了基础;还发展了一个地表积水与径流过程的机理模型,提高了模式对地表水分平衡过程的模拟能力;最后,使用"中国西北干旱区陆-气相互作用观测试验"平凉站的资料对模式进行了检验并与NOAH(National Center for Environmental Prediction, Oregon State University, Air Force, and Hydrology Lab model)陆面过程模式的模拟结果进行了比较,结果表明PKULM能够较好地模拟西北半干旱区农田下垫面地气交换过程.     

同化站点观测和SSM／I亮温改善冻土活动层状态变量的模拟精度

以考虑了土壤冻融过程的一维水-热-盐分耦合模型SHAW为冻土活动层数据同化系统的动力学约束框架,通过集合卡尔曼滤波算法同化土壤水分和温度的站点观测数据以及被动微波辐射计SSM／I19GHz亮温观测数据,以改善冻土活动层水热状态变量的估计精度,实现模型模拟和观测信息的融合。冬季活动层冻结,同化的关键变量为土壤温度;而夏季同化的关键变量为土壤水分。通过单点同化试验表明,该同化系统能显著改善土壤表层水分和温度的估计精度;同时,在同化过程中给定合理的模型误差协方差项,可将表层优化后的信息迅速传递给深层土壤,达到改善整个土壤廓线状态变量估计的目的。同化结果表明,相对于SHAW模拟结果,同化4cm土壤温度观测后,各层土壤温度RMSE平均减小0.96℃,而同化4cm土壤水分观测数据后,各层土壤水分RMSE平均减小0.020m^3·m^-3;同化SSM／I 19GHz亮温后,各层土壤温度RMSE平均减小0.76℃,各层土壤水分RMSE平均减小0.018m^3·m^-3。     

一种求解贝叶斯模型平均的新方法

贝叶斯模型平均（Bayesian model averaging,BMA）是最近提出的一种用于多模式集合预报的统计方法.进行贝叶斯模型平均需要准确估算模型集合中每个竞争模型的权重与方差,经常采用的方法是期望最大化（Expectation-Maximization,EM）方法与马尔可夫链蒙特卡洛（Markov Chain Monte Carlo,MCMC）方法,两种方法各有优劣.本文首先对BMA的（对数）似然函数进行改进使之无需BMA权重之和为1的显式约束,并利用一种有限记忆的拟牛顿优化算法（LBFGS-B）对其进行极大化,由此提出了一种求解贝叶斯模型平均的新方法（BMA-BFGS）.采用三个陆面模式进行的土壤湿度多模式数值模拟试验表明：在计算精度方面,BMA-BFGS的精度与MCMC方法几乎一致,优于EM算法;在计算耗时性方面,BMA-BFGS的计算耗时与EM算法相当,远小于MCMC方法.     

综合数据分析青藏高原东北缘六盘山地区构造形变及其构造成因独特性探讨

青藏高原边缘是研究青藏高原构造生长的重要场所.然而,青臧高原各边界却呈现出不同的地貌形态响应.尤其是青藏高原东北缘的六盘山地区,与青藏高原东缘相比,它与邻近稳定鄂尔多斯地台之间表现出了截然不同的地形变化.青藏高原东边界所对应的龙门山构造带呈现出高陡的地貌形态：在100 km范围内,海拔高程从四川盆地的500 m陡升至临近的龙门山构造带的3500 m.而青藏高原东北边界所对应的六盘山构造带则与邻近的鄂尔多斯盆地表现为宽缓的地形变化.之前由于缺少高精度的数据资料,对造成这一地表形态差异所对应的地壳结构缺少必要的了解.在本次研究中,将着重利用前期在青藏高原东北缘六盘山地区所获得的165 km长高分辨率深反射地震数据,并结合在此区域所获得的航磁数据资料进行该地区地壳结构的综合解释,得出青藏高原东北缘—鄂尔多斯地块构造转换带的地壳结构变形模型.研究表明六盘山地区主要物质组成为构造增生楔,其两侧分别存在陇西火山岛弧和鄂尔多斯结晶基底.高原生长所产生的构造应力并不能使相对松散的构造增生楔无限制的抬高而是容易发生重力坍塌,从而造成六盘山地区比较宽缓的地形结构.同时本文还将此地壳结构研究结果与前人在青藏高原东缘所获得的地壳结构及变形机制进行对比分析,探讨这两个地区的构造变形模式,并找出两个地区的构造变形共性和差异.研究结果也将为了解青藏高原侧向构造生长过程提供理论和数据支持.

     

Seasonal variations of stable isotope in precipitation and moisture transport at Yushu,eastern Tibetan Plateau

Precipitation δ 18O at Yushu, eastern Tibetan Plateau, shows strong fluctuation and lack of clear seasonality. The seasonal pattern of precipitation stable isotope at Yushu is apparently different from either that of the southwest monsoon region to the south or that of the inland region to the north. This different seasonal pattern probably reflects the shift of different moisture sources. In this paper, we present the spatial comparison of the seasonal patterns of precipitation δ 18O, and calculate the moisture transport flux by using the NCAR/NCEP reanalysis data. This allows us to discuss the relation between moisture transport flux and precipitation δ 18O. This study shows that both the southwest monsoon from south and inland air mass transport from north affected the seasonal precipitation δ 18O at Yushu, eastern Tibetan Plateau. Southwest monsoon brings the main part of the moisture, but southwest transport flux is weaker than in the southern part of the Tibetan Plateau. However, contribution of the inland moisture from north or local evaporation moisture is enhanced. The combined effect is the strong fluctuation of summer precipitation δ 18O at Yushu and comparatively poor seasonality.     

Pollen-inferred vegetation and environmental changes in the central Tibetan Plateau since 8200 yr BP

The ecotone between alpine steppe and meadow in the central Tibetan Plateau is sensitive to climate changes. Here we used the pollen records from three lakes in this region to reconstruct the evolution of local vegetation and climate since 8200 cal. yr BP. The history of temperature and precipitation was reconstructed quantitatively with multi-bioclimatic indexes and a transfer function from pollen records. Results show that the steppe/meadow dominated during the period of 8200–6500 cal. yr BP, especially 8200–7200 cal. yr BP, indicating the central Tibetan Plateau was controlled by strong monsoon. The steppe dominated during the periods of 6000–4900, 4400–3900, and 2800–2400 cal. yr BP. The steppe decreased gradually and the meadow expanded during the period of 4900–4400 cal. yr BP. Three century-scale drought events occurred during 5800–4900, 4400–3900 and 2800 cal. yr BP, respectively. The first time when the regional climate shifted to the present level was at 6500 cal. yr BP in the central Plateau. Since 3000 cal. yr BP, the temperature and precipitation have decreased gradually to the present level. However, the cold climate between 700–300 cal. yr BP likely corresponds to the Little Ice Age. Supported by Chinese Academy of Sciences 100 Talents Project (Grant No. 29082762), National Natural Science Foundation of China (Grant Nos. 40671196, 40372085, 49371068, 49871078), and U.S. National Science Foundation (Grant Nos. ATM-9410491, ATM-008194)     

青藏高原北部活动层土壤热力特性的研究

利用2003年10月～2004年9月期间高原北部可可西里(QT01)、北麓河(QT02)、开心岭(QT05)、通天河(QT06)等地活动层土壤温度梯度、土壤热通量及土壤水分的观测资料,计算了高原北部活动层土壤的导热率、土壤容积热容量、导温率等土壤热力参数.结果显示,QT02、QT05、QT06三站导热率、导温率夏秋季节较大而冬季较小,容积热容量则相反,表现为秋冬季节大而夏季较小;QT01站导热率表现为春季大,夏季较小;表层土壤粒度较小及较低的土壤湿度是冬季导热率较小的可能原因;冻土的热力特征参量可描述为相应深度的温度、体积含冰量及土壤盐度的函数,土壤含水量是融土热特征参数的主要影响因子;土壤水分含量小于某一临界值时,导温率随土壤水分含量的增大而增大,反之则减小.     

青藏高原东缘峨眉山新生代加速抬升剥蚀作用

本文通过峨眉山基底卷入构造带低温热年代学（磷灰石和锆石裂变径迹、锆石（U-Th）/He）研究,结合典型构造-热结构特征诠释峨眉山晚中-新生代冲断扩展变形与热年代学耦合性.峨眉山磷灰石裂变径迹（AFT）和锆石（U-Th）/He（ZHe）年龄值分别为4~30 Ma和16~118 Ma.ZHe年龄与海拔高程关系揭示出ZHe系统抬升剥蚀残存的部分滞留带（PRZ）.低温热年代学年龄与峨眉山构造分带性具有明显相关性特征：万年寺逆断层上盘基底卷入构造带AFT年龄普遍小于10 Ma,万年寺逆断层下盘扩展变形带AFT年龄普遍大于10 Ma;且空间上AFT年龄与断裂带具有明显相关性,它揭示出峨眉山扩展变形带中新世晚期以来断层冲断缩短构造活动.低温热年代学热史模拟揭示峨眉山构造带晚白垩世以来的多阶段性加速抬升剥蚀过程,基底卷入构造带岩石隆升幅度大约达到7~8 km,渐新世以来抬升剥蚀速率达0.2~0.4 mm·a^-1,其新生代多阶段性构造隆升动力学与青藏高原多板块间碰撞过程及其始新世大规模物质东向扩展过程密切相关.

     

青藏高原及其周缘地区各向异性研究进展

首先简要介绍了青藏高原目前主流的4种动力学模型, 即俯冲模型、 碰撞模型、 挤出模型和拆沉-板片断离模型. 然后概述了青藏高原及其周地区各向异性的研究进展, 展望各向异性研究的方向, 并着重探讨了各向异性研究中需要重视的几个问题： ① 各向异性的多种来源; ② 各向异性与深部结构的关系; ③ 面波等新方法的应用. 为了更好地定量解释各向异性, 需要了解深部结构与各向异性之间的关系, 发展更加精细的研究手段. 就目前来看, 面波与体波的联合反演可以更好地约束各向异性的分辨率, 而将地球动力学模拟等正演手段与地震波各向异性等反演手段相结合也可能是未来的趋势之一.     

青藏高原春季土壤湿度与我国长江流域夏季降水的联系及其可能机理

土壤湿度作为陆面过程的重要因子,对局地及邻近地区的大气环流和天气气候有重要影响.青藏高原的土壤湿度观测站点稀少,时间较短,鉴于此,本文使用经过部分观测站点检验的卫星反演数据,研究了春季高原土壤湿度的年际变化与后期夏季我国东部降水的联系和可能机理.结果表明：在全球变暖的背景下,高原土壤湿度总体呈现出显著增加的趋势,去除该线性趋势后,我们定义了一个高原土壤湿度指数TPSMI来定量表征高原土壤湿度的年际变化特征,发现表层、中层、深层的土壤湿度年际变率趋于一致,且春季土壤湿度与夏季土壤湿度显著相关（相关系数可达0.56）.当TPSMI偏大时,即高原东部土壤湿度偏大,而西部偏小时,夏季在高原东部（西部）存在一个潜热（感热）热源,二者共同作用下,在对流层中高层从高原西部经我国大陆直至东北地区激发出一个气旋-反气旋-气旋波列,该波列呈相当正压结构,有利于东北冷涡的加强及冷空气向南爆发;与此同时,南亚高压加强东伸,西太副高西伸加强,低空南方暖湿气流与北方干冷气流在长江流域汇合,伴随着上升运动加强,从而有利于夏季长江流域降水增多;反之,当TPSMI偏小时,夏季长江流域降水减少.     

Heterogeneous strain regime in the eastern margin of Tibetan Plateau and its tectonic implications

The eastern margin of Tibetan Plateau is one of the most active zones of tectonic deformation and seismicity in China. To monitor strain buildup and benefit seismic risk assessment, we constructed 14 survey-mode global position system(GPS) stations throughout the northwest of Longmenshan fault. A new GPS field over 1999–2011 is derived from measurements of the newly built and pre-existing stations in this region. Sequentially,two strain rate fields, one preceding and the other following the 2008 MW7.9 Wenchuan earthquake, are obtained using the Gausian weighting approach. Strain field over1999–2007 shows distinct strain partitioning prior to the2008 MW7.9 Wenchuan earthquake, with compression spreading over around Longmenshan area. Strain field derived from the two measurements in 2009 and 2011 shows that the area around Longmenshan continues to be under striking compression, as the pattern preceding the Wenchuan earthquake, implying a causative factor of the sequent of 2013 MW6.7 Lushan earthquake. Our GPSderived dilatation shows that both the Wenchuan and Lushan earthquakes occurred within the domain of pronounced contraction. The GPS velocities demonstrate that the Longriba fault underwent slight motion with the faultnormal and-parallel rates at 1.0 ± 2.5 mm and 0.3 ± 2.2 mm/a; the Longmenshan fault displayed slow activity, with a fault-normal rate at 0.8 ± 2.5 mm/a, and a fault-parallel rate at 1.8 ± 1.7 mm/a. Longriba fault is on a par with Longmenshan fault in strain partitioning to accommodate the southeastward motion of eastern margin of the Tibetan Plateau. Integrated analysis of principal strain tensors, mean principal stress, and fast directions of mantle anisotropy shows that west of Sichuan is characterized as mechanically strong crust-mantle coupling.     

High-resolution peat records for Holocene monsoon history in the eastern Tibetan Plateau

Holocene peat sediment has been attached impor-tance to reconstruct the Holocene climatic variations because it can provide much palaeoclimatic informa-tion with high resolution. Analysis on the plant mac-rofossil[1], pollen[2―4], isotope ratio[5―9], element con-tent[10,11], total organic carbon (TOC)[12], humifica-tion[13,14] and grayscale[12] for peat sediment has shown its superiorities as a recorder medium for reconstruct-ing the Holocene climate. Hong et al. have done great fruitful w…     

Evaluation of snow products over the Tibetan Plateau

Four satellite‐based snow products are evaluated over the Tibetan Plateau for the 2007–2010 snow seasons. The Moderate Resolution Imaging Spectroradiometer (MODIS) Terra and Aqua snow cover daily L3 Global 500‐m grid products (MOD10A1 and MYD10A1), the National Oceanic and Atmospheric Administration Interactive Multisensor Snow and Ice Mapping System (IMS) daily Northern Hemisphere snow cover product and the Advanced Microwave Scanning Radiometer – Earth Observing System Daily Snow Water Equivalent were validated against Thematic Mapper (TM) snow cover maps of Landsat‐5 and meteorological station snow depth observations. The overall accuracy of MOD10A1, MYD10A1 and IMS is higher than 91% against stations observations and than 79% against Landsat TM images. In general, the daily MODIS snow cover products show better performance than the multisensor IMS product. However, the IMS snow cover product is suitable for larger scale (~4km) analysis and applications, with the advantage over MODIS to allow for mitigation for cloud cover. The accuracy of the three products decreases with decreasing snow depth. Overestimation errors are most common over forested regions; the IMS and Advanced Microwave Scanning Radiometer – Earth Observing System Snow Water Equivalent products also show poorer performance that the MODIS products over grassland. By identifying weaknesses in the satellite products, this study provides a focus for the improvement of snow products over the Tibetan plateau. The quantitative evaluation of the products proposed here can also be used to assess their relative weight in data assimilation, against other data sources, such as modelling and in situ measurement networks. Copyright © 2015 John Wiley & Sons, Ltd.     

Sensitivity of the central Asian climate to uplift of the Tibetan Plateau in the coupled climate model (MRI-CGCM1)

Abstract   The relationship between the altitude of the Tibetan Plateau and climate change in central Asia was investigated through a numeric experiment using the Meteorological Research Institute (MRI) coupled atmosphere–ocean general circulation model I (MRI-CGCM1). The results suggest that summer precipitation in central Asia decreased significantly as the Tibetan Plateau rose in height. Spring precipitation, however, increased during initial growth stages when the plateau height was up to 40% of its present-day height, and then decreased with further plateau growth. During the Tibetan Plateau uplift, the difference between precipitation and evaporation was minimal during spring. When the plateau attained a height exceeding 60% of its present height, relatively low precipitation but high evaporation in spring led to a lower amount of ground moisture. In the case of the high plateau, sensible heat flux during summer and fall largely exceeded latent heat flux. Change was particularly significant for cases when the plateau reached 40–60% of its present-day height. The duration of the predominant sensible heat flux became longer with the uplift of the Tibetan Plateau. The period in which latent heat exceeded sensible heat seems to have been restricted to winter and early spring. The numeric experiments suggest that a significant drying of central Asia corresponded to the period in which the Tibetan Plateau exceeded approximately half its present-day height.