Numerical simulation of a heavy rainfall event in China during July 1998

Summary A detailed analysis associated with this case has been carried out (Zhao et al., 2001). In order to conduct further research on the meso-β scale system, which is the directly influencing system, the heavy rainfall that occurred in Wuhan (Station no.: 57494) and Huangshi (Station no.: 58407), Hubei Province during July 1998 are simulated using higher resolution and more complete initial data, after the large scale fields and rainfall areas have been simulated successfully. The simulation results indicate that there are meso-β scale weather systems which developed and dissipated near Wuhan and Huangshi during 1800 UTC 20 July to 0600 UTC 21 July and 1800 UTC 21 July to 0600 UTC 22 July in 1998, respectively. The life cycle of the meso-scale system is about 12 hours and its horizontal scale is from 100 to 200 km. These are characteristic of a typical meso-β scale system. By analyzing the vertical section of wind field and other physical variables during the mentioned-above two periods, it is found that horizontal convergence, ascending motion and positive vorticity of the middle and lower troposphere are strengthened during the heavy rainfall periods near the above mentioned two places. In addition, the wind disturbance in middle and lower troposphere may be a possible triggering mechanism for the occurrence of the meso-β weather system. A budget analysis of the meso-scale system indicates that the sources of moisture and positive vorticity are different during the different stages of the meso-scale systems. Finally, a three dimensional conceptual model of the meso-β scale systems causing the sudden heavy rainfall in Wuhan and Huangshi is suggested. Received November 4, 2001 Revised December 28, 2001     

梅汛期100 hPa南亚高压特征与江苏梅雨关系研究

通过2002～2005年南亚高压特征指数、高空槽变化过程分析,讨论了南压高压对江苏梅雨期和主要降水落区的影响.并结合近15年南亚高压特征指数,探讨了不同梅雨年型的特征指数区域分布关系.同时利用2002～2005年45年NCEP 100 hPa高度场资料,分析了不同梅雨年型高空环流形势差异.得出:(1) 南亚高压特征指数变化和西风槽移动与江苏梅期(入梅、出梅、梅期、梅雨量和落区)特征有密切关系.(2) 梅雨期100 hPa南亚高压的平均特征对梅期特征和梅雨年型有很好的对应关系.6～7月和梅雨期间南亚高压脊线和东伸指数平均值对梅雨强度指数具有一定的预报指示意义.     

南海海温和西南地区土壤湿度异常与中国东部夏季降水的可能联系

利用1958—2001年NOAA海温资料、欧洲中心(ECMWF)ERA40土壤湿度再分析资料和中国100 °E以东444站的降水资料,探讨了南海海温和土壤湿度异常与我国东部夏季降水之间的可能联系,并初步讨论其可能的物理过程。结果表明,春季南海海温与西南地区东部土壤湿度的异常变化之间存在显著的负相关关系,而土壤湿度的异常与我国东部夏季降水之间也存在密切的联系。当春季南海海温异常偏高(低)时,我国西南地区东部的土壤通常出现异常偏干(湿),而夏季长江流域降水偏多(少)、东南沿海地区降水偏少(多)。进一步分析表明,春季南海海温异常偏高(低),有利于我国南部区域低层西南风减弱(偏强),西南地区东部水汽输送减少(增加),导致该地区春季的降水异常减少(增加)、土壤偏干(湿);通过蒸发反馈机制使得夏季西南地区东部地表温度偏高(低),引起副高西伸(东退)发展,最终导致我国东部地区夏季降水的异常。      

2013年1月江苏雾霾天气持续和增强机制分析

利用江苏省能见度监测资料、自动站气象要素资料、探空资料、NCEP(1°×1°)和CFSV2(0.5°×0.5°)再分析资料,对2013年1月江苏雾霾持续性和13—14日大雾形成机制展开分析,结果表明:(1)中高纬平直的纬向环流,江苏位于地面高压底部偏东气流中,冷高压主体偏北,是1月发生持续雾霾天气的大背景。较弱的偏北经向风导致冷空气势力较弱,为1月江苏雾霾天气持续发生提供了近地层有利的稳定形势。(2)近地面相对湿度85%以上,风速小于3 m·s~(-1),风向以偏东风为主,凌晨与夜间温度露点差小于3℃。这些条件的稳定为持续雾霾发生提供了良好的气象因子。(3)地面辐射降温和弱冷平流共同作用引起的温度快速下降以及日出后潮湿地面蒸发增强对雾的加强起到一定的触发作用。近地面冷平流和混合层以上暖平流为本次雾增强提供了稳定的大气层结条件。近地面弱上升运动、中高层弱的下沉运动是14日凌晨雾快速加强的动力机制。     

基于风暴数值模拟的冰雹临近预报方法研究

该文利用基于格点冰雹识别的研究成果,结合ARPS风暴数值模式的输出结果,提出基于风暴数值模式的冰雹临近预报方法,即用风暴数值预报的水物质场反演的反射率因子场作为冰雹的预报因子,并通过建立基于格点的强冰雹识别算法作为冰雹预报模型,从而对冰雹的落区及大小做出预报。与一般的冰雹预报模型相比,新的方法有以下特点：选取的冰雹预报因子物理意义更加明确,更加全面;建立的冰雹预报模型比较稳定;建立冰雹预报模型的过程相对简单。新的方法在一次强冰雹过程中得到了成功应用,在3h的临近预报中基本准确预报了强冰雹的落区位置。     

勉略构造带硅质岩元素地球化学特征及其形成环境

勉略构造带古生代硅质岩发育,其对西秦岭造山带古生代沉积环境与构造背景具有重要指示意义。本文研究了勉略构造带西段文县地区泥盆纪硅质岩的野外露头产状、岩石学与矿物学及全岩主微量元素地球化学特征,对比分析了该带东段硅质岩性质,综合剖析了勉略构造带古生代硅质岩的沉积环境,探讨了西秦岭造山带古生代岩相古地理环境及大地构造背景。文县硅质岩有灰白色块状硅质岩和灰黑色角砾状硅质岩两种类型,两者均具层状、条带状等沉积构造,并与上覆、下伏地层整合接触,为典型热水沉积硅质岩。岩石主要组成矿物为细晶-微晶石英,含有少量的方解石、绢云母及泥质等。岩石地球化学分析显示,硅质岩SiO2含量较高,为84.85%~99.07%,平均为91.99%,且灰白色硅质岩质地更纯,SiO2含量明显高于灰黑色硅质岩。硅质岩主微量、稀土元素Fe2O3/TiO2-Al2O3/(Al2O3+Fe2O3)、V/Y-Ti/V及LaN/CeN-Al2O3/(Al2O3+Fe2O3)图解表明该区硅质岩主要形成于大陆边缘及近大陆边缘环境。稀土元素显示灰黑色角砾状硅质岩稀土总量较高,为171.3×10-6~236.1×10-6,而灰白色块状硅质岩仅为11.96×10-6~51.06×10-6,表明前者所含陆源物质组分更多;稀土元素北美页岩标准化后两者整体显示了相似的轻重稀土分异不明显的平坦型稀土配分模式,其中灰黑色硅质岩δCe为0.95~1.05、δEu为0.66~0.87、(La/Yb)SN值为0.95~1.10,反映基本无Ce异常、弱Eu负异常及轻重稀土分异不明显;灰白色硅质岩的δCe为1.07~1.12、δEu为0.70~0.90、(La/Yb)SN值为1.64~4.07显示了弱Ce正异常、弱Eu负异常及弱轻重稀土分异,两者稀土元素特征与世界典型大陆边缘(裂陷)盆地硅质岩相近。文县硅质岩地质、元素地球化学特征表明其整体形成于大陆边缘及近大陆边缘沉积环境,但相比于灰白色块状硅质岩,灰黑色角砾状硅质岩有更多陆源物质加入。结合勉略构造带东段古生代硅质岩野外产出及地球化学特征分析,该区在早古生代-晚古生代早期主要处于扬子板块北部大陆边缘海盆沉积环境,有较多的陆源物质加入到富硅的热水沉积中,在勉略构造带内自西向东形成了一系列不同时代的热水沉积硅质岩。与此同时,西秦岭主要处于大陆裂陷构造背景之中,多期次的裂陷活动形成了一系列裂陷盆地及深大断裂,这对西秦岭古生代热水沉积硅质岩的形成具有重要意义。     

Soil CO2 efflux along an elevation gradient in Qinghai spruce forests in the upper reaches of the Heihe River,northwest China

This study was conducted in six plots along an elevation gradient in the Qinghai spruce (Picea crassifolia Kom.) forest ecosystem of the Qilian Mountains, northwest China. Soil CO₂ efflux over bare soil (R _s) and moss covered soil (R _s+m) were investigated from June to September in 2010 and 2011 by means of an automated soil CO₂ flux system (LI-8100). The results showed that R _s ranged from 1.51 to 3.96 (mean 2.64 ± 0.72) μmol m^?2 s^?1 for 2010, and from 1.41 to 4.09 (mean 2.55 ± 0.70) μmol m^?2 s^?1 for 2011. The daily change trend of R _s resembled that of air temperature (T _a), and there was a hysteresis between R _s and soil temperature (T _s). The seasonal variations of R _s at lowlands (i.e., Plot 1, Plot 2 and Plot 3) were driven by soil moisture and temperature (T _a and T _s), while that at highlands (i.e., Plot 4, Plot 5 and Plot 6) were obviously affected by temperature. There were higher values at Plot 2 and Plot 6, which were caused by the interaction between soil moisture and temperature. In addition, soil CO₂ efflux over moss covered soil (R _s+m) was 8.83 % less than that over bare soil (R _s), indicating that moss was another factor affecting R _s. It was concluded that R _s had temporal and spatial variations and was mainly controlled by temperature and soil moisture; the main determinants differed at different elevations; moss could reduce R _s.     

大陆深俯冲的最大深度——来自数值模拟实验的结果

采用粘弹性材料8块体有限元模型并设定温度场后进行的大陆深俯冲二维数值模拟表明,在组合载荷（负浮力、洋中脊推力从上到下10～30MPa和地幔对流拖曳力100MPa）作用下,陆壳俯冲实际垂向位移可达117km,最终俯冲深度达到147km,而洋壳实际垂向位移约162km,最终俯冲深度达到231km;在洋壳、陆壳俯冲到一定深度以前,它们的俯冲速度基本保持不变,表现为洋壳、陆壳底端的位移一时间曲线近似为直线;当俯冲时间超过9Ma,洋壳、陆壳分别达到167km、96km深度后,俯冲速度会越来越慢。     

内蒙古苏尼特左旗卓仑音诺尔地区中二叠统哲斯组沉积环境、形成时代及意义

内蒙古苏尼特左旗卓仑音诺尔地区哲斯组可以分为下部的粉砂岩、页岩段和上部的砾岩-砂岩段,分别代表扇中亚相的漫流沉积和扇根亚相的近源快速沉积,反映研究区二叠纪以陆相盆地干旱型冲积扇为特征的岩相古地理面貌。碎屑岩年代学研究揭示,哲斯组的物源为兴安-艾力格庙地块、早古生代的岛弧岩浆岩带及晚石炭世和早二叠世的岩浆岩体,表明盆地具有复杂源区。测年样品中最年轻一组锆石年龄的峰值为281Ma,侵入该组的石英闪长玢岩年龄为248±3Ma,限定陆相盆地的形成时代为中二叠世—三叠纪初。区域地质分析表明,中—晚二叠世兴蒙造山带中西部的不同地区均发育陆源碎屑沉积盆地,但层序特征各不相同,可能属于互不连通的小型盆地,代表二叠纪的盆岭构造,揭示兴蒙造山带在二叠纪整体处于陆内伸展的构造环境。     

基于DEM的任意方向坡度计算方法

坡度是数字地形分析中重要的地形因子,在水文分析、土壤侵蚀模拟、地貌类型划分等地学分析及工程上均有广泛的应用。由于地形的各向异性,坡度在各个方向上并不相同。目前,基于DEM所提取的坡度,均是位于最陡方向上的坡度,而任意给定方向坡度计算是地学分析和工程应用中较为常见的问题。在对目前DEM坡度提取算法研究的基础上,通过数学分析,给出了格网DEM上任意方向格网点的坡度计算模型和计算流程,并给出了相应的计算实例,从而将坡度计算模型从特定方向推向任意方向,使DEM坡度计算更具普适性。