A modified nearly analytic discrete method and wavefield simulations in transversely isotropic media     

LU Ming & YANG Dinghui Department of Mathematical Sciences  Tsinghua University  Beijing  China 《中国科学D辑(英文版)》2005,48(8):1321-1328

Under the general case, rocks under the ground can be approximately considered as an elastic medium. Elastic wave equation is a partial differential equation, which describes the elastic wave propagation in elastic media. Simple elastic wave equation can be solved analytically, however most wave equations are very complex, which can only be solved by using numerical methods. Numerical simulations of seismic wave fields have become an important method for studying seismic wave propagation in co…  相似文献   

95年来青岛气候变化的分析     

常美桂  胡基福  鄢利农 《中国海洋大学学报(自然科学版)》1995,(3)

根据１８９８—１９９２年青岛年平均温度和降水资料，分析了青岛９５年来的气候变化，指出年平均气温有明显变暖趋势，而降水量变化不显著。分析了年平均温度和降水的气候阶段，还采用信噪比方法检验了９５年来青岛气候突变。利用谱分析方法分析了气温和降水的主要周期。这些结果与北半球和我国近百年的气候变化趋势基本一致。  相似文献   

Characteristics of Temperature Change in China over the Last 2000 years and Spatial Patterns of Dryness/Wetness during Cold and Warm Periods     

Quansheng GE  Haolong LIU  Xiang MA  Jingyun ZHENG  Zhixin HAO 《大气科学进展》2017,34(8):941-951

This paper presents new high-resolution proxies and paleoclimatic reconstructions for studying climate changes in China for the past 2000 years. Multi-proxy synthesized reconstructions show that temperature variation in China has exhibited significant 50–70-yr, 100–120-yr, and 200–250-yr cycles. Results also show that the amplitudes of decadal and centennial temperature variation were 1.3℃ and 0.7℃, respectively, with the latter significantly correlated with long-term changes in solar radiation, especially cold periods, which correspond approximately to sunspot minima. The most rapid warming in China occurred over AD 1870–2000, at a rate of 0.56°± 0.42℃(100 yr)~(-1); however, temperatures recorded in the 20 th century may not be unprecedented for the last 2000 years, as data show records for the periods AD 981–1100 and AD1201–70 are comparable to the present. The ensemble means of dryness/wetness spatial patterns in eastern China across all centennial warm periods illustrate a tripole pattern: dry south of 25°N, wet from 25°–30°N, and dry to the north of 30°N. However, for all centennial cold periods, this spatial pattern also exhibits a meridional distribution. The increase in precipitation over the monsoonal regions of China associated with the 20 th century warming can primarily be attributed to a mega El Nino–Southern Oscillation and the Atlantic Multidecadal Oscillation. In addition, a significant association between increasing numbers of locusts and dry/cold conditions is found in eastern China. Plague intensity also generally increases in concert with wetness in northern China, while more precipitation is likely to have a negative effect in southern China.  相似文献   

近两百年江苏省城乡建设用地数量估算与空间重建     

林忆南  金晓斌  杨绪红  龙瀛  周寅康 《地理学报》2017,72(3):488-506

以典型历史断面下的建设用地为研究对象,以数量估算控制下的空间格局重建为基本思路,在200 m×200 m网格下,估算并重建了近200年5个时间断面下的江苏省建设用地（城镇用地和农村聚落用地）的空间格局。在数量估算方面,历史时期（1820年）的城镇用地主要采用城垣、市镇四栅等作为代用指标;近现代时期（1911年、1936年、1952年）,主要通过人口、社会经济等数据,结合一定假设确定人均用地数量进行推导;各时期的农村聚落用地均以人口数量为基础,根据人均住房面积和社会经济数据修正确定。在空间重建方面,结合遥感数据解译获得的现代（1985年）土地利用数据,借助基础地理数据,在一定假设条件下,通过数量控制、边界控制、适宜性控制,兼顾用地连片性等予以确定。结果表明：① 各时间断面下的江苏省建设用地数量分别为963.46 km²（1820年）、1041.94 km²（1911年）、1672.40 km²（1936年）、1980.34 km²（1952年）和10687.18 km²（1985年）;② 建设用地在空间分布上具有亲水网、路网等特征,并随居民点极化与扩散效应而不断扩张;③ 通过变化过程与演化趋势检验、建设用地与生产协调性分析、居民点空间数量与格局分析等方法,间接证明了重建结果的合理性。  相似文献   

Spatio-temporal analysis of cropland change in the Guanzhong area,China, from 1650 to 2016     

WEI Xueqiong  LI Yuanfang  GUO Yu  CHEN Tiexi  LI Beibei 《地理学报(英文版)》2021,31(9):1381-1400

As one of the most critical impact factors of global change, historical land-use change is an indispensable input in climate and environment simulations. To better understand the cropland change in the Guanzhong area, gazetteers, statistics, and survey data were collected as data sources. Methods of registered tax-paying cropland data collection, selection of time points, and data interpolation and calibration were used to reconstruct changes in the cropland area. The cropland area data at the county level were allocated to 1 km×1 km grid cells. The total cropland area in the Guanzhong area was influenced by changes in population, wars, natural disasters, and land-use types, and it fluctuated from 1650 to 2016. From 1780 to 1830, the cropland expanded in the northern and western parts of Guanzhong area, and the cropland in the north of Qinling Mountains increased slightly. The spatial pattern of cropland reached its maximum range in 1980, and the cropland area declined in the whole study area, especially in the cities of Xi'an and Xianyang in 2016. The comparison between HYDE 3.2 and the data obtained in this study showed that the grid cells of HYDE 3.2 exhibit lower values of cropland area fractions in the Guanzhong Basin and higher values in high-altitude areas around the Guanzhong Basin as compared to those in this study.  相似文献   

甘肃省地矿局六十年地质工作综述 ——纪念甘肃省地矿局建局60周年     

张新虎  王世宇  牛洪斌  丁宏伟  刘建宏  贾志磊 《甘肃地质》2016,25(3):1-12

甘肃省地矿局建局60年来,先后完成了全省中小比例尺的区域地质矿产调查,发现并探明了资源储量世界排名第3的金川铜镍矿和白银铜矿、镜铁山铁矿、玛曲大水金矿、敦煌方山口钒矿、肃北塔尔沟钨矿、合作早子沟金矿、西和大桥金矿、肃南卡瓦铁矿、阿克塞余石山铌钽矿等为代表的大中型矿床180余处,发现各类矿产地875余处;完成了全省中小比例尺区域地质、水工环地质调查,评价了主要水源地和地质灾害的勘察;取得了一批地质科研成果,获得多项国家及省级科技成果奖励;为我国及甘肃省的经济社会发展做出了贡献。文章对甘肃省地矿局承担的基础地质调查、矿产地质勘查、水工环地质、地质科技等方面进行较系统、全面总结,对今后地质工作具有启示和借鉴意义。  相似文献   

Ovi-caprid dung as an indicator of paleovegetation and paleoclimate in northwestern China     

Ruby Ghosh  Subir Bera  Hong-en Jiang  Cheng-Sen Li 《Quaternary Research》2008,70(2):149-157

Diverse palynomorphs and phytoliths recovered from coprolites of ovi-caprids (sheep, goat) collected from Yang-Hai Tomb at Xinjiang Province, China, have been used to elucidate the dietary pattern of ancient livestock and to reconstruct the paleovegetation and paleoclimate of this part of northwest China ca. 2500 ¹⁴C yr BP. Palynological and phytolith data suggest that a rich dry temperate vegetation prevailed in the area during the said period. Climatic conditions and grassland vegetation type of the area are explored using phytolith indices.  相似文献   

近40a贵州主汛期降水时空变化及其异常年低频特征分析          下载免费PDF全文

孔德璇  杨春艳  严锐  池再香  赵琨 《中低纬山地气象》2018,42(5):14-19

选取1977—2016年国家气象信息中心提供的贵州82站逐日降水资料,利用合成分析、显著性检验、小波分析、带通滤波等方法,分析了近40 a贵州5—8月(简称主汛期,下同)降水的时空分布特征,以及典型涝年、典型旱年的低频降水特征。结果表明:贵州主汛期降水呈现明显的年代际变化特征,其多年平均总降水量呈现南多北少的趋势,总降水量大值区主要集中在贵州的西南部地区(六盘水市、安顺市中西部和黔西南州西部)。典型涝年和典型旱年的平均主汛期总降水量以西南部最为明显,且各自主汛期降水的低频振荡周期差别不明显;10～20 d是贵州主汛期降水普遍存在的显著低频周期,典型涝年存在30～40 d低频周期,典型旱年存在较弱的35～45 d低频周期,低频降水主要发生在6月和7月。  相似文献   

近2000年来内蒙后套平原黄河河道演变   总被引：6，自引：0，他引：6  

李炳元  葛全胜  郑景云 《地理学报》2003,58(2):239-246

通过遥感影像、地貌沉积、历史文献与地图等相关资料分析集成研究,将后套平原分为西部冲积扇平原,东部是泛滥冲积平原,并详细探讨了近2000年来本区黄河河道的演变。公元前2世纪时,后套西部平原南 (上) 冲积扇停止发育, 北(下) 冲积扇河道发育,黄河主河道的位置与现代不同,它偏于泛滥平原北部的阴山山前东流;公元6世纪后套平原西部北 冲积扇上黄河河道向东移,在东部泛滥平原上黄河明显地分为南北两汊,而黄河主流仍位于河套平原北部山前;18世纪早期至末期,黄河主河道从河套平原的北部山前南移至平原南部;19世纪中叶‘北河’淤塞,现代黄河形成。  相似文献   

天山山区与南、北疆近40a来的年温度变化特征比较研究   总被引：21，自引：7，他引：14  

袁玉江  何清  魏文寿  喻树龙 《中国沙漠》2003,23(5):521-526

分析天山山区近40 a来年温度变化的基本特征,并与南疆、北疆进行比较,其结果是:(1)天山山区年平均温度在冷暖变化阶段上与北疆的相似性强于南疆。(2)新疆三大区域年平均温度的最主要空间分布特征均是同步变化,但同步性的程度北疆较好,南疆及天山山区较差;而空间分布的反向变化性,南疆及天山山区较好,北疆较差。(3)三大区域年平均温度的年代际变化趋势是不同的,但均以20世纪90年代为最暖。(4)近40 a的显著线性增温趋势以年平均最低温度及年平均温度表现得空间范围最广,年平均最高温度最差;年平均温度的长期增温率以北疆最大,天山山区和南疆较小;年平均最低温度的10 a增温率变化在0.34~0.37℃之间。(5)三大区域最佳升温趋势出现的时段比较一致,增温率以北疆为最大,天山山区和南疆相同。(6)北疆与南疆年平均温度分别在1960年和1978年发生了由低向高的突变。  相似文献