Calculation of circulation in the South China Sea during summer of 2000 by the modified inverse method

On the basis of hydrographic data obtained in August 2000 cruise, the circulation in the South China Sea (SCS) is computed by the modified inverse method in combination with SSH data from TOPEX/ERS-2 analysis. For study of the dynamical mechanism, which causes the pattern of summer circulation in the SCS, the diagnostic model (Yuan et al. 1982. Acta Oceanologica Sinica,4(1):1-11; Yuan and Su. 1992. Numerical Computation of Physical Oceanography.474-542) is used to simulate numerically the summer circulation in the SCS. The following results     

2000年东海黑潮和琉球群岛以东海流的变异Ⅰ.东海黑潮及其附近中尺度涡的变异

基于日本“长风丸”调查船在2000年5个航次水文资料及同时期QuikSCAT风场资料,采用改进逆方法计算了东海黑潮的流速与流量等,获得了这5个航次期间的主要结果:(1)在东海海区风速1~2月比其他月份时大,风海流也最强.只在7月表层风海流为北向,加强了黑潮流速.(2)表层最低盐度值夏季时最小,1~2月时最大.这再次表明,夏季时长江冲淡水向东北方向扩散,冬季时基本上向南,其他季节在上述两者之间.(3)PN断面流速结构及其变化:黑潮流核在1~2,10和11月时有两个,在4和7月皆只有1个.黑潮主流核在1月位于计算点9,在4,7,10与11月都位于计算点8,即向陆架方向移动.(4)黑潮在TK断面出现多流核结构特性.11月主流核出现在TK断面中部,存在于水深大于1 200 m区域,其余月份主流核皆出现在TK断面北部,存在于深度400m以浅水层.(5)通过PN断面的净东北向流量在11月最大,为28.1×106m3/s,7月时其次,10月时最小,为24.6×106m3/s.通过PN断面的净东北向流量年平均值为26.4×106m3/s.(6)1~2,4,7与10月在PN断面以东都出现暖的、反气旋式涡,10月份时,反气旋式涡最强.只在11月时出现弱的、气旋式涡.黑潮以东反气旋涡加强时,黑潮流量似乎减小(例如10月);相反,当黑潮以东反气旋涡减弱(例如7月)或者代之出现气旋涡时(例如11月),黑潮流量似乎增大.10和11月在PN断面附近流态的比较,揭示了环流变化较大,这进一步表明,黑潮和其附近中尺度涡的相互作用是重要的.(7)通过TK断面的净东向流量,11月最大,7月其次,10与1~2月最小.通过TK断面净东向流量年平均值为21.9×106m3/s.(8)通过A断面的北向流量在1~2与4月较大,分别为3.5×106与3.1×106m3/s,7月最小.通过A断面的年平均北向流量约为2.7×106m3/s,这表明,在2000年1~2与4月通过对马暖流的流量最大,7月时最小.     

中亚地区过去2000年气候变化研究的数据挖掘

中亚地区是古丝绸之路的主要廊道,气候变率时空差异大,随着"一带一路"倡议的逐步推进,该地区过去2000年气候变化研究备受关注。文章参照世界数据中心古气候资料共享网收录文献的关键词,从Web of Science数据库检索该地区过去2000年气候变化研究文献;并结合中亚自然资源图集的政区、湖泊、山脉等地名信息,构建了面向该类文献的数据挖掘技术;据此提取了研究区（点）、时间、代用资料与研究结果等信息,分析了其间该地区冷暖与干湿变化研究的主要进展。主要结论有：1）中亚地区过去2000年气候变化的已有研究重点为局地温度、降水/干湿变化重建与冷暖、干湿、湖泊水位等的阶段性差异分析,其中尤以干湿相关研究居多;所用代用资料主要有树轮（占44.2%）、湖泊沉积物（占41.9%）、冰芯（占9.3%）等,其中湖泊沉积物、冰芯、石笋可覆盖整个2000年,而最长的树轮仅覆盖过去1100年,且多数集中在1700年之后;研究区集中分布于西天山及帕米尔高原、巴尔喀什湖、咸海及周边地区;研究时段虽覆盖整个2000年,但高分辨率重建工作主要集中于16世纪之后。2）中亚地区公元1~3世纪末、15世纪中期~19世纪中期气候相对寒冷,5世纪中期~9世纪末、12世纪中期~14世纪末和19世纪中期以后气候总体温暖,但在1230年前后和1680年前后也分别出现过显著转冷和回暖;20世纪后期的温暖程度可能与其前千年的最暖时段相当。西天山、帕米尔和咸海三地干湿的百年尺度阶段变化并不同步;其中在百年以上尺度,咸海及周边地区公元1~5世纪、10~12世纪中期相对偏干,5世纪~9世纪、12世纪后期~15世纪中期相对偏湿,此后缓慢转干持续至今;而在年代际尺度上,西天山和帕米尔山地降水自1980年起曾显著增加,但至2000年以后又显著转干。     

2000年夏季南海环流的改进逆方法计算

基于2000年8月航次在南海调查资料,采用改进逆方法,并结合TOPEX/ERS分析的SSH分布,获得以下的主要结果:(1)南海中部和西南部环流系统主要受反气旋环流所支配.主要有越南东南反气旋涡W₁,其水平尺度约为300km,垂向深度可达1000m以深,流速很强,其最大流速为79cm/s左右,还有暖涡W₂以及吕宋岛西南反气旋涡环流系统W₃.其次,在反气旋涡W₁与W₂之间还存在气旋式涡C₁.其水平尺度比暖涡W₁小得多,流速也较强.两涡W₁与C₁之间存在一支南向流,它们组成一个准偶极子.(2)在暖涡W₁的西侧存在西边界流,即北向射流,其流速很强,约在12°N流向转向东北.(3)南海北部环流系统主要受气旋环流所支配.在断面N2附近及以北存在一个气旋式环流系统.其次,在海南岛东南存在一个尺度不大的反气旋环流系统.(4)南海东南部环流系统主要受气旋环流所支配.主要有在巴拉望岛以西存在尺度较大的气旋环流系统,以及暖涡W₁东南存在一个气旋环流系统.其次,在加里曼丹岛西北还存在范围不大的反气旋环流.(5)比较1998年夏季航次与2000年夏季航次时计算结果,虽然它们在定量上有些变化与差别,但在定性上它们的环流结构有十分相似之处.这表明,南海环流具有明显的季节特性.(6)比较2000年夏季南海水文结构,流函数分布以及TOPEX/ERS的SSH分布,它们在定性上十分吻合.     

EMTF在宽频大地电磁测深数据处理中的应用

如何有效地压制各种电磁噪声,提高信噪比,保证大地电磁测深数据质量,始终是大地电磁资料采集与处理的核心问题。为寻求更好的处理效果,使用EMTF系统(单点,远参考以及多站同步MMT)对华北多个宽频MT测点数据进行了处理,并编写Matlab接口来方便地改写处理参数。与SSMT-2000对比,结果表明,EMTF系统在多数情况下可以压制噪声,并获得较好的处理效果,提高数据处理的效率。     

V5-2000大地电磁测深仪文件头数据格式研究

V5-2000大地电磁测深仪由于其功能强、轻便、勘探范围大等特点,在国内已得到了广泛应用,但其后期数据解释软件却显得相对薄弱。要想解决解释软件的问题,首先所面临的是测量数据的格式问题。由于其保存的测量数据为特殊格式,为了便于对V5-2000测量数据进行后期处理与分析,这里对V5-2000测量数据的特殊数据格式进行了剖析,并用现今流行的,面向对象化的VB6.0编程语言,编写了相关读取及修改程序,以作为下一步的后期数据解释软件开发之基础。     

Estimation of the spatial distribution of ground motion parameters for two recent earthquakes in Japan

A recent development in strong motion instrumentation in Japan provides an opportunity to collect valuable data sets, especially after moderate and large magnitude events. Gathering and modeling these data is a necessity for better understanding of regional ground motion characteristics. Estimations of the spatial distribution of earthquake ground motion plays an important role in early-stage damage assessments for both rescue operations by disaster management agencies as well as damage studies of urban structures. Subsurface geology layers and local soil conditions lead to soil amplification that contributes to the estimated ground motion parameters of the surface. We present a case study of the applicability of the nationally proposed GIS-based soil amplification ratios [J. Soil Dyn. Earthqu. Eng. 19 (2000) 41–53] to the October 6, 2000 Tottori-ken Seibu (western Tottori Prefecture) and the March 24, 2001 Geiyo earthquakes in Japan. First, ground motion values were converted to those at a hypothetical ground base-rock level (outcrop) using an amplification ratio for each 1×1 km area, based on geomorphological and subsurface geology information. Then a Kriging method, assuming an attenuation relationship at the base-rock as a trend component, is applied. Finally, the spatial distribution of ground motion at ground surface is obtained by applying GIS-based amplification factors for the entire region. The correlation between the observed and estimated ground motion values is reasonable for both earthquakes. Thus, the proposed method is applicable in near real-time early-damage assessments and seismic hazard studies in Japan.     

AMT近源干扰压制方法

音频大地电磁法( AMT)在野外采集的是包含了多种频率的时间序列数据,这些数据中常含有干扰信号。大量查看音频大地电磁法野外实测时间序列数据,发现测量数据受到严重的近源干扰,但干扰信号不是连续出现的。于是通过分析V5-2000大地电磁仪的原始数据格式,根据干扰信号的特征,提出一种自动筛选时间序列数据的方法。宁芜地区的实测资料处理结果表明,该方法能在一定程度上压制近源干扰。     

Seismic activity related to the 2000 eruption of the Hekla volcano, Iceland

The 2000 Hekla eruption took place from February 26 to March 8. Its seismic expressions were a swarm of numerous small earthquakes related to its onset, and low-frequency volcanic tremor that continued throughout the eruption. A swarm of small earthquakes was observed some 80 min before the onset of the eruption, and the size of the events increased with time. Low-frequency volcanic tremor, with a characteristic frequency band of 0.5–1.5 Hz and dominant spectral peak(s) at 0.7–0.9 Hz, became visible at 18:19 GMT on February 26, marking the onset of the eruption. The tremor amplitude rose quickly and was very high in the beginning of the eruption. However, it soon began to decrease after about an hour. In general, the seismic activity related to the 2000 Hekla eruption was very similar to what was observed in the previous eruption in 1991. Based on knowledge gained from seismicity and strain observations from 1991, this was the first time that a Hekla eruption was predicted.Editorial responsibility: J Stix     

The contribution of Very Long Baseline Interferometry to ITRF2005

The contribution of the International VLBI Service for Geodesy and Astrometry (IVS) to the ITRF2005 (International Terrestrial Reference Frame 2005) has been computed by the IVS Analysis Coordinator’s office at the Geodetic Institute of the University of Bonn, Germany. For this purpose the IVS Analysis Centres (ACs) provided datum-free normal equation matrices in Solution INdependent EXchange (SINEX) format for each 24 h observing session to be combined on a session-by-session basis by a stacking procedure. In this process, common sets of parameters, transformed to identical reference epochs and a prioris, and especially representative relative weights have been taken into account for each session. In order to assess the quality of the combined IVS files, Earth orientation parameters (EOPs) and scaling factors have been derived from the combined normal equation matrices. The agreement of the EOPs of the combined normal equation matrices with those of the individual ACs in terms of weighted root mean square (WRMS) is in the range of 50–60 μas for the two polar motion components and about 3 μs for UT1−UTC. External comparisons with International GNSS Serive (IGS) polar motion components is at the level of 130–170 μas and 21 μs/day for length of day (LOD). The scale of the terrestrial reference frame realized through the IVS SINEX files agrees with ITRF2000 at the level of 0.2 ppb.