基于高斯束理论的有限频核函数计算

相对于常规射线层析速度建模,基于波动理论的层析速度建模考虑了波的带限特性,反演分辨率更高.波动理论层析的核心在于波路径(有限频核函数)的计算.文中详细介绍了一种基于高斯束算子计算有限频核函数的方法,分析了初始束宽度和高斯束出射角度间隔对计算精度的影响;并针对高斯束近源处误差较大的缺陷,提出了改进的束参数以提高近源精度;详细分析了初始束宽度和角度间隔对改进高斯束方法的影响及改进高斯束的聚焦特性;数值算例验证了该方法在缓变介质中计算有限频核函数的可行性,计算效率较高且可处理回折波的核函数.     

地铁隧道盾构施工引起的工程性地面沉降研究

基于上海地区地铁隧道盾构施工引发的工程性地面沉降机理分析,采用数值分析和数学拟合方法,对盾构埋深、地层损失率、盾构半径和穿越土层性质等因素与地面沉降影响范围和最大沉降量之间的基本规律分别进行了深入的分析研究,给出了它们之间各自的定量关系式,并在盾构施工实例中进行了分析和验证。     

额尔齐斯河上游西伯利亚云杉树轮宽度年表特征分析及其对气候的响应

利用采自阿尔泰山南坡额尔齐斯河上游森林6个采样点的低海拔西伯利亚云杉（Picea obovata Ledeb）树轮样本,建立6个树轮宽度指数年表。分析标准化树轮宽度年表的特征参数及对气候的响应发现：（1）可可托海北（KKT）年表包含的气候信息最多,其次是塔里德萨依（TLD）年表。（2）6个标准化年表及区域年表（HEC）与临近的富蕴气象站与生长季及生长季前期的降水呈正相关,与上年7月到当年6月降水量相关最高达0.755,该研究结果与新疆天山山区云杉对气候的响应完全一致。降水是森林下限西伯利亚云杉树轮宽度生长的主要限制因子。（3）海拔相对较高的协特克阔依汗（XTK）和KKT年表除与其它年表具有对降水相同的响应特点外,还与当年8月的平均最低气温呈显著正相关。（4）区域年表树轮宽度指数经历了9个偏高时段和8个偏低时段,揭示了该地区降水的长期变化。     

湖南郴州树轮宽度的雪灾和气候环境变化记录

2008年1月至2月, 我国南方经历了罕见的大范围低温、雨雪和冰冻灾害, 人民生命财产安全和地方经济遭受了巨大损失。为了评估2008年雪灾事件及气候变化对树木生长的影响, 本研究在湖南省宜章县境内采集了一组马尾松树木年轮样本, 并建立了树轮宽度年表。虽然Pearson相关分析揭示树轮宽度年表与当年6月至10月的平均最低温度(r =-0.636, n=69, p < 0.01)和前一年2月至12月的相对湿度(r =0.619, n=68, p < 0.01)相关性最强, 但滑动相关分析结果表明, 树轮宽度与气候要素的关系随时间变化并不稳定, 其表现在2008年雪灾事件之后研究区树木生长对气候要素的响应显著增强。为了进一步确认雪灾事件对树木生长的影响, 通过历史文献记载搜集了2008年之前研究区发生的多次雪灾事件年份(1865年、1930年、1955年、1964年、1969年、1976年、1984年、1993年、1996年和2000年), 并开展了时序叠加分析。结果表明, 在历史时期, 树轮宽度仅在雪灾发生当年略有降低, 雪灾对随后年份的树木生长影响不大; 而2008年雪灾导致当年及其后5年树轮宽度都显著下降, 表明2008年雪灾的严重程度至少在过去166年内是史无前例的。进一步分析发现, EASM(东亚夏季风)及与之相关的大尺度环流变化如ENSO(厄尔尼诺-南方涛动)、PDO(太平洋年代际振荡)和WPSH(西太平洋副热带高压)影响着研究区过去166年来的气候环境变化, 进而影响了树木生长。

     

树轮记录的阿尔泰山南坡过去304年夏季温度变化及水热配置模式

阿尔泰山南坡受到西风急流、北冰洋冷湿气流、蒙古-西伯利亚高压和亚洲低压共同影响,形成了当地特有的气候模式;同时,阿尔泰山地区是欧亚沟通的枢纽地带,气候变化对周边人类生产生活以及生态系统影响显著。因此有必要了解阿尔泰山周边气候变化长期历史,识别气候变化特征,总结规律以应对未来气候变化带来的灾害。本研究利用相关分析发现阿尔泰山南坡西伯利亚落叶松树轮宽度年表与夏季(6~7月)温度呈显著关系(r=0.626,n=58,p＜0.001),进而建立一阶线性回归模型方程定量重建了阿尔泰山南坡过去304年(1715~2018年)夏季温度变化。统计结果显示重建序列稳定可靠,并有能力代表大范围的温度变化特征。重建存在5个暖期(1740~1767年、1775~1793年、1837~1847年、1898~1909年、1990~2018年)和5个冷期(1715~1727年、1807~1828年、1848~1858年、1876~1897年、1927~1940年)。虽然自1990年来温度持续上升(1990~2018年温度距平0.33 ℃),但并未超过1740~1767年的温度(温度距平0.49 ℃)。结合周边降水重建序列,发现研究区域在过去3个多世纪表现出夏季水热同步的配置模式,即暖湿/冷干模态占主导地位。

     

武昌电离层E-F谷区白天变化形态

本文利用文献[4]的分析程序对武昌地区三年共300多张频高图作了剖面换算和统计分析,得出白天E-F谷区电离的基本形态并发现一些新的变化特征;对分析结果的可能原因提出了讨论。     

High-resolution magnetostratigraphy and micropalaeontology across the J/K boundary strata at Brodno near ilina, western Slovakia: summary of results

This study summarizes the final results of magnetostratigraphic and micropalaeontological investigations of the Tithonian/Berriasian boundary (J/K) limestones at the locality of Brodno near ilina, Western Carpathians, West Slovakia. The aim is to prepare the background for correlation of a Late Tithonian and Early Berriasian biostratigraphic zonation with global magnetoevents (manifested in detailed magnetostratigraphic profiles) between the Tethyan realm and other regions, particularly the Boreal and Pacific realms. Suitable physical properties of the limestones studied, a favourable geological setting and rich microfossil assemblages (calpionellids) at Brodno (magnetozones M21r to M18r) allowed a systematic collection of new data on the original synoptic section, which now has the character of a high-resolution profile across the J/K boundary. Two reverse subzones detected within magnetozones M20n and M19n are named ‘Kysuca Subzone’ and ‘Brodno Subzone’, respectively. Both can be correlated with analogous subzones in the M-sequence of marine anomalies. Their existence can also be confirmed in the Bosso Valley section in Umbria, central Italy. A detailed study of the interval between magnetozones M20n and M17r in the Bosso Valley profile is presently in its final stage. Both magnetostratigraphic profiles, from the Brodno and Bosso Valley localities, were thoroughly investigated in the intervals close to the J/K boundary and are still unique among continent-based profiles in the detection and precise definition of both reverse subzones within M20n and M19n. Samples collected from the boundary strata of the reverse Kysuca Subzone at Brodno indicated a transition from N (R) to R (N) polarity of the Earth's palaeomagnetic field within a time interval of c. ±5 ka. Limestone samples (total number N=368) were subjected to progressive thermal demagnetization in 10–12 thermal fields and to subsequent multi-component analysis of remanence. The C-component, as the carrier of palaeomagnetic directions, was determined in the temperature interval of 300° to 540°, or possibly 580°C. Magnetomineralogical analyses of pilot samples and unblocking temperatures determined for all samples showed that magnetite is the carrier of remanent magnetization. The positions of the individual events of calpionellid stratigraphy relative to the global magnetic polarity timescale are precisely defined. The base of the Calpionella Standard Zone, which is considered a provisional J/K boundary indicator in ammonite-free sections in the Tethyan realm, lies within magnetozone M19n at the level of 35% of its local thickness. None of the boundaries in the calpionellid zonation coincides precisely with any of those in the palaeomagnetic zonation, but the first appearance ofCalpionella grandalpina , indicating the base of the Intermedia Subzone, lies in close proximity to the base of magnetozone M19r.     

海浪谱型对最大波高估算的影响研究

无论是对于各种涉海水工建筑物的设计还是对于它们的防护而言,最大波高的预测都是非常重要的工作。目前常用的海浪预报模式多以相位平均模型为主,其能直接给出的计算结果是海浪谱,因此基于海浪谱给出合理的最大波高估算具有重要的意义。前人对波陡、谱宽等参数对最大波高公式的影响都有了较为清楚的认知,然而相关研究大多围绕单峰谱开展,尚没有考虑包括双峰谱在内的海浪谱型最大波高公式的影响。本文首先探讨了海浪谱对最大波高的影响特性,进而提出了海浪谱谱型的参数化定义,最后给出了考虑谱型因子的最大波高公式。     

飓风Juan(2003)路径附近实测飓风浪的谱特性研究

Hurricane Juan provides an excellent opportunity to probe into the detailed wave spectral patterns and spectral parameters of a hurricane system, with enough wave spectral observations around Juan＇s track in the deep ocean and shallow coastal water. In this study, Hurricane Juan and wave observation stations around Juan＇s track are introduced. Variations of wave composition are discussed and analyzed based on time series of one-dimensional frequency spectra, as well as wave steepness around Juan＇s track： before, during, and after Juan＇s passing. Wave spectral involvement is studied based on the observed one-dimensional spectra and two-dimensional spectra during the hurricane. The standardization method of the observed wave spectra during Hurricane Juan is discussed, and the standardized spectra show relatively conservative behavior, in spite of the huge variation in wave spectral energy, spectral peak, and peak frequency during this hurricane. Spectral widths＇ variation during Hurricane Juan are calculated and analyzed. A two-layer nesting WW3 model simulation is applied to simulate the one-dimensional and two-dimensional wave spectra, in order to examine WW3＇s ability in simulating detailed wave structure during Hurricane Juan.