重庆风暴尺度集合预报系统降水预报性能分析

基于在重庆市气象局业务运行的对流可分辨尺度（3 km）集合预报系统,在已有初值扰动、模式物理过程扰动和侧边界扰动的基础上,对不同集合成员采用不同地形插值方案和地形平滑方案实现对模式静态地形高度的扰动,体现数值模式中地形转换过程的不确定性,开展集合预报批量平行试验。结果表明：（1）实现对模式静态地形高度的扰动后,各集合成员地形高度的离散度与实际地形的起伏程度对应关系较好,两者空间分布特征非常相似,地形较平坦的平原地区离散度较小,而地形较复杂的高原地区或山区离散度较大;（2）加入模式地形扰动方案后,集合扰动能量总体上有所增大,且低层比中、高层更明显,能量增幅在较短预报时效（12 h）内最显著,随着预报时效延长呈逐渐减小趋势,且能量增幅大值中心主要出现在地形较复杂、集合成员地形高度离散度较大地区;（3）模式地形扰动方案一定程度上能提高降水概率预报技巧及改进集合平均降水预报,在对高空要素和2 m温度、10 m风场等近地面要素的集合平均均方根误差和集合离散度无负面影响的前提下,能一定程度上优化集合分布。

     

Potential cauchy-poisson waves generated by submarine eruptions of kick 'em Jenny volcano

Kick 'em Jenny is the only known currently active submarine volcano in the Lesser Antilles. The volcano has erupted at least 10 times since first being discovered in 1939 and the summit has shoaled from a depth of 232 m in 1962 to its present-day depth of 150 m. Kick 'em Jenny is located in a province of explosive volcanism, has a known history of explosive eruptions and erupts magma of an explosive type. Future eruptions are likely to become increasingly more violent as the effect of the overlying water pressure becomes less. A preliminary study (Smith and Shepherd, 1993) suggests that Kick 'em Jenny is a prime candidate for tsunamigenic eruptions on a potentially hazardous scale, possibly affecting the whole of the eastern Caribbean region.The classic approach to problems of water waves generated by sudden disturbances of the free surface makes use of the Cauchy-Poisson-Lamb theory. A large number of theoretical developments to this theory have been made for specific forms of surface disturbance. A development by Unoki and Nakano (1953a, b) considers both two- and three-dimensional Cauchy-Poisson waves generated by finite initial elevations and impulses applied to a free surface of infinitely deep water. Unoki and Nakano's results compared well to the wave systems recorded following submarine eruptions of the Myojinsho Reef volcano in 1952–53.Given the similarity of the two situations, Unoki and Nakano's theory is applied to Kick 'em Jenny to provide estimates of potential Cauchy-Poisson wave heights throughout the eastern Caribbean for a range of eruption magnitudes. The results show that, although the waves generated are unlikely to pose much of a threat to the eastern Caribbean as a whole, they should be considered a hazard to the islands immediately adjacent to the volcano including Grenada, the Grenadines, and St Vincent.     

Seafloor topography and landform characteristics of Zengmu Shoal waters and their evolvement

The topography data of the Zengmu Shoal and its adjacent area are acquired by the SeaBat-8111 multibeam system.The full survey covering over the Zengmu Shoal area gives us new knowledge about the area. It is a flat underwater platform consisting ofcoral reefs, its fathom line is like a trap in near SN direction and its shape is like an isosceles triangle with the acute angle pointing to the north. The east and west sides ofthe shoal are steep while its south side is more gentle. As viewed from geological evolution, the Zengmu Shoal is a typical biologic coral landform caused by tectonic uplift.     

用合成孔径雷达图像反演浅海水下地形的一种方法

海流与海底地形的相互作用导致了海表面的粗糙起伏,从而引起对海面观测的雷达散射截面的变化。在浅海海流速度垂直分布廓线为均匀的假定下,由流体连续性方程和驰豫时间近似下流体力学弱相互作用的理论,已证明雷达散射截面的空间变化正比于海流方向上海流速度变化的梯度。研究了合成孔径雷达(SAR)对海面的观测图像在无槽道信息和海流方向预知条件下,提出用散射系数的二维相关函数确定海流方向。在海流速度和方向已知条件下,推导了由雷达散射截面的空间变化迭推反演浅海水下地形的公式,并研究了航天飞机SIR-CSAR在我香港特区海域的二维图像反演浅海水下地形的应用。     

水下地形三维建模Surfer与MATLAB比较分析

目前国内外对水下地形三维建模一般采用Surfer软件,MATLAB在图像处理方面功能强大,在很多专业领域得到广泛应用。本文利用MATLAB进行水下地形三维建模,并与Surfer绘制效果进行比较,显示MATLAB三维建模较Surfer透彻,可展现Surfer建模成果,更可反映清晰的横断面效果,可为岸带调查研究提供技术支持。     

极化信息在水下地形SAR探测中的应用

现有的水下地形SAR(Synthetic Aperture Radar)探测模型尚未综合应用SAR的极化信息。本文基于Valenzuela的雷达散射截面表达式与袁业立提出的海波高频谱表达式,并结合全极化SAR相干斑抑制的极化白化滤波法,将极化信息有效地运用到水下地形SAR探测中去。最后,以中国台湾浅滩为例,分别利用Radarsat-2单一极化和全极化影像开展水下地形SAR探测研究,探测结果表明充分利用全极化信息的探测精度明显优于单一极化信息的探测精度,利用极化信息可以有效地提高水下地形SAR探测精度。     

Generation of Porphyritic and Equigranular Mafic Enclaves During Magma Recharge Events at Unzen Volcano, Japan

Mafic to intermediate enclaves are evenly distributed throughoutthe dacitic 1991–1995 lava sequence of Unzen volcano,Japan, representing hundreds of mafic recharge events over thelife of the volcano. This study documents the morphological,textural, chemical, and petrological characteristics of theenclaves and coexisting silicic host lavas. The eruptive productsdescribed in this study appear to be general products of magmamingling, as the same textural types are seen at many othervolcanoes. Two types of magmatic enclaves, referred to as Porphyriticand Equigranular, are easily distinguished texturally. Porphyriticenclaves display a wide range in composition from basalt toandesite, are glass-rich, spherical and porphyritic, and containlarge, resorbed, plagioclase phenocrysts in a matrix of acicularcrystals and glass. Equigranular enclaves are andesitic, non-porphyritic,and consist of tabular, medium-grained microphenocrysts in amatrix glass that is in equilibrium with the host dacite magma.Porphyritic enclaves are produced when intruding basaltic magmaengulfs melt and phenocrysts of resident silicic magma at theirmutual interface. Equigranular enclaves are a product of a moreprolonged mixing and gradual crystallization at a slower coolingrate within the interior of the mafic intrusion. KEY WORDS: mafic enclaves; quenched mafic inclusions; magma mingling; Unzen volcano; Unzen Scientific Drilling Project; resorbed plagioclase     

长白山天池火山天文峰期黄色浮岩成因研究

长白山天池火口北侧天文峰之上,一套醒目的黄色浮岩引起广泛的关注,其颜色成因问题更是讨论的热点。本文通过野外地质调查、显微形貌和地球化学分析等方法,探索了黄色浮岩的颜色成因问题,并对此次喷发活动（天文峰期喷发）有了更进一步的认识。黄色浮岩与其下部灰白色浮岩应为同一期喷发所形成,两者成分一致且特征相似。黄色浮岩初始颜色为灰白色,后期受所处环境（降水丰富）与本身气孔特征的影响,浮岩内发生了元素析出和元素沉淀的过程。首先,浮岩内Si与H₂O结合形成弱硅酸（H₂SiO₃）,而大气中CO₂与H₂O结合形成弱碳酸（H₂CO₃）,在弱酸环境下火山玻璃逐渐析出Si、K、Al、Ca和Fe等阳离子,而析出的元素易溶于水的部分被流水带走,难溶于水的Fe与Al富集并粘附在火山玻璃壁上,同时由于Fe可与H₂O络合形成黄色的Fe的水合物（Fe₂O₃·nH₂O）,而Al与H₂O络合形成凝胶状白色水合物（Al₂O₃·nH₂O）,两者混合形成了黄色胶状物粘附在火山玻璃壁上,改变了浮岩原本的灰白色,形成了黄色浮岩。因此,天文峰期浮岩的黄色是由于后期风化淋滤作用所造成,属于次生色。本研究提高了对火山喷发堆积物风化淋滤作用过程的认识,也为其他地区相似颜色变化问题的讨论提供了借鉴。

     

Major and trace element geochemistry of neutral and acidic thermal springs at El Chichón volcano,Mexico: Implications for monitoring of the volcanic activity

Four groups of thermal springs with temperatures from 50 to 80 °C are located on the S–SW–W slopes of El Chichón volcano, a composite dome-tephra edifice, which exploded in 1982 with a 1 km wide, 160 m deep crater left. Very dynamic thermal activity inside the crater (variations in chemistry and migration of pools and fumaroles, drastic changes in the crater lake volume and chemistry) contrasts with the stable behavior of the flank hot springs during the time of observations (1974–2005). All known groups of hot springs are located on the contact of the basement and volcanic edifice, and only on the W–SW–S slopes of the volcano at almost same elevations 600–650 m asl and less than 3 km of direct distance from the crater. Three groups of near-neutral (pH ≈ 6) springs at SW–S slopes have the total thermal water outflow rate higher than 300 l/s and are similar in composition. The fourth and farthest group on the western slope discharges acidic (pH ≈ 2) saline (10 g/kg of Cl) water with a much lower outflow rate (< 10 l/s).