Seasonal and interannual variability of phytoplankton pigment in the Laccadive (Lakshadweep) Sea as observed by the Coastal Zone Color scanner

Based on Coastal Zone Color Scanner data from November 1978 through December 1981, the seasonal cycle of phytoplankton pigment in the upper part of the euphotic zone is established for the offshore Laccadive Sea. Year-round, the pigment content is low and the seasonal range is small, following the pattern of the nutrient-poor Arabian Sea to the west. Apparently, indigenous phytoplankton blooms are absent. July and August, however, were poorly studied because of cloud cover. Interannual differences during the northeast monsoon and the spring intermonsoon periods are minor. The abundant phytoplankton caused by the upwelling off India during the southwest monsoon remains essentially restricted to the shelf, but there are occasional large, zonal outbreaks into the Laccadive Sea, as well as others advected to the south of India. Visual inspection of the raw CZCS scenes for June through November 1982–1985, with almost no data until August or even September, shows such outbreaks of pigment-rich water to be common. Inspection of monthly SeaWiFS images for 1997 through part of 2001 confirms the absence of indigenous phytoplankton blooms.     

典型带状云系强降雨过程卫星云图演变特征分析

通过对两个典型的带状云系的强降水过程的卫星云图进行定量分析,初步验证了可以用云带0℃边界反映冷高压和副高的活动态势,揭示了降雨强度与云带强度指数及TBB面积指数有很好的对应关系。同时,还研究了暴雨落区与对流云团活动范围的关系,强降水时段与对流云团的发展阶段的对应关系。     

卫星云图、雷达回波在人工增雨时机选择中的应用

概述了干旱期间选择飞机和高炮人工增雨作业时机的方法，以2000年6～7月哈尔滨地区特大干旱期间进行的飞机和高炮人工增雨作业为例，利用卫星云图和雷达回波资料选择的作业时间和作业区域应是比较有利的。因为从卫星云图中的水汽图、红外和可见光云图上可分析出云系中的含水量、云顶温度、云系强度，在此基础上利用天气雷达跟踪订正，可直接指挥飞机和高炮在有利的区域和时间内进行作业，获得了明显的效果。     

Tectonometamorphic evolution of the Himalayan metamorphic core between the Annapurna and Dhaulagiri, central Nepal

The metamorphic core of the Himalaya in the Kali Gandaki valley of central Nepal corresponds to a 5-km-thick sequence of upper amphibolite facies metasedimentary rocks. This Greater Himalayan Sequence (GHS) thrusts over the greenschist to lower amphibolite facies Lesser Himalayan Sequence (LHS) along the Lower Miocene Main Central Thrust (MCT), and it is separated from the overlying low-grade Tethyan Zone (TZ) by the Annapurna Detachment. Structural, petrographic, geothermobarometric and thermochronological data demonstrate that two major tectonometamorphic events characterize the evolution of the GHS. The first (Eohimalayan) episode included prograde, kyanite-grade metamorphism, during which the GHS was buried at depths greater than c. 35 km. A nappe structure in the lowermost TZ suggests that the Eohimalayan phase was associated with underthrusting of the GHS below the TZ. A c. 37 Ma ⁴⁰Ar/³⁹Ar hornblende date indicates a Late Eocene age for this phase. The second (Neohimalayan) event corresponded to a retrograde phase of kyanite-grade recrystallization, related to thrust emplacement of the GHS on the LHS. Prograde mineral assemblages in the MCT zone equilibrated at average T =880 K (610 °C) and P =940 MPa (=35 km), probably close to peak of metamorphic conditions. Slightly higher in the GHS, final equilibration of retrograde assemblages occurred at average T =810 K (540 °C) and P=650 MPa (=24 km), indicating re-equilibration during exhumation controlled by thrusting along the MCT and extension along the Annapurna Detachment. These results suggest an earlier equilibration in the MCT zone compared with higher levels, as a consequence of a higher cooling rate in the basal part of the GHS during its thrusting on the colder LHS. The Annapurna Detachment is considered to be a Neohimalayan, synmetamorphic structure, representing extensional reactivation of the Eohimalayan thrust along which the GHS initially underthrust the TZ. Within the upper GHS, a metamorphic discontinuity across a mylonitic shear zone testifies to significant, late- to post-metamorphic, out-of-sequence thrusting. The entire GHS cooled homogeneously below 600–700 K (330–430 °C) between 15 and 13 Ma (Middle Miocene), suggesting a rapid tectonic exhumation by movement on late extensional structures at higher structural levels.     

滇西下关温泉水化观测项目的主成分分析及有关地震异常研究

根据对下关温泉１９９２年８个水化观测项目主成分进行的分析及影响因素的研究，发现氡和气压、水温和ＰＨ值、氩和氮、二氧化碳分别构成独立性较强的４个主成分．气压和流量是化学组分的主要影响因素     

湖南汛期降水异常的时空分布特征研究

利用湖南19个测站23年(1959～2001年)4～9月的降水量资料，用EOF、REOF、小波分析对湖南汛期降水的特征场分布、分区特征、周期性和突变性等时空分布特征进行了诊断研究。研究结果表明：EOF分析得到的前三个典型场可以很好的反映湖南汛期降水空间分布的异常结构，即具有整体一致的空间结构，南北相反的空间结构，中部和周围地区相反变化的空间结构。旋转后的前6个空间模态可以较好地代表湖南汛期降水的6个异常敏感区：湘北、湘中、湘南、湘东南、湘西、湘东北。利用小波分析方法研究湖南汛期降水的周期性及其突变性发现，湖南汛期降水存在着明显的3年、7年和23年的特征时间尺度和周期性振荡；并且在今后相当长的一段时间内，湖南汛期的降水将逐年减少，并将转入干旱时期。     

Late Miocene movement within the Himalayan Main Central Thrust shear zone, Sikkim, north-east India

In the Sikkim region of north‐east India, the Main Central Thrust (MCT) juxtaposes high‐grade gneisses of the Greater Himalayan Crystallines over lower‐grade slates, phyllites and schists of the Lesser Himalaya Formation. Inverted metamorphism characterizes rocks that immediately underlie the thrust, and the large‐scale South Tibet Detachment System (STDS) bounds the northern side of the Greater Himalayan Crystallines. In situ Th–Pb monazite ages indicate that the MCT shear zone in the Sikkim region was active at c. 22, 14–15 and 12–10 Ma, whereas zircon and monazite ages from a slightly deformed horizon of a High Himalayan leucogranite within the STDS suggest normal slip activity at c. 17 and 14–15 Ma. Although average monazite ages decrease towards structurally lower levels of the MCT shear zone, individual results do not follow a progressive younging pattern. Lesser Himalaya sample KBP1062A records monazite crystallization from 11.5 ± 0.2 to 12.2 ± 0.1 Ma and peak conditions of 610 ± 25 °C and 7.5 ± 0.5 kbar, whereas, in the MCT shear zone rock CHG14103, monazite crystallized from 13.8 ± 0.5 to 11.9 ± 0.3 Ma at lower grade conditions of 525 ± 25 °C and 6 ± 1 kbar. The P–T–t results indicate that the shear zone experienced a complicated slip history, and have implications for the understanding of mid‐crustal extrusion and the role of out‐of‐sequence thrusts in convergent plate tectonic settings.     

川滇地区单断裂强震区与多断裂强震区

以《全国小震目录》(1965年1月1日～2002年lO月31日)和《四川地震台网快报目录》(2002年11月1日～2003年9月30日)为基础资料，研究了川滇地区地震活动性发展变化的主要特征，并提出“单断裂强震区”和“多断裂强震区”概念。发现川滇地区主要单断裂强震区在发生一些强震之后，已经陆续进入地震平静时段，近期发生强震的能力明显减弱。与此同时，“滇西南”、“龙陵-腾冲”、“丽江-武定”地区分别在较短时段内发生多次强震，表明这几个多断裂强震区陆续进入活跃时段，成为1984年以来川滇地区的地震主体活动区域。多断裂强震区具有区内中小断裂汇集、地质构造复杂、地震活跃时段多次出现、在同一活跃时段内又具有活跃小段与小段间距的小段组合形式等特征。对已有的和可能新生的多断裂强震区进行早期判定，以及对活跃时段、小段组合进行动态跟踪，对于川滇地区地震预报具有重要意义。     

Obsidian from the northern sector of the Main Ethiopian Rift: implications for archeology

Obsidian is abundant in the Main Ethiopian Rift (MER). Petrological and geochemical features of obsidian from four volcanic centers in the MER, namely Birenti, Dofen, Fentale and Kone, are presented. Compositional and petrological variability is noted among the Dofen and Fentale obsidian, but not in those from Kone and Birenti where each have separate but uniform elemental composition. The Fentale and Kone obsidian were source materials for the artifacts of a number of Middle Stone Age and Later Stone Age/Neolithic sites in the region. We have yet to determine whether Dofen and Birenti were sources for archeological artifacts. The study also shows that volcanic episodes from a single center do not necessarily result in compositional variability.     

Effects of wave directionality on extreme response for a long end-anchored floating bridge

Reliable design codes are of great importance when constructing new civil engineering concepts such as floating bridges. Previously only a scarce number of floating bridges have been built in rough wave conditions and only limited knowledge of the extreme environmental conditions and the associated extreme response exists. To form a better design basis an increased understanding of the sensitivity in the structural response towards changes in short-crested sea parameters is needed. Furthermore, acquiring the necessary accuracy in simulated extreme response is often a computationally expensive endeavour and the number of simulations needed is often based on experience. The present study investigates the wave-induced short-term extreme response of a simplified end-anchored floating bridge concept for several wave environments with a return period of 100 years. The study includes convergence of the coefficient of variation for the extreme response for different realization lengths as well as number of realizations. The sensitivity in the structural response towards different main wave directions and spreading exponents is investigated and includes both transverse and vertical displacement response spectra and extreme Von Mises stress in the bridge girder cross-section. The extreme response is based on an accuracy of 2% in the coefficient of variation equivalent to 40 3-h realizations and a low sensitivity in the response is found for natural occurring spreading exponents and for main wave directions within 15° from beam sea.