南海夏季风爆发前后扰动演变及其数值研究

以球面正压涡度方程为数学模型，建立了线性和非线性的数值积分模式，通过在模式中设置不同的基本流场和初始扰动场，研究基流和初始场对扰动发展的作用，揭示在球面正压大气中扰动发展的动力学机制。数值试验结果表明:在线性模式中，扰动的移动和发展与基流的分布有着很密切的关系，基流影响着扰动纬向传播的速度和方向； 在非线性模式中，当基流稳定时，扰动的移动以及传播与线性模式的结果相同，但与线性情况的最大区别在于，此时扰动能量的增长存在上限。同时发现，扰动的发展既依赖于基本气流的分布，也依赖初始扰动的结构；南海夏季风爆发前后的基本流场是正压不稳定的，且这种不稳定在季风爆发时达到最强，这可以成为季风爆发的动力学解释。     

中尺度对称不稳定和横波不稳定的波动性质

使用纬向线性以及非线性切变基流下中尺度扰动的Boussinesq近似方程组，讨论了两种典型的中尺度扰动发生对称不稳定或者横波不稳定时，其不稳定的一些特征以及扰动的波动性质。研究结果表明：（1）对于扰动的等位相面平行于基本气流方向的对称性扰动来说，对称不稳定的波动实质是沿着与基本气流方向相垂直的方向传播的重力惯性内波的不稳定。基流二次切变对于中尺度对称扰动来说是一个不稳定因子，并且驱动不稳定的中尺度对称扰动在南北方向传播；（2）对于扰动的等位相面垂直于基本气流方向的横波性扰动来说，在基本气流为常数或者只具有线性切变的情况下，此时根本不存在涡旋Rossby波，横波不稳定的波动实质则是沿着基本气流方向双向传播的重力惯性内波的不稳定。如果考虑基本流场的风速存在二次切变或者非线性切变时，此时就会产生一支新的波动（涡旋Rossby波），涡旋Rossby波相对于基本气流^-U0是单向传播的，涡旋Rossby波产生的物理根源是基本流场的风速^-U二次切变（β＊=^-Uzz≠0），此时横波型不稳定可能是混合的涡旋Rossby——重力波的不稳定。实际大气中，涡旋Rossby波对于中够尺度对流云核、暴雨团等天气系统的发生、发展和演变的物理机制具有极其重要的意义。     

梅雨锋降水运动诊断分析与（大）暴雨形成——江淮梅雨锋暴雨的天气学成因个例分析

对T213 L31再分析模式大气,在等熵坐标系上对天气学大尺度凝结函数降水、水汽通量散度降水做了诊断计算;同时,对整层对流不稳定性降水和气块（团）湿不稳定降水做了理想设计与诊断计算.对2003年7月江淮梅雨锋暴雨的计算与分析表明：两种天气尺度波动的大尺度稳定性降水运动的降水量级较小,都不足以直接形成暴雨;而对流不稳定降水运动可以形成暴雨,却不足以形成大暴雨;只有气块不稳定降水运动,才是梅雨锋上大暴雨的自组织、正反馈的唯一降水机制.研究表明,该江淮梅雨锋暴雨虽然存在着明显的梅雨锋天气尺度降水系统,但充沛的水汽通量和异常高温高湿气团的维持,使得在梅雨锋上发生着的非等熵湿绝热运动及其对流不稳定降水和气块不稳定降水,是（大）暴雨发生的天气学成因.     

球面正压大气的不稳定与南亚夏季风爆发动力机制的探讨

通过球坐标正压原始方程谱点的计算,发现南亚夏季风爆发前有正压不稳定发生,不稳定罗斯贝波其最大增幅位于南半球的西风急流处,可向低纬传播并能在低纬激发出旺盛的积云对流,该积云对流可造成已失稳的大气基本场发生重大调整,从而导致南亚夏季风的爆发.     

2005年6月华南持续性暴雨爆发和维持机制分析

利用常规气象资料及T213分析场资料,对2005年6月18日~23日华南大范围持续性暴雨过程的高低空形势、能量及动力条件进行诊断分析。发现:这次过程低空急流维持了低空对流不稳定形势,高空急流维持了高空辐散、低空辐合的有利形势,高空西南急流与高空西北急流一样,能造成暴雨区高空有利的辐散形势,形成高层辐散、底层辐合,触发强烈的上升运动,高低空耦合是此次强降雨爆发的重要机制,强降雨落区位于低空西南风急流出口区的左侧和200hPa西北风急流的出口区西南侧,即低空急流的左侧与切变线的前沿;暴雨区域高湿能条件的维持,保证了强降雨过程的能量供给,是强降雨持续的重要条件。     

"02.6"陕南大暴雨的结构及成因分析

通过诊断分析发现:(1)“02.6”强降水与6月上旬越赤道气流和季风爆发密切相关,携带大量水汽的偏南气流与冷空气于6月8日交汇在西北地区东部,导致了这次强降水的发生;(2)与暴雨区相联系,存在横越低空急流的经向垂直环流,暴雨区处于该垂直环流的上升支;(3)偏南和偏东气流水汽通道在西北地区东部交汇,水汽的辐合积聚主要在对流层低层和行星边界层内完成;(4)整层的视热源高值区在暴雨区附近呈东北—西南向分布,与切变线走向非常一致,降水产生的凝结潜热释放是强降水区大气的主要热源。同时,在大尺度上升运动区中低层存在一个条件对称不稳定建立的机制,使得在暴雨区,既存在深厚的热力不稳定机制,又存在水汽输入机制和热力不稳定的触发机制,从而形成强暴雨。     

Measuring the Performance of Mineral-Potential Maps

D. P. Harris and others have proposed a new method for comparative analysis of favorability mappings. In their approach, Weights-of-Evidence (WofE) consistently shows poorer results than other more flexible methods. Information loss because of discretization would be a second drawback of WofE. In this paper, we discuss that the random cell selection method proposed by Harris and others necessarily results in higher success ratios for more flexible methods but this does not necessarily indicate that these methods provide better mineral-potential maps. For example, a good point density contouring method that does not use any geoscience background information also would score high in the random cell selection approach. Additionally, we show that discretization usually is advantageous because it prevents occurrences of overly high posterior probabilities. For more detailed comparison, we have conducted a number of experiments on 90 gold deposits in the Gowganda Area of the Canadian Shield comparing WofE with the more flexible weighted logistic regression method. Mineral occurrences should be modeled as discoveries at points instead of randomly sampling them together with their surrounding environments in small cells.     

The deviation of light path in Einstein–Brans–Dicke theory

Both Jordan–Brans–Dicke (shortened JBD) theory and Brans–Dicke theory in the Einstein’s frame (shortened EBD) are treated as Brans–Dicke theory. However, we learn that only Pauli metric represents the massless spin-two graviton and thus, should be identified as physical. If one just considers the weak field approximation and Newtonian limit, EBD theory gives the same results with Einstein’s general relativity. So, it is necessary to consider strong field effects and cosmological model. The purpose of this paper is to find the exact spherically symmetric metric in the strong field situation, and deduce the deviation of light path in EBD theory.     

Large-scale failures on domes and stratocones situated on caldera ring faults: sand-box modeling of natural examples from Kamchatka, Russia

Edifices of stratocones and domes are often situated eccentrically above shallow silicic magma reservoirs. Evacuation of such reservoirs forms collapse calderas commonly surrounded by remnants of one or several volcanic cones that appear variously affected and destabilized. We studied morphologies of six calderas in Kamchatka, Russia, with diameters of 4 to 12 km. Edifices affected by caldera subsidence have residual heights of 250–800 m, and typical amphitheater-like depressions opening toward the calderas. The amphitheaters closely resemble horseshoe-shaped craters formed by large-scale flank failures of volcanoes with development of debris avalanches. Where caldera boundaries intersect such cones, the caldera margins have notable outward embayments. We therefore hypothesize that in the process of caldera formation, these eccentrically situated edifices were partly displaced and destabilized, causing large-scale landslides. The landslide masses are then transformed into debris avalanches and emplaced inside the developing caldera basins. To test this hypothesis, we carried out sand-box analogue experiments, in which caldera formation (modeled by evacuation of a rubber balloon) was simulated. The deformation of volcanic cones was studied by placing sand-cones in the vicinity of the expected caldera rim. At the initial stage of the modeled subsidence, the propagating ring fault of the caldera bifurcates within the affected cone into two faults, the outermost of which is notably curved outward off the caldera center. The two faults dissect the cone into three parts: (1) a stable outer part, (2) a highly unstable and subsiding intracaldera part, and (3) a subsiding graben structure between parts (1) and (2). Further progression of the caldera subsidence is likely to cause failure of parts (2) and (3) with failed material sliding into the caldera basin and with formation of an amphitheater-like depression oriented toward the developing caldera. The mass of material which is liable to slide into the caldera basin, and the shape of the resulted amphitheater are a function of the relative position of the caldera ring fault and the base of the cone. A cone situated mostly outside the ring fault is affected to a minor degree by caldera subsidence and collapses with formation of a narrow amphitheater deeply incised into the cone, having a small opening angle. Accordingly, the caldera exhibits a prominent outward embayment. By contrast, collapse of a cone initially situated mostly inside the caldera results in a broad amphitheater with a large opening angle, i.e. the embayment of the caldera rim is negligible. The relationships between the relative position of an edifice above the caldera fault and the opening angle of the formed amphitheater are similar for the modeled and the natural cases of caldera/cone interactions. Thus, our experiments support the hypothesis that volcanic edifices affected by caldera subsidence can experience large-scale failures with formation of indicative amphitheaters oriented toward the caldera basins. More generally, the scalloped appearance of boundaries of calderas in contact with pre-caldera topographic highs can be explained by the gravitational influence of topography on the process of caldera formation.Editorial responsibility: J. Stix     

Last interglacial and Holocene climatic development in the Norwegian Sea region: Ocean front movements and ice-core data

Planktonic foraminiferal evidence suggests that the ocean front systems between Polar and Atlantic surface waters in the Norwegian Sea generally were located closer to Greenland during Oxygen Isotope Substage 5e than in the Holocene. During both these periods oscillations have occurred in the position of the fronts. In the western Norwegian Sea region, the substage 5e influence of warm Atlantic waters was interrupted by a return to polar conditions. These findings support both ice-core data and evidence from Europe that the last interglacial was a period of rapid climatic shifts.