Statistical Simulation of Boxing Day Tsunami of The Indian Ocean and a Predictive Equation for Beach Run up Heights Based on Work-Energy Theorem

The tsunami similar to the one that has occurred in December 26, 2004 (Boxing Day Tsunami) in the Indian Ocean is simulated using the expression derived from Modified Weibull Distribution (for maximum wave height simulation) for extreme wave height predictions. The tuning coefficient plays a significant role in estimating the tsunami heights at various stages. It follows well defined mathematical laws at different stages. It is time dependent in the first three stages and depth dependent in the last two stages. The beach run-up heights estimated by the expression derived from the work-energy relation are comparable with observed values with reasonable accuracy.     

Steady motion and spiral patterns in typhoon

INTRODUCTIONItiswellknownthattyphoonSareakindofmooscaleatmosphericvortexovertheoceaninthelOwerlatitudes.Thethree-dimenSionalstructures(Anthes,1976)oftyphoonS,inwhichthereareaneyeandthewarrncenterwheretherearealocallOwpressurewithcycloniccirculationan...     

高空冷涡影响台风Meranti(1010)北翘路径的集合预报分析

路径突变是台风路径预报中的一个难题。2010年第10号台风Meranti（1010）在台湾岛南部海域西移过程中突然北折,而欧洲中期天气预报中心（ECMWF）集合预报对其北翘路径存在较大分歧。选取预报成功与不成功两组集合成员各8例,对比分析台风Meranti路径变化的主要原因。结果表明:（1）一个来自热带对流层上部槽的切断高空冷涡（UTCL）是该台风路径变化的一个重要影响系统。Meranti北翘路径跟它与UTCL的南北向耦合有关;（2）UTCL通过改变台风上层的环境气流影响台风引导气流。在UTCL移至台风北部过程中,台风的偏南风引导气流明显加强,有利于其路径北翘;（3）UTCL对台风Meranti北翘路径的影响还与其自身结构有关。水平环流宽且气旋性涡旋向下垂直伸展更深的UTCL对台风路径变化影响更明显;（4）位涡倾向方程的诊断分析表明,在TC与UTCL南北向耦合过程中,台风北部的正位涡水平平流项输送显著,有利于台风向北运动,且UTCL影响下产生的非对称风场在其中起主要作用。     

Stellar populations in barred spirals

OASIS observations obtained at the Canada–France–Hawaii Telescope for the spiral galaxies NGC 4900 and NGC 5430 produce one spectrum for each 0.41″ element of the 11″ × 15″ field of view. This allows for the spatial characterisation of the different stellar populations. From these observations we study the young (10 Myr) and older stellar populations using evolutionary synthesis codes. Based on the gas emission lines, we find that the young populations are located in relatively small regions and dominate the integrated flux. In NGC 4900, the young populations are distributed in a bar-like structure featuring a hole near the position of the galaxy’s centre. The young stellar populations of NGC 5430 form a nuclear ring and two patches at the base of the spiral arms. Based on Mg₂ and FeI absorption lines, we find that in both galaxies, the young stars are superimposed on a relatively homogenous population of a few Gyr.     

Stellar and gas dynamics of late-type barred-spiral galaxies: NGC 3359, a test case

We study the dynamics of a model for the late-type barred-spiral galaxy NGC 3359 by using both observational and numerical techniques. The results of our modelling are compared with photometric and kinematical data. The potential used is estimated directly from observations of the galaxy. It describes with a single potential function, a barred-spiral system with an extended spiral structure. Thus, the study of the dynamics in this potential has an interest by itself. We apply orbital theory and response models for the study of the stellar component, and smoothed particle hydrodynamics for modelling the gas. In particular, we examine the pattern speed of the system and the orbital character (chaotic or ordered) of the spiral arms. We conclude that the spiral pattern rotates slowly, in the sense that its corotation is close to or even beyond the end of the arms. Although a single, slow pattern speed could, under certain assumptions, characterize the whole disc, the comparison with the observational data indicates that probably the bar and the spirals have different angular velocities. In our two pattern speeds model, the best fit is obtained with a bar ending close to its 4:1 resonance and a more slowly rotating spiral. Assuming an 11 Mpc distance to the galaxy, a match of our models with the observed data indicates a pattern speed of about  39 km s⁻¹ kpc⁻¹  for the bar and about  15 km s⁻¹ kpc⁻¹  for the spiral. We do not find any indication for a chaotic character of the arms in this barred-spiral system. The flow in the region of the spirals can best be described as a regular 'precessing-ellipses flow'.     

Orbital structure in N-body models of barred-spiral galaxies

We study the orbital structure in a series of self-consistent N -body configurations simulating rotating barred galaxies with spiral and ring structures. We perform frequency analysis in order to measure the angular and the radial frequencies of the orbits at two different time snapshots during the evolution of each N -body system. The analysis is done separately for the regular and the chaotic orbits. We thereby identify the various types of orbits, determine the shape and percentages of the orbits supporting the bar and the ring/spiral structures, and study how the latter quantities change during the secular evolution of each system. Although the frequency maps of the chaotic orbits are scattered, we can still identify concentrations around resonances. We give the distributions of frequencies of the most important populations of orbits. We explore the phase-space structure of each system using projections of the 4D surfaces of section. These are obtained via the numerical integration not only of the orbits of test particles, but also of the real N -body particles. We thus identify which domains of the phase space are preferred and which are avoided by the real particles. The chaotic orbits are found to play a major role in supporting the shape of the outer envelope of the bar as well as the rings and the spiral arms formed outside corotation.