High-resolution photography of the solar chromosphere

A method is described for reconstructing the true geometry of a solar loop observed on the disk which takes account of tilt in its own plane. Reconstructions of three H loops yield small tilt angles (14°) and provide further evidence that H loops show a close correspondence to the field lines of a magnetic dipole. The method offers new opportunities for exploring the physics of individual solar loops.     

冬季地面温度和500hPa高度场的适应关系及其客观诊断

实况资料表明,冬季地面的距平高温(或低温)往往对应于高空的距平高压(或低压)。为此,本文建立了一个地面温度距平和500 hPa高度距平之间只带一个比例系数的适应模式。如果这个比例系数看作坐标的函数,它比用常数作比例系数的适应模式更能反映客观实际。     

哀牢山-红河剪切带的热年代学研究——多重扩散域模式的应用实例

洛弗拉等人(1989)把Dodson(1973)建立的单一扩散域模式扩展成矿物扩散域不连续分布的模式,即多重扩散域模式,与之对应具有某一封闭温度范围,因此利用单个K-长石矿物样品可以揭示更长时间段上的冷却过程。对云南哀牢山-红河剪切带的K-长石样品(FA-2-1)进行40Ar/39Ar同位素分析,利用多重扩散域模式,揭示在距今约20～19Ma问该带存在一快速冷却过程,这与西藏南部曲水地区快速抬升的时间是一致的     

Shear-induced instability and arch filament eruption: A magnetohydrodynamic (MHD) numerical simulation

We investigate, via a two-dimensional (nonplanar) MHD simulation, a situation wherein a bipolar magnetic field embedded in a stratified solar atmosphere (i.e., arch-filament-like structure) undergoes symmetrical shear motion at the footpoints. It was found that the vertical plasma flow velocities grow exponentially leading to a new type of global MHD-instability that could be characterized as a Dynamic Shearing Instability, with a growth rate of about 8{ovV} _A a, where {ovV} _A is the average Alfvén speed and a ^–1 is the characteristic length scale. The growth rate grows almost linearly until it reaches the same order of magnitude as the Alfvén speed. Then a nonlinear MHD instability occurs beyond this point. This simulation indicates the following physical consequences: the central loops are pinched by opposing Lorentz forces, and the outer closed loops stretch upward with the vertically-rising mass flow. This instability may apply to arch filament eruptions (AFE) and coronal mass ejections (CMEs).To illustrate the nonlinear dynamical shearing instability, a numerical example is given for three different values of the plasma beta that span several orders of magnitude. The numerical results were analyzed using a linearized asymptotic approach in which an analytical approximate solution for velocity growth is presented. Finally, this theoretical model is applied to describe the arch filament eruption as well as CMEs.     

Numerical case study of the Altai-Sayan lee cyclogenesis over East Asia

Summary Climatological studies show that the Altai-Sayan lee side is one of the major cyclogenesis areas in the Northern Hemisphere. In case of the Altai-Sayan lee cyclogenesis, the surface cyclone is generated when a primary cyclone is swept north of the mountains. In the mid-troposphere, a trough develops and finally turns into a cutoff low within 48 h. The main synoptic features are similar to those of Alpine cyclogenesis. Numerical simulations are performed to assess the effect of different representation of orography on the Altai-Sayan cyclogenesis. Two experiments are performed, a step-mountain (ETA) and an envelope orography (SGM) experiment. The ETA experiment produced the cyclogenesis in a way similar to that in the analysis both at the surface and at mid-troposphere. The SGM experiment failed in the simulation of the upper cutoff low. The difference in predicted pressure between the ETA and the SGM experiment shows a dipolar structure suggesting that the blocking effect of the mountains is essential in the development of the Altai-Sayan lee cyclogenesis.With 7 Figures     

Dynamical interpretation of observed plasmasphere deformations

Based on all of the OGO-5 light ion density measurements (covering the period from March, 1968 to May, 1969), a definition of “isolated plasma regions” was employed to locate the most prominent patches of enhanced light ion densities in the midst of the depleted region, outside of the main plasmasphere. On the dayside, the distribution of these isolated plasma in L.T. vs. L coordinates was quite similar to that of the “detached plasma regions” by Chappell (1974a). On the nightside, however, the new distribution revealed more frequent occurrence of these regions. Elongated thick plasmatails produced during periods of sudden enhancement of convection electric fields and subsequentially thinning and corotating of the plasmatails during quieting periods, in general, could account for the statistical distribution as well as the individual events, such as those between March 27 and April 2, 1968 and Oct. 21 and Oct. 24, 1968. As demonstrated by Kivelson (1976), wave-particle interactions could produce tremendously complicated structures observed in the near vicinity of the plasmapause and far away from the plasmasphere. Examination of H⁺ and He⁺ density measurements for period of Aug. 12–Aug. 20, 1968 indicated that the density reduction of the plasmasphere during a magnetic storm was on the same order of magnitude as that obtained from whistler techniques during a magnetospheric substorm.     

Impact of Flood Disasters on Taiwan in the Last Quarter Century

The increasing natural disasters, especially floods during the last quarter century, are raising the economic losses in Taiwan. The most severe hazard in Taiwan is flooding induced by typhoons and storms in summer and autumn. By comparing the rivers around the world, the ones in Taiwan have the steepest slopes, the largest discharge per unit drainage area, and the shortest time of concentrations. Rapid urbanization without proper land uses managements usually worsen the flood problems. Consequently, flood hazards mitigation has become the most essential task for Taiwan to deal with. Although the government keeps improving flood defense structures, the flood damage grows continuously. In this article, possible flood mitigation strategies are identified for coping with complex environmental and social decisions with flood risk involved.