Coronal fast wave trains of the decimetric type IV radio event observed during the decay phase of the June 6, 2000 flare

The 22 min long decimetric type IV radio event observed during the decay phase of the June 6, 2000 flare simultaneously by the Brazilian Solar Spectroscope (BSS) and the Ond?ejov radiospectrograph in frequency range 1200–4500 MHz has been analyzed. We have found that the characteristic periods of about 60 s belong to the long-period spectral component of the fast wave trains with a tadpole pattern in their wavelet power spectra. We have detected these trains in the whole frequency range 1200–4500 MHz. The behavior of individual wave trains at lower frequencies is different from that at higher frequencies. These individual wave trains have some common as well as different properties. In this paper, we focus on two examples of wave trains in a loop segment and the main statistical parameters in their wavelet power and global spectra are studied and discussed.     

基于激光反射层析法的换能器声场测量技术及仿真研究

换能器的辐射声场分布能够直接反映出换能器声学性能的好坏,若不能精确测量出换能器的辐射声场,则会对换能器的诊断和评估造成严重影响。从理论仿真的角度出发,推导了运用激光反射层析法重建换能器辐射声场的理论公式,着重利用推导出的理论公式对激光反射层析法进行了仿真计算。结果表明激光反射层析法能够精确地重建出换能器的辐射声场分布及声场中的声压量值,这为换能器的声场重建及声压测量提供了一种可行的方法。     

声发射检验技术进展

本文简要介绍了声发射技术的发展史，并从声发射技术的原理、波形分析法、参数分析法、声源定位技术和声发射仪器几个方面进行了综述，主要讨论了最新的波形分析技术和检测仪器的构成。最后指出了声发射检测的发展方向是声发射信号的模拟识别及人工神经网络模式识别分析。     

功能梯度压电材料层状结构中的SH波

基于线性压电弹性理论,利用传递矩阵法,分析了功能梯度压电材料层状结构中的SH波传播特性,研究了压电梯度覆盖层中初始应力对SH波传播的影响。压电覆盖层的材料性能如弹性、压电、介电系数和密度沿厚度方向呈梯度变化。数值分析结果表明,适当的材料梯度分布,可使SH波倾向于沿覆盖层表面传播,由此能够获得更好的机电耦合性能;同时,初始应力使得波传播的相速度减小,但增大了机电耦合系数。文中的分析方法和结论,对固体火箭发动机超声探伤及其压电类传感器的研制和选择有一定的参考意义。     

A comparative and numerical study of effects of gravity waves in small miss-distance and miss-time GPS radio occultation temperature profiles

The Global Positioning System (GPS) Radio Occultation (RO) technique has global coverage and is capable of generating high vertical resolution temperature profiles of the upper troposphere and lower stratosphere with sub-Kelvin accuracy and long-term stability, regardless of weather conditions. In this work, we take advantage of the anomalously high density of occultation events at the eastern side of the highest Andes Mountains during the initial mission months of COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate). This region is well-known for its high wave activity. We choose to study two pairs of GPS RO, both containing two occultations that occurred close in time and space. One pair shows significant differences between both temperature profiles. Numerical simulations with a mesoscale model were performed, in order to understand this discrepancy. It is attributed to the presence of a horizontal inhomogeneous structure caused by gravity waves.     

Gravity wave momentum flux generation close to mid-latitude Andes in mesoscale simulations of late 20th and 21st centuries

Adequate representations of diverse dynamical processes in general circulation models (GCM) are necessary to obtain reliable simulations of the present and the future. The parameterization of orographic gravity wave drag (GWD) is one of the critical components of GCM. It is therefore convenient to evaluate whether standard orographic GWD parameterizations are appropriate. One alternative is to study the generation of gravity waves (GW) with horizontal resolutions that are higher than those used in current GCM simulations. Here we assess the seasonal pattern of topographic GW momentum flux (GWMF) generation for the late 20th and 21st centuries in a downscaling using the Rossby Centre regional atmospheric model under the Intergovernmental Panel on Climate Change A1B emission conditions. We focus on one of the world’s strongest extra-tropical GW zones, the Andes Mountains at mid-latitudes in the Southern Hemisphere. The presence of two GCM sub-grid scale structures locally contributing to GWMF (one positive and one negative) is found to the East of the mountains. For the late 21st century the strength of these structures during the GW high season increases around 23% with respect to the late 20th century, but the GWMF average over GCM grid cell scales remains negative and nearly constant around −0.015 Pa. This constitutes a steady significant contribution during GW high season, which is not related to the GWMF released by individual sporadic strong GW events. This characteristic agrees with the fact that no statistically significant variation in GWMF at source level has been observed in recent GCM simulations of atmospheric change induced by increases in greenhouse gases.     

考虑粘性相互作用的跨音速机翼分析

本文将一些已有的三维全位势方程计算方法和一种三维积分边界层方法作了弱相互作用的耦合计算。计算了三种机翼并与已有的试验数据作了比较。     

Alfvénic Electron Acceleration in Aurora Occurs in Global Alfvén Resonosphere Region

Auroral emission caused by electron precipitation (Hardy et al., 1987, J. Geophys. Res. 92, 12275–12294) is powered by magnetospheric driving processes. It is not yet fully understood how the energy transfer mechanisms are responsible for the electron precipitation. It has been proposed (Hasegawa, 1976, J. Geophys. Res. 81, 5083–5090) that Alfvén waves coming from the magnetosphere play some role in powering the aurora (Wygant et al., 2000, J. Geophys. Res. 105, 18675–18692, Keiling et al., 2003, Science 299, 383–386). Alfvén-wave-induced electron acceleration is shown to be confined in a rather narrow radial distance range of 4–5 R _E (Earth radii) and its importance, relative to other electron acceleration mechanisms, depends strongly on the magnetic disturbance level so that it represents 10% of all electron precipitation power during quiet conditions and increased to 40% during disturbed conditions. Our observations suggest that an electron Landau resonance mechanism operating in the “Alfvén resonosphere” is responsible for the energy transfer.     

Fe/O Ratios in Interplanetary Shock Accelerated Particles

It is widely accepted that diffusive shock acceleration is an important process in the heliosphere, in particular in producing the energetic particles associated with interplanetary shocks driven by coronal mass ejections. In its simplest formulation shock acceleration is expected to accelerate ions with higher mass to charge ratios less efficiently than those with lower mass to charge. Thus it is anticipated that the Fe/O ratio in shock-accelerated ion populations will decrease with increasing energy above some energy. We examine the circumstances of five interplanetary shocks that have been reported to have associated populations in which Fe/O increases with increasing energy. In each event, the situation is complex, with particle contributions from other sources in addition to the shock. Furthermore, we show that the Fe/O ratio in shock-accelerated ions can decrease even when the shock is traveling through an Fe-rich ambient ion population. Thus, although shock acceleration of an Fe-rich suprathermal population has been proposed to explain large Fe-rich solar particle events, we find no support for this proposal in these observations.