Microinstabilities associated with a high Mach number,perpendicular bow shock

The instabilities associated with a high Mach number perpendicular shock are reexamined in light of recent enhanced understanding of the Earth's bow shock. The insights provided by both the ISEE observations and hybrid simulations are reviewed and subsequently incorporated into the instability analyses. The discussion of the instabilities is divided according to their location in the shock layer. In the regions in front of and at the shock transition the cross-field instabilities are subdivided into low frequency modes (e.g. ion-ion streaming, kinetic cross-field streaming, drift lower hybrid instabilities) and high frequency modes (electron cyclotron drift, ion sound and electron whistler instabilities). Further downstream various ion ring-like and anisotropy driven instabilities are considered. In each case the instability analysis is reviewed and recent developments are emphasized. Implications of these results concerning the wave signatures and plasma heating and acceleration are also discussed.     

Critical Issues on Magnetic Reconnection in Space Plasmas

The idea of expedient energy transformation by magnetic reconnection (MR) has generated much enthusiasm in the space plasma community. The early concept of MR, which was envisioned for the solar flare phenomenon in a simple two-dimensional (2D) steady-state situation, is in dire need for extension to encompass three-dimensional (3D) non-steady-state phenomena prevalent in space plasmas in nature like in the magnetosphere. A workshop was organized to address this and related critical issues on MR. The essential outcome of this workshop is summarized in this review. After a brief evaluation on the pros and cons of existing definitions of MR, we propose essentially a working definition that can be used to identify MR in transient and spatially localized phenomena. The word “essentially” reflects a slight diversity in the opinion on how transient and localized 3D MR process might be defined. MR is defined here as a process with the following characteristics: (1) there is a plasma bulk flow across a boundary separating regions with topologically different magnetic field lines if projected on the plane of MR, thereby converting magnetic energy into kinetic particle energy, (2) there can be an out-of-the-plane magnetic field component (the so-called guide field) present such that the reconnected magnetic flux tubes are twisted to form flux ropes, and (3) the region exhibiting non-ideal MHD conditions should be localized to a scale comparable to the ion inertial length in the direction of the plasma inflow velocity. This definition captures the most important 3D aspects and preserves many essential characteristics of the 2D case. It may be considered as the first step in the generalization of the traditional 2D concept. As a demonstration on the utility of this definition, we apply it to identify MR associated with plasma phenomena in the dayside magnetopause and nightside magnetotail of the Earth’s magnetosphere. How MR may be distinguished from other competing mechanisms for these magnetospheric phenomena are then discussed.This revised version was published online in July 2005 with a corrected cover date.     

Detection and diagnosis of sensor and actuator failures using IMMestimator

An approach to detection and diagnosis of multiple failures in a dynamic system is proposed. It is based on the interacting multiple-model (IMM) estimation algorithm, which is one of the most cost-effective adaptive estimation techniques for systems involving structural as well as parametric changes. The proposed approach provides an integrated framework for fault detection, diagnosis, and state estimation. It is able to detect and isolate multiple faults substantially more quickly and more reliably than many existing approaches. Its superiority is illustrated in two aircraft examples for single and double faults of both sensors and actuators, in the forms of “total”, “partial”, and simultaneous failures. Both deterministic and random fault scenarios are designed and used for testing and comparing the performance fairly. Some new performance indices are presented. The robustness of the proposed approach to the design of model transition probabilities, fault modeling errors, and the uncertainties of noise statistics are also evaluated     

基于三维GIS的机场飞行区运行数字化管理系统

基于地理信息系统软件平台,利用空间信息显 示与数据管理技术,研究了由机场净空评价管理,机场道面评价管理和飞行区地下管线管理 3个子系统组成的机场飞行区运行数字化管理系统。净空评价管理系统通过坐标变换、净空 限制面三维场景建模、障碍物评价算法研究等,实现了基于地理信息的障碍物三维可视化管 理与评价及基于飞行程序的飞机进、离场动态仿真。道面评价管理系统进行了机场道面三维 场景及道面属性信息数字化、属性信息数据库分析、道面各项性能指标和功能模块的算法研 究。实现了机场道面信息的三维场景显示与属性信息查询、基于现场调查和测试数据的场道 PCN、PCI计算;场道剩余使用寿命预测;根据评价结果智能提供维修建议及辅助决策等功能 ,并据此提出了基于空间数据的道面综合评价管理理念。地下管线管理系统研究了基于管线 地理信息数据的三维可视化管理模型,实现了地下管线的三维数字化查询与管理。本系统 整合了机场飞行区运行管理的各项功能,使管理工作数字化、智能化,为机场高效运行提 供了有力保障。     

三维曲面部分匹配的算法研究

将基于曲率分析的曲面片形状划分方法和几何哈希相结合，提出一种通用的空间曲面匹配算法。对待匹配的三维曲面模型，计算其网格顶点的主曲率和法矢；由主曲率和该点所在的曲面片类型来构造其无向脚标，有向脚标为该点的法矢。按照多重筛选标准生成数量少却有效的匹配点对，建立候选点对列表。由候选点对所生成的三维空间变换组成哈希表，运用双层哈希投票机制得出使模型能够正确匹配的三维坐标变换矩阵。实验表明，该算法适用于具有部分重叠的曲面模型的匹配，并能保证较好的匹配精度和速度。     

Location of layered structures in the ionosphere and atmosphere by use of GPS occultation data

A method is introduced to locate the layered structures in the atmosphere and ionosphere based on simultaneous observations of radio wave intensity and phase variations in trans-ionospheric satellite-to-satellite links. The method determines location of a tangent point on the trans-ionospheric ray trajectory where gradient of refractivity is perpendicular to the ray trajectory and influence of a layered structure on radio wave parameters is maximal. An estimate of the location of a layer can be obtained from a combination of the phase and intensity variations. This new technique was applied to measurements provided during FORMOSAT-3 and CHAMP radio occultation (RO) missions. For the considered RO events the location of the inclined plasma layer in the lower ionosphere is found and the electron density distribution is retrieved. The method is checked by measuring the location of the tangent point on the ray trajectory in the neutral gas in the atmosphere. The results showed a fairly good agreement.     

First MAGDAS installation at Fayum in Egypt

We have installed the first MAGDAS magnetometer at Fayum in Egypt. The ambient temperature in the initial sensor house varied more than ±4 °C in one day (24 h period). This variation made the magnetic data useless. To correct this problem, (1) a new sensor house was re-constructed which reduced the diurnal variation to less than ±1 °C, and (2) the “Uozumi Temperature Correction Method” was introduced. As a result, good data is now arriving in real time at a central facility in Japan.     

Response of the mid-latitude D-region ionosphere to the total solar eclipse of 22 July 2009 studied using VLF signals in South Korean peninsula

In this paper, we analyze VLF signals received at Busan to study the the D-region changes linked with the solar eclipse event of 22 July 2009 for very short (∼390 km) transmitter–receiver great circle path (TRGCP) during local noon time 00:36–03:13 UT (09:36–12:13 KST). The eclipse crossed south of Busan with a maximum obscuration of ∼84%. Observations clearly show a reduction of ∼6.2 dB in the VLF signal strength at the time of maximum solar obscuration (84% at 01:53 UT) as compared to those observed on the control days. Estimated values of change in Wait ionospheric parameters: reflection height (h′) in km and inverse scale height parameter (β) in km⁻¹ from Long Wave Propagation Capability (LWPC) model during the maximum eclipse phase as compared to unperturbed ionosphere are 7 km and 0.055 km⁻¹, respectively. Moreover, the D-region electron density estimated from model computation shows 95% depletion in electron density at the height of ∼71 km. The reflection height is found to increase by ∼7 km in the D-region during the eclipse as compared to those on the control days, implying a depletion in the Lyman-α flux by a factor of ∼7. The present observations are discussed in the light of current understanding on the solar eclipse induced D-region dynamics.