子午面太阳风结构及其对日冕抛射物运动的影响

本文提出了一种求解二维理想磁流体力学方程组的组合格式-网格方法。该方法在保证一定精度的前提下稳定性好,计算量小。文中使用该方法算得了子午面太阳风的盔状流动解。以该解作为初态,研究了盔状冕旒位形对日冕抛射物运动的影响,发现该位形使得抛射物向低纬赤道方向偏转,较好地解释了观测结果。     

Relationships between energetic storm particle events and interplanetary shocks driven by full and partial halo coronal mass ejections

We have analysed energetic storm particle (ESP) events in 116 interplanetary (IP) shocks driven by front-side full and partial halo coronal mass ejections (CMEs) with speeds $>$400 km s^?1during the years 1996–2015. We investigated the occurrence and relationships of ESP events with several parameters describing the IP shocks, and the associated CMEs, type II radio bursts, and solar energetic particle (SEP) events. Most of the shocks (57 %) were associated with an ESP event at proton energies $>$1 MeV.The shock transit speeds from the Sun to 1 AU of the shocks associated with an ESP event were significantly greater than those of the shocks without an ESP event, and best distinguished these two groups of shocks from each other. The occurrence and maximum intensity of the ESP events also had the strongest dependence on the shock transit speed compared to the other parameters investigated. The correlation coefficient between ESP peak intensities and shock transit speeds was highest (0.73 $\pm$ 0.04) at 6.2 MeV. Weaker dependences were found on the shock speed at 1 AU, Alfvénic and magnetosonic Mach numbers, shock compression ratio, and CME speed. On average all these parameters were significantly different for shocks capable to accelerate ESPs compared to shocks not associated with ESPs, while the differences in the shock normal angle and in the width and longitude of the CMEs were insignificant.The CME-driven shocks producing energetic decametric–hectometric (DH) type II radio bursts and high-intensity SEP events proved to produce also more frequently ESP events with larger particle flux enhancements than other shocks. Together with the shock transit speed, the characteristics of solar DH type II radio bursts and SEP events play an important role in the occurrence and maximum intensity of ESP events at 1 AU.     

基于极化时频分布的改进DOA估计算法

针对雷达回波信号波达方向估计精度差和时频分析方法运算量大的问题,以极化敏感阵列为模型,结合时频分析方法,充分利用回波信号的空域、时频域和极化域信息,对雷达回波信号进行更准确的估计,并简化其计算量。分析基于空间极化时频分布的多重信号分类(MUSIC)和旋转不变子空间(ESPRIT)算法,并结合两者的优缺点提出了一种改进算法。改进算法用极化时频ESPRIT算法对来波信号确定大致的方位角,以每个方位角为中心确定一个小角度范围,在此范围内用MUSIC算法进行谱峰搜索,得到较准确的波达方向(DOA)估计值,在确保DOA估计精度的基础上节省大部分运算时间。仿真试验验证了该改进算法的有效性。     

Scientific requirements for future spatially resolved white-light and broad-band high-cadence observations of the Sun

Several important issues are open in the field of solar variability and they wait their solution which up to now was attempted using critical ground-based instrumentations. However, accurate photometric data are attainable only from space. New observational material should be collected with high enough spatial and spectral resolution, covering the whole visible range of the electromagnetic spectrum as well infrared and ultraviolet to reconstruct the total solar irradiance: (1) the absolute contributions of different small-scale structural entities of the solar atmosphere from the white light flares and from micro-flares are still poorly known; (2) we do not know the absolute contributions of different structural elements of the solar atmosphere to the long-term and to the cyclic variations of the solar irradiance, including features of the polar regions of the Sun; (3) the variations of the chromospheric magnetic network are still poorly evaluated; (4) only scarce information is available about the spectral variations of different small-scale features in the high photosphere. Variability of the Sun in white light can be studied with higher spectral, spatial and time resolution using space-born telescopes, which are more appropriate for this purpose than ground based observatories because of better seeing conditions, no interference of the terrestrial atmosphere and a more precise calibration procedure. Scientific requirements for such observations and the possible experimental tools proposed for their solution. Suggested solar studies have broader astrophysical importance.     

Contribution of ionospheric TEC anomalies to detecting the seismic precursors related to the 2008 Oran-Algeria event

The ionospheric anomalies observed before any notable earthquake have become the subject of predictive research in the field of seismo-ionospheric coupling and/or Solid Earth-Atmosphere. In this paper, the concept of ionospheric modeling has been applied using total electronic content (TEC); derived from dual-frequency GPS recordings from about sixty permanent geodetic stations. The study and the analysis of the anomalous TEC variations, quantifiable on a regional scale, allowed us to detect the principal precursors of the M_w 5.5 earthquake that hit Oran on June 06th, 2008. The envisaged analytical approach is based principally on the time delays estimation relating to the seismic responses from the triggering (lithospheric seismic source) until their recording in data Rinex (GPS_IGS stations) through the reflection system of the electromagnetic waves on the ionospheric level (F2-layer).Indeed, in term of location, the longitude-latitude coordinates of the Oran event epicenter (0.658°W, 35.883°N) affecting the coastal margin of Western Algeria without too much material damage. Although the magnitude of this earthquake is qualified moderate (M_w 5.5, seismic intensity scale V-VI), one can observe apparent disturbances in the terrestrial electromagnetic spectrum associated with ionospheric TEC variations. In the domain of geodetic data analysis, we have noted a significant increase in the ionospheric TEC, which announces the arrival of a seismic precursor several days before the main studied event. Against this background, we emphasize that any seismic event, of significant magnitude, often carries information associated with other variants involved in the package of earthquake studied. Among these variants we evoke the effect of the magnetic field and the effect of the surrounding environment, etc. As for the specific behavior of the GPS_TEC signal, obtained from the Rinex data, and its interaction with the associated seismic activity, we highlight the existence of a spectral conformity between the geomagnetic field and that of the TEC content (spontaneous polarization of the TEC).Finally, we have just confirmed the effectiveness of this forecasting approach which relates the seismo-ionospheric precursors that are embedded in the physical trace of the electromagnetic signal relative to significant and/or moderate earthquakes (M ≥ 5); such as the envisaged case of the 2008 Oran event.     

On the nature of coronal loops above the quiet sun network

The structure and dynamics of a box in a stellar corona can be modeled employing a 3D MHD model for different levels of magnetic activity. Depending on the magnetic flux through the surface the nature of the resulting coronal structures can be quite different. We investigate a model of an active region for two sunspots surrounded by magnetic field patches comparable in magnetic flux to the sunspots. The model results in emission from the model corona being concentrated in loop structures. In Gudiksen and Nordlund (2005) the loops seen in EUV and X-ray emission outline the magnetic field, following the general paradigm. However, in our model, where the magnetic field is far from a force-free state, the loops seen in X-ray emission do not follow the magnetic field lines. This result is of interest especially for loops as found in areas where the magnetic field emerging from active regions interacts with the surrounding network.     

CME-geometry and cosmic-ray anisotropy observed by a prototype muon detector network

We analyze the cosmic-ray anisotropy observed by a prototype network of muon detectors during geomagnetic storms associated with coronal mass ejections (CMEs). The network currently consists of multidirectional surface muon detectors at Nagoya (Japan) and Hobart (Australia), together with a prototype detector at São Martinho (Brazil) which has been in operation since March, 2001. In this report, we analyze the anisotropy recorded in both the muon detector and neutron monitor (the Spaceship Earth) networks and find significant enhancements of cosmic-ray anisotropy during geomagnetic storms. Following the analysis by Bieber and Evenson [Bieber, J.W., Evenson, P. CME geometry in relation to cosmic ray anisotropy. Geophys. Res. Lett. 25 (1998) 2955–2958] for the neutron monitor data at 10 GeV, we also derive cosmic-ray density gradients from muon data at higher-energy (50 GeV), possibly reflecting the larger-scale geometry of CMEs causing geomagnetic storms. We particularly find in some events the anisotropy enhancement clearly starting prior to the storm onset in both the muon and neutron data. This is the first result of the CME-geometry derived from simultaneous observations of the anisotropy with networks of multidirectional muon detectors and neutron monitors.     

某型直升机动态RCS测量数据分析

动态目标测量是雷达目标RCS特性研究必不可少的一种手段。简要介绍了RCS特性测量数据分析方法,设计了某型直升机动态飞行测量实验,分析了目标航迹数据、姿态角数据和RCS测量值,应用χ2分布模型拟合目标在2.5GHz测量频率水平极化和垂直极化两种方式下RCS测量数据的统计特征,并分析该目标RCS的起伏规律。     

基于FY4A-AGRI反演东北地区云顶高度

云对全球的能量收支及大气循环系统具有不可替代的调节作用,是影响天气及气候变化的重要因子。云顶高度作为云的重要参数,有助于分析云在大气中的物理机制,对局部地区监测和预报具有实质性作用。基于多通道扫描辐射成像仪(AGRI)数据反演东北地区云顶高度,采用红外分裂窗查算表方法,并对不同季节和不同云类型建立查算表,探讨基于静止卫星反演中高纬度地区云顶高度的可行性。同时,引入主动式高精度仪器正交偏振云-气溶胶偏振雷达(CALIOP),结合11、12 通道亮温数据搭建云顶高度反演模型。分析结果表明:1) AGRI遥感的云顶高度与CALIPSO搭载的CALIOP云顶高度变化趋势一致,算法计算效率较高;2) 从4个季节的统计结果来看,均方根误差(RMSE)上都小于2.3 km,平均偏差在500 m左右,受季节的影响较小,反演结果与CALIOP探测结果具有较高的一致性;3) 利用该方法基于AGRI结果精度不亚于官方采用的CO2薄片法,该方法估算的RMSE和相对误差较小,并且该算法的反演模型只提取红外分裂窗区通道数据,无需大气廓线资料进行辅助计算,节省计算资源,提高计算效率。     

基于2×2 MIMO的星地双圆极化通信系统验证

卫星通信因通信距离远、覆盖面积大、机动灵活等优势,广泛应用在抗震救灾、广播电视与移动通信中。然而,卫星通信因长距离通信和环境对信号的阻塞等问题,导致通信质量下降。为提高卫星通信质量,可以增加地面站发射功率或者采用分集技术。由于电磁波具备极化特性,左旋圆极化电磁波与右旋圆极化电磁波相互正交,利用其正交特性可实现长距离通信中传输路径相互独立,可以应用于星地MIMO通信中。主要研究双圆极化分集2×2 MIMO相关内容,对开阔环境和城市环境的信道参数进行研究,建立了窄带卫星双圆极化卫星2×2 MIMO信道模型,设计了一套具备在地面模拟双圆极化卫星和个人移动终端收发系统,并在该系统上验证双圆极化分集2×2 MIMO,相比于SISO获得的信噪比改善。