土星磁层顶的Kelvin-Helmholtz不稳定性和磁流体表面波

本文采用可压缩磁流体力学近似并选取Voyager-1的观测数据,讨论了土星磁层顶的Kelvin-Helmholtz不稳定性和磁流体表面波.计算表明,土星磁层随星体自转同磁鞘流之间的速度差,可以在地方时午前、中午和距中午不远的午后磁层顶激发不稳定性;午前和午后区有很强的非对称性.计算所得的波的特性与观测一致.      

夜侧极区电离层对流对行星际激波的响应

利用超级双子极光雷达网（Super Dual Aurora Radar Network,SuperDARN）高频雷达、北半球IMAGE地磁台链以及南极中山站的极光观测数据,研究电离层对流对2012年7月14日一个行星际激波扰动事件的响应.在18:10UT行星际激波到达地球并与磁层相互作用触发地磁急始和磁层亚暴,SuperDARN雷达观测到北半球夜侧极区电离层对流显著增强,观测视野覆盖黄河站的Hankasalmi雷达观测到从激波到达地球至18:33UT,电离层F层出现剧烈扰动,雷达回波数明显增多,并出现局部对流速度反转现象.18:33UT之后,观测到F层出现三块速度高达600m·s-1的逆阳运动不规则体.而与Hankasalmi雷达地磁共轭的南半球Kerguelen雷达探测到的回波主要来自E层,回波数量几乎无变化,但是Kerguelen雷达观测视野内的中山站全天空光学成像仪观测到极光活动显著增强.南北半球夜侧电离层观测结果的差异,主要是由于它们分别处于极夜和极昼.      

北极黄河站极光亚暴期间低热层大气中性风研究

极光亚暴是地球空间基本的能量输入、耦合及耗散过程,其对低热层大气中性风的影响不容忽视,对这一问题进行深入研究具有重要意义.2010年11月,中国北极黄河站(78.92°N,11.93°E)安装了一台自主研制的全天空法布里-珀罗干涉仪(FPI)并开始进行正常观测,为中国首次获得了极光亚暴期间的FPI观测数据.根据2012年越冬期间的观测情况,对2012年11月12-14日及12月09-11日两个极光亚暴事件期间的数据进行处理,计算得到了5级干涉环对应的风场.亚暴期间风场变化与地磁活动变化的对比分析表明,风速的剧烈变化可能是由地磁活动剧烈扰动造成的.针对2012年11月13日00:00UT-02:00UT和2012年12月10日05:00UT-07:30UT的亚暴事件,将全天空相机拍摄到的极光图像与FPI干涉图像对应的视线风场进行对比分析.结果表明在极光活动中,视线风速加强的方向与极光弧的方向垂直,而在极光弧的平行方向,风速相对较小.      

极向运动极光结构和喉区极光光学观测特征的对比分析

利用中国北极黄河站高时间分辨率的三波段全天空成像仪极光观测数据,联合太阳风和行星际磁场等观测,分析了极向运动极光结构（PMAFs）和喉区极光的形成及演化特征.研究发现:一系列PMAFs与喉区极光事件同时出现在观测视野中,其中PMAFs主要发生在日侧极隙区极光卵赤道向边界的极向一侧,沿东西方向分布,点亮后向高纬运动;喉区极光紧靠PMAF一侧发生,从极光卵赤道向边界向低纬延伸,沿南北方向分布,点亮后向高纬偏西方向运动;观测期间PMAFs发生频率高于喉区极光;当PMAFs与喉区极光同时出现时,PMAFs可以与喉区极光几乎同时出现或略晚于喉区极光出现,持续时间较喉区极光短.观测结果表明:与PMAF相对应的磁层顶重联过程和与喉区极光对应的磁层顶凹陷导致的磁重联过程在日侧磁层顶上的相邻区域分别发生,两种极光事件的形成过程相对独立,可能不存在相互触发关系.      

磁壳参数L与磁暴Dst指数和行星际条件的关系

用磁坐标L-/A来描述地球近地空间粒子特性和卫星位置是近年来空间物理探测研究和数据分析中的一个新趋势.利用T96磁场模型计算了L值,并比较了在地球磁层剧烈活动期间和不同行星际条件下,用偶极子模型,国际参照磁场(IGRF)模型,和T96磁场模型这三种方式计算得到的地球表面L-A磁坐标之间的区别.在地磁纬度大于30°时偶极子近似和IGRF磁场模型计算得到的L值差别开始增大.在地磁纬度大于50°时,用IGRF磁场模型和T96磁场模型计算得到的L值差别开始增大.由于T96磁场模型引入了行星际磁场南北和东西分量,计算的L值包含了行星际条件的影响,并具有了随地方时变化的特性.本工作对于辐射带粒子动态模式的建立,以及正确理解卫星磁坐标位置等具有重要意义.     

质子地磁垂直截止刚度在2004年11月7-8日两个时刻处的数值模拟

利用单粒子轨道理论, 在T04和IGRF2000磁场模式建立的磁层模型基础上, 应用四阶龙格库塔方法, 模拟计算宇宙线带电质子在地球磁层中的运动以及沿天顶方向入射到达地球磁场内的某一特定位置, 得到了距地球表面450km高度处全球质子垂直截止刚度在2004年11月7-8日中两个时刻的计算值. 根据计算得到的684个不同位置处的截止刚度值, 分析了同一时刻地磁垂直截止刚度随磁纬和磁经的变化. 与此同时, 模拟计算了相同时刻下磁纬为30°, 磁经为0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°处, 地磁有效垂直截止刚度随高度的变化情况. 结果表明, 在磁纬30°处, 其质子有效垂直截止刚度随距离地心高度的变化沿向阳处向磁尾处方向, 变化越来越缓慢.      

不同速度运动汽车的磁异信号研究与探测

运动汽车随着速度的增加伴随着非稳态材料的产生,如汽油高温燃烧、高速摩擦引起自由电荷累积等。针对这些磁异信号难以采用适用于铁磁性材料的磁偶极子模型描述的问题,提出了结合磁偶极子模型和运动电荷等效模型的方法,理论计算不同速度运动汽车的磁异信号并分析其时域、频域特征,获得磁异信号与速度的依赖关系。采用隧道磁阻传感器（TMR）结合滤波、放大、模数转换技术构建弱磁信号探测实验装置,探测不同速度运动汽车的时域磁异信号,并采用傅里叶变换获得其频域信息,与理论模型相吻合。随着速度的增加,频域信号向高频方向偏移,对于从低频地磁背景场中提取目标弱磁信号极其重要。      

电离层等效电流体系对行星际激波的响应研究

行星际激波是导致地球磁层-电离层系统发生扰动的重要原因之一,其可以通过对磁层-电离层系统电流体系的改变来影响地磁变化.本文采用全球三维磁流体力学数值模拟方法,分析了行星际激波作用下电离层等效电流体系的即时响应.模拟结果表明,在激波作用下伴随着异常场向电流对的产生,电离层在午前午后出现一对反向的等效电流涡.这对涡旋一边向极侧和夜侧运动,一边经历强度增强和减弱直至消失的过程.激波过后等效电流体系图像逐渐演化为激波下游行星际条件控制的典型图像.这个响应过程与行星际激波强度有关,激波强度越强,则反向的等效电流涡旋强度越大,寿命也就越短.      

午后极光强度与太阳风-磁层耦合函数的相关

利用1997年和1998年南极中山站多通道扫描光度计的地面观测数据和Wind卫星在弓激波上游对行星际磁场和太阳风参数的观测数据,对午后高纬极光强度与太阳风-磁层耦合函数之间的相关性进行定量研究.研究表明,午后630.0nm极光强度与太阳风-磁层耦合函数间有很好的相关,而557.7nm的相关性差一些;在考察的所有耦合函数中,午后极光受太阳风电场和能量的影响更直接;同时,行星际磁场的时钟角对午后极光也有很强的控制作用.      

基于代理模型的制导火箭炮发射诸元计算方法

针对制导火箭炮发射诸元的快速计算问题,提出了一种结合大样本数据和代理模型计算发射诸元的新方法。运用代理模型建立射角、无控弹道侧偏与炮位纬度、炮位高程、射向、射程、目标点高程及药温之间的函数关系,并根据射程和无控弹道侧偏的预测值对射向进行修正。仿真结果表明,高阶多项式响应面、相关函数为高斯函数的Kriging、高阶单项式径向基函数、核函数为高斯函数的最小二乘支持向量机、激活函数为正弦函数的超限学习机以及由上述单一代理模型构建的组合代理模型均具有较高的预测精度,各种单一代理模型对射角和无控弹道侧偏的预测时间均小于1 ms,证明了基于代理模型的射角和无控弹道侧偏预测方法切实可行,且通过对射向进行修正有效减小了由于地球自转引起的无控弹道侧偏。      

喉区极光的机器识别

喉区极光是一种发生在电离层对流喉区附近的极光现象,是极光卵向低纬侧延伸出的南北向分立结构,其可能对应由磁鞘高速流与磁层顶作用引发的磁层顶重联过程.喉区极光研究对深入理解太阳风—磁层—电离层耦合过程具有重要意义.从长期观测所积累的大量全天空极光观测数据中准确高效识别出喉区极光结构,是开展喉区极光统计研究的基础.本文利用北极黄河站2003—2017年全天空成像仪的极光观测数据,建立了喉区极光图像标注数据集;基于密集连接卷积神经网络（DenseNet）对极光图像全局高维表征的自动学习,首次实现了喉区极光结构的机器识别.算法对喉区极光识别准确率达96%,且具有良好的泛化性能.研究表明基于深度学习的图像识别方法可用于从海量极光观测数据中自动识别喉区极光事件.      

黄河站和Tromso站亚暴期间热层风场观测结果

中高层大气风场探测对研究大气物理过程具有极为重要的意义，尤其是在极地地区，风场对大气结构的影响更为剧烈.针对亚暴期间中国北极黄河站和日本Tromso站上空OI557.7nm气辉层（低热层）中性风场，利用全天空法布里-珀罗干涉仪（all-sky Fabry-Perot Interferometer，all-sky FPI）探测气辉谱线的多普勒频移，反演气辉层的大气风场信息.结果表明，低热层风场平均水平在100m·s-1左右，热层风场在极地地区更为剧烈，纬度相对较低的Tromso站探测到的风速整体小于同期黄河站上空的风速.结合离子风数据，分析离子拖拽和焦耳加热对中性风的影响过程，发现极光亚暴不仅对低热层风场有增强作用，也有明显的抑制效果，但整体风向都垂直于极光弧变化.      

Probing afternoon detached aurora and high-latitude trough based on DMSP observations

The present work displays the observations of an afternoon detached aurora along with ionospheric high-latitude trough. The event was observed by DMSP F17 on 19 September 2014. The afternoon detached aurora was isolated from the auroral oval and was located between 12:00–18:00 magnetic local time (MLT) and 65–70° geomagnetic latitude (MLAT). Particle observations indicate that the afternoon detached aurora was produced by energetic ring current ions with energies above ~10 keV where the main ion energy was likely to be above the upper limit of DMSP measurement (~30 keV). Magnetometer observation from the ground implies that the energetic ions were likely scattered by EMIC waves. Both the detached aurora and the auroral oval are found to be well inside the high-latitude trough with MLAT between ~64° and ~76° (68–80° GLAT). The auroral oval corresponds to a westward (sunward) plasma drift. It is expected that the westward drift transports the low-density plasma in the nightside toward the dayside, leading to the high-latitude trough formation. The afternoon detached aurora was well equatorward of the high-latitude trough, and the corresponding plasma drift was nearly zero. The plasma associated with the detached aurora is expected to be stagnant, and broaden the high-latitude trough equatorward.     

Dynamics of the dayside Aurora Australis

Current dayside optical studies of Aurora Australis from the Amundsen-Scott Research Station at the South Pole (74 degrees magnetic latitude) show some striking differences from optical results reported from Svalbard. A 6-channel meridian scanning photometer operating during the past three austral winters shows, in particular, the 630 nm emission is much lower, on average, than the Arctic dayside aurora and very weak on some days. The 558 nm intensity is higher relative to 630 nm suggesting the incoming electrons have a higher average energy. There are notable differences in auroral forms, giving further evidence of asymmetries in the two dayside ovals.     

Is the poleward edge of the trough a sensitive indicator of geospace interactions?

The poleward edge of the main ionospheric trough can often be regarded as the ionospheric signature of the equatorward boundary of the plasma sheet. We use Advanced Ionospheric Sounder observations of the poleward edge from Halley, Antarctica (76°S, 27°W; L=4.2) to investigate some aspects of its dynamics with respect to changes of magnetospheric and solar wind conditions. We find that there is frequently rapid equatorward motion of the poleward edge from ∼20 minutes before to ∼30 minutes after the onset of the main phase of a substorm. These observations are discussed in terms of the dynamics of the plasma sheet during substorm activity. Another class of rapid equatorward motion of the poleward edge of the trough has no apparent cause in the magnetosphere or solar wind. Possible explanations involving longitudinal structure of the trough or small-scale structure of the solar wind are considered.     

Morphology of high latitude auroral electron precipitations obtained by the Aureol-3 satellite

Latitudinal distribution of auroral electron precipitations was studied using the Aureol-3 satellite data. Analysis of 148 events in the morning, night, and evening sectors showed that structures of all types have a wide MLT distribution. However, during low geomagnetic activity the distribution of latitudinally asymmetric events is close to Iijima and Potemra's Region 1 and 2 current picture: the equatorward events prevail in the morning and postmidnight sectors, and the polarward ones — in the evening and premidnight. An increase in geomagnetic activity makes the MLT distribution of different types of events more uniform. This fact may indicate existence of the multi-layer structure of currents and consequently medium scale electric fields, in which the maximum currents considerably exceed the average values observed in the Region 1 and 2.     

Some peculiarities of longitudinal distribution of proton fluxes at high latitudes

Dynamical features of proton fluxes at high and middle latitudes were studied based on data measured by Sun-synchronous low-altitude (800 km height) polar-orbiting three NOAA series satellites: POES 15, 16, and 17 during the geomagnetic storm on January, 21–22, 2005. Data from three satellites that passed the Northern hemisphere along different MLTs allow reconstructing the longitudinal distribution of the proton fluxes. Measurements of protons with energies of 30–80 keV and 80–240 keV (the ring current energy range) by 0- and 90-detectors were used to evaluate and compare the longitudinal asymmetry of proton flux distribution measured in the regions equatorward and poleward of the isotropic boundary. It was found that during all the phases of the geomagnetic storm distribution of the maximum flux of precipitating protons (0-detector data) is sufficiently asymmetric. The maximal flux position along MLT is moving from pre-midnight sector in quiet time to post-midnight one before and during SSC and moving back during recovery phase. The longitudinal distribution of precipitation maxima demonstrates the local increase in afternoon sector (approximately at 13:30 MLT) and decrease in the dusk one during SSC. These features are evident consequence of the magnetosphere compression. To identify the origin of the particles, the locations of maximum fluxes have been projected to the magnetosphere. It was determined that during geomagnetic storm main and recovery phases maximum fluxes were measured at latitudes poleward of the isotropic boundary. To evaluate the trapped particle flux asymmetry, the particle fluences (90-detector data) were calculated along the satellite orbit from L = 2 to the isotropic boundary. The total fluences of trapped particles calculated along the satellite orbit show regular asymmetry between dusk and dawn during main and recovery phases. The maximal intensity of proton fluxes of both investigated populations located poleward and equatorward of the isotropic boundary is achieved during SSC. The total flux measured during crossing the anisotropic region can be considered as a proxy for ring current injection rate.     

120°E附近电离层赤道异常峰运动

本文研究了120°E北半球五个电离层站之f_oF₂的变化。指出了赤道异常北峰的运动规律:（1）日出-“日当头”时段,该峰向赤道运动,午后时段则向极运动。（2）运动的反向时间随太阳的最小天顶角的大小而变化,随太阳活动而变化。（3）向极运动主要受电离输运过程所支配,向赤道运动主要为光电离过程所支配。（4）120°E附近电离层赤道异常北峰上午段在海南岛附近,下午段在广州附近。