A New Method for Finding Topological Separators in a Magnetic Field

Magnetic topology is a powerful tool for constraining certain physical properties of a given magnetic configuration, including the strengths and locations of current sheets, relative helicity and the magnetic free energy available for reconnection. A critical feature of magnetic topology is the separator, a field line bordering several different regions of connectivity. With existing methods, these field lines are at best computationally expensive and at worst impossible to find. A new method is presented for finding the Minimal Separator Set, all of the separators that necessarily exist in a configuration, and to use this information in combination with the optical analogy and a simulated annealing method to ‘cool’ an initial guess for each separator into a good approximation.     

太阳活动区磁场观测的一种新方法

在太阳活动区的物理研究中,特别是在二维动力学光谱分析中,迫切需要相应活动区的磁图资料。本文介绍了在太阳光谱仪的入射狭缝后安装一种新型偏振器进行活动区二维磁场观测的新方法。这种方法不仅能获得日面上任一点的磁场强度,且可快速获得活动区的纵向场磁图。除此之外,还可利用多条谱线的同时观测,获得有关磁力线管结构等方面的资料。     

Polar Ring Currents on the sun During a Polar Magnetic Field Reversal

We have studied the variations of the height of polar crown prominences according to daily observations of the Sun at the Kodaikanal Observatory (India) during 1905–1975. Polar ring filaments at latitudes 60°–80° are related to the polar magnetic field reversal. A double decrease of the height of polar ring filaments was found in the course of their migration from 40°to the poles. We estimated the limiting height of the equilibrium of polar ring filaments from the stability condition of a strong electric current. We found that the transition from large-scale to small-scale ring filaments reduces the critical height of the stability for the prominences. A model of an inverse-polarity filament was used.     

A New Method for Modeling the Coronal Magnetic Field with STEREO and Submerged Dipoles

Recent magnetic modeling efforts have shown substantial misalignment between theoretical models and observed coronal loop morphology as observed by STEREO/EUVI, regardless of the type of model used. Both potential field and non-linear force-free field (NLFFF) models yielded overall misalignment angles of 20??C?40 degrees, depending on the complexity of the active region (Sandman et al., Solar Phys. 259, 1, 2009; DeRosa et al., Astrophys. J. 696, 1780, 2009) We demonstrate that with new, alternative forward-fitting techniques, we can achieve a significant reduction in the misalignment angles compared with potential field source surface (PFSS) models and NLFFF models. Fitting a series of submerged dipoles to the field directions of stereoscopically triangulated loops in four active regions (30 April, 9 May, 19 May, and 11 December 2007), we find that 3??C?5 dipoles per active region yield misalignment angles of ???11°??C?18°, a factor of two smaller than those given by previously established extrapolation methods. We investigate the spatial and temporal variation of misalignment angles with subsets of loops for each active region, as well as loops observed prior to and following a flare and filament eruption, and find that the spatial variation of median misalignment angles within an active region (up to 75%) exceeds the temporal variation associated with the flare (up to 40%). We also examine estimates of the stereoscopic error of our analysis. The corrected values yield a residual misalignment of 7°??C?13°, which is attributed to the non-potentiality due to currents in the active regions.     

A Volterra Adaptive Filtering Method for Polar Motion Prediction Based on Chaotic Time Series

In consideration of the complex time-varying characteristics of polar motion (PM), this paper takes PM as chaotic time series. A Volterra adaptive filter is employed for predicting PM based on the state space reconstruction of delay-coordinate embedding of dynamic system. This method first uses the Least Squares (LS) technology to estimate the harmonic models for the linear trend, Annual and Chandler Wobbles (AW and CW) in PM. The selected LS deterministic models are subsequently used to extrapolate the linear trend, AW, and CW, and obtain the LS residues (the difference between the LS model and PM data themselves). Secondly, the phase space and largest Lyapunov exponent of the LS residues are reconstructed, and calculated by means of the C-C and small data-set algorithm, respectively. Further, a Volterra adaptive filter is designed for generating the extrapolations of the LS residues. The extrapolated LS residues are then added to the LS deterministic models in order to obtain the predicted PM values. The EOP C04 time series released by the International Earth Rotation and Reference Systems Service (IERS) are selected as data base to generate the PM predictions up to 60 days in the future. The results of the predictions are analyzed and compared with those obtained by the Earth Orientation Parameters Prediction Comparison Campaign (EOP PCC) and IERS Bulletin A. The results show that the accuracy of the predictions up to 30 days is comparable with that by the most accurate prediction techniques participating in the EOP PCC for PM, but worse than that by those most accurate techniques beyond 30 days in the future. The results also illustrate that the short-term predictions are better than those published by the IERS Bulletin A. However, the errors of the predictions rapidly increase with the prediction days. It is therefore concluded that the proposed method is a potential technology for short-term PM prediction.     

基于混沌时间序列的Volterra自适应滤波极移预报方法

针对极移复杂的时变特性, 根据混沌相空间坐标延迟重构理论, 提出一种基于Volterra自适应滤波的极移预报方法. 首先, 利用最小二乘拟合算法分离极移序列中的线性趋势项、钱德勒项和周年项, 获得线性极移、钱德勒极移和周年极移的外推值; 其次, 通过C-C关联积分法对最小二乘拟合残差序列进行相空间重构, 并利用小数据量法计算残差序列的最大Lyapunov指数验证其混沌特性, 在此基础上, 构建Volterra自适应滤波器对残差序列进行预测; 最后, 将线性极移、钱德勒极移和周年极移的外推值以及最小二乘拟合残差的预测值相加获得极移最终预报值. 利用国际地球自转服务局(International Earth Rotation and Reference Systems Service, IERS)提供的极移数据进行1--60d跨度预报, 并将预报结果分别与国际地球定向参数预报比较竞赛(Earth Orientation Parameters Prediction Comparison Campaign, EOP PCC)结果和IERS A公报发布的极移预报产品进行对比, 结果表明: 对于1--30d的短期预报, 该方法的预报精度与EOP PCC最优预报方法相当, 当预报跨度超过30d时, 该方法的预报精度低于EOP PCC最优预报方法, 优于参与EOP PCC的其他方法; 与IERS A公报相比, 该方法的短期预报效果较好, 当预报跨度增加时预报精度低于IERS A公报. 预报结果表明该方法更适合于极移短期预报.     

关于一行《大衍历》的插值法

论证一行《大衍历》（Ａ．Ｄ．７２９）的二次不等间距插值法和刘焯《皇极历》（Ａ．Ｄ．６０４）的二次等间距插值法的实质完全相同，并没有一般所说的推广意义；否定了以往人们关于一行有意识地应用了三次插值法近似公式的说法．     

一种测定望远镜极轴偏差的方法

利用望远镜的恒动跟踪，对两颗恒星进行无斗星曝光０．５小时，扣除蒙气差影响，用球面三角方法计算出望远镜极轴指向的偏差在赤经和赤纬方向上的分量，据此对望远镜极轴进行调整，就可以方便地把望远镜极轴指向调整到较高精度。     

Nitrate in Polar Ice: A New Tracer of Solar Variability

Knowledge of the long-term variability of solar activity is of both astrophysical and geoscientific interest. Reconstructions of solar activity over multiple millennia are traditionally based on cosmogenic isotopes ¹⁴C or ¹⁰Be measured in natural terrestrial archives, but the two isotopes exhibit significant differences on millennial time scales, so that our knowledge of solar activity at this time scale remains somewhat uncertain. Here we present a new potential proxy of solar activity on the centennial-millennial time scale, based on a chemical tracer, viz. nitrate content in an ice core drilled at Talos Dome (Antarctica). We argue that this location is optimal for preserving the solar signal in the nitrate content during the Holocene. By using the firn core from the same location we show that the 11-year and Gleissberg cycles are present with the variability of 10??C?25?% in nitrate content in the pre-industrial epoch. This is consistent with the results of independent efforts of modeling HNO₃ and NO _y in Antarctic near surface air. However, meteorological noise on the interannual scale makes it impossible to resolve individual solar cycles. Based on different processes of formation and transport compared to cosmogenic isotopes, it provides new, independent insight into long-term solar activity and helps resolve the uncertainties related to cosmogenic isotopes as diagnostics of solar activity.     

Using Polar Coronal Hole Area Measurements to Determine the Solar Polar Magnetic Field Reversal in Solar Cycle 24

An analysis of solar polar coronal hole (PCH) areas since the launch of the Solar Dynamics Observatory (SDO) shows how the polar regions have evolved during Solar Cycle 24. We present PCH areas from mid-2010 through 2013 using data from the Atmospheric Imager Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) instruments onboard SDO. Our analysis shows that both the northern and southern PCH areas have decreased significantly in size since 2010. Linear fits to the areas derived from the magnetic-field properties indicate that, although the northern hemisphere went through polar-field reversal and reached solar-maximum conditions in mid-2012, the southern hemisphere had not reached solar-maximum conditions in the polar regions by the end of 2013. Our results show that solar-maximum conditions in each hemisphere, as measured by the area of the polar coronal holes and polar magnetic field, will be offset in time.     

Observations and Simulations of the Polar Field Reversals in Cycle 23

We have used observations obtained by the National Solar Observatory at Kitt Peak to study the reversals of the polar magnetic fields in Cycle 23. We have compared them with corresponding data obtained by the Mt. Wilson Observatory, when these are available, testing both data sets against the locations of H filaments. Because of the unreliability of the data at extreme latitudes and because the apparent time of reversal varies with the degree of smoothing applied to the data, it is difficult to determine precise reversal time in each hemisphere from direct observations. However, we show that it is possible to obtain a better-defined and more precise reversal time using polar maps derived from simulations of the synoptic fields. These indirect values, however, depend critically on the diffusivity used in the simulations. We applied various tests to confirm an empirical value for the diffusivity parameter of about 600 km ² s ^–1 and hence determined empirical reversal times of CR 1976 in the northern hemisphere and CR 1981 in the south.     

Simulations of the Polar Field Reversals during Cycle 22

The revised Mount Wilson synoptic magnetic data for the period September 1987 through March 1996 are used as the basis of numerical simulations of the evolution of both the northern and southern polar magnetic fields during the reversal and declining phases of cycle 22. The simulations are based on numerical solutions of the flux-transport equation which involve, as parameters, the maximum meridional flow speed, v ₀, and the supergranule diffusivity, . By matching characteristics of the observed and simulated fields, such as the observed reversal times, the evolution of the net flux above 60 °, and the migration of the polar crown, empirical values of these parameters, i.e., v ₀=11 m s^–1,=600 km² s^–1, may be determined. Further, the observed decrease in the mean net flux above 60 ° during the late declining phase of cycle 22 can be simulated only by increasing the diffusivity to 900 km² s^–1. However, direct observations of the supergranule velocities yield values of the diffusivity of order 200 km² s^–1, and we show that the inclusion of a pattern of emerging bipoles in the simulations can increase the diffusion of these fields and that, together with a more realistic value of the diffusivity, it is possible to reproduce qualitatively the features of the observed polar field reversals.     

确定太阳横向磁场方位角的综合方法

本文分析了现有几种常用的确定太阳磁场横向分量方位角的方法，如势场法，Ｋｒａｌｌ法、吴－艾法和＂方位角连续＂法，作者认为这些方法各有不同的适用范围，其中任何一种方法都不能单独确定太阳横向磁场。在此分析的基础上，提出了确定太阳横向磁场方位角的综合方法。该法的要点是：用势场法和Ｋｒａｌｌ法分别处理同一磁场观测资料，比较这两种方法所得到的横场分布图，找出它们的相同区域和有差别区域。从相同区域出发，利用＂无力因子相近＂假定，可以推断有差异区域的横场方位角。本文提供的应用实例初步显示了综合方法的有效性。     

Polar Coronal Structures and the Global Magnetic Field Evolution Through the Cycle

We compare the shape and position of some plasma formations visible in the polar corona with the cyclic evolution of the global magnetic field. The first type of object is polar crown prominences. A two-fold decrease of the height of polar crown prominences was found during their poleward migration from the middle latitudes to the poles before a polar magnetic field reversal. The effect could be assigned to a decrease of the magnetic field scale. The second type of object is the polar plumes, ray like structures that follow magnetic field lines. Tangents to polar ray structures are usually crossed near some point, “a magnetic focus,” below the surface. The distance q between the focus and the center of the solar disk changes from the maximum value about 0.65 R _⊙ at solar minimum activity to the minimum value about 0.45 R _⊙ at solar maximum. At first glance this behaviour seems to be contrary to the dynamics of spherical harmonics of the global magnetic field throughout a cycle. We believe that the problem could be resolved if one takes into account not only scale changes in the global magnetic field but also the phase difference in the cyclic variations of large-scale and small-scale components of the global field.     

实测大气折射值的新方法

简单评述了现有各种版本的大气折射表所依据的理论基础和编制方法，指出了实测大气折射值、建立随地形而异的实测大气折射模型的必要性和应具备的基本条件；在分析了长期以来不能直接测定大气折射值的原因后，介绍了一种在不同方向精确测定大气折射值和建立观测点大气折射模型的新方法，以及所依赖的观测仪器具备的特性，最后给出了用实测数据建立的本地大气折射模型。     

A Method for the Construction of a Restricted Motion in an Arbitrary Central Field

The well-known problem of motion in a central field integrable in quadratures is considered. The force function of the problem depends only on the particle distance to the chosen coordinate origin. In the general case of an arbitrary central force, a rigorous analytical solution of the problem cannot be obtained due to the complexity of the integrals. In this paper we propose a semi-analytical method of constructing an approximate solution for the case where the distance varies in a limited range that allows the time dependences of the polar coordinates to be obtained using elliptic functions and integrals. As an example, we consider the model problems of the perturbed motion of hypothetical Jovian and lunar equatorial satellites as well as the problem of the motion of a single star in the principal plane of a galaxy. The methodical accuracy has been estimated by a comparison with the numerical solution.     

基于图像叠加的GEO目标探测方法

为了满足地球同步轨道(Geosynchronous Orbit,GEO)空间目标的探测要求,克服长时间曝光CCD像元出现饱和溢出的情况,提出使用多帧连续曝光图像叠加的方法,增加图像的存储范围,同时提升目标的信噪比,保证系统的探测能力.实验结果表明,利用10帧连续图像叠加的方法,可以有效消除像元饱和的情况,提升目标信噪比约3.2倍,提升探测能力近似2.5星等,且序列图像的底片常数精度可靠,用底片常数的均值计算目标位置,精度符合要求.结果验证了使用图像叠加方法探测GEO目标的可行性.     

利用大视场测光系统评估观测天气质量

介绍一种利用大视场测光系统对观测天气质量进行评估的统计方法．此方法可以 给出大气透明度、背景天光、视宁度和观测极限星等等多种与天文观测有关的天气质 量参数．通过检验证明,此方法可提供一个天气状况的实时监视方法,对北京天文台 施密特ＣＣＤ测光系统以及制定观测计划和评估观测质量有重要意义．