太阳表面米粒结构观测对比度分析

分析以观测系统焦面上和探测器测到的太阳表面米粒结构的对比度与观测系统口径，大气湍流相干长度以及系统探测灵敏度的关系，给出了不同口径，不同大气湍流相干长度以及不同系统探测灵敏度时的米粒结构对比值计算结果，此外还给出了实验结果。     

太阳目标哈特曼波前探测研究

分别对Hinode光学望远镜SOT观测太阳黑子的本影和半影图像以及太阳米粒组织图像进行了空间频谱计算和相关计算,分析了太阳不同结构区域图像的时域和空域特性对哈特曼波前探测精度的影响。计算和分析结果表明,在子孔径波面倾斜小于0.25″情况下,米粒组织图像采样时间在2 min内、本影和半影采样时间在4 min内,对子孔径波面倾斜探测精度的影响极小;并且由太阳目标特性引起的哈特曼波面探测误差随波面畸变量的增大而增大。这些研究结果可为太阳望远镜哈特曼波前探测器研制和应用提供依据和参考。     

太阳宁静区磁场的功率谱分析

利用１９９８年１０月３日北京天文台怀柔太阳观测站的高质量磁图,对给定的太阳宁静区两种不同极性的磁场进行了功率谱分析．结果表明,空间功率谱在超米粒和中米粒尺度具有明显的尖峰结构,这对应于空间周期性分布的网络和内网络磁结构．结果也显示出,超米粒边缘所包含的两种极性场中,其中的一种极性占优势．通过瞬态功率谱的分析,得出网络和内网络场寿命之间的比例关系,这一结果和其他学者得出的超米粒和中米粒对流寿命之间的关系相符．     

太阳宁静区磁场的功率谱分析

利用１９９８年１０月３日北京天台怀柔太阳观测站的高质量磁图,对给定的太阳宁静区两种不同极性的磁场进行为分析。结果表明,空间功率谱在超米粒和中米粒尺度具有明显的尖峰结构,这对应于空间周期性分布的网络和内网络磁结构。结果也显示出,超米粒边缘所包含的两种极性场中,其中的一种极性占优势。通过瞬态功率谱的分析,得出网络和内网络场寿命之间的比例关系,这一结果和其他学得出的超米粒和中米粒对流寿命之间的关系相     

自适应光学技术应用于激光测月中大气波前倾斜量的探测与计算

针对云南天文台1.2米望远镜在激光测月中回波光子数太少的问题，将大气湍流效应考虑到激光测月中，研究了互相关和绝对差分两种跟踪算法的原理，并编写了算法程序，利用太阳数据验证了程序的正确性,给出了根据所采集的月面感兴趣区域的图像数据，用不同方法在不同条件下处理所得的大气波前整体倾斜信号，比较了算法的优劣。     

表面边界位置对太阳ρ模本征振荡频率的影响

本文研究了表面边界位置对太阳ρ模绝热本征振荡频率的影响。数值计算结果表明，对于ｖ４０００μＨｚ的中低阶ｐ模，表面边界置于温度极小点所引起的本征振荡频率的计算误差随着ｖ和ｌ的增大，表面边界点位置对太阳理论振荡频率的影响增大，色球结构对太阳ｐ模振荡频率的影响已变得不可忽略。     

基于直方图规定化的太阳图像增强方法

太阳图像中包含了各种不同尺度、不同结构以及不同亮度的活动现象,它们都是实测太阳物理的研究目标。这些活动现象经常使图像显示的跨度过大,导致图像暗弱细节结构被隐藏。对于地基望远镜,由于地球大气对观测数据的影响,也造成图像整体对比度下降。这些都不利于人们直观地从图像中发现感兴趣的太阳活动现象或结构特征。针对这些问题,运用直方图规定化的方法对实测太阳物理中常遇到的几类观测目标图像(太阳极紫外像,太阳光球黑子像,色球活动区像以及色球日珥像)进行处理,通过瑞利分布、双高斯分布以及三重瑞利混合分布等直方图形式,实现对这几类图像的显示对比度增强。通过对空间望远镜太阳动力天文台(Solar Dynamic Observatory,SDO)的极紫外太阳像和1 m新真空太阳望远镜(New Vacuum Solar Telescope,NVST)的色球和光球像的处理展示了该方法的处理效果。结果表明,方法可以有效提高各类太阳活动现象的显示度,便于人们在研究初期发现感兴趣的活动现象。     

90年代太阳模型和太阳震荡研究进展(I):太阳模型研究进展(英)

太阳模型的研究是了解太阳整体结构和性质的极为重要的手段。90年代以来太阳模型研究取得了进展。随着MHD及OPAL物态方程的引入,理论上的太阳振荡频率与观测值的差别已大为减小,而考虑湍流频谱分布的局域对流理论和三维流体动力学模拟结果可对太阳内部对流能量传输过程有更深刻的理解．以前所发现的理论模型与反演结果得到的初始氦丰度的差别已能由扩散过程加以解释,而太阳表面锂丰度亏损问题也可以由扩散过程或早期演化星风来加以解决,太阳中微子问题则似应由粒子物理而不是天体物理来解决。     

太阳大气中矢量磁场信息的推导

一种能从观测到的斯托克斯轮廓中提取太阳表面矢量磁场信息的方法在本文中提出，它利用斯托克斯轮廓非线心的极值点处相应参量对波长的导数为零这一数学事实，假设表面附近磁场矢量及热力学参量的变化梯度足够小以致所考虑的极值点的波长位置不随深度改变或此变化呆忽则使得偏振辐射围方程组得到极大的简化；再应用数值方法从此简化方程组中解出辐射表面附近的磁场矢量参数。通过拟合理论轮廓表明该法确实可以得到表面近似的磁场矢量     

月球激光测距的新技术方法研究

月球激光测距是国内外所瞩目的宏伟目标，代表着单光子探测技术的高峰。本论文的目的是探索提高激光测月回波光子数的新方法，进而增加激光测月成功的几率。其思路是源于一个新的想法：在激光测月过程中引入大气波前倾斜量实时补偿的技术。首先介绍激光测月的现状和其难度所在：回波光子数太少，基本上属于亚光子探测范畴。在现有技术条件下，本文对影响激光测月回波光子数的因素逐一进行分析讨论，提出应该把激光束截面能量分布和大气湍流效应包括进去。为此分析讨论了大气湍流和大气中光场的基本统计性质、激光束在大气中传输时所受大气湍流的影响以及大气湍流对激光测距的影响，得出大气湍流特别对激光测月有着明显影响的结论。在此基础上对传统的激光测距方程进行了修正，使其应用到激光测月时更符合真实的情况，从而指导补偿的进行。涉及到在激光测月中对受大气湍流而畸变的激光束进行补偿，本文抓住重点，通过分析看出对大气倾斜量的实时补偿是提高激光测月回波光子数的重要因素。结合激光测月以及云南天文台现有测距系统的实际情况，本文独创性地提出利用激光测月目标近旁一定大小区域的扩展面源探测与计算大气倾斜量，然后对激光测月中的激光束进行大气倾斜量实时补偿的新技术方法。在分析比较各种从低对比度扩展源中计算大气倾斜量的算法后，本文认为采用绝对差分法最佳。最后是具体的激光测月的新技术方案，同时对此方法的理论与技术进行了分析讨论，推导出新技术方法的理论依据、补偿效果、可行性与实用性。     

Reconstruction of the Heliospheric Current Sheet Tilts Using Sunspot Numbers

We have investigated the correlation between the relative sunspot number and tilt of the heliospheric current sheet (HCS) in solar cycles 21–23. Strong and highly significant positive correlation (r > 0.8, P < 0.001) was found for corresponding data in the time interval from May 1976 through December 2004. Cross-correlation analysis does not reveal any time shift between the data sets. Reconstructed values of the HCS tilt, for the time interval before 1976, are found using sunspot numbers. To take different amplitude of solar cycles into account they were then normalized to zero in the minima of the solar activity and to average in solar cycles 21–23 maximal calculated HCS tilt in the maxima. These normalized reconstructed HCS data are compared with the angular positions of the brightest coronal streamers observed during total solar eclipses in 1870–2002, and their agreement is better for the minima of the solar activity than for the maxima.     

Tilt-angle variations of active regions

An examination of the tilt angles of multi-spot sunspot groups and plages shows that on average they tend to rotate toward the average tilt angle in each hemisphere. This average tilt angle is about twice as large for plages as it is for sunspot groups. The larger the deviation from the average tilt angle, the larger, on average, is the rotation of the magnetic axis in the direction of the average tilt angle. The rate of rotation of the magnetic axis is about twice as fast for sunspot groups as it is for plages. Growing plages and spot groups rotate their axes significantly faster than do decaying plages and spot groups. There is a latitude dependence of this effect that follows Joy's law. The fact that these tilt angles move toward the average tilt angle and not toward 0 deg (the east-west orientation), combined with other results presented here, suggest that a commonly accepted view of the origin of active region magnetic flux at the solar surface may have to be re-examined.Operated by the Association of Universities for Research in Astronomy, Inc., under Cooperative Agreement with the National Science Foundation.     

Axial tilt angles of active regions

Separate Mount Wilson plage and sunspot group data sets are analyzed in this review to illustrate several interesting aspects of active region axial tilt angles. (1) The distribution of tilt angles differs between plages and sunspot groups in the sense that plages have slightly higher tilt angles, on average, than do spot groups. (2) The distributions of average plage total magnetic flux, or sunspot group area, with tilt angle show a consistent effect: those groups with tilt angles nearest the average values are larger (or have a greater total flux) on average than those farther from the average values. Moreover, the average tilt angles on which these size or flux distributions are centered differ for the two types of objects, and represent closely the actual different average tilt angles for these two features. (3) The polarity separation distances of plages and sunspot groups show a clear relationship to average tilt angles. In the case of each feature, smaller polarity separations are correlated with smaller tilt angles. (4) The dynamics of regions also show a clear relationship with region tilt angles. The spot groups with tilt angles nearest the average value (or perhaps 0-deg tilt angle) have on average a faster rotation rate than those groups with extreme tilt angles.All of these tilt-angle characteristics may be assumed to be related to the physical forces that affect the magnetic flux loop that forms the region. These aspects are discussed in this brief review within the context of our current view of the formation of active region magnetic flux at the solar surface.Dedicated to Cornelis de JagerOperated by the Association of Universities for Research in Astronomy, Inc., under Cooperative Agreement with the National Science Foundation.     

Active region magnetic fields

The tilt angles of sunspot groups are defined, using the Mount Wilson data set. It is shown that groups with tilt angles greater than or less than the average value (&amp;#x2248; 5 deg) show different latitude dependences. This effect is also seen in synoptic magnetic field data defining plages. The fraction of the total sunspot group area that is found in the leading spots is discussed as a parameter that can be useful in studying the dynamics of sunspot groups. This parameter is larger for low tilt angles, and small for extreme tilt angles in either direction. The daily variations of sunspot group tilt angles are discussed. The result that sunspot tilt angles tend to rotate toward the average value is reviewed. It is suggested that at some depth, perhaps 50 Mm, there is a flow relative to the surface that results from a rotation rate faster than the surface rate by about 60 m/sec and a meridional drift that is slower than the surface rate by about 5 m/sec. This results in a slanted relative flow at that depth that is in the direction of the average tilt angle and may be responsible for the tendency for sunspot groups (and plages) to rotate their magnetic axes in the direction of the average tilt angle.     

Measurement of Kodaikanal white-light images – IV. Axial Tilt Angles of Sunspot Groups

The Kodaikanal sunspot data set, covering the interval 1906–1987, is used in conjunction with the similar Mount Wilson sunspot data set, covering the interval 1917–1985, to examine characteristics of sunspot group axial tilt angles. Good agreement is demonstrated between various results derived from the two independent data sets. In particular, the tendency for sunspot groups near the average tilt angle to be larger than those far from the average tilt angle is confirmed. Similarly the faster residual rotation rate for groups near the average tilt angle is also confirmed. Other confirmations are made for the relationships between latitude drift of sunspot groups and tilt angle, polarity separations, and axial expansion. Evidence is presented that tilt angles averaged over these long time intervals differ between the north and south hemispheres by about 1.4 deg. It is suggested that residual tilt angles show a slight systematic variation with phase in the activity cycle.     

Differential rotation of the sun determined tracing sunspots and oscillations of sunspot tilt angle

The time and spatial characteristics of 324 large sunspots (S50 millionths of the solar hemisphere) selected from the Abastumani Astrophysical Observatory photoheliogram collection (1950–1990) have been studied. The variations of sunspot angular rotation velocity residuals and oscillations of sunspot tilt angle were analyzed. It has been shown that the differential rotation rate of selected sunspots correlates on average with the solar cycle. The deceleration of differential rotation of large sunspots begins on the ascending arm of the activity curve and ends on the descending arm reaching minimum near the epochs of solar activity maxima. This behavior disappears during the 21st cycle. The amplitudes and periods of sunspot tilt-angle oscillations correlate well with the solar activity cycle. Near the epochs of activity maximum there appear sunspots with large amplitudes and periods showing a significant scatter while the scatter near the minimum is rather low. We also found evidence of phase difference between the sunspot angular rotation velocity and the amplitudes and periods of tilt-angle oscillations.     

Long-term modulation of cosmic ray intensity in relation to sunspot numbers and tilt angle

A detailed correlative analysis between sunspot numbers (SSN) and tilt angle (TA) with cosmic ray intensity (CRI) in the neutron monitor energy range has been performed for the solar cycles 21, 22 and 23. It is found that solar activity parameters (SSN and TA) are highly (positive) correlated with each other and have inverse correlation with cosmic ray intensity (CRI). The ‘running cross correlation coefficient’ between cosmic ray intensity and tilt angle has also been calculated and it is found that the correlation is positive during the maxima of odd cycles 21 and 23. Moreover, the time lag analysis between CRI and SSN, and between CRI and TA has also been performed and is supported by hysteresis curves, which are wide for odd cycles and narrow for even cycles.     

Sunspot groups at high latitude

Data of sunspot groups at high latitude (35°), from the year 1874 to the present (2000 January), are collected to show their evolutional behaviour and to investigate features of the yearly number of sunspot groups at high latitude. Subsequently, an evolutional pattern of sunspot group number at high latitude is given in this paper. Results obtained show that the number of sunspot groups of a solar cycle at high latitude rises to a maximum value about 1 yr earlier than the time of the maximum of sunspot relative numbers of the solar cycle, and then falls to zero more rapidly. The results also show that, at the moment, solar activity described by the sunspot relative numbers has not yet reached its minimum. In general, sunspot groups at high latitude have not appeared on the solar disc during the last 3 yr of a Wolf solar cycle. The asymmetry of the high latitude sunspot group number of a Wolf solar cycle can reflect the asymmetry of solar activity in the Wolf solar cycle, and it is suggested that one could further use the high latitude sunspot group number during the rising time of a Wolf solar cycle, maximum year included, to judge the asymmetry of solar activity over the whole solar cycle.     

A model combining the polar and the sector structured solar magnetic fields

A phenomenological model of the interplay between the polar magnetic fields of the Sun and the solar sector structure is discussed. Current sheets separate regions of opposite polarity and mark the sector boundaries in the corona. The sheets are visible as helmet streamers. The solar sector boundary is tilted with respect to central meridian, and boundaries with opposite polarity change are oppositely tilted. The tilt of a given type of boundary [(+, ?) or (?, +)] changes systematically during the sunspot cycle as the polarity of the polar fields reverses. Similar reversals of the position of the streamers at the limbs takes place. If we consider (a) a sunspot cycle where the northern polar field is inward (?) during the early part of the cycle and (b) a (+, ?) sector boundary at central meridian then the model predicts the following pattern; a streamer at high northern latitudes should be observed over the west limb together with a corresponding southern streamer over the east limb. The current sheet runs now NW-SE. At sunspot maximum the boundary is more in the N-S direction; later when the polar fields have completed their reversal the boundary runs NE-SW and the northern streamer should be observed over the east limb and the southern streamer over the west limb. Observational evidence in support of the model is presented, especially the findings of Hansen, Sawyer and Hansen and Koomen and Howard that the K-corona is highly structured and related to the solar sector structure.     

Nature of Tilt Angles of Sunspot Groups During the 22nd Solar Cycle

Daily white-light images from Kodaikanal Observatory have been utilized to study the nature of tilt angles of sunspot groups during the 22nd solar cycle. 2416 spot groups have been measured to find the tilt angle. An average tilt angle of +4.6 ± 0.4 deg has been obtained for all these spot groups, where the positive sign indicates that the leading part of the group is closer to the equator. It is found that the number of poleward and equatorward spot groups showed an opposite trend as the cycle advanced. The spot groups with positive (equatorward) tilt angles declined in number whereas the spot groups with negative (poleward) tilt angles increased towards the end of the cycle. It is also noticed that the number of spot groups, which changed the sign of tilt angle during their lifetime or passage across the disc, increased during the maximum activity period of the cycle. These findings were confirmed from the analysis of data from the 21st cycle. These results are discussed in this paper along with the daily variation of tilt angles of some of the spot groups from the selected data.