太阳频率漂移的扰动层位置的变化

太阳p模频率随太阳磁活动的变化被称为频率漂移.频率漂移被认为是起源于太阳近表面的一个薄层受到的扰动.利用磁活动指数和太阳模型来计算频率漂移的方法之前已经建立起来了.在这种方法中,频率漂移值依赖于磁活动强度和扰动源位置.磁活动强度正比于磁活动指数.扰动源的位置之前被认为是固定的.研究了扰动源位置的变化.利用观测的太阳p模震动频率和Ca II指数,发现了扰动源的位置可能是随着太阳磁活动而变化的.在太阳活动极大时,扰动源位置较深,而在太阳活动极小时,扰动源位置较浅.     

太阳p模振动的激发机制

本估计了激发单个太阳ｐ模振动需要的能量输入率Ｅ≡ＥＴ,其中谱线宽度Г假设是振动模能量衰减率的观测值,在改进后的对流湍流三维时空分离描述的基础上,利用太阳对流区的混合长流模型计算了振动模的激发率,认为太阳Ｐ模振动主要是由雷诺应力扰动激发的,即Ｐ模激发对应着地流湍流运动引起声波发射,对于频率ｖ〈３ｍＨｚ,振动模的激发率为Ｅ∝ｖ＾７频率ｖ〉３ｍＨｚ,振动模的激发率为Ｅ∝ｖ＾－５,理论计算的振动能谱与观     

太阳p模振动的激发机制

本文估计了激发单个太阳ｐ模振动需要的能量输入率Ｅ≡ＥΓ,其中谱线宽度Γ假设是振动模能量衰减率的观测值．在改进后的对流湍流三维时空分离描述的基础上,利用太阳对流区的混合长模型计算了振动模的激发率．认为太阳ｐ模振动主要是由雷诺应力扰动激发的,即ｐ模激发对应着对流湍流运动引起的声波发射．对于频率ν＜３ｍＨｚ,振动模的激发率为Ｅ∝ν７;频率ν＞３ｍＨｚ,振动模的激发率为Ｅ∝ν－５．理论计算的振动能谱与观测结果基本符合．     

太阳黑子发展中的磁扩散不稳定性

根据太阳发电机理论中的ω-效应,在太阳对流层内将产生纬向磁场,它的磁浮力要促使流团上浮。在文[5]中讨论了在流团上浮过程中,流团表面的磁扩散率梯度将对纬向磁场产生扰动,这一扰动使纬向磁场集积在流团表面磁扩散率梯度大的地方,围绕流团表面形成了黑子磁环。 本文进一步从磁流力学方程组的小扰动方程出发探讨了太阳黑子磁环发展的不稳定性问题。结果表明:在扰动方程中存在着不稳定模式。这一不稳定性产生的原因是由于当温度(或者说磁扩散率)受到小扰动时,纬向磁场要集积在磁扩散率(或温度)梯度大的地方,而磁场的集积将导致磁压增强及气压减低。在绝热条件下,这将使温度减低,而温度的减低又加强了温度梯度的增大,这又进一步促使磁场在梯度大的地方集积。这种磁场与温度发展的相互促进关系可以称它为磁扩散不稳定性。本文认为太阳黑子磁环和它低温的形成正是由于这种不稳定性发展起来的。     

太阳P模振动理论的研究

日震学是太阳物理的一个前沿分支学科,是根据太阳振动的观测来研究太阳的内部结构与运动的一种方法学。太阳５ｍｉｎ振动频率的理论计算和实测之间存在的显著偏差和振动模的激发问题一直是困扰日震学的两大难题,经过多年的研究仍然没有解决。然而太阳的表面层内绝热假设条件与真实情况有很大的偏差,我们认为绝大多数标准太阳模型的Ｐ模频率计算忽略了非绝热效应对频率的影响,忽略了振动的激发和衰减机制以及缺乏振动与对流湍流相互作用的知识。因此,我们必须发展非绝热理论来处理太阳５ｍｉｎ的振动问题     

太阳P模振动理论的研究

日震学是太阳物理的一个前沿分支学科,是根据太阳振动的观测来研究太阳的内部结构与运动的一种方法学。太阳５ｍｉｎ振动频率的理论计算和实测之间存在显著偏差和振动模的激发问题一直是困扰日震学的两大难题。经过多年的研究仍然没有解决。然而太阳表面层内绝热假设条件与真实情况有很大的偏差,我们认为绝大多数标准太阳模型的Ｐ模频率计算忽略了非绝热效应对频率的影响,忽略了振动的激发和衰减机制以及缺乏振动与对流湍流相互作     

太阳宁静区磁元的空间结构

利用怀柔太阳磁场望远镜,我们对太阳宁静区光球和色球磁场进行了观测。日面中心到边缘的观测表明,太阳宁静区中的小尺度磁结构在从光球到色球的扩展过程中变化不大。日面边缘的观测表明,小尺度磁结构的水平分量在光球和色球都不大。对极区和赤道边缘纵向磁场的比较发现,极区磁场与赤道边缘磁场有着不同的磁结构特性     

非绝热过程对太阳p模振动的影响

本文讨论了与非绝热性有关的辐射损失和对流转移对太阳ｐ模振动的影响．在非绝热情况下，ｐ模的本征频率增加了虚部σ（１）ｉ和σ（２）ｉ．本文试图探讨一种渐进方法研究非绝热效应对太阳ｐ模振动的影响．在渐进近似失效的太阳外大气层，利用表面相移的相关关系给出了非绝热振动方程的严格解．对低、中间频率的振动模，通过渐进解和表面解在外大气层的拟合，得到表面相移只是频率的函数．与绝热振动相比，考虑非绝热效应有可能改善太阳５分钟振动的理论频率和观测频率之间存在的偏差．     

天体物理中的重力波和磁重力波

本文简要综述重力波和磁重力波在各种天体物理场合中的应用 ,我们描述在具有开放径向磁场的恒星大气各种磁流体波之间的相互转换过程 ,强调磁重力波被束缚在恒星冕内的可能性 ,并探讨恒星内部高频的声波模 (p -模 )被低频的重力波模 (g -模 )所调制的过程 ,一旦有了足够长时间未间断高质量的日震数据 ,太阳内部的重力波模对声波模的调制效应—即每一个分立声波模的频率精细结构—则可被用来寻找深陷于太阳内部的重力波模或进一步独立地约束重力波模的振幅上限     

卫星黑子衰减触发的喷流事件

详细分析了一次太阳低层大气磁场重联触发的喷流事件.这次喷流发生在2014年8月1日,爆发自美国国家海洋和大气管理局(National Oceanic and Atmospheric Administration, NOAA)活动区12127边缘的一个卫星黑子处.该喷流爆发包括日浪、紫外喷流、极紫外高温和低温喷流.大熊湖太阳天文台(Big Bear Solar Observatory,BBSO)的Goode Solar Telescope (GST)高分辨率氧化钛(TiO)谱线的光球观测显示,喷流爆发过程中,卫星黑子一直衰减.到喷流结束,卫星黑子面积共减少了80%.在此过程中,太阳动力学天文台(Solar Dynamics Observatory, SDO)日球磁场成像仪(Helioseismic and Magnetic Imager, HMI)的视向磁场观测表明,该卫星黑子对应的负极磁场与相邻的正极磁场发生明显对消,产生喷流足部亮点.根据SDO卫星太阳大气成像仪(Atmospheric Imaging Assembly, AIA)的多波段观测,该足部亮点首先出现在紫外1600?波段.待紫外(1600?)喷流从紫外足部亮点顶部向上喷发,在极紫外波段也观测到相应的亮源.随着足点源亮度突然增强,有明显的极紫外低温喷流和日浪从足部亮点侧面喷发.从GST的高分辨率Hα图像上,可见日浪由许多精细纤维组成,这些纤维扎根在足点源的东南侧.根据从光球层过色球层再到日冕层的多波段高分辨率观测,色球中下层的磁场对消触发了这次喷流事件.向上喷发的物质流可以携带能量进入上层大气,并加热上层大气.研究结果表明,低层大气磁重联可能对解决日冕加热问题起重要作用.     

High resolution observations of white‐light emissions from the opacity minimum during an X‐class flare

Using high cadence, high resolution near infrared (NIR) observations of the X10 white‐light flare (WLF) on 2003 October 29, we investigated the evolution of the core‐halo structure of white‐light emission during the two‐second period flare peak. We found that size and intensity of the halo remained almost constant in the range of 10 Mm². However, the core area was very compact and expanded rapidly from about 1 Mm² to 4 Mm². At the same time, the total emission of the core increased nearly twenty times. This distinct behavior indicates that different heating mechanisms might be responsible for core and halo emissions. In addition to the temporal analysis, we compared the intensity enhancements of the flare core and halo. The result shows that the halo contrast increased by about 8% compared to the flare‐quiet region, which could be explained by a combination of direct‐heating and backwarming models (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

YAOPBM – yet another peak bagging method

I present and discuss the fitting methodology I developed for very‐long time series (2088‐day‐long). This new method was first used to fit low degree modes, 𝓁 ≤ 25. That time series was also sub‐divided in somewhat shorter segments (728‐daylong) and also fitted for these low degrees, in order to measure changes with the solar activity level. I have recently extended the fitting in several “directions”: 1) to substantially higher degrees (𝓁 ≤ 125), 2) to shorter time series (364‐ and 182‐day‐long), and, 3) to additional 728‐day‐long segments, covering now some 10 years of observations. I present and discuss issues related to this expansion, namely problems at low frequencies affecting the f and p₁ modes, and the inadequacy of the leakage matrix at higher degrees. I also present some of the characteristics of the observed temporal changes in the resulting frequencies. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Eruption of an Active-Region Filament Driven by an Emerging Bipole

1 INTRODUCTION Filaments are cool, dense material suspended in the hot, tenuous corona. It is widely accepted that the global magnetic field surrounding the filaments plays a key role in their formation, structure and stability (Tandberg-Hanssen1995). Fil…     

Variations of the low‐degree solar p‐mode frequencies for 10 years of GOLF observations

We experiment with a method of measuring the frequency of solar p modes, intended to extend the passband for the variations of the frequency spectrum as high as possible. So far this passband is limited to a fraction of μ Hz for the classical analysis based on numerical fits of a theoretical line profile to a power spectrum averaged over periods lasting at least several weeks. This limit for the present analysis can be shifted to the mHz range, corresponding to some of the “5 min” oscillations, but in this range we use a lower resolution which allows us to separate odd and even p modes. We show an example of the results for long term variations and apply this analysis to search for a modulation of the p‐mode frequency spectrum by asymptotic series of solar g modes. A faint signal is found in the analysis of 10 years of GOLF data. This very preliminary result possibly indicates the detection of a small number of g modes of degree l = 1. A tentative determination of an observational value of the parameter P₀ follows. P₀ is the scaling factor of the asymptotic series of g modes and is a key data for solar core physics. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Review of Hinode results

Hinode is an observatory‐style satellite, carrying three advanced instruments being designed and built to work together to explore the physical coupling between the photosphere and the upper layers for understanding the mechanism of dynam‐ ics and heating. The three instruments aboard are the Solar Optical Telescope (SOT), which can provide high‐precision photometric and polarimetric data of the lower atmosphere in the visible light (388–668 nm) with a spatial resolution of 0.2–0.3 arcseconds, the X‐Ray Telescope (XRT) which takes a wide field of full sun coverage X‐ray images being capable of diagnosing the physical condition of coronal plasmas, and the EUV Imaging Spectrometer (EIS) which observes the upper transition region and coronal emission lines in the wavelength ranges of 17–21 nm and 25–29 nm. Since first‐light observations in the end of October 2006, Hinode has been continuously providing unprecedented high‐quality solar data. We will present some new findings of the sun with Hinode, focusing on those from SOT (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Downflow-induced brightening following a filament eruption

The plasma from solar filament eruptions sometimes falls down to the lower solar atmosphere. These interesting events can help us to understand the properties of downflows, such as the temperature and the conversion between kinetic energy and thermal energy. We analyze the case of a filament eruption in active region NOAA 11283 and brightening caused by the return of filament material on September 7 and 8, 2011, observed by the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) aboard the Solar Dynamics Observatory (SDO). Magnetic flux cancellation was observed as a result of the eruption after the eruptive filament started to ascend. Another filament near the eruptive filament was disturbed by an extreme ultraviolet (EUV) wave that was triggered by the eruptive filament, causing it to oscillate. Based on coronal seismology, the mean magnetic field strength in the oscillatory filament was estimated to be approximately 18 ± 2 G. Some plasma separated from the filament and fell down to the solar northwest surface after the filament eruption. The velocities of the downflows increased at accelerations lower than the gravitational acceleration. The main characteristic temperature of the downflows was about 5 × 10⁴ K. When the plasma blobs fell down to lower atmospheric heights, the high-speed downward-travelling plasma collided with plasma at lower atmospheric heights, causing the plasma to brighten. The brightening was observed in all 8 AIA channels, demonstrating that the temperature of the plasma in the brightening covered a wide range of values, from 10⁵ K to 10⁷ K. This brightening indicates the conversion between kinetic energy and thermal energy.     

Intermediate‐term variations in solar radius during solar cycle 23

In this study, we look for the mid‐term variations in the daily average data of solar radius measurements made at the Solar Astrolabe Station of TUBITAK National Observatory (TUG) during solar cycle 23 for a time interval from 2000 February 26 to 2006 November 15. Due to the weather conditions and seasonal effect dependent on the latitude, the data series has the temporal gaps. For spectral analysis of the data series, thus, we use the Date Compensated Discrete Fourier Transform (DCDFT) and the CLEANest algorithm, which are powerful methods for irregularly spaced data. The CLEANest spectra of the solar radius data exhibit several significant mid‐term periodicities at 393.2, 338.9, 206.5, 195.2, 172.3 and 125.4 days which are consistent with periods detected in several solar time series by several authors during different solar cycles. The knowledge relating to the origin of solar radius variations is not yet present. To see whether these variations will repeat in next cycles and to understand how the amplitudes of such variations change with different phases of the solar cycles, we need more systematic efforts and the long‐term homogeneous data. Since most of the periodicities detected in the present study are frequently seen in solar activity indicators, it is thought that the physical mechanisms driving the periodicities of solar activity may also be effective in solar radius variations (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Solar internal rotation rate and the latitudinal variation of the tachocline

A new set of accurately measured frequencies of solar oscillations is used to infer the rotation rate inside the Sun, as a function of radial distance as well as latitude. We have adopted a regularized least-squares technique with iterative refinement for both 1.5D inversion, using the splitting coefficients, and 2D inversion using individual m splittings. The inferred rotation rate agrees well with earlier estimates showing a shear layer just below the surface and another one around the base of the convection zone. The tachocline or the transition layer where the rotation rate changes from differential rotation in the convection zone to an almost latitudinally independent rotation rate in the radiative interior is studied in detail. No compelling evidence for any latitudinal variation in the position and width of the tachocline is found, although it appears that the tachocline probably shifts to a slightly larger radial distance at higher latitudes and possibly also becomes thicker. However, these variations are within the estimated errors and more accurate data would be needed to make a definitive statement about latitudinal variations.     

A study of possible temporal and latitudinal variations in the properties of the solar tachocline

Temporal variations of the structure and the rotation rate of the solar tachocline region are studied using helioseismic data from the Global Oscillation Network Group (GONG) and the Michelson Doppler Imager (MDI) obtained during the period 1995–2000. We do not find any significant temporal variation in the depth of the convection zone, the position of the tachocline or the extent of overshoot below the convection zone. No systematic variation in any other properties of the tachocline, like width, etc., is found either. The possibility of periodic variations in these properties is also investigated. Time-averaged results show that the tachocline is prolate with a variation of about 0.02 R_⊙ in its position. Neither the depth of the convection zone nor the extent of overshoot shows any significant variation with latitude.