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1.
Powerful flares are closely related to the evolution of the complex magnetic field configuration at the solar surface. The strength of the magnetic field and speed of its evolution are two vital parameters in the study of the change of magnetic field in the solar atmosphere. We propose a dynamic and quantitative depiction of the changes in complexity of the active region: E=u×B, where u is the velocity of the footpoint motion of the magnetic field lines and B is the magnetic field. E represents the dynamic evolution of the velocity field and the magnetic field, shows the sweeping motions of magnetic footpoints, exhibits the buildup process of current, and relates to the changes in nonpotentiality of the active region in the photosphere. It is actually the induced electric field in the photosphere. It can be deduced observationally from velocities computed by the local correlation tracking (LCT) technique and vector magnetic fields derived from vector magnetograms. The relationship between E and ten X-class flares of four active regions (NOAA 10720, 10486, 9077, and 8100) has been studied. It is found that (1) the initial brightenings of flare kernels are roughly located near the inversion lines where the intensities of E are very high, (2) the daily averages of the mean densities of E and its normal component (E n) decrease after flares for most cases we studied, whereas those of the tangential component of E (E t) show no obvious regularities before and after flares, and (3) the daily averages of the mean densities of E t are always higher than those of E n, which cannot be naturally deduced by the daily averages of the mean densities of B n and B t.  相似文献   

2.
We have found that solar flares in NOAA active region (AR) 10696 were often associated with large-scale trans-equatorial activities. These trans-equatorial activities appeared to be very common and manifest themselves through i) the formation and eruption of trans-equatorial loops (TELs), ii) the formation and eruption of trans-equatorial filaments (TEFs), and iii) the trans-equatorial brightening (TEB) in the chromosphere. It is determined that the TEF was formed following episodic plasma ejecta from flares occurring in the AR. The TEF eruption was associated with a trans-equatorial flare. All flares in the AR that were accompanied by trans-equatorial activities were associated with halo coronal mass ejections (CMEs). It was noticed that one or several major flares in the AR were followed by an increase of brightness and nonpotentiality of a TEL. These coupled events had a lifetime of more than 12 hours. In addition their associated halo CMEs always had a positive acceleration, indicating prolonged magnetic reconnections in the outer corona at high altitudes.  相似文献   

3.
Halo coronal mass ejections (HCMEs) are responsible of the most severe geomagnetic storms. A prediction of their geoeffectiveness and travel time to Earth’s vicinity is crucial to forecast space weather. Unfortunately, coronagraphic observations are subjected to projection effects and do not provide true characteristics of CMEs. Recently, Michalek (Solar Phys. 237, 101, 2006) developed an asymmetric cone model to obtain the space speed, width, and source location of HCMEs. We applied this technique to obtain the parameters of all front-sided HCMEs observed by the SOHO/LASCO experiment during a period from the beginning of 2001 until the end of 2002 (solar cycle 23). These parameters were applied for space weather forecasting. Our study finds that the space speeds are strongly correlated with the travel times of HCMEs to Earth’s vicinity and with the magnitudes related to geomagnetic disturbances.  相似文献   

4.
Various solar wind forecasting methods have been developed during the past decade, such as the Wang?–?Sheeley model and the Hakamada?–?Akasofu?–?Fry Version 2 (HAFv2) model. Also, considerable correlation has been found between the solar wind speed v and the coronal hole (CH) area A M on the visible side of the Sun, showing quantitative improvement of forecasting accuracy in low CME activity periods (e.g., Vr?nak, Temmer, and Veronig, Solar Phys. 240, 315, 2007a). Properties of lower layers of the solar atmosphere are good indications of the subsequent interplanetary and geomagnetic activities. We analyze the SOHO/EIT 284 Å images and construct a new forecasting factor (Pch) from the brightness of the solar EUV emission, and a good correlation is found between the Pch factor and the 3-day-lag solar wind velocity (v) probed by the ACE spacecraft. The main difference between the Pch and A M factor is that Pch does not depend on the CH-boundary estimate and can reflect both the area and brightness of CH. A simple method of forecasting the solar wind speed near Earth in low CME activity periods is presented. Between Pch and v from 21 November until 26 December 2003, the linear correlation coefficient is R=0.89. For comparison we also analyze the data in the same period (DOY 25?–?125, 2005) as Vr?nak, Temmer, and Veronig (Solar Phys. 240, 315, 2007a), who used the CH areas A M for predicting the solar wind parameters. In this period the correlation coefficient between Pch and v is R=0.70, whereas for A M and v the correlation coefficient is R=0.62. The average relative difference between the calculated and the observed values is $\overline{|\delta|}\approx 12.15\%Various solar wind forecasting methods have been developed during the past decade, such as the Wang – Sheeley model and the Hakamada – Akasofu – Fry Version 2 (HAFv2) model. Also, considerable correlation has been found between the solar wind speed v and the coronal hole (CH) area A M on the visible side of the Sun, showing quantitative improvement of forecasting accuracy in low CME activity periods (e.g., Vršnak, Temmer, and Veronig, Solar Phys. 240, 315, 2007a). Properties of lower layers of the solar atmosphere are good indications of the subsequent interplanetary and geomagnetic activities. We analyze the SOHO/EIT 284 ? images and construct a new forecasting factor (Pch) from the brightness of the solar EUV emission, and a good correlation is found between the Pch factor and the 3-day-lag solar wind velocity (v) probed by the ACE spacecraft. The main difference between the Pch and A M factor is that Pch does not depend on the CH-boundary estimate and can reflect both the area and brightness of CH. A simple method of forecasting the solar wind speed near Earth in low CME activity periods is presented. Between Pch and v from 21 November until 26 December 2003, the linear correlation coefficient is R=0.89. For comparison we also analyze the data in the same period (DOY 25 – 125, 2005) as Vršnak, Temmer, and Veronig (Solar Phys. 240, 315, 2007a), who used the CH areas A M for predicting the solar wind parameters. In this period the correlation coefficient between Pch and v is R=0.70, whereas for A M and v the correlation coefficient is R=0.62. The average relative difference between the calculated and the observed values is . Furthermore, for the ten peaks during the analysis period, Pch and v show a correlation coefficient of R=0.78, and the average relative difference between the calculated and the observed peak values is . Moreover, the Pch factor can eliminate personal bias in the forecasting process, which existed in the method using CH area as input parameter, because CH area depends on the CH-boundary estimate but Pch does not. Until now the CH-boundary could not be easily determined since no quantitative criteria can be used to precisely locate CHs from observations, which led to differences in forecasting accuracy.  相似文献   

5.
The Solar Weather Browser (SWB) is a standalone, open-source software tool designed to display solar images with context overlays. It was originally developed for the space-weather forecast activities of the Solar Influence Data analysis Center (SIDC) but it is more generally well suited to display the output of solar-feature recognition methods. The SWB is also useful in the context of distributed solar-image archives, where it could play the role of a quick-look viewer. The SWB allows the user to visually browse large solar data sets and investigate the solar activity for a given date. It has a client – server design that minimizes the bandwidth from the network to the user’s monitor. The server processes the data using the SolarSoft library and distributes them through a Web server to which the SWB client connects. The client is readily available for Linux, Mac OS X, and Windows at . We discuss the software technology embedded in the SWB as well as its use for solar physics and space weather.  相似文献   

6.
Two different multiresolution analyses are used to decompose the structure of active-region magnetic flux into concentrations of different size scales. Lines separating these opposite polarity regions of flux at each size scale are found. These lines are used as a mask on a map of the magnetic field gradient to sample the local gradient between opposite polarity regions of given scale sizes. It is shown that the maximum, average, and standard deviation of the magnetic flux gradient for α,β,β γ, and β γ δ active-regions increase in the order listed, and that the order is maintained over all length scales. Since magnetic flux gradient is strongly linked to active-region activity, such as flares, this study demonstrates that, on average, the Mt. Wilson classification encodes the notion of activity over all length scales in the active-region, and not just those length scales at which the strongest flux gradients are found. Further, it is also shown that the average gradients in the field, and the average length-scale at which they occur, also increase in the same order. Finally, there are significant differences in the gradient distribution, between flaring and non-flaring active regions, which are maintained over all length scales. It is also shown that the average gradient content of active-regions that have large flares (GOES class “M” and above) is larger than that for active regions containing flares of all flare sizes; this difference is also maintained at all length scales. All of the reported results are independent of the multiresolution transform used. The implications for the Mt. Wilson classification of active-regions in relation to the multiresolution gradient content and flaring activity are discussed.  相似文献   

7.
Solar flares are known to release a large amount of energy. It is believed that the flares can excite velocity oscillations in active regions. We report here the changes in velocity signals in three active regions which have produced large X-class flares. The enhanced velocity signals appeared during the rise time of the GOES soft X-ray flux. These signals are located close to the vicinity of the hard X-ray source regions as observed with RHESSI. The power maps of the active region show enhancement in the frequency regime 5–6.5 mHz, while there is feeble or no enhancement of these signals in 2–4 mHz frequency band. High energy particles with sufficient momentum seem to be the cause for these observed enhanced velocity signals.  相似文献   

8.
The Solar Optical Telescope (SOT) aboard the Solar-B satellite (Hinode) is designed to perform high-precision photometric and polarimetric observations of the Sun in visible light spectra (388 – 668 nm) with a spatial resolution of 0.2 – 0.3 arcsec. The SOT consists of two optically separable components: the Optical Telescope Assembly (OTA), consisting of a 50-cm aperture Gregorian with a collimating lens unit and an active tip-tilt mirror, and an accompanying Focal Plane Package (FPP), housing two filtergraphs and a spectro-polarimeter. The optomechanical and optothermal performance of the OTA is crucial to attain unprecedented high-quality solar observations. We describe in detail the instrument design and expected stable diffraction-limited on-orbit performance of the OTA, the largest state-of-the-art solar telescope yet flown in space.  相似文献   

9.
Geomagnetic super-storms of October and November 2003 are compared in order to identify solar and interplanetary variables that influence the magnitude of geomagnetic storms. Although these superstorms (DST < -300 nT) are associated with high speed CMEs, their DST indices show large variation. The most intense storm of November 20, 2003 (DSt∼ - 472 nT) had its source in a comparatively small active region and was associated with a relatively weaker, M-class flare, while the others had their origins in large active regions and were associated with strong X-class flares. An attempt has been made to implement a logistic regression model for the prediction of the occurrence of intense/superintense geomagnetic storms. The model parameters (regression coefficients) were estimated from a training data-set extracted from a data-set of 64 geo-effective CMEs observed during 1996–2002. The results indicate that logistic regression models can be effectively used for predicting the occurrence of major geomagnetic storms from a set of solar and interplanetary factors. The model validation shows that 100% of the intense storms (-200 nT < DSt < -100 nT) and only 50% of the super-intense (DST < -200 nT) storms could be correctly predicted.  相似文献   

10.
Helioseismic techniques such as ring-diagram analysis have often been used to determine the subsurface structural differences between solar active and quiet regions. Results obtained by inverting the frequency differences between the regions are usually interpreted as the sound-speed differences between them. These in turn are used as a measure of temperature and magnetic-field strength differences between the two regions. In this paper we first show that the “sound-speed” difference obtained from inversions is actually a combination of sound-speed difference and a magnetic component. Hence, the inversion result is not directly related to the thermal structure. Next, using solar models that include magnetic fields, we develop a formulation to use the inversion results to infer the differences in the magnetic and thermal structures between active and quiet regions. We then apply our technique to existing structure inversion results for different pairs of active and quiet regions. We find that the effect of magnetic fields is strongest in a shallow region above 0.985R ⊙ and that the strengths of magnetic-field effects at the surface and in the deeper (r<0.98R ⊙) layers are inversely related (i.e., the stronger the surface magnetic field the smaller the magnetic effects in the deeper layers, and vice versa). We also find that the magnetic effects in the deeper layers are the strongest in the quiet regions, consistent with the fact that these are basically regions with weakest magnetic fields at the surface. Because the quiet regions were selected to precede or follow their companion active regions, the results could have implications about the evolution of magnetic fields under active regions.  相似文献   

11.
A statistical study is carried out on the photospheric magnetic nonpotentiality in solar active regions and its relationship with associated flares. We select 2173 photospheric vector magnetograms from 1106 active regions observed by the Solar Magnetic Field Telescope at Huairou Solar Observing Station, National Astronomical Observatories of China, in the period of 1988??C?2008, which covers most of the 22nd and 23rd solar cycles. We have computed the mean planar magnetic shear angle ( $\overline{\Delta\phi}$ ), mean shear angle of the vector magnetic field ( $\overline{\Delta\psi}$ ), mean absolute vertical current density ( $\overline{|J_{z}|}$ ), mean absolute current helicity density ( $\overline{|h_{\mathrm{c}}|}$ ), absolute twist parameter (|?? av|), mean free magnetic energy density ( $\overline{\rho_{\mathrm{free}}}$ ), effective distance of the longitudinal magnetic field (d E), and modified effective distance (d Em) of each photospheric vector magnetogram. Parameters $\overline{|h_{\mathrm{c}}|}$ , $\overline{\rho_{\mathrm{free}}}$ , and d Em show higher correlations with the evolution of the solar cycle. The Pearson linear correlation coefficients between these three parameters and the yearly mean sunspot number are all larger than 0.59. Parameters $\overline {\Delta\phi}$ , $\overline{\Delta\psi}$ , $\overline{|J_{z}|}$ , |?? av|, and d E show only weak correlations with the solar cycle, though the nonpotentiality and the complexity of active regions are greater in the activity maximum periods than in the minimum periods. All of the eight parameters show positive correlations with the flare productivity of active regions, and the combination of different nonpotentiality parameters may be effective in predicting the flaring probability of active regions.  相似文献   

12.
文中评价了２３ 周以来北京天文台的短期太阳活动预报工作,Ｘ 射线耀斑的报准率为８９ ．６ ％ ,太阳质子事件的报准率为６２ ．５ ％ 。另外,还叙述了第２３ 周峰年北京天文台太阳活动预报工作的选题（ 包括研究课题和实施课题  相似文献   

13.
The aim of the present paper is to explore the mechanism of fast Sweet–Parker’s magnetic reconnection with the Cowling’s conductivity. Cowling derived the resistivity of plasma with three components: electrons, ions and neutral particles in magnetic field theoretically after Spitzer. The resistivity is much larger than the Spitzer’s. According to the idea of partially ionized plasmas ejected into the corona as the trigger of flares, we adopt Cowling’s Conductivity to Sweet–Parker’s reconnection model in this paper. The result shows that the reconnection rate can be improved a lot in solar corona and approaches the timescale of solar flare in the absence of anomalous resistivity.  相似文献   

14.
The minimum dissipative rate (MDR) method for deriving a coronal non-force-free magnetic field solution is partially evaluated. These magnetic field solutions employ a combination of three linear (constant-α) force-free-field solutions with one being a potential field (i.e., α=0). The particular case of the solutions where the other two α’s are of equal magnitude but of opposite sign is examined. This is motivated by studying the SOLIS (Synoptic Optical Long-term Investigation of the Sun (SOLIS), a National Solar Observatory facility) vector magnetograms of AR 10987, which show a global α value consistent with an α=0 value as evaluated by (∇×B) z /B z over the region. Typical of the current state of the observing technology, there is no definitive twist for input into the general MDR method. This suggests that the special α case, of two α’s with equal magnitudes and opposite signs, is appropriate given the data. Only for an extensively twisted active region does a dominant, nonzero α normally emerge from a distribution of local values. For a special set of conditions, is it found that (i) the resulting magnetic field is a vertically inflated magnetic field resulting from the electric currents being parallel to the photosphere, similar to the results of Gary and Alexander (Solar Phys. 186:123, 1999), and (ii) for α≈(α max /2), the Lorentz force per unit volume normalized by the square of the magnetic field is on the order of 1.4×10−10 cm−1. The Lorentz force (F L) is a factor of ten higher than that of the magnetic force d(B 2/8π)/dz, a component of F L. The calculated photospheric electric current densities are an order of magnitude smaller than the maximum observed in all active regions. Hence both the Lorentz force density and the generated electric current density seem to be physically consistent with possible solar dynamics. The results imply that the field could be inflated with an overpressure along the neutral line. However, the implementation of this or any other extrapolation method using the electric current density as a lower boundary condition must be done cautiously, with the current magnetography.  相似文献   

15.
A database combining information about solar proton enhancements (SPEs) near the Earth and soft X-ray flares (GOES measurements) has been used for the study of different correlations through the period from 1975 to May 2006. The emphasis of this work is on the treatment of peak-size distributions of SXR flares and SPEs. The frequency of SXR flares and solar proton events (>10 and >100 MeV, respectively) for the past three solar cycles has been found to follow mainly a power-law distribution over three to five orders of magnitude of fluxes, which is physically correct beyond the “sensitivity” problem with the smallest peak values. The absence of significant spectral steepening in the domain of the highest peak values demonstrates that during the period considered, lasting 30 years, the limit of the highest flare’s energy release has not yet been achieved. The power-law exponents were found to be −2.19±0.04, −1.34±0.02, and −1.46±0.04, for the total SXR flare distribution and the total SPE distributions (for both E P>10 MeV and E P>100 MeV), respectively. For SPEs associated with flares located to the West of 20° W, the exponents are −1.22±0.05 (E P>10 MeV) and −1.26±0.03 (E P>100 MeV). The size distribution for corresponding flares follows a power law with a slope of −1.29±0.12. Thus, X-ray and proton fluxes produced in the same solar events have very similar distribution shapes. Moreover, the derived slopes are not incompatible with a linear dependence between X-ray flare power and proton fluxes near the Earth. A similar statistical relation is obtained independently from the direct comparison of the X-ray and proton fluxes. These all argue for a statistically significant relationship between X-ray and proton emissions.  相似文献   

16.
Reliable measurements of the solar magnetic field are restricted to the level of the photosphere. For about half a century attempts have been made to calculate the field in the layers above the photosphere, i.e. in the chromosphere and in the corona, from the measured photospheric field. The procedure is known as magnetic field extrapolation. In the superphotospheric parts of active regions the magnetic field is approximately force-free, i.e. electric currents are aligned with the magnetic field. The practical application to solar active regions has been largely confined to constant-α or linear force-free fields, with a spatially constant ratio, α, between the electric current and the magnetic field. We review results obtained from extrapolations with constant-α force-free fields, in particular on magnetic topologies favourable for flares and on magnetic and current helicities. Presently, different methods are being developed to calculate non-constant-α or nonlinear force-free fields from photospheric vector magnetograms. We also briefly discuss these methods and present a comparison of a linear and a nonlinear force-free magnetic field extrapolation applied to the same photospheric boundary data. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

17.
太阳活动区的模糊分类与活动性预测   总被引：2，自引：0，他引：2  
韩正忠  唐玉华 《天文学报》2002,43(3):242-246
运用模糊聚类分析的方法，研究太阳活动区特性。根据Hα、软X射线耀斑与黑子群各项特征因子的数据，进行标准化处理，分别运用模糊理论中的夹角余弦法，算术平均最小法进行标定，构造模糊相似矩阵与等价矩阵，根据模糊动态聚类分析方法，确定不同λ阈值，按照活动性强弱，对24个活动区进行分类。理论计算结果表明，不同等级类型的活动区强度预测与活动区实际活动性相一致，作为太阳活动水平预报，模糊聚类分析也是一种有效的方法。  相似文献   

18.
Solar flares are powered by the energy stored in magnetic fields, so evolutionary information of the magnetic field is important for short-term prediction of solar flares. However, the existing solar flare prediction models only use the current information of the active region. A sequential supervised learning method is introduced to add the evolutionary information of the active region into a prediction model. The maximum horizontal gradient, the length of the neutral line, and the number of singular points extracted from SOHO/MDI longitudinal magnetograms are used in the model to describe the nonpotentiality and complexity of the photospheric magnetic field. The evolutionary characteristics of the predictors are analyzed by using autocorrelation functions and mutual information functions. The analysis results indicate that a flare is influenced by the 3-day photospheric magnetic field information before flare eruption. A sliding-window method is used to add evolutionary information of the predictors into machine learning algorithms, then C4.5 decision tree and learning vector quantization are employed to predict the flare level within 48 hours. Experimental results indicate that the performance of the short-term solar flare prediction model within the sequential supervised learning framework is significantly improved.  相似文献   

19.
Relationship between Rotating Sunspots and Flares   总被引：2，自引：0，他引：2  
Active Region (AR) NOAA 10486 was a super AR in the declining phase of solar cycle 23. Dominated by the rapidly rotating positive polarity of an extensive δ sunspot, it produced several powerful flare-CMEs. We study the evolution and properties of the rotational motion of the major poles of positive polarities and estimate the accumulated helicity injected by them. We also present two homologous flares that occurred in the immediate periphery of the rotating sunspots. The main results are as follows: i) anticlockwise rotational motions are identified in the main poles of positive polarities in the AR; the fastest of them is about 220° for six days. ii) The helicity injection inferred from such rotational motion during the interval from October 25 to 30 is about − 3.0×1043 Mx2, which is comparable that calculated by the local correlation tracking (LCT) method (− 5.2×1043 Mx2) in the whole AR. It is suggested that both methods reveal the essential topological properties of the AR, even if the former includes only the major poles and the fine features of the magnetic field are neglected. iii) It is found that there is a good spatial and temporal correspondence between the onset of two homologous CME-associated flares and the rotational motion of sunspots. This suggests that the rotational motions of sunspots not only relate to the transport of magnetic energy and complexity from the low atmosphere to the corona but may also play a key role in the onset of the homologous flares. Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users.  相似文献   

20.
We have used Ramaty High Energy Solar Spectroscopic Imager (RHESSI) modulation profiles in the 25 – 300 keV range to construct high-fidelity visibilities of 25 flares having at least two components. These hard X-ray visibilities, which are mathematically identical to the visibilities of radio imaging, were input to software developed for mapping solar flares in the microwave domain using the Maximum Entropy Method (MEM). We compared and contrasted the MEM maps with Clean and Pixon maps made with RHESSI software. In particular, we assessed the reliability of the maps and their morphologies for future investigations of the symmetry of bipolar electron beaming in the sample set.  相似文献   

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