检索结果-南通市图书馆

Flare evolution and polarization changes in fine structures of solar radio emission in the 2013 April 11 event

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2016年第2期16卷 69-80页

作者： Gennady Chernov Robert Sych Bao-Lin Tan Yi-Hua Yan Cheng-Ming Tan Qi-Jun Fu Marian Karlicky Valery Fomichev Key Laboratory of Solar activity National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100012China Pushkov Institute of Terrestrial Magnetism Ionosphere and Radio Wave PropagationRussian Academy of Sciences(IZMIRAN)TroitskMoscow region142190Russia Yunnan Observatories Chinese Academy of SciencesKunming 650011China Institute of Solar-Terrestrial Physics Russian Academy of SciencesSiberian BranchIrkutsk 664033Russia Astronomical Institute of the Academy of Sciences of the Czech Republic Ondrejov 15165Czech Republic

The measurement of positions and sizes of radio sources in observations is important for un- derstanding of the flare evolution. For the first time, solar radio spectral fine structures in an M6.5 flare that occurred on 2013 April 11 were observed simultaneously by several radio instruments at four different observatories： Chinese Solar Broadband Radio Spectrometer at Huairou （SBRS/Huairou）, Ondrejov Radio Spectrograph in the Czech Republic （ORSC/Ondrejov）, Badary Broadband Microwave Spectropolarimeter （BMS/Irkutsk）, and spectrograph/IZMIRAN （Moscow, Troitsk）. The fine structures included microwave zebra patterns （ZPs）, fast pulsations and fiber bursts. They were observed during the flare brightening lo- cated at the tops of a loop arcade as shown in images taken by the extreme ultraviolet （EUV） telescope onboard NASA＇s satellite Solar Dynamics Observatory （SDO）. The flare occurred at 06：58-07：26 UT in solar active region NOAA 11719 located close to the solar disk center. ZPs appeared near high frequency boundaries of the pulsations, and their spectra observed in Huairou and Ondrejov agreed with each other in terms of details. At the beginning of the flare＇s impulsive phase, a strong narrowband ZP burst occurred with a moderate left-handed circular polarization. Then a series of pulsations and ZPs were observed in almost unpolarized emission. After 07：00 UT a ZP appeared with a moderate right-handed polarization. In the flare decay phase （at about 07：25 UT）, ZPs and fiber bursts become strongly right-hand polarized. BMS/Irkutsk spectral observations indicated that the background emission showed a left-handed circular polarization （similar to SBRS/Huairou spectra around 3 GHz）. However, the fine structure appeared in the right-handed polarization. The dynamics of the polarization was associated with the motion of the flare ex- citer, which was observed in EUV images at 171 A and 131 A by the SDO Atmospheric Imaging Assembly （AIA）. Combining magnetograms observed by the SDO Helioseismic and Magnetic Imager （HMI） wi

关键词： sun activity -- sun flares -- sun particle emission -- sun radio radiation -- zebra-pattern

Small-Scale Brightenings in the UV Continuum of an M9.1 Solar Flare

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Astronomy and Astrophysics 2007年第5期7卷 721-732页

作者： Lin Wang Cheng Fang Ming-De Ding Department of Astronomy Nanjing University Nanjing 210093

We analyze an M9.1 two-ribbon solar flare which occurred on 2004 July 22 using the TRACE white-light and 1700 A images, the RHESSI, and the SOHO/MDI data. We find many small-scale fast-varying brightenings that appeared in the white-light and 1700 A images along the flare ribbons. Some of them underwent rapid motions in weak magnetic field regions. We identify these short-lived brightenings as UV continuum enhancement. Our preliminary result shows that the brightenings are closely related to the HXR emission. They have a lifetime of 30-60 s and a typical size of about 1＂-2＂. The intensity enhancement is about 150-200 times the mean value of the quiet-sun. According to previous works, we infer that the 1700A enhancement may be dominated by the increased emission of 1680A continuum coming from the temperature minimum region. The impulsive feature in the 1700 A light curves of the small-scale brightenings may be due to the irradiation of the impulsive CIv line intensity caused by the bombardment of non-thermal electron beams.

关键词： sun activity -- sun flares -- sun UV radiation

A Statistical Study of Rapid sunspot Structure Change Associated with Flares

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Astronomy and Astrophysics 2007年第5期7卷 733-742页

作者： Wei-Zhong Chen Chang Liu Hui Song Na Deng Chang-Yi Tan Hai-Min Wang Center for Solar-Terrestrial Research New Jersey Institute of Technology University Heights Newark N J 07102-1982 USA

We reported recently some rapid changes of sunspot structure in white-light （WL） associated with major flares. We extend the study to smaller events and present here results of a statistical study of this phenomenon. In total, we investigate 403 events from 1998 May 9 to 2004 July 17, including 40 X-class, 174 M-class, and 189 C-class flares. By monitoring the structure of the flaring active regions using the WL observations from the Transition Region and Coronal Explorer （TRACE）, we find that segments in the outer sunspot structure decayed rapidly right after many flares; and that, on the other hand, the central part of sunspots near the flare-associated magnetic neutral line became darkened. These rapid and permanent changes are evidenced in the time profiles of WL mean intensity and are not likely resulted from the flare emissions. Our study further shows that the outer sunspot structure decay as well as the central structure darkening are more likely to be detected in larger solar flares. For X-class flares, over 40% events show distinct sunspot structure change. For M- and C-class flares, this percentage drops to 17% and 10%, respectively. The results of this statistical study support our previously proposed reconnection picture, i.e., the flare-related magnetic fields evolve from a highly inclined to a more vertical configuration.

关键词： sun activity -- sun flares -- sun magnetic fields -- sunspots

A study of short-period variation in solar activity

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2014年第8期14卷 1011-1018页

作者： Ji-Long Chen Juan Zhao Department of Astronomy Beijing Normal University

We introduce two methods to detect short-period variation in solar activity. These are called amplitude of low frequency fluctuation （ALFF） and fractional am- plitude of low frequency fluctuation （FALFF）. We find a positive correlation between short-period variation and 11-year variation of solar activity using these two methods. Through ALFF, we find that solar activity over a short period becomes intensive when the 11-year solar activity is intensive. The ALFF value of the short period activity varies with the peak in sunspot number as a quadratic function. Through FALFF we find that the ratio of short-period spectral intensity to intensity over the whole period of solar activity will increase when the 11-year period of solar activity is intensive. The short-period FALFF value varies with the peak in sunspot number according to a cubic function. Using ALFF, we obtain a yearly series of solar activity that varies over a short period of 1-5 yr from 1860 to 2003, which shows an obvious periodicity of about 22 yr, 33 yr, 11 yr and a century. These short period variations show good correlations with long term variations in solar activity.

关键词： sun activity -- sun sunspots -- methods data analysis

Does a low solar cycle minimum hint at a weak upcoming cycle?

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2010年第10期10卷 950-955页

作者： Zhan-Le Du Hua-Ning Wang Key Laboratory of Solar activity National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China

The maximum amplitude （Rm） of a solar cycle, in the term of mean sunspot numbers, is well-known to be positively correlated with the preceding minimum （Rmin）. So far as the long term trend is concerned, a low level of Rmin tends to be followed by a weak Rm, and vice versa. We found that the evidence is insufficient to infer a very weak Cycle 24 from the very low Rmin in the preceding cycle. This is concluded by analyzing the correlation in the temporal variations of parameters for two successive cycles.

关键词： sun activity -- sun general -- sunspots

Forecast daily indices of solar activity, F10.7, using support vector regression method

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2009年第6期9卷 694-702页

作者： Cong Huang Dan-Dan Liu Jing-Song Wang National Center For Space Weather CMA Beijing 100081 China

The 10.7 cm solar radio flux （F10.7）, the value of the solar radio emission flux density at a wavelength of 10.7 cm, is a useful index of solar activity as a proxy for solar extreme ultraviolet radiation. It is meaningful and important to predict F10.7 values accurately for both long-term （months-years） and short-term （days） forecasting, which are often used as inputs in space weather models. This study applies a novel neural network technique, support vector regression （SVR）, to forecasting daily values of F10.7. The aim of this study is to examine the feasibility of SVR in short-term F10.7 forecasting. The approach, based on SVR, reduces the dimension of feature space in the training process by using a kernel-based learning algorithm. Thus, the complexity of the calculation becomes lower and a small amount of training data will be sufficient. The time series of F10.7 from 2002 to 2006 are employed as the data sets. The performance of the approach is estimated by calculating the norm mean square error and mean absolute percentage error. It is shown that our approach can perform well by using fewer training data points than the traditional neural network.

关键词： methods data analysis -- sun activity -- sun radio radiation

A Running Average Method for Predicting the Size and Length of a Solar Cycle

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Astronomy and Astrophysics 2008年第4期8卷 477-488页

作者： Zhan-Le Du Hua-Ning Wang Li-Yun Zhang National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China

The running correlation coefficient between the solar cycle amplitudes and the max-max cycle lengths at a given cycle lag is found to vary roughly in a cyclical wave with the cycle number, based on the smoothed monthly mean Group sunspot numbers available since 1610. A running average method is proposed to predict the size and length of a solar cycle by the use of the varying trend of the coefficients. It is found that, when a condition （that the correlation becomes stronger） is satisfied, the mean prediction error （16.1） is much smaller than when the condition is not satisfied （38.7）. This result can be explained by the fact that the prediction must fall on the regression line and increase the strength of the correlation. The method itself can also indicate whether the prediction is reasonable or not. To obtain a reasonable prediction, it is more important to search for a running correlation coefficient whose varying trend satisfies the proposed condition, and the result does not depend so much on the size of the correlation coefficient. As an application, the peak sunspot number of cycle 24 is estimated as 140.4 ± 15.7, and the peak as May 2012 ±11 months.

关键词： sun activity -- sun sunspots - sun general

Observations of EUV and soft X-ray recurring jets in an active region

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2011年第10期11卷 1229-1242页

作者： Li-Heng Yang Yun-Chun Jiang Jia-Yan Yang Yi Bi Rui-Sheng Zheng National Astronomical Observatories / Yunnan Observatory Chinese Academy of SciencesKunming 650011 China

We present simultaneous observations of three recurring jets in EUV and soft X-ray （SXR）, which occurred in an active region on 2007 June 5. By comparing their morphological and kinematic characteristics in these two different wavelengths, we found that EUV and SXR jets had similar locations, directions, sizes and velocities. We also analyzed their spectral properties by using six spectral lines from the EUV Imaging Spectrometer （EIS） onboard Hinode and found that these jets had temperatures from 0.05 to 2.0MK and maximum electron densities from 6.6× 10^9 to 3.4× 10^10cm^-3. For each jet, an elongated blue-shifted component and a red- shifted component at the jet base were simultaneously observed in the Fe XII A195 and the He II A256 lines. The three jets had maximum Doppler velocities from 25 to 121 km s-1 in the FexII A195 line and from 115 to 232 km s -1 in the HeII A256 line. They had maximum non-thermal velocities from 98 to 181 km s-1 in the Fe xII A195 line and from 196 to 399 km s-1 in the He II A256 line. We also examined the relationship between averaged Doppler velocities and maximum ionization temperatures of these three jets and found that averaged Doppler velocities decreased with the increase of maximum ionization temperatures. In the photosphere, magnetic flux emergences and cancelations continuously took place at the jet base. These observa- tional results were consistent with the magnetic reconnection jet model, implying that magnetic reconnection between emerging magnetic flux and ambient magnetic field occurred in the lower atmosphere.

关键词： sun activity -- sun corona -- sun UV radiation -- sun magnetic fields

The hemispheric asymmetry of solar activity during the last century and the solar dynamo

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Astronomy and Astrophysics 2009年第1期9卷 115-126页

作者： Ashish Goel Arnab Rai Choudhuri Department of Physics Indian Institute of Technology Department of Physics Indian Institute of Science

We believe the Babcock-Leighton process of poloidal field generation to be the main source of irregularity in the solar cycle. The random nature of this process may make the poloidal field in one hemisphere stronger than that in the other hemisphere at the end of a cycle. We expect this to induce an asymmetry in the next sunspot cycle. We look for evidence of this in the observational data and then model it theoretically with our dynamo code. Since actual polar field measurements exist only from the 1970s, we use the polar faculae number data recorded by Sheeley （1991, 2008） as a proxy of the polar field and estimate the hemispheric asymmetry of the polar field in different solar minima during the major part of the twentieth century. This asymmetry is found to have a reasonable correlation with the asymmetry of the next cycle. We then run our dynamo code by feeding information about this asymmetry at the successive minima and compare the results with observational data. We find that the theoretically computed asymmetries of different cycles compare favorably with the observational data, with the correlation coefficient being 0.73. Due to the coupling between the two hemispheres, any hemispheric asymmetry tends to get attenuated with time. The hemispheric asymmetry of a cycle either from observational data or from theoretical calculations statistically tends to be less than the asymmetry in the polar field （as inferred from the faculae data） in the preceding minimum. This reduction factor turns out to be 0.43 and 0.51 respectively in observational data and theoretical simulations.

关键词： sun activity -- sun magnetic fields -- sunspots