共查询到17条相似文献,搜索用时 281 毫秒
1.
Zhong-Quan Qu Shuai Wang Cheng-Lin Xu XiaoYu Zhang Ming-Guo Sun Chun-Lan Jin National Astronomical Observatories/Yunnan Astronomical Observatory Chinese Academy of Sciences Kunming zqqu@vip.km.net Graduate School of the Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2005,5(4):426-432
We analyze the spectral line broadening of those magneto-sensitive lines in solar magnetized atmospheres. The broadening at the line wings is due to the increase of the effective width of energy levels involved in Zeeman splitting, and the broadening at the line core also originated in Zeeman splitting under the condition that the Zeeman components are mixed. Therefore, the magnetoinduced or Zeeman broadening take effects on the whole line. The observed Stokes parameter data in a sunspot and outside it acquired by Solar Stokes Spectrum Telescope (S3T) are analyzed for the demonstration of this mechanism, and the Zeeman broadening rates are calculated for FeI6302.5 under some assumptions. Our result shows that the broadening is increased as the magnetic field strength becomes stronger, but the rate of increase at the line core is decreased as the field strength increases, while the rate at the wing does not show such an obvious regularity. The broadening is more effective in the line core than in the wings. 相似文献
2.
The Prediction of Maximum Amplitudes of Solar Cycles and the Maximum Amplitude of Solar Cycle 24 总被引:1,自引:0,他引:1
Jia-Long Wang Jian-Cun Gong Si-Qing Liu Gui-Ming Le Jing-Lan Sun National Astronomical Observatories Chinese Academy of Sciences Beijing Center for Space Science Applied Research Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2002,2(6)
We present a brief review of predictions of solar cycle maximum amplitude with a lead time of 2 years or more. It is pointed out that a precise prediction of the maximum amplitude with such a lead-time is still an open question despite progress made since the 1960s. A method of prediction using statistical characteristics of solar cycles is developed: the solar cycles are divided into two groups, a high rising velocity (HRV) group and a low rising velocity (LRV) group, depending on the rising velocity in the ascending phase for a given duration of the ascending phase. The amplitude of Solar Cycle 24 can be predicted after the start of the cycle using the formula derived in this paper. Now, about 5 years before the start of the cycle, we can make a preliminary prediction of 83.2-119.4 for its maximum amplitude. 相似文献
3.
Support Vector Machine combined with K-Nearest Neighbors for Solar Flare Forecasting 总被引:1,自引:0,他引:1
Rong Li Hua-Ning Wang Han He Yan-Mei Cui Zhan-Le Du 《中国天文和天体物理学报》2007,7(3):441-447
A method combining the support vector machine (SVM) the K-Nearest Neighbors (KNN), labelled the SVM-KNN method, is used to construct a solar flare forecasting model. Based on a proven relationship between SVM and KNN, the SVM-KNN method improves the SVM algorithm of classification by taking advantage of the KNN algorithm according to the distribution of test samples in a feature space. In our flare forecast study, sunspots and 10cm radio flux data observed during Solar Cycle 23 are taken as predictors, and whether an M class flare will occur for each active region within two days will be predicted. The SVM- KNN method is compared with the SVM and Neural networks-based method. The test results indicate that the rate of correct predictions from the SVM-KNN method is higher than that from the other two methods. This method shows promise as a practicable future forecasting model. 相似文献
4.
Cheng-Gang Shu Hou-Jun Mo Shu-De Mao Joint Center for Astrophysics Shanghai Normal University Shanghai cgshu@center. shao. ac. cn Shanghai Astronomical Observatory Chinese Academy of Sciences Shanghai Max-Planck-Institut fur Astrophysik Karl-Schwarzschild-Strasse Postfach D- Garching Germany Astronomy Department University of Massachusetts Amherst MA USA Jodrell Bank Observatory Univ. of Manchester Macclesfield Cheshire SK DL UK 《中国天文和天体物理学报》2005,5(4):327-346
Galactic winds and mass outflows are observed both in nearby starburst galaxies and in high-redshift star-forming galaxies. We develop a simple analytic model to understand the observed superwind phenomenon with a discussion of the model uncertainties. Our model is built upon the model of McKee & Ostriker for the interstellar medium. It allows one to predict how properties of a superwind, such as wind velocity and mass outflow rate, are related to properties of its starforming host galaxy, such as size, gas density and star formation rate. The model predicts a threshold of star formation rate density for the generation of observable galactic winds. Galaxies with more concentrated star formation activities produce superwinds with higher velocities. The predicted mass outflow rates are comparable to (or slightly larger than) the corresponding star formation rates. We apply our model to both local starburst galaxies and high-redshift Lyman break galaxies, and find its predictions to be in good agreement with current observations. Our model is simple and so can be easily incorporated into numerical simulations and semi-analytical models of galaxy formation. 相似文献
5.
Christopher A. Tout 《中国天文和天体物理学报》2006,6(4):461-469
A carbon-oxygen white dwarf may explode in a Type Ia supernova by accreting matter from its companion via either Roche lobe overflow or from winds, but there exists a critical accretion rate of the progenitor system for the explosion. We study the relation between the critical accretion rate and the metallicity via an AGB star approach. The result indicates that the critical accretion rate depends not only on the hydrogen mass fraction and the white dwarf mass, but also on the metallicity. The effect of the metallicity is smaller than that of the white dwarf mass. We show that it is reasonable to use the model with stellar mass 1.6 M⊙for real white dwarfs. 相似文献
6.
Jiu-Li Li Xu Zhou Jun Ma Jian-Sheng ChenNational Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2004,4(2):143-152
Based on the large field multicolor observations of Beijing-Arizona-Taiwan-Connecticut (BATC) program, we obtain the spectral energy distribution (SED) for individual regions of M81. We study the structure and evolution of M81 with an evolutionary population synthesis (EPS) model, PEGASE. We find that the exponentially deceasing star formation rate (SFR) with star formation scale 3 Gyr (hereafter Exp, τ=3 Gyr) gives the best agreement between the model predictions and the observed SEDs. We then obtain the structure, age distribution and evolutionary history of M81. There is a clear age gradient between the central and outer regions. The populations in the central regions are older than 7 Gyr,those in the outer regions are younger, at about 4.5 Gyr. The youngest components in the spiral arms have ages of about 2.5 Gyr or less. 相似文献
7.
Verification of a Similar Cycle Prediction for the Ascending and Peak Phases of Solar Cycle 23 总被引:3,自引:0,他引:3
Reviews of long-term predictions of solar cycles have shown that a precise prediction with a lead time of 2 years or more of a solar cycle remains an unsolved problem. We used a simple method, the method of similar cycles, to make long-term predictions of not only the maximum amplitude but also the smoothed monthly mean sunspot number for every month of Solar Cycle 23. We verify and compare our prediction with the latest available observational results. 相似文献
8.
《天文和天体物理学研究(英文版)》2020,(1)
Predictions of the strength of solar cycles are important and are necessary for planning long-term missions.A new solar cycle 25 is coming soon,and the amplitude is needed for space weather operators.Some predictions have been made using different methods and the values are drastically different.However,since 2015 July 1,the original sunspot number data have been entirely replaced by the Version 2.0 data series,and the sunspot number values have changed greatly.In this paper,using Version 2 smoothed sunspot numbers and aa indices,we verify the predictions for cycles 18–24 based on Ohl’s Precursor Method.Then a similar-cycles method is used to evaluate the aa minimum of 9.7(±1.1)near the start of cycle 25 and based on the linear regression relationship between sunspot maxima and aa minima,our predicted Version 2maximum sunspot number for cycle 25 is 121.5(±32.9). 相似文献
9.
Zhi Xu Cheng Fang Wei-Qun Can Astronomy Department of Nanjing University Nanjing Purple Mountain Observatory Chinese Academy of Sciences Nanjing 《中国天文和天体物理学报》2005,5(5):519-530
Chromospheric lines, including Ha, Lyα, Lyβand CaⅡK, CaⅡ8542, are systemically and quantitatively investigated with respect to the non-thermal excitation and ionization due to particle beam bombardment for a series of solar semi-empirical atmospheric models. As a result we propose to use the contrast in the integrated intensity of hydrogen lines to estimate the total energy flux of the bombarding beam during the solar flare impulsive phase. Partial frequency redistribution is considered in the Lyαline calculation and a smaller intensity enhancement in the Ha line-centers is found than in the previous results of Fang et al. 相似文献
10.
Yu-Qin Chen Gang Zhao Jian-Rong ShiNational Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2002,2(5):419-428
We have calculated the orbital parameters for 90 stars in Chen et al. and updated the kinematic data for stars in Edvardsson et al. by using the accurate Hipparcos parallaxes and proper motions, and recalculated the \\\\\\\\\\\\-element abundances in Edvardsson et al. in a way consistent with Chen et al. The two sets of data are combined in a study of stellar populations and characteristics of F & G stars in the solar neighborhood. We confirm the result of Chen et al. that a distinguishable group of stars may belong to the thick disk rather than the thin disk. The ages for the stars are determined using the theoretical isochrones of VandenBerg et al. The age-metallicity relation is investigated for different subgroups according to distance from the sun and galactic orbital parameters. It is found that a mixing of stars with different orbital parameters significantly affect the age-metallicity relation for the disk. Stars with orbits confined to the solar circle all have metallicities [Fe/H] > -0.3 irresp 相似文献
11.
朱翠莲 《中国天文和天体物理学报》2000,20(2)
以22周太阳活动低年(1993-1995)质子事件及其对应活动区的综合分析结果为判据,预报23周太阳活动上升阶段的质子事件.从1997年11月开始到1998年12月,用该方法预报的质子事件共6个,报准3个,不确定一个,虚报1个,漏报1个(太阳背面产生的事件).本文对用该方法预报的结果进行了分析讨论,并与世界警报中心的预报结果进行了比对,结果表明,该方法对于质子事件的短期预报是有效的. 相似文献
12.
Mausumi Dikpati Peter A. Gilman Giuliana de Toma Siddhartha S. Ghosh 《Solar physics》2007,245(1):1-17
We use the flux-transport dynamo prediction scheme introduced by Dikpati, de Toma, and Gilman (Geophys. Res. Lett.
33, L05102, 2006) to make separate simulations and predictions of sunspot cycle peaks for northern and southern hemispheres. Despite the division
of the data, the skill level achieved is only slightly lower than that achieved for the sum of both hemispheres. The model
shows skill at simulating and predicting the difference in peaks between North and South, provided that difference is more
than a few percent. The simulation and prediction skill is achieved without adjustment to any parameters of the model that
were used when peaks for the sum of North and South sunspot areas was simulated. The results are also very insensitive to
the averaging length applied to the input data, provided the simulations and predictions are for peaks defined by averaging
the observations over at least 13 rotations. However, in its present form, the model is not capable of skillfully simulating
or predicting short-time-scale features of individual solar cycles. 相似文献
13.
This paper presents general relations for the intensity of the resonant transition radiation (RTR) and their detailed analysis.
This analysis shows that the spectrum amplitude of the x-mode at some frequencies for high-energy electrons can grow with
the magnetic field increase in some interval from zero value; it can even dominate over that for the o-mode. With further
magnetic field increase, the intensity of the RTR x-mode decreases in comparison with the intensity of the o-mode and this
decrease is higher for higher velocities of energetic electrons. The polarization of the RTR depends on the velocity of energetic
electrons, too. For velocities lower than some velocity limit v<v
i
the RTR emission is unpolarized in a broad interval of magnetic field intensities in the radio source. For reasonable values
of indices of the power-law distribution functions of energetic electrons, the RTR is broadband in frequencies (df/f≈0.2−0.4). Furthermore, we show various dependencies of the RTR and its spectral characteristics. Assuming the same radio
flux of the transition radiation and the gyro-synchrotron one at the Razin frequency, we estimate the limit magnetic field
in the radio source of the transition radiation. Then, we analyze possible sources of small-scale inhomogeneities (thermal
density fluctuations, Langmuir and ion-sound waves), which are necessary for the transition radiation. Although the small-scale
inhomogeneities connected with the Langmuir waves lead to the plasma radiation, which is essentially stronger than RTR, the
inhomogeneities of the ion-sound waves are suitable for the RTR without any other radiation.
We present the relations describing the RTR for anisotropic distribution functions of fast electrons. We consider the distribution
functions of fast electrons in the form of the Legendre polynomials which depend on the pitch-angle. We analyze the influence
of the degree of the anisotropy (an increase of the number of terms in the Legendre polynomial) on spectral characteristics
of the RTR. A comparison with previous studies is made. As an example of the use of the derived formulas for the RTR, the
24 December 1991 event is studied. It is shown that the observed decimetric burst can be generated by the RTR in the plasma
with the density inhomogeneities at the level 〈ΔN
2〉/N
2=2.5⋅10−5. 相似文献
14.
研究发现,太阳自转速率的变化与太阳活动之间存在一定的联系,但是不同学者的研究结论存在着矛盾:有的认为两者为正相关,而有的却认为是负相关.究竟两者之间是什么关系,需要做进一步深入的分析.利用EEMD (Ensemble Empirical Mode Decomposition)等方法对太阳自转速率和太阳黑子数据序列进行相关关系以及相位关系的计算和分析,以探讨太阳自转速率变化与太阳活动之间的关系.研究发现:两者的长期趋势项分量呈显著负相关;在11 yr左右周期分量上,观测到的太阳自转速率滞后太阳黑子的变化约2 yr时,呈显著负相关关系,超前3 yr时呈现次显著的正相关;对太阳活动第12–23周各周内部太阳黑子与太阳自转速率的相关分析表明,两者的关系比较复杂,但负相关关系更为显著.这为进一步理解太阳活动变化与太阳自转速率变化之间的成因联系提供了新的依据. 相似文献
15.
H. M. Antia Sarbani Basu & S. M. Chitre 《Monthly notices of the Royal Astronomical Society》1998,298(2):543-556
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. 相似文献
16.
Solar diameter measurements have been made nearly continuously through different techniques for more than three centuries.
They were obtained mainly with ground-based instruments except for some recent estimates deduced from space observations.
One of the main problems in such space data analysis is that, up to now, it has been difficult to obtain an absolute value
owing to the absence of an internally calibrated system. Eclipse observations provide a unique opportunity to give an absolute
angular scale to the measurements, leading to an absolute value of the solar diameter. However, the problem is complicated
by the Moon limb, which presents asphericity because of the mountains. We present a determination of the solar diameter derived
from the total solar eclipse observation in Turkey and Egypt on 29 March 2006. We found that the solar radius carried back
to 1 AU was 959.22±0.04 arcsec at the time of the observations. The inspection of the compiled 19 modern eclipses data, with
solar activity, shows that the radius changes are nonhomologous, an effect that may explain the discrepancies found in ground-based
measurements and implies the role of the shallow subsurface layers (leptocline) of the Sun. 相似文献
17.
We analyze the high-frequency drift radio structures observed by the spectrometer at Purple Mountain Observatory (PMO) over
the frequency range of 4.5 – 7.5 GHz during the 18 March 2003 solar flare. The drifting structures take place before the soft
X-ray maximum, almost at the maximum of hard X-ray flux at 25 – 50 keV. For the first time, the positive drift in this kind
of radio structures is detected in such a high frequency range. Their global drifting rate is roughly estimated as 3.6 GHz s−1. They appear in four groups, lasting in total for less than 6 s, and have a broad bandwidth of more than 2 GHz but a smaller
ratio of the bandwidth of the drifting structures to mean frequency than that of the lower frequency range. The lifetime of
each individual burst in this event can be derived by using the high temporal resolution of the spectrometer at PMO and has
an average value of 36.3 ms. Since the negative drifting structures observed in the 0.6 – 4.5 GHz frequency range were interpreted
to be a radio signature of a plasmoid ejected upward (moving out of the Sun), the present observation may imply that it is
possible for a plasmoid to move downward during a solar flare. However, for a confirmation of this suggestion direct radio
imaging observation would be needed. 相似文献