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1.
太阳活动周期的小波分析   总被引：5，自引：0，他引：5  
运用小波技术对太阳射电流量2800 MHz,太阳黑子数和太阳黑子面积数周期进行分析．其结果表明: (1)这3个系列的数据显示最显著的周期是10．69年,其他周期并不明显．(2)小波功率谱给出了全部时间-周期范围的功率谱变化,它显示了在某个周期处于某个时段的局部功率的变化,小波功率谱分析表明,小于1年的周期仅仅在太阳活动最大期附近比较明显．(3)太阳射电2800 MHz,太阳黑子数和太阳黑子面积数的几个周期(10．69年,5．11年, 155．5天)的小波功率谱比较相似,出现峰值的时间相同;曲线的起伏相似,周期越小,曲线起伏的频率越大．  相似文献   

2.
We have performed a statistical study of 152 Type III radio bursts observed by Solar TErrestrial RElations Observatory (STEREO)/Waves between May 2007 and February 2013. We investigated the flux density between 125 kHz and 16 MHz. Both high- and low-frequency cutoffs were observed in 60 % of events, suggesting an important role of propagation. As already reported by previous authors, we observed that the highest flux density occurs at 1 MHz on both spacecraft. We developed a simplified analytical model of the flux density as a function of radial distance and compared it with the STEREO/Waves data.  相似文献   

3.
The fractal dimensions of solar radio fluxes at 245, 410, 610, 1415, 2695, 2800, 4995, 8800, and 15400 MHz are calculated for the data period 1976–1990. The fractal dimension used here is an index to quantify the time variability of radio emission. The fractal dimensions were found to have values in the range of 1.2–2.0 for time scales of 10 days, 1–10 months, and 10 months. The lowest values were found around 3 GHz. The annual variations of fractal dimensions are small and are not in concert with the solar cycle for most of the fractal dimension at the analyzed frequencies except those for 4995 and 8800 MHz. The annual variations of the fractal dimensions are similar for the sunspot number and radio emission around 3 GHz; this implies a close relation between them. According to a simulation, larger fractal dimensions correspond to shorter e-folding time constants in the distribution of radio-source lifetimes.  相似文献   

4.
Coronal Mass Ejections (CMEs) are important sources of Solar Proton Events (SPEs). Their speeds and source region locations have significant effects on the occurrence of SPEs. In this paper, all the halo CMEs observed in recent five years are statistically analyzed. The results show that the fast halo CMEs with small angular distances are more likely to produce SPEs, especially, those halo CMEs with a speed greater than 1200 km s?1 and an angular distance less than 60°. Three fast halo CMEs with no SPEs caused are elaborately studied. The results show that the ejection direction of the CME's main body and the variation of interplanetary magnetic field also have important impacts on the occurrence of SPEs. Consequently, in the practical daily space environment forecasts, an accurate forecast for SPEs must take various factors into account, such as the eruption speed, source region location, the main-body ejection direction of CMEs, and the interplanetary environment, etc.  相似文献   

5.
Pulsating structures recorded at 237 MHz that are associated to decimetric continuum enhancement during the September 9, 2001 solar radio burst are described. We analyzed the radiopolarimetric data recorded at the Trieste Solar Radio System (INAF—Trieste Astronomical Observatory—Basovizza Observing Station) with very high time resolution (1 ms) at metric frequencies. Two different types of pulsations that occur in about 4 minutes at the same frequency are described. The possible mechanisms are analyzed and some parameters of the associated magnetic structure are estimated.  相似文献   

6.
We investigated the solar cycle distribution of strong solar proton events (SPEs, peak flux ≥1000 pfu) and the solar-terrestrial phenomena associated with the strong SPEs during solar cycles 21–23. The results show that 37 strong SPEs were registered over this period of time, where 20 strong SPEs were originated from the super active regions (SARs) and 28 strong SPEs were accompanied by the X-class flares. Most strong SPEs were not associated with the ground level enhancement (GLE) event. Most strong SPEs occurred in the descending phases of the solar cycles. The weaker the solar cycle, the higher the proportion of strong SPES occurred in the descending phase of the cycle. The number of the strong SPEs that occurred within a solar cycle is poorly associated with the solar cycle size. The intensity of the SPEs is highly dependent of the location of their source regions, with the super SPEs (≥20000 pfu) distributed around solar disk center. A super SPE was always accompanied by a fast shock driven by the associated coronal mass ejection and a great geomagnetic storm. The source location of strongest GLE event is distributed in the well-connected region. The SPEs associated with super GLE events (peak increase rate ≥100%) which have their peak flux much lower than 10000 pfu were not accompanied by an intense geomagnetic storm.  相似文献   

7.
We present the results of a deep 610-MHz survey of the 1 H XMM–Newton / Chandra survey area with the Giant Metre-wave Radio Telescope. The resulting maps have a resolution of ∼7 arcsec and an rms noise limit of 60 μJy. To a 5σ detection limit of 300 μJy, we detect 223 sources within a survey area of 64 arcmin in diameter. We compute the 610-MHz source counts and compare them to those measured at other radio wavelengths. The well-known flattening of the Euclidean-normalized 1.4-GHz source counts below ∼2 mJy, usually explained by a population of starburst galaxies undergoing luminosity evolution, is seen at 610 MHz. The 610-MHz source counts can be modelled by the same populations that explain the 1.4-GHz source counts, assuming a spectral index of −0.7 for the starburst galaxies and the steep spectrum active galactic nucleus (AGN) population. We find a similar dependence of luminosity evolution on redshift for the starburst galaxies at 610 MHz as is found at 1.4 GHz (i.e.  ' Q '= 2.45+0.3−0.4  ).  相似文献   

8.
Radio science and meteor physics issues regarding meteor “head-echo” observations with high power, large aperture (HPLA) radars, include the frequency and latitude dependency of the observed meteor altitude, speed, and deceleration distributions. We address these issues via the first ever use and analysis of meteor observations from the Poker Flat AMISR (PFISR: 449.3 MHz), Sondrestrom (SRF: 1,290 MHz), and Arecibo (AO: 430 MHz) radars. The PFISR and SRF radars are located near the Arctic Circle while AO is in the tropics. The meteors observed at each radar were detected and analyzed using the same automated FFT periodic micrometeor searching algorithm. Meteor parameters (event altitude, velocity, and deceleration distributions) from all three facilities are compared revealing a clearly defined altitude “ceiling effect” in the 1,290 MHz results relative to the 430/449.3 MHz results. This effect is even more striking in that the Arecibo and PFISR distributions are similar even though the two radars are over 2,000 times different in sensitivity and at very different latitudes, thus providing the first statistical evidence that HPLA meteor radar observations are dominated by the incident wavelength, regardless of the other radar parameters. We also offer insights into the meteoroid fragmentation and “terminal” process.  相似文献   

9.
We used an automatic image-processing method to detect solar-activity features observed in white light at the Kislovodsk Solar Station. This technique was applied to automatically or semi-automatically detect sunspots and active regions. The results of this automated recognition were verified with statistical data available from other observatories and revealed a high detection accuracy. We also provide parameters of sunspot areas, of the umbra, and of faculae as observed in Solar Cycle 23 as well as the magnetic flux of these active elements, calculated at the Kislovodsk Solar Station, together with white-light images and magnetograms from the Michaelson Doppler Imager onboard the Solar and Heliospheric Observatory (SOHO/MDI). The ratio of umbral and total sunspot areas during Solar Cycle 23 is ≈?0.19. The area of sunspots of the leading polarity was approximately 2.5 times the area of sunspots of the trailing polarity.  相似文献   

10.
The data of the latest decametric band survey performed with the UTR-2 radio telescope are used along with other results obtained at higher frequencies (below 1415 MHz) for plotting spectra of 114 radio sources located in a sky strip between declinations 52° and 60°. Some parameters of the source spectra in the frequency range 12.6–1415 MHz are presented.  相似文献   

11.
Studying the evolution of magnetic clouds entrained in coronal mass ejections using in-situ data is a difficult task, since only a limited number of observational points is available at large heliocentric distances. Remote sensing observations can, however, provide important information for events close to the Sun. In this work we estimate the flux rope orientation first in the close vicinity of the Sun (2?–?20 R ⊙) using forward modeling of STEREO/SECCHI and SOHO/LASCO coronagraph images of coronal mass ejections and then in situ using Grad–Shafranov reconstruction of the magnetic cloud. Thus, we are able to measure changes in the orientation of the erupted flux ropes as they propagate from the Sun to 1 AU. We present both techniques and use them to study 15 magnetic clouds observed during the minimum following Solar Cycle 23 and the rise of Solar Cycle 24. This is the first multievent study to compare the three-dimensional parameters of CMEs from imaging and in-situ reconstructions. The results of our analysis confirm earlier studies showing that the flux ropes tend to deflect towards the solar equatorial plane. We also find evidence of rotation on their travel from the Sun to 1 AU. In contrast to past studies, our method allows one to deduce the evolution of the three-dimensional orientation of individual flux ropes rather than on a statistical basis.  相似文献   

12.
IPS observations with the Big Scanning Array of Lebedev Physical Institute (BSA LPI) radio telescope at the frequency 111 MHz have been monitored since 2006. All the sources, about several hundred daily, with a scintillating flux greater than 0.2 Jy are recorded for 24 hours in the 16 beams of the radio telescope covering a sky strip of 8° declination width. We present some results of IPS observations for the recent period of low solar activity considering a statistical ensemble of scintillating radio sources. The dependences of the averaged over ensemble scintillation index on heliocentric distance are considerably weaker than the dependence expected for a spherically symmetric geometry. The difference is especially pronounced in the year 2008 during the very deep solar activity minimum period. These features are explained by the influence of the heliospheric current sheet that is seen as a strong concentration of turbulent solar wind plasma aligned with the solar equatorial plane. A local maximum of the scintillation index is found in the anti-solar direction. Future prospects of IPS observations using BSA LPI are briefly discussed.  相似文献   

13.
The Sun is the only star for which individual surface features can be observed directly. For other stars, the properties of starspots, stellar rotation, stellar flares, etc, are derived indirectly via variation of star‐integrated spectral line profiles or their luminosity measurements. Solar disk‐integrated and disk‐resolved observations allow for investigations of the contribution of individual solar disk features to sun‐as‐a‐star spectra. Here, we provide a brief overview of three sun‐as‐a‐star programs, currently in operation, and describe recent improvements in observations and data reduction for the Integrated Sunlight Spectrometer (ISS), one of three instruments comprising the Synoptic Optical Long‐term Investigations of the Sun (SOLIS) system. Next, we discuss studies employing sun‐as‐a‐star observations (including Ca II K line as proxy for total unsigned magnetic flux and 2800 MHz radio flux) as well as the effects of flares on solar disk‐integrated spectra. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

14.
Based on the new catalogue of solar proton events (SPEs) for the period of 1997?–?2009 (Solar Cycle 23) we revisit the long-studied problem of the event-size distributions in the context of those constructed for other solar-flare parameters. Recent results on the problem of size distributions of solar flares and proton events are briefly reviewed. Even a cursory acquaintance with this research field reveals a rather mixed and controversial picture. We concentrate on three main issues: i) SPE size distribution for \({>}\,10~\mbox{MeV}\) protons in Solar Cycle 23; ii) size distribution of \({>}\,1~\mbox{GV}\) proton events in 1942?–?2014; iii) variations of annual numbers for \({>}\,10~\mbox{MeV}\) proton events on long time scales (1955?–?2015). Different results are critically compared; most of the studies in this field are shown to suffer from vastly different input datasets as well as from insufficient knowledge of underlying physical processes in the SPEs under consideration. New studies in this field should be made on more distinct physical and methodological bases. It is important to note the evident similarity in size distributions of solar flares and superflares in Sun-like stars.  相似文献   

15.
Here we report an in-depth reanalysis of an article by Vats et al. (Astrophys. J. 548, L87, 2001) that was based on measurements of differential rotation with altitude as a function of observing frequencies (as lower and higher frequencies indicate higher and lower heights, respectively) in the solar corona. The radial differential rotation of the solar corona is estimated from daily measurements of the disc-integrated solar radio flux at 11 frequencies: 275, 405, 670, 810, 925, 1080, 1215, 1350, 1620, 1755, and 2800 MHz. We use the same data as were used in Vats et al. (2001), but instead of the twelfth maxima of autocorrelograms used there, we use the first secondary maximum to derive the synodic rotation period. We estimate synodic rotation by Gaussian fit of the first secondary maximum. Vats et al. (2001) reported that the sidereal rotation period increases with increasing frequency. The variation found by them was from 23.6 to 24.15 days in this frequency range, with a difference of only 0.55 days. The present study finds that the sidereal rotation period increases with decreasing frequency. The variation range is from 24.4 to 22.5 days, and the difference is about three times larger (1.9 days). However, both studies give a similar rotation period at 925 MHz. In Vats et al. (2001) the Pearson’s factor with trend line was 0.86, whereas present analysis obtained a \({\sim}\,0.97\) Pearson’s factor with the trend line. Our study shows that the solar corona rotates more slowly at higher altitudes, which contradicts the findings reported in Vats et al. (2001).  相似文献   

16.
A. Khlystova 《Solar physics》2013,284(2):329-341
A statistical study has been carried out of the relationship between plasma flow Doppler velocities and magnetic field parameters during the emergence of active regions at the solar photospheric level with data acquired by the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO). We have investigated 224 emerging active regions with different spatial scales and positions on the solar disc. The following relationships for the first hours of the emergence of active regions have been analysed: i) of peak negative Doppler velocities with the position of the emerging active regions on the solar disc; ii) of peak plasma upflow and downflow Doppler velocities with the magnetic flux growth rate and magnetic field strength for the active regions emerging near the solar disc centre (the vertical component of plasma flows); iii) of peak positive and negative Doppler velocities with the magnetic flux growth rate and magnetic field strength for the active regions emerging near the limb (the horizontal component of plasma flows); iv) of the magnetic flux growth rate with the density of emerging magnetic flux; v) of the Doppler velocities and magnetic field parameters for the first hours of the appearance of active regions with the total unsigned magnetic flux at the maximum of their development.  相似文献   

17.
Mountain Wumingshan (Mt. WMS) is located in the southeastern foot of the Tibet Plateau with an altitude of 4,800 m. It is one of the candidate sites to place China’s next-generation large-scale solar telescope. A temporary observation platform has been built at Mt. WMS, but there is still a great need of a stable solar-seeing monitoring for long-term observations. Based on the preliminary studies on the Solar Differential Image Motion Monitor (SDIMM) of the Yunnan Observatories, we built an improved version of this early prototype, which is called Wumingshan Mountain Automated Solar Differential Image Motion Monitor (WMA-SDIMM). We develop the automatic system of the WMA-SDIMM, investigate the reliability and precision of our measurements by error analysis and comparison testing, and present the statistical results from October 2016 to September 2017 at Mt. WMS. WMA-SDIMM works very well at Mt. WMS and is quite suitable for long-period daytime seeing observations.  相似文献   

18.
We analyze the 26 November 2005 solar radio event observed interferometrically at frequencies of 244 and 611 MHz by the Giant Metrewave Radio Telescope (GMRT) in Pune, India. These observations are used to make interferometric maps of the event at both frequencies with the time cadence of 1 s from 06:50 to 07:12 UT. These maps reveal several radio sources. The light curves of these sources show that only two sources at 244 MHz and 611 MHz are well correlated in time. The EUV flare is more localized with flare loops located rather away from the radio sources. Using SoHO/MDI observations and potential magnetic field extrapolation we demonstrate that both the correlated sources are located in the fan structure of magnetic field lines starting from a coronal magnetic null point. Wavelet analysis of the light curves of the radio sources detects tadpoles with periods in the range P=10?–?83 s. These wavelet tadpoles indicate the presence of fast magnetoacoustic waves that propagate in the fan structure of the coronal magnetic null point. We estimate the plasma parameters in the studied radio sources and find them consistent with the presented scenario involving the coronal magnetic null point.  相似文献   

19.
Spectrum of average flux of the S-component of solar radio emission observed during the peak phase of the present solar cycle has been determined statistically. Daily values of the mean solar flux at 606, 1415, 2695, 4995 and 8800 MHz observed at the Sagamore Hill Solar Radio Observatory have been examined. The superposed epoch method (Chree analysis) has been used for determining the true nature of the S-component at all these frequencies. Spectrum has been obtained after elimination of the basic components at the respective frequencies. The important results obtained from the present statistical investigation are: (1) the basic component increases with frequency, (2) the S-component shows a maximum at 4995 MHz (6 cm), (3) the spectrum is independent of the phase of the 27-day cycle and (4) S-components at all the frequencies have slopes which are both more uniform and higher in the ascending phase than those in the descending phase of the 27-day cycle. In the descending phase slopes increase with frequency.  相似文献   

20.
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   

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