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1.
Several series of coordinated observations on decaying active regions and enhanced magnetic network regions have been carried out jointly at Big Bear Solar Observatory (BBSO) and Huairou Solar Observing Station of the Bejing Astronomical Observatory in China. The evolution of magnetic fields in several regions was followed closely for 3 to 7 days. The transport of magnetic flux from the remnants of decayed active regions was studied. Three related topics are included in this paper. (1) We studied the evolution and lifetime of the magnetic network which defines the boundaries of supergranules. The results are consistent with our earlier studies: network cells have an average lifetime of about 70 hours; 68% of new cells appeared by growing from a single network magnetic element; 50% of decaying cells disappeared by contracting to a network element. (2) We studied the magnetic flux transport in an enhanced network region in detail, and found the diffusion rate to be negative, i.e., there was more flux moving towards the decayed active region than away from it. We found several other cases where the magnetic diffusion rate does not agree with Leighton's model. The slow diffusion rate is likely due to the fact that the average velocity of larger magnetic elements, which carry most of the magnetic flux, is less than 0.1 km s–1; their average lifetime is longer than 100 hours. (3) We briefly described some properties of Moving Magnetic Features (MMFs) around a sunspot (detailed discussion on MMFs will be presented in a separate paper). In this particular case, the MMFs did not carry net flux away from the central spot. Instead, the polarities of MMFs were essentially mixed so that outflowing positive and negative fluxes were roughly balanced. During the 3-day period, there was almost no net flux accumulation to form a moat. The cancellation of MMFs of opposite polarities at the boundary of the super-penumbra caused quite a few surges and H brightenings. 相似文献
2.
Using one-minute cadence time-series full disk magnetograms taken by the SOHO/MDI, we have studied the magnetic field elements
at high latitude (poleward of 65° in latitude). It is found that an average lifetime of the magnetic field elements is 16.5
h during solar minimum, much longer than that during solar maximum (7.3 h). During solar minimum, number of the magnetic field
elements with the dominant polarity is about 3 times as that of the opposite polarity elements. Their lifetime is 21.0 h on
average, longer than that of the opposite polarity elements (2.3 h). It is also found that the lifetime of the magnetic field
elements is related with their size, consistent with the magnetic field elements in the quiet sun at low latitude found by
Hagenaar et al. (Astrophys. J. 511:932, 1999). During solar maximum, the polar regions are equally occupied by magnetic field elements with both polarities, and their
lifetimes are roughly the same on average. No evidence shows there is a correlation between the lifetime and size of the magnetic
field elements. Using an image cross-correlation method, we also measure the solar rotation rate at high latitude, up to 85°
in latitude. The rate is ω=2.914−0.342sin 2
φ−0.482sin 4
φ μrad s−1 sidereal. It agrees with previous studies using the spectroscopic and image cross-correlation methods, and also agrees with
the results using the element tracking method when the sample of the tracked magnetic field elements is large. The consistency
of those results strongly suggests that this rate at high latitude is reliable. 相似文献
3.
Haimin Wang 《Solar physics》1988,117(2):343-358
We studied the size, correlation lifetime and horizontal velocity amplitude of supergranules in regions with different magnetic activity. We found that the supergranule velocity cells have similar scale, correlation lifetime and horizontal velocity amplitude in the unipolar enhanced magnetic network regions and in the mixed-polarity quiet Sun. However, the correlation lifetime of magnetic structure is much longer in the enhanced network. We investigated the velocity pattern of moving magnetic features (MMF) surrounding a decaying sunspot. The velocity of MMFs is consistent with the outflow surrounding the sunspot as measured by Dopplergrams. The velocity cell surrounding the sunspot has a much larger velocity amplitude and a longer lifetime than regular supergranule cells. We found that ephemeral regions (ER) have a slight tendency to emerge at or near boundaries of supergranules. Almost all the magnetic flux disappears at the supergranule boundaries. In most cases, two poles of cancelling features with opposite magnetic polarities approach along the boundaries of supergranules. 相似文献
4.
The active region NOAA 8032 of April 15, 1997 was observed to evolve rapidly. The GOES X-ray data showed a number of sub-flares
and two C-class flares during the 8–9 hours of its evolution. The magnetic evolution of this region is studied
to ascertain its role in flare production. Large changes were observed in magnetic field configuration due to the emergence
of new magnetic flux regions (EFR). Most of the new emergence occured very close to the existing magnetic regions, which resulted
in strong magnetic field gradients in this region. EFR driven reconnection of the field lines and subsequent flux cancellation
might be the reason for the continuous occurrence of sub-flares and other related activities. 相似文献
5.
由磁绳结构主导、平均尺度约二、三十个小时的行星际磁云是日冕物质抛射在行星际膨胀、传播的体现。最近，Moldwin等人报道在太阳风中还观测到一些尺度在几十分钟的小尺度磁绳结构，并认为太阳风中的磁绳结构在尺度分布上可能具有双峰特征，在全面检视了WIND卫星(1995年-2000年)和ACE卫星(1998年-2000年)的观测资料后，发现了在行星际太阳风中一些尺度为几个小时的中尺度磁绳结构，利用初步整理的其中28个中尺度磁绳结构事件，认为太阳风中的磁绳结构在尺度分布上可能是连续的，这对行星际太阳风中磁绳结构物理起源的研究可能提出重要的物理限制。 相似文献
6.
Cornelis Zwaan 《Solar physics》1978,60(2):213-240
Ideas and models for the appearance of photospheric magnetic structure are confronted with observational data. Some findings are: The magnetic flux emerging in an active region consists of a bundle of flux tubes which were already concentrated before penetrating into the photosphere. A model of a rising bunch of flux tubes joining into a few strands at larger depths describes the coalescence of spots near the leading and following edges of the active region while more flux may surface near the center of the region. There is no observational evidence for appreciable helical twists in the flux bundles.Throughout the region's lifetime the magnetic elements move coherently, the whole magnetic structure rotates faster than the quiet photosphere. In active regions the convective flow at scales larger than the granulation is arrested by the magnetic structure. The long-lived supergranular cells around spots and in the enhanced network in turn determine the decay properties of spots and facular clusters. The modulation of the convective flow by the magnetic structure explains the slow dispersal of faculae.The hierarchy of magnetic elements (sunspots-pores-knots-facular clusters-facular points) may be explained by a set of magnetostatic flux tube models in the top of the convection zone. The underlying assumptions are that the heat flow along the magnetic field is reduced and that there is no heat exchange across the field except by radiation.A tentative model is proposed to account for the amplification, ascent and emergence of intense flux bundles. The assumptions are: (i) the field is concentrated in toroidal bundles by differential rotation, (ii) in the deep convection zone flux bundles are contained by the external turbulent pressure, and (iii) for field strengths up to the equipartition value efficient lateral heat exchange is possible. After a loop has surfaced radiative cooling and subsequent convective downflow reduce the temperature in the top of the flux tubes which then contract to field strengths well above the local equipartition value. There the heat flow is channelled along the field, which creates the conditions for the magnetostatic flux tube models without requiring a blocking of the heat flow somewhere within the tubes.The paper contains a brief review on the evolution of the magnetic field from the emergence in active regions up to the enigmatic disappearance, and a list of topics for further observational investigation. 相似文献
7.
8.
By analyzing data on background magnetic fields (BMF) covering a significant portion of solar activity cycles 20 and 21, it is shown that cellular structure is characteristic for BMF, irrespective of the cycle phase. According to present views, cellular structure in the distribution of different parameters, the magnetic field in particular, can be a consequence of the mass motion of a convective or some other origin. The size, lifetime and some rotation characteristics of BMF cells are estimated experimentally.It is found that BMF cell rotation characteristics undergo cyclic variations. The character of the cyclic variations in rotation differentiality of BMF cells is in agreement with those observed for sunspots, chromospheric filaments, green corona and coronal holes. It is shown that a detailed correspondence exists between cyclic variations in rotation differentiality of BMF cells and coronal holes, which undoubtedly bears witness to the presence of a correlation between these phenomena. 相似文献
9.
C. J. Nelson J. G. Doyle R. Erdélyi Z. Huang M. S. Madjarska M. Mathioudakis S. J. Mumford K. Reardon 《Solar physics》2013,283(2):307-323
The properties of Ellerman bombs (EBs), small-scale brightenings in the Hα line wings, have proved difficult to establish because their size is close to the spatial resolution of even the most advanced telescopes. Here, we aim to infer the size and lifetime of EBs using high-resolution data of an emerging active region collected using the Interferometric BIdimensional Spectrometer (IBIS) and Rapid Oscillations of the Solar Atmosphere (ROSA) instruments as well as the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We develop an algorithm to track EBs through their evolution, finding that EBs can often be much smaller (around 0.3″) and shorter-lived (less than one minute) than previous estimates. A correlation between G-band magnetic bright points and EBs is also found. Combining SDO/HMI and G-band data gives a good proxy of the polarity for the vertical magnetic field. It is found that EBs often occur both over regions of opposite polarity flux and strong unipolar fields, possibly hinting at magnetic reconnection as a driver of these events.The energetics of EB events is found to follow a power-law distribution in the range of a nanoflare (1022?25 ergs). 相似文献
10.
首先是对太阳光球亮点近年来研究工作的总结。光球亮点是一种发生在太阳光球上宁静区域的的小尺度和短寿命增亮现象,平均直径在100～300knm之间,平均寿命约为几分钟。光球亮点的研究对于光球辐射和磁场性质的认识具有重要意义。过去的观测显示,绝大多数光球亮点的产生和演化与磁场,特别是光球上的小尺度磁场的演化密切相关,比如,两个同极性磁场的合并,或者反极性磁场的对消,或者一个同极性磁场的分裂,均可以促使光球亮点产生或消失。基于这样的观测结果,统计研究了2722个光球亮点(1600A)与光球上偶极磁元的关系,发现大约有1/3的光球亮点出现在偶极磁元中心附近。 相似文献
11.
Analysis of SOHO longitudinal magnetograms and Dopplergrams has revealed the appearance of a region of enhanced upflow of matter in the photosphere when the top of a loop-shaped magnetic flux tube forming a large active region passed through it. The maximum upflow velocity reached 2 km s?1, the maximum size exceeded 20 000 km, and the lifetime was about 2 h. 相似文献
12.
Lin Wang Cheng Fang Ming-De Ding 《中国天文和天体物理学报》2007,7(5):721-732
We analyze an M9.1 two-ribbon solar flare which occurred on 2004 July 22 us- ing the TRACE white-light and 1700A~。images,the RHESSI,and the SOHO/MDI data.We find many small-scale fast-varying brightenings that appeared in the white-light and 1700A~。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 1680 A con- tinuum 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. 相似文献
13.
A method is presented for obtaining information about the unresolved filamentary structure of solar magnetic fields. A comparison is made of pairs of Mount Wilson magnetograph recordings made in the two spectral lines Fei 5250 Å and Fei 5233 Å obtained on 26 different days. Due to line weakenings and saturation in the magnetic filaments, the apparent field strengths measured in the 5250 Å line are too low, while the 5233 Å line is expected to give essentially correct results. From a comparison between the apparent field strengths and fluxes and their center to limb variations, we draw the following tentative conclusions: (a) More than 90 % of the total flux seen with a 17 by 17 arc sec magnetograph aperture is channeled through narrow filaments with very high field strengths in plages and at the boundaries of supergranular cells. (b) An upper limit for the interfilamentary field strength integrated over the same aperture seems to be about 3 G. (c) The field lines in a filament are confined in a very small region in the photosphere but spread out very rapidly higher up in the atmosphere. (d) All earlier Mount Wilson magnetograph data should be multiplied by a factor that is about 1.8 at the center of the disk and decreased toward the limb in order to give the correct value of the longitudinal magnetic field averaged over the scanning aperture.Guest Investigator at the Hale Observatories, on leave from Astronomical Observatory, Lund, Sweden.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
14.
Skylab observations of the Sun in soft X-rays gave us the first possibility to study the development of a complex of activity in the solar corona during its whole lifetime of seven solar rotations. The basic components of the activity complex were permanently interconnected (including across the equator) through sets of magnetic field lines, which suggests similar connections also below the photosphere. However, the visibility of individual loops in these connections was greatly variable and typically shorter than one day. Each brightening of a coronal loop in X-rays seems to be related to a variation in the photospheric magnetic field near its footpoint. Only loops (rarely visible) connecting active regions with remnants of old fields can be seen in about the same shape for many days. The interconnecting X-ray loops do not connect sunspots.We point out several examples of possible reconnections of magnetic field lines, giving rise to the onset of the visibility or, more likely, to sudden enhancements of the loop emission. In one case a new system of loops brightened in X-rays, while the field lines definitely could not have reconnected. Some striking brightenings show association with flares, but the flare occurrence and the loop brightening seem to be two independent consequences of a common triggering action: emergence of new magnetic flux. In old active regions, growing and/or brightened X-ray loops can be seen quite often without any associated flare; thus, the absence of any flaring in the chromosphere does not necessarily mean that the overlying coronal active region is quiet and inactive.We further discuss the birth of the interconnecting loops, their lifetime, altitude, variability in shape in relation to the photospheric magnetic field, the similarity of interconnecting and internal loops in the late stages of active regions, phases of development of an active region as manifested in the corona, the remarkably linear boundary of the X-ray emission after the major flare of 29 July 1973, and a striking sudden change in the large-scale pattern of unipolar fields to the north of the activity complex.The final decay of the complex of activity was accompanied by the penetration of a coronal hole into the region where the complex existed before. 相似文献
15.
The morphological features of Pc5 pulsations during a solar cycle are studied using Fort Churchill data for the years 1962–1972. Some of the characteristics noted are as follows: (1) Increasing sunspot numbers show little influence on the diurnal variation of the occurrence, amplitude and the period except perhaps some noticeable change in the absolute magnitude of these parameters during different hours of the day. (2) The morning occurrence peak dominates during all phases of the solar cycle. (3) As noted earlier (Gupta 1973a), with increasing magnetic activity the day side region(s) of generation of Pc5 is found to shift closer to the subsolar point and in the midnight sector, the occurrence region (presumably the region of open and closed field lines) seemed to shift towards earlier hours with increasing magnetic activity and towards later hours with increasing sunspot numbers. (4) Despite the smaller number of data points for high magnetic activity levels the analysis indicates that the amplitude of Pc5 pulsations is directly related to all the levels of magnetic activity. (5) The periods of Pc5 pulsations show strong correlation with increasing sunspot numbers and the amplitude and occurrences are found to vary in accordance with the magnetic activity all through the cycle. (6) The annual and semi-annual variations of Pc5 parameters have been demonstrated especially for the pulsations occurring in the morning close to 8 ± 1 h LT and for those occurring near the midnight hours. (7) A suspected 27-day recurrence tendency has been clearly noticed for the occurrence, amplitude and period of Pc5 pulsations. 相似文献
16.
A remarkable north-south pattern of symmetry in the location of filaments on 11 June, 1972 together with an analysis of surface magnetic field harmonics by Altschuler et al. (1974) is offered as evidence for the existence of giant convective cells. Both data suggest a longitudinal wave number of 5, a value which seems to exclude this symmetry being due to effects of a solar -dynamo. The lifetime of these cells was about 2–4 months. This was apparently the only instance from 1959 to 1973 of such cells being manifested in magnetic field patterns which were evident by harmonic analyses or by filament inspections. 相似文献
17.
On September 22, 2001 the Deep Space 1 spacecraft performed a flyby at comet 19P/Borrelly at a solar distance of 1.36 AU leading the Earth by 74° in longitude. The spacecraft-comet distance at closest approach was 2171 km. The bow shock had a magnetic compression ratio of 2.5 at a distance of 147 100 km from the nucleus. Deep Space 1 first entered the sheath region essentially from the north polar region. Fluctuations from the cometary ion pickup were present throughout the sheath region and even well upstream of the shock, as expected. The magnetic field pileup region had a peak field strength of 83 nT and was shown to be consistent with a pressure equal to the solar wind ram pressure. The peak field location was offset from the time of closest approach. It is uncertain whether this is a spatial or temporal variation. Draping of magnetic fields around the nucleus was sought, but evidence for this was not apparent in the data. A possible explanation is that the interplanetary solar wind was composed of turbulent short-scale fields, and thus the fields were not symmetric about the point of closest approach. During the flyby phase there were in general few intervals of ACE data where there were large scale Parker spiral fields. With the addition of plasma data, the shock properties are investigated. The characteristics of magnetic draping, pileup and fluctuations are explored. These comet 19P/Borrelly results are contrasted with other cometary flyby results. 相似文献
18.
The Solar TErrestrial RElations Observatory (STEREO) requires powerful tools for the three-dimensional (3D) reconstruction of the solar corona. Here we test such a program
with data from SOHO and TRACE. By taking advantage of solar rotation, a newly developed stereoscopy tool for the reconstruction
of coronal loops is applied to the solar active region NOAA 8891 observed from 1 March to 2 March 2000. The stereoscopic reconstruction
is composed of three steps. First, we identify loop structures in two TRACE images observed from two vantage viewpoints approximately
17 degrees apart, which corresponds to observations made about 30 hours apart. In the second step, we extrapolate the magnetic
field in the corona with the linear force-free field model from the photospheric line-of-sight SOHO/MDI data. Finally, combining
the extrapolated field lines and one-dimensional loop curves from two different viewpoints, we obtain the 3D loop structures
with the magnetic stereoscopy tool. We demonstrate that by including the magnetic modeling this tool is more powerful than
pure geometrical stereoscopy, especially in resolving the ambiguities generated by classical stereoscopy. This work will be
applied to the STEREO mission in the near future. 相似文献
19.
W. Schmidt S.K. Solanki P. Barthol T. Berkefeld A. Gandorfer M. Knlker V. Martínez Pillet M. Schüssler A. Title 《Astronomische Nachrichten》2010,331(6):601-604
SUNRISE is a balloon‐borne telescope with an aperture of one meter. It is equipped with a filter imager for the UV wavelength range between 214 nm and 400 nm (SUFI), and with a spectro‐polarimeter that measures the magnetic field of the photosphere using the Fe I line at 525.02 nm that has a Landé factor of 3. SUNRISE performed its first science flight from 8 to 14 June 2009. It was launched at the Swedish ESRANGE Space Center and cruised at an altitude of about 36 km and geographic latitudes between 70 and 74 degrees to Somerset Island in northern Canada. There, all data, the telescope and the gondola were successfully recovered. During its flight, Sunrise achieved high pointing stability during 33 hours, and recorded about 1.8 TB of science data. Already at this early stage of data processing it is clear that SUNRISE recorded UV images of the solar photosphere, and spectropolarimetric measurements of the quiet Sun's magnetic field of unprecedented quality (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
20.
A simple method of estimating the coronal magnetic field is suggested. It is based on the observational fact that the duration of the highly polarized part in type III bursts can be different, varying from a small fraction of the burst length to its total duration. We suggest that this difference is determined by the relation between the size of the region where only the ordinary wave can propagate and the size of the region where the burst is generated at a fixed frequency. The magnetic field is estimated at several tens of gauss in regions emitting highly polarized type III bursts at frequencies over 200 MHz. Density and magnetic field scales are estimated. 相似文献