共查询到20条相似文献，搜索用时 31 毫秒
1.
Coronal mass ejections (CMEs) are considered to be associated with large-scale, closed magnetic field structures in the corona. These structures change throughout the solar activity cycle following the evolution of the general solar magnetic field. To study the variation of CME characteristics with the evolution of coronal magnetic structures, we compute the 3-D coronal magnetic field at minimum and maximum of activity with a source-surface potential field model. In particular, we study the central latitude distribution of CMEs and the frequency of occurrence of the different CME types in these two periods. We find that most CMEs are indeed associated with large-scale, magnetically closed structures, and their latitudinal distribution follows the solar cycle latitudinal changes of the location of these structures. We also find that different CME types, which constitute different fractions of the total during the maximum and the minimum, are associated with different shapes and orientations of the closed structures at different times of the solar cycle. 相似文献
2.
The relevance of the occurrence rate and location of CME events to two main systems (giant and supergiant) of the large-scale solar magnetic field structure has been investigated. The clustering of CME events and solar flares toward the neutral line of the global field system (neutral line of the source surface field) corroborates the finding by Hundhausen that CME locations track the heliomagnetic equator. A good correlation has been revealed between the CME occurrence rate and variations of the index of the effective solar multipole, that characterizes the typical scale of the global solar magnetic field. The CME rate exhibits sharp jumps/decreases when the index of the effective solar multipole passes through n=4. The observations of X-ray 'blow-out' effects have been analyzed as probable manifestations of CMEs on the disk and have been compared with the large-scale magnetic field structure. As shown by the analysis, the X-ray arcades straddle the neutral line and occur, or at least tend to occur, where the neutral line exhibits a sharp bend. A conclusion is made that CME events are caused by interaction of two large-scale field systems, one of them (the global field system) determining the location of CMEs and another (the system of closed magnetic fields) their occurrence rate. 相似文献
3.
The paper considers the relationship between the cyclic variations in the velocity of coronal mass ejections (CME) and the large-scale magnetic field structure (LSMF) in cycles 21??C?23. To characterize a typical size of the LSMF structure, we have used the index of the effective solar multipole (ESMI). The cyclic behavior of the CME occurrence rate and velocity proved to be similar to that of ESMI. The hysteresis observed in variations of the CME maximum velocity is interpreted as a manifestation of different contributions from the two field structures (local and global magnetic fields) in different phases of the 11-year activity cycle. It is suggested that cyclic variations in the maximum velocity of coronal mass ejections are due to different conditions for the formation of the complexes of active regions connected by coronal arch systems, which are the main source of high-velocity CMEs. 相似文献
4.
To investigate the relations between coronal mass ejection (CME) speed and magnetic field properties measured in the photospheric surface of CME source regions, we selected 22 disk CMEs in the rising and early maximum phases of the current Solar Cycle 24. For the CME speed, we used two-dimensional (2D) projected speed observed by the Large Angle and Spectroscopic Coronagraph onboard the Solar and Heliospheric Observatory (SOHO/LASCO), as well as a 3D speed calculated from the triangulation method using multi-point observations. Two magnetic parameters of CME source regions were considered: the average of magnetic helicity injection rate and the total unsigned magnetic flux. We then classified the selected CMEs into two groups, showing: i) a monotonically increasing pattern with one sign of helicity (group A: 16 CMEs) and ii) a pattern of significant helicity injection followed by its sign reversal (group B: 6 CMEs). We found that: 1) 3D speed generally shows better correlations with the magnetic parameters than the 2D speed for 22 CME events in Solar Cycle 24; 2) 2D speed and the magnetic parameters of 22 CME events in this solar cycle have lower values than those of 47 CME events in Solar Cycle 23; 3) all events of group B in Solar Cycle 24 occur only after the beginning of the maximum phase, a trend well consistent with that shown in Solar Cycle 23; 4) the 2D speed and the helicity parameter of group B events continue to increase in the declining phase of Solar Cycle 23, while those of group A events abruptly decrease in the same period. Our results indicate that the two CME groups have a different tendency in the solar cycle variations of CME speed and the helicity parameters. Active regions that show a complex helicity evolution pattern tend to appear in the maximum and declining phases, while active regions with a relatively simple helicity evolution pattern appear throughout the whole solar cycle. 相似文献
5.
We present a review of the different aspects associated with the interaction of successive coronal mass ejections (CMEs) in the corona and inner heliosphere, focusing on the initiation of series of CMEs, their interaction in the heliosphere, the particle acceleration associated with successive CMEs, and the effect of compound events on Earth’s magnetosphere. The two main mechanisms resulting in the eruption of series of CMEs are sympathetic eruptions, when one eruption triggers another, and homologous eruptions, when a series of similar eruptions originates from one active region. CME?–?CME interaction may also be associated with two unrelated eruptions. The interaction of successive CMEs has been observed remotely in coronagraphs (with the Large Angle and Spectrometric Coronagraph Experiment – LASCO – since the early 2000s) and heliospheric imagers (since the late 2000s), and inferred from in situ measurements, starting with early measurements in the 1970s. The interaction of two or more CMEs is associated with complex phenomena, including magnetic reconnection, momentum exchange, the propagation of a fast magnetosonic shock through a magnetic ejecta, and changes in the CME expansion. The presence of a preceding CME a few hours before a fast eruption has been found to be connected with higher fluxes of solar energetic particles (SEPs), while CME?–?CME interaction occurring in the corona is often associated with unusual radio bursts, indicating electron acceleration. Higher suprathermal population, enhanced turbulence and wave activity, stronger shocks, and shock?–?shock or shock?–?CME interaction have been proposed as potential physical mechanisms to explain the observed associated SEP events. When measured in situ, CME?–?CME interaction may be associated with relatively well organized multiple-magnetic cloud events, instances of shocks propagating through a previous magnetic ejecta or more complex ejecta, when the characteristics of the individual eruptions cannot be easily distinguished. CME?–?CME interaction is associated with some of the most intense recorded geomagnetic storms. The compression of a CME by another and the propagation of a shock inside a magnetic ejecta can lead to extreme values of the southward magnetic field component, sometimes associated with high values of the dynamic pressure. This can result in intense geomagnetic storms, but can also trigger substorms and large earthward motions of the magnetopause, potentially associated with changes in the outer radiation belts. Future in situ measurements in the inner heliosphere by Solar Probe+ and Solar Orbiter may shed light on the evolution of CMEs as they interact, by providing opportunities for conjunction and evolutionary studies. 相似文献
6.
7.
8.
Nishant Mittal Kumud Pandey Udit Narain S. S. Sharma 《Astrophysics and Space Science》2009,323(2):135-145
We have investigated properties such as speed, angular width, location, acceleration and occurrence rate of narrow CMEs (defined
as having angular width ≤20°) observed during 1996–2007 by SOHO/LASCO. The results obtained are compared with those of normal
CMEs (angular width >20°) from the same time interval to find whether there are any real differences between the two populations.
Our study of 3464 narrow CMEs from the online SOHO/LASCO, CME catalogue leads us to conclude that (1) the fraction of narrow
CMEs during solar minimum is 38% and during solar maximum 19%, (2) during solar maximum narrow CMEs are generally faster than
normal CMEs, (3) the maximum speed of narrow CMEs is much smaller than that of the normal CMEs, (4) during solar maximum narrow
CMEs appear at all latitudes similar to normal CMEs, (5) narrow and normal CMEs have unequal deceleration and (6) the occurrence
rate of narrow CMEs remain constant after 1998 until the beginning of 2006 while the normal CMEs occurrence rate seems to
follow solar cycle variation until 2004. Thus narrow CMEs and normal CMEs have some differences, in disagreement with previous
studies. 相似文献
9.
R. P. Kane 《Solar physics》2008,248(1):177-190
From the LASCO CME (Coronal Mass Ejection) catalog, the occurrence frequencies of all CMEs (all strong and weak CMEs, irrespective
of their widths) were calculated for 3-month intervals and their 12-month running means determined for cycle 23 (1996 – 2007)
and were compared with those of other solar parameters. The annual values of all-CME frequency were very well correlated (+ 0.97)
with sunspot numbers, but several other parameters also had similarly high correlations. Comparisons of 12-month running means
indicated that the sunspot numbers were very well correlated with solar electromagnetic radiations (Lyman-α, 2800-MHz flux,
coronal green line index, solar flare indices, and X-ray background); but for corpuscular radiations [proton fluxes, solar
energetic particles (SEP), CMEs, interplanetary CMEs (ICMEs), and stream interaction regions (SIR)] and solar open magnetic
fields, the correlations were lower. A notable feature was the appearance of two peaks during 2000 – 2002, and those double
peaks in different parameters matched approximately except for proton fluxes and SEP and SIR frequencies. When hemispheric
intensities were considered, north – south asymmetries appeared, more in some parameters than in others. When intensities
in smaller latitude belts (10°) were compared, sunspot group numbers (SGN) were found to be confined mostly to latitudes within
± 30° of the solar equator, showing two peaks in all latitude belts, and during the course of the 11-year cycle, the double peaks shifted from middle to equatorial
solar latitudes, just as seen in the Maunder butterfly diagrams. In contrast, CME frequency was comparable at all latitude
belts (including high, near-polar latitudes), having more than two peaks in almost all latitude belts, and the peaks were
almost simultaneous in all latitude belts. Thus, the matching of SGN peaks with those of CME peaks was poor. Incidentally,
the CME frequency data for all events (all widths) after 2003 are not comparable to earlier data, owing to inclusion of very
weak (narrow) CMEs in later years. The frequencies are comparable with earlier data only for widths exceeding about 70°. 相似文献
10.
Large-scale solar eruptions, known as coronal mass ejections (CMEs), are regarded as the main drivers of space weather. The exact trigger mechanism of these violent events is still not completely clear; however, the solar magnetic field indisputably plays a crucial role in the onset of CMEs. The strength and morphology of the solar magnetic field are expected to have a decisive effect on CME properties, such as size and speed. This study aims to investigate the evolution of a magnetic configuration when driven by the emergence of new magnetic flux in order to get a better insight into the onset of CMEs and their magnetic structure. The three-dimensional, time-dependent equations for ideal magnetohydrodynamics are numerically solved on a spherical mesh. New flux emergence in a bipolar active region causes destabilisation of the initial stationary structure, finally resulting in an eruption. The initial magnetic topology is suitable for the ??breakout?? CME scenario to work. Although no magnetic flux rope structure is present in the initial condition, highly twisted magnetic field lines are formed during the evolution of the system as a result of internal reconnection due to the interaction of the active region magnetic field with the ambient field. The magnetic energy built up in the system and the final speed of the CME depend on the strength of the overlying magnetic field, the flux emergence rate, and the total amount of emerged flux. The interaction with the global coronal field makes the eruption a large-scale event, involving distant parts of the solar surface. 相似文献
11.
In order to investigate the relationship between magnetic-flux emergence, solar flares, and coronal mass ejections (CMEs), we study the periodicity in the time series of these quantities. It has been known that solar flares, sunspot area, and photospheric magnetic flux have a dominant periodicity of about 155 days, which is confined to a part of the phase of the solar cycle. These periodicities occur at different phases of the solar cycle during successive phases. We present a time-series analysis of sunspot area, flare and CME occurrence during Cycle 23 and the rising phase of Cycle 24 from 1996 to 2011. We find that the flux emergence, represented by sunspot area, has multiple periodicities. Flares and CMEs, however, do not occur with the same period as the flux emergence. Using the results of this study, we discuss the possible activity sources producing emerging flux. 相似文献
12.
C. R. A. Augusto C. E. Navia M. N. de Oliveira A. A. Nepomuceno J. P. Raulin E. Tueros R. R. S. de Mendonça A. C. Fauth H. Vieira de Souza V. Kopenkin T. Sinzi 《Solar physics》2018,293(5):84
We report on the 22?–?23 June 2015 geomagnetic storm that occurred at the summer solstice. There have been fewer intense geomagnetic storms during the current solar cycle, Solar Cycle 24, than in the previous cycle. This situation changed after mid-June 2015, when one of the largest solar active regions (AR 12371) of Solar Cycle 24 that was located close to the central meridian, produced several coronal mass ejections (CMEs) associated with M-class flares. The impact of these CMEs on the Earth’s magnetosphere resulted in a moderate to severe G4-class geomagnetic storm on 22?–?23 June 2015 and a G2 (moderate) geomagnetic storm on 24 June. The G4 solstice storm was the second largest (so far) geomagnetic storm of Cycle 24. We highlight the ground-level observations made with the New-Tupi, Muonca, and the CARPET El Leoncito cosmic-ray detectors that are located within the South Atlantic Anomaly (SAA) region. These observations are studied in correlation with data obtained by space-borne detectors (ACE, GOES, SDO, and SOHO) and other ground-based experiments. The CME designations are taken from the Computer Aided CME Tracking (CACTus) automated catalog. As expected, Forbush decreases (FD) associated with the passing CMEs were recorded by these detectors. We note a peculiar feature linked to a severe geomagnetic storm event. The 21 June 2015 CME 0091 (CACTus CME catalog number) was likely associated with the 22 June summer solstice FD event. The angular width of CME 0091 was very narrow and measured \({\sim}\, 56^{\circ }\) degrees seen from Earth. In most cases, only CME halos and partial halos lead to severe geomagnetic storms. We perform a cross-check analysis of the FD events detected during the rise phase of Solar Cycle 24, the geomagnetic parameters, and the CACTus CME catalog. Our study suggests that narrow angular-width CMEs that erupt in a westward direction from the Sun–Earth line can lead to moderate and severe geomagnetic storms. We also report on the strong solar proton radiation storm that began on 21 June. We did not find a signal from this SEP at ground level. The details of these observations are presented. 相似文献
13.
During solar cycle 23, 82 interplanetary magnetic clouds (MCs) were identified by the Magnetic Field Investigation (MFI) team
using Wind (1995 – 2003) solar wind plasma and magnetic field data from solar minimum through the maximum of cycle 23. The average occurrence
rate is 9.5 MCs per year for the overall period. It is found that some of the anomalies in the frequency of occurrence were
during the early part of solar cycle 23: (i) only four MCs were observed in 1999, and (ii) an unusually large number of MCs
(17 events) were observed in 1997, just after solar minimum. We also discuss the relationship between MCs, coronal mass ejections
(CMEs), and geomagnetic storms. During the period 1996 – 2003, almost 8000 CMEs were observed by SOHO-LASCO. The occurrence
frequency of MCs appears to be related neither to the occurrence of CMEs as observed by SOHO LASCO nor to the sunspot number.
When we included “magnetic cloud-like structures” (MCLs, defined by Lepping, Wu, and Berdichevsky, 2005), we found that the
occurrence of the joint set (MCs + MCLs) is correlated with both sunspot number and the occurrence rate of CMEs. The average
duration of the MCL structures is ~40% shorter than that of the MCs. The MCs are typically more geoeffective than the MCLs,
because the average southward field component is generally stronger and longer lasting in MCs than in MCLs. In addition, most
severe storms caused by MCs/MCLs with Dst
min≤ −100 nT occurred in the active solar period. 相似文献
14.
An investigation of the large-scale magnetic field variations in the corona prior to and after CME eruptions 总被引：1，自引：0，他引：1
The magnetic field changes in the corona at the site of coronal mass ejections (CMEs) have been investigated using the potential field-source surface model. It is shown that a CME is accompanied by the opening of closed field lines that formed the streamer's helmet base prior to the onset of a coronal disturbance. Two to three days after the appearance of the CME, the field configuration at the location of the coronal ejection reverts approximately to the state pre-existing before the generation of the CME. The appearance of small transient open magnetic tubes has been found after eruption of the coronal mass. These magnetic tubes seem to be the analogs for transient coronal holes.Taking into account the results of calculations of the field changes in the neighbourhood of the CME occurrence site, we have suggested a possible mechanism governing the spatio-temporal correlation between some flares and CMEs. Also, a possible mechanism has been proposed for field reconfiguration in the corona, leading to loss of the equilibrium of the magnetic configuration and to the subsequent generation of a CME in the region of coronal streamer chains separating coronal holes with same-polarity magnetic field. 相似文献
15.
E. K. J. Kilpua M. Mierla L. Rodriguez A. N. Zhukov N. Srivastava M. J. West 《Solar physics》2012,279(2):477-496
We study the relationship between the speeds of coronal mass ejections (CMEs) obtained close to the Sun and in the interplanetary medium during the low solar-activity period from 2008 to 2010. We use a multi-spacecraft forward-modeling technique to fit a flux-rope-like model to white-light coronagraph images from the STEREO and SOHO spacecraft to estimate the geometrical configuration, propagation in three-dimensions (3D), and the radial speeds of the observed CMEs. The 3D speeds obtained in this way are used in existing CME travel-time prediction models. The results are compared to the actual CME transit times from the Sun to STEREO, ACE, and Wind spacecraft as well as to the transit times calculated using projected CME speeds. CME 3D speeds give slightly better predictions than projected CME speeds, but a large scatter is observed between the predicted and observed travel times, even when 3D speeds are used. We estimate the possible sources of errors and find a weak tendency for large interplanetary CMEs (ICMEs) with high magnetic fields to arrive faster than predicted and small, low-magnetic-field ICMEs to arrive later than predicted. The observed CME transit times from the Sun to 1?AU show a particularly good correlation with the upstream solar-wind speed. Similar trends have not been observed in previous studies using data sets near solar maximum. We suggest that near solar minimum a relatively narrow range of CME initial speeds, sizes, and magnetic-field magnitudes led to a situation where aerodynamic drag between CMEs and ambient solar wind was the primary cause of variations in CME arrival times from the Sun to 1?AU. 相似文献
16.
M. Youssef 《Earth, Moon, and Planets》2013,110(3-4):185-195
The aim of this paper is studying the relation between the coronal mass ejections (CMEs), and their associated solar flares. I used the CMEs data (obtained from CME catalogue) which observed by SOHO/LASCO, during the Solar Cycle 23rd (1996–2006), during this period I selected 12,433 CME records. Also I used the X-ray flares data which provided geostationary operational environmental satellite (GOES), during the same interval in the 1–8 Å GOES channel, the recorded flare events are 22,688. I filtered these CMEs and solar flare events to select 529 CME-Flare events. I found that there is a moderate relation between the solar flare fluxes and their associated CME energies, where R = 58 %. In addition I found that 61 % of the CME-Flare associated events ejected from the solar surface after the occurrence of the associated flare. Furthermore I found that the CME-Flare relation improved during the period of high solar activity. Finally, I examined the CME association rate as a function of flare longitude and I found that the CME association rate of the total 529 selected CME-Flare events are mostly disk-Flare events. 相似文献
17.
Yoichiro Hanaoka Jun Nakazawa Osamu Ohgoe Yoshiaki Sakai Kazuo Shiota 《Solar physics》2014,289(7):2587-2599
White-light observations of the total solar eclipse on 13 November 2012 were made at two sites, where the totality occurred 35 min apart. The structure of the corona from the solar limb to a couple of solar radii was observed with a wide dynamic range and a high signal-to-noise ratio. An ongoing coronal mass ejection (CME) and a pre-CME loop structure just before the eruption were observed in the height range between 1?–?2 R⊙. The source region of CMEs was revealed to be in this height range, where the material and the magnetic field of CMEs were located before the eruption. This height range includes the gap between the extreme ultraviolet observations of the low corona and the spaceborne white-light observations of the high corona, but the eclipse observation shows that this height range is essential for the study of CME initiation. The eclipse observation is basically just a snapshot of CMEs, but it indicates the importance of a continuous coverage of CME observations in this height range in the future. 相似文献
18.
The observed CME (coronal mass ejection) is its projection on the sky plane, and this leads to certain discrepancies between the observational and true parameters of the CME. For example, the observed velocity is generally smaller than the true velocity. The method of making projection correction for the CME velocity based on the conical model is utilized to analyze the velocity distributions of the 1691 CMEs which are only correlated to flares (called the class FL CMEs for short) and the 610 CMEs which are only correlated to filament eruptions (called the class FE CMEs for short) before and after the projection correction. These CMEs were observed with the Large Angle and Spectrometric Coronograph on the Solar and Heliospheric Observatory from September 1996 to September 2007 (close to a solar cycle). The obtained results are as follows: (1) before and after the projection correction the velocity distribution of FL CMEs is quite similar to that of FE CMEs, and before and after the projection correction the mean velocities of the two classes of CMEs are almost the same; (2) before and after the projection correction, the natural logarithm distribution of the FL CME velocities is also very similar to that of the FE CME velocities. 相似文献
19.
A method for the full three-dimensional (3-D) reconstruction of the trajectories of coronal mass ejections (CMEs) using Solar TErrestrial RElations Observatory (STEREO) data is presented. Four CMEs that were simultaneously observed by the inner and outer coronagraphs (COR1 and 2) of the Ahead and Behind STEREO satellites were analysed. These observations were used to derive CME trajectories in 3-D out to ～?15?R ⊙. The reconstructions using COR1/2 data support a radial propagation model. Assuming pseudo-radial propagation at large distances from the Sun (15?–?240?R ⊙), the CME positions were extrapolated into the Heliospheric Imager (HI) field-of-view. We estimated the CME velocities in the different fields-of-view. It was found that CMEs slower than the solar wind were accelerated, while CMEs faster than the solar wind were decelerated, with both tending to the solar wind velocity. 相似文献
20.
综述日冕物质抛射的观测和持性，简短的前言之后，给出ＣＭＥ的发现经过及统计特性，着重介绍ＣＭＥ与其他种类太阳活动的相关。然后介绍ＣＭＥ的一般特性，包括可能与ＣＭＥ相关的一些物理过程的观测特性。初步结论是：ＣＭＥ是一种演变中的磁结构现象。 相似文献