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1.
W. B. Song 《Solar physics》2010,261(2):311-320
Referring to the aerodynamic drag force, we present an analytical model to predict the arrival time of coronal mass ejections
(CMEs). All related calculations are based on the expression for the deceleration of fast CMEs in the interplanetary medium
(ICMEs),
[(v)\dot]=-\frac115 700(v-VSW)2\dot{v}=-\frac{1}{15\,700}(v-V_{\mathrm{SW}})^{2}
, where V
SW is the solar wind speed. The results can reproduce well the observations of three typical parameters: the initial speed of
the CME, the speed of the ICME at 1 AU and the transit time. Our simple model reveals that the drag acceleration should be
really the essential feature of the interplanetary motion of CMEs, as suggested by Vršnak and Gopalswamy (J. Geophys. Res.
107, 1019, 2002). 相似文献
2.
Bojan Vršnak Darije Maričić Andrew L. Stanger Astrid M. Veronig Manuela Temmer Dragan Roša 《Solar physics》2007,241(1):85-98
We study kinematics of 22 coronal mass ejections (CMEs) whose motion was traced from the gradual pre-acceleration phase up
to the post-acceleration stage. The peak accelerations in the studied sample range from 40, up to 7000 m s−2, and are inversely proportional to the acceleration phase duration and the height range involved. Accelerations and velocities
are, on average, larger in CMEs launched from a compact source region. The acceleration phase duration is proportional to
the source region dimensions; i.e., compact CMEs are accelerated more impulsively. Such behavior is interpreted as a consequence of stronger Lorentz force and
shorter Alfvén time scales involved in compact CMEs (with stronger magnetic field and larger Alfvén speed being involved at
lower heights). CMEs with larger accelerations and velocities are on average wider, whereas the widths are not related to
the source region dimensions. Such behavior is explained in terms of the field pile-up ahead of the erupting structure, which
is more effective in the case of a strongly accelerated structure. 相似文献
3.
It is generally believed that gradual solar energetic particles (SEPs) are accelerated by shocks associated with coronal mass
ejections (CMEs). Using an ice-cream cone model, the radial speed and angular width of 95 CMEs associated with SEP events
during 1998 – 2002 are calculated from SOHO/LASCO observations. Then, we investigate the relationships between the kinematic
properties of these CMEs and the characteristic times of the intensity-time profile of their accompanied SEP events observed
at 1 AU. These characteristic times of SEP are i) the onset time from the accompanying CME eruption at the Sun to the SEP arrival at 1 AU, ii) the rise time from the SEP onset to the time when the SEP intensity is one-half of peak intensity, and iii) the duration over which the SEP intensity is within a factor of two of the peak intensity. It is found that the onset time
has neither significant correlation with the radial speed nor with the angular width of the accompanying CME. For events that
are poorly connected to the Earth, the SEP rise time and duration have no significant correlation with the radial speed and
angular width of the associated CMEs. However, for events that are magnetically well connected to the Earth, the SEP rise
time and duration have significantly positive correlations with the radial speed and angular width of the associated CMEs.
This indicates that a CME event with wider angular width and higher speed may more easily drive a strong and wide shock near
to the Earth-connected interplanetary magnetic field lines, may trap and accelerate particles for a longer time, and may lead
to longer rise time and duration of the ensuing SEP event. 相似文献
4.
We performed a detailed analysis of 27 slow coronal mass ejections (CMEs) whose heights were measured in at least 30 coronagraphic
images and were characterized by a high quality index (≥4). Our primary aim was to study the radial evolution of these CMEs
and their properties in the range 2 – 30 solar radii. The instantaneous speeds of CMEs were calculated by using successive
height – time data pairs. The obtained speed – distance profiles [v(R)] are fitted by a power law v = a(R−b)
c
. The power-law indices are found to be in the ranges a=30 – 386, b=1.95 – 3.92, and c=0.03 – 0.79. The power-law exponent c is found to be larger for slower and narrower CMEs. With the exception of two events that had approximately constant velocity,
all events were accelerating. The majority of accelerating events shows a v(R) profile very similar to the solar-wind profile deduced by Sheeley et al. (Astrophys. J.
484, 472, 1997). This indicates that the dynamics of most slow CMEs are dominated by the solar wind drag. 相似文献
5.
We have analyzed five solar energetic particle (SEP) events observed aboard the SOHO spacecraft during 1996–1997. All events
were associated with impulsive soft X-ray flares, Type II radio bursts and coronal mass ejections (CMEs). Most attention is
concentrated on the SEP acceleration during the first 100 minutes after the flare impulsive phase, post-impulsive-phase acceleration,
being observed in eruptions centered at different solar longitudes. As a representative pattern of a (nearly) well-connected
event, we consider the west flare and CME of 9 July 1996 (S10 W30). Similarities and dissimilarities of the post-impulsive-phase
acceleration at large heliocentric-angle distance from the eruption center are illustrated with the 24 September 1997 event
(S31 E19). We conclude that the proton acceleration at intermediate scales, between flare acceleration and interplanetary
CME-driven shock acceleration, significantly contributes to the production of ≳10 MeV protons. This post-impulsive-phase acceleration
seems to be caused by the CME lift-off. 相似文献
6.
We present an analysis of all the events (around 400) of coronal shocks for which the shock-associated metric type IIs were
observed by many spectrographs during the period April 1997– December 2000. The main objective of this analysis is to give
evidence for the type IIs related to only flare-blast waves, and thus to find out whether there are any type II-associated
coronal shocks without mass ejections. By carefully analyzing the data from multi-wavelength observations (Radio, GOES X-ray,
Hα, SOHO/LASCO and SOHO/EIT-EUV data), we have identified only 30 events for which there were actually no reports of CMEs.
Then from the analysis of the LASCO and EIT running difference images, we found that there are some shocks (nearly 40%, 12/30)
which might be associated with weak and narrow mass ejections. These weak and narrow ejections were not reported earlier.
For the remaining 60% events (18/30), there are no mass ejections seen in SOHO/LASCO. But all of them are associated with
flares and EIT brightenings. Pre-assuming that these type IIs are related to the flares, and from those flare locations of
these 18 cases, 16 events are found to occur within the central region of the solar disk (longitude ≤45^∘). In this case,
the weak CMEs originating from this region are unlikely to be detected by SOHO/LASCO due to low scattering. The remaining
two events occurred beyond this longitudinal limit for which any mass ejections would have been detected if they were present.
For both these events, though there are weak eruption features (EIT dimming and loop displacement) in the EIT images, no mass
ejection was seen in LASCO for one event, and a CME appeared very late for the other event. While these two cases may imply
that the coronal shocks can be produced without any mass ejections, we cannot deny the strong relationship between type IIs
and CMEs. 相似文献
7.
This paper is a qualitative study of 42 events of solar filament/prominence sudden disappearances (“disparitions brusques”;
henceforth DBs) around two solar minima, 1985 – 1986 and 1994. The studied events were classified as 17 thermal and 25 dynamic
disappearances. Associated events, i.e. coronal mass ejections (CMEs), type II bursts, evolution of nearby coronal holes, as well as solar wind speed, and geomagnetic
disturbances are discussed. We have found that about 50% of the thermal DBs with adjacent (within 15° from the DB) coronal
holes were associated with CMEs within a selected time window. All the studied thermal disappearances with adjacent coronal
holes or accompanied by dynamic disappearances were associated with weak and medium geomagnetic storms. Also, nearly 64% of
dynamic DBs were associated with CMEs. Ten (40%) dynamic disappearances were associated with intense geomagnetic storms, even
when no CMEs was reported, six (24%) dynamic disappearances corresponded to extreme storms, and five (20%) corresponded to
medium geomagnetic storms. The extreme geomagnetic storms appeared to be related to combined events, involving dynamic disappearances
with adjacent coronal holes or including thermal disappearances. Furthermore, the geomagnetic activity (Dst index) increased
if the source was close to the central meridian (±30°). The highest interplanetary magnetic field (B), longest duration, lowest southward direction B
z
component, and lowest Dst were highly correlated for all studied events. The Sun – Earth transit time computed from the starting
time of the sudden disappearance and the time its effect was measured at Earth was about 4.3 days and was mainly well correlated
with the solar wind speed measured in situ (daily value). 相似文献
8.
We present a statistical analysis of the relationship between the kinematics of the leading edge and the eruptive prominence
in coronal mass ejections (CMEs). We study the acceleration phase of 18 CMEs in which kinematics was measured from the pre-eruption
stage up to the post-acceleration phase. In all CMEs, the three part structure (the leading edge, the cavity, and the prominence)
was clearly recognizable from early stages of the eruption. The data show a distinct correlation between the duration of the
leading edge (LE) acceleration and eruptive prominence (EP) acceleration. In the majority of events (78%) the acceleration
phase onset of the LE is very closely synchronized (within ± 20 min) with the acceleration of EP. However, in two events the
LE acceleration started significantly earlier than the EP acceleration (> 50 min), and in two events the EP acceleration started
earlier than the LE acceleration (> 40 min). The average peak acceleration of LEs (281 m s−2) is about two times larger than the average peak acceleration of EPs (136 m s−2). For the first time, our results quantitatively demonstrate the level of synchronization of the acceleration phase of LE
and EP in a rather large sample of events, i.e., we quantify how often the eruption develops in a “self-similar” manner. 相似文献
9.
A. Hillaris O. Malandraki K.-L. Klein P. Preka-Papadema X. Moussas C. Bouratzis E. Mitsakou P. Tsitsipis A. Kontogeorgos 《Solar physics》2011,273(2):493-509
On 17 January 2005 two fast coronal mass ejections were recorded in close succession during two distinct episodes of a 3B/X3.8
flare. Both were accompanied by metre-to-kilometre type-III groups tracing energetic electrons that escape into the interplanetary
space and by decametre-to-hectometre type-II bursts attributed to CME-driven shock waves. A peculiar type-III burst group
was observed below 600 kHz 1.5 hours after the second type-III group. It occurred without any simultaneous activity at higher
frequencies, around the time when the two CMEs were expected to interact. We associate this emission with the interaction
of the CMEs at heliocentric distances of about 25 R
⊙. Near-relativistic electrons observed by the EPAM experiment onboard ACE near 1 AU revealed successive particle releases
that can be associated with the two flare/CME events and the low-frequency type-III burst at the time of CME interaction.
We compare the pros and cons of shock acceleration and acceleration in the course of magnetic reconnection for the escaping
electron beams revealed by the type-III bursts and for the electrons measured in situ. 相似文献
10.
With the use of interplanetary coronal mass ejections (ICMEs) compiled by Richardson and Cane from 1996 to 2007 and the associated
coronal mass ejections (CMEs) observed by the Large Angle and Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric
Observatory (SOHO), we investigate the solar cycle variation of real ICME-associated CME latitudes during solar cycle 23 using
Song et al.’s method. The results show the following:
| • |
Although most of ICME-associated CMEs are distributed at low latitudes, there is a significant fraction of ICME-associated
CMEs occurring at high latitudes. 相似文献
11.
Halo coronal mass ejections (HCMEs) originating from regions close to the center of the Sun are likely to be responsible for
severe geomagnetic storms. It is important to predict geoeffectiveness of HCMEs by using observations when they are still
near the Sun. Unfortunately, coronagraphic observations do not provide true speeds of CMEs because of projection effects.
In the present paper, we present a new technique to allow estimates of the space speed and approximate source location using
projected speeds measured at different position angles for a given HCME (velocity asymmetry). We apply this technique to HCMEs
observed during 2001 – 2002 and find that the improved speeds are better correlated with the travel times of HCMEs to Earth
and with the magnitudes of ensuing geomagnetic storms. 相似文献
12.
13.
Solar transient activities such as solar flares, disappearing filaments, and coronal mass ejections (CMEs) are solar manifestations
of interplanetary (IP) disturbances. Forecasting the arrival time at the near Earth space of the associated interplanetary
shocks following these solar disturbances is an important aspect in space weather forecasting because the shock arrival usually
marks the geomagnetic storm sudden commencement (SSC) when the IMF Bz component is appropriately southward and/or the solar wind dynamic pressure behind the shock is sufficiently large. Combining
the analytical study for the propagation of the blast wave from a point source in a moving, steady-state, medium with variable
density (wei, 1982; wei and dryer 1991) with the energy estimation method in the ISPM model (smith and dryer 1990, 1995),
we present a new shock propagation model (called SPM below) for predicting the arrival time of interplanetary shocks at Earth.
The duration of the X-ray flare, the initial shock speed and the total energy of the transient event are used for predicting
the arrival of the associated shocks in our model. Especially, the background speed, i.e., the convection effect of the solar
wind is considered in this model. Applying this model to 165 solar events during the periods of January 1979 to October 1989
and February 1997 to August 2002, we found that our model could be practically equivalent to the prevalent models of STOA,
ISPM and HAFv.2 in forecasting the shock arrival time. The absolute error in the transit time in our model is not larger than
those of the other three models for the same sample events. Also, the prediction test shows that the relative error of our
model is ≤10% for 27.88% of all events, ≤30% for 71.52%, and ≤50% for 85.46%, which is comparable to the relative errors of
the other models. These results might demonstrate a potential capability of our model in terms of real-time forecasting. 相似文献
14.
Solar coronal mass ejections (CMEs) observed in 1980 with the HAO Coronagraph/Polarimeter on the Solar Maximum Mission (SMM) satellite are compared with other forms of solar activity that might be physically related to the ejections. The solar phenomena checked and the method of association used were intentionally patterned after those of Munro et al.'s (1979) analysis of mass ejections observed with the Skylab coronagraph to facilitate comparison of the two epochs. Comparison of the results reveals that the types and degree of CME associations are similar near solar activity minimum and at maximum. For both epochs, most CMEs with associations had associated eruptive prominences and the proportions of association of all types of activity were similar. We also found a high percentage of association between SMM CMEs and X-ray long duration events (LDEs), in agreement with Skylab results. We conclude that most CMEs are the result of the destabilization and eruption of a prominence and its overlying coronal structure, or of a magnetic structure capable of supporting a prominence.Much of this work was performed as a Visiting Scientist at the High Altitude Observatory/NCAR.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
15.
S. Pohjolainen L. van Driel-Gesztelyi J. L. Culhane P. K. Manoharan H. A. Elliott 《Solar physics》2007,244(1-2):167-188
We explore the relationship among three coronal mass ejections (CMEs), observed on 28 October 2003, 7 November 2004, and 20 January 2005, the type II burst-associated shock waves in the corona and solar wind, as well as the arrival of their related shock waves and magnetic clouds at 1 AU. Using six different coronal/interplanetary density models, we calculate the speeds of shocks from the frequency drifts observed in metric and decametric radio wave data. We compare these speeds with the velocity of the CMEs as observed in the plane-of-the-sky white-light observations and calculated with a cone model for the 7 November 2004 event. We then follow the propagation of the ejecta using Interplanetary Scintillation measurements, which were available for the 7 November 2004 and 20 January 2005 events. Finally, we calculate the travel time of the interplanetary shocks between the Sun and Earth and discuss the velocities obtained from the different data. This study highlights the difficulties in making velocity estimates that cover the full CME propagation time. 相似文献
16.
A mechanism of damped oscillations of a coronal loop is investigated. The loop is treated as a thin toroidal flux rope with
two stationary photospheric footpoints, carrying both toroidal and poloidal currents. The forces and the flux-rope dynamics
are described within the framework of ideal magnetohydrodynamics (MHD). The main features of the theory are the following:
i) Oscillatory motions are determined by the Lorentz force that acts on curved current-carrying plasma structures and ii) damping is caused by drag that provides the momentum coupling between the flux rope and the ambient coronal plasma. The
oscillation is restricted to the vertical plane of the flux rope. The initial equilibrium flux rope is set into oscillation
by a pulse of upflow of the ambient plasma. The theory is applied to two events of oscillating loops observed by the Transition Region and Coronal Explorer (TRACE). It is shown that the Lorentz force and drag with a reasonable value of the coupling coefficient (c
d
) and without anomalous dissipation are able to accurately account for the observed damped oscillations. The analysis shows
that the variations in the observed intensity can be explained by the minor radial expansion and contraction. For the two
events, the values of the drag coefficient consistent with the observed damping times are in the range c
d
≈2 – 5, with specific values being dependent on parameters such as the loop density, ambient magnetic field, and the loop
geometry. This range is consistent with a previous MHD simulation study and with values used to reproduce the observed trajectories
of coronal mass ejections (CMEs). 相似文献
17.
V. K. Verma 《Astrophysics and Space Science》2011,334(1):83-102
We present study of relationship of GSXR flares with Hα flares, hard X-ray (HXR) bursts, microwave (MW) bursts at 15.4 GHz, type II/IV radio bursts, coronal mass ejections (CMEs),
protons flares (>10 MeV) and ground level enhancement (GLE) events we find that about 85.7%, 93%, 97%, 69%, 60%, 11.1%, 79%,
46%, and 23%% GSXR flares are related/associated with observed Hα flares, HXR bursts, MW bursts at 15.4 GHz, type II radio bursts, type IV radio bursts, GLE events, CMEs, halo CMEs, and proton
flares (>10 MeV), respectively. In the paper we have studied the onset time delay of GSXR flares with Hα flares, HXR, and MW bursts which shows the during majority GSXR flares SXR emissions start before the Hα, HXR and MW emissions, respectively while during 15–20% of GSXR flares the SXR emissions start after the onset of Hα, HXT and MW emissions, respectively indicating two types of solar flares. The, onset time interval between SXR emissions
and type II radio bursts, type IV radio bursts, GLE events CMEs, halo CMEs, and protons flares are 1–15 min, 1–20 min, 21–30 min,
21–40 min, 21–40 min, and 1–4 hrs, respectively. Following the majority results we are of the view that the present investigations
support solar flares models which suggest flare triggering first in the corona and then move to chromospheres/ photosphere
to starts emissions in other wavelengths. The result of the present work is largely consistent with “big flare syndrome” proposed
by Kahler (1982). 相似文献
18.
The Electron Energy Spectrum from Large Solar Flares 总被引：2，自引：0，他引：2
G. M. Simnett 《Solar physics》2006,237(2):383-395
We report on the differential electron spectrum for intense transient events seen at one AU by the EPAM instrument on the
Advanced Composition Explorer (ACE) spacecraft. Over an observing period from September 1997 to September 2005, there were 45 major events that could be
reliably identified with a source flare on the Sun. In the ∼40 – 300 keV energy range, the electron spectral index was between
one and three for all but two of the events. Twenty-five of the events were associated with Geostationary Operational Environmental
Satellites (GOES) X-ray class X flares. We compare this result with the spectral index measured from electron pulse events,
lasting approx. one hour or less, where the spectral index is typically much softer than three. This suggests that the measured
spectral index of near-relativistic electrons at one AU may be a reliable indicator of the source. We also examine the likelihood
that fast coronal mass ejections (CMEs) are responsible in themselves for accelerating near-relativistic electrons and conclude
that they do not. 相似文献
19.
It is well known that there is a temporal relationship between coronal mass ejections (CMEs) and associated flares. The duration of the acceleration phase is related to the duration of the rise phase of a flare. We investigate CMEs associated with slow long duration events (LDEs), i.e. flares with the long rising phase. We determined the relationships between flares and CMEs and analyzed the CME kinematics in detail. The parameters of the flares (GOES flux, duration of the rising phase) show strong correlations with the CME parameters (velocity, acceleration during main acceleration phase, and duration of the CME acceleration phase). These correlations confirm the strong relation between slow LDEs and CMEs. We also analyzed the relation between the parameters of the CMEs, i.e. a velocity, an acceleration during the main acceleration phase, a duration of the acceleration phase, and a height of a CME at the end of the acceleration phase. The CMEs associated with the slow LDEs are characterized by high velocity during the propagation phase, with the median equal to 1423 km?s?1. In half of the analyzed cases, the main acceleration was low (a<300 m?s?2), which suggests that the high velocity is caused by the prolonged acceleration phase (the median for the duration of the acceleration phase is equal 90 minutes). The CMEs were accelerated up to several solar radii (with the median ≈?7 R ⊙), which is much higher than in typical impulsive CMEs. Therefore, slow LDEs may potentially precede extremely strong geomagnetic storms. The analysis of slow LDEs and associated CMEs may give important information for developing more accurate space-weather forecasts, especially for extreme events. 相似文献
20.
We discuss the consequences of momentum conservation in processes related to solar flares and coronal mass ejections (CMEs),
in particular describing the relative importance of vertical impulses that could contribute to the excitation of seismic waves
(“sunquakes”). The initial impulse associated with the primary flare energy transport in the impulsive phase contains sufficient
momentum, as do the impulses associated with the acceleration of the evaporation flow (the chromospheric shock) or the CME
itself. We note that the deceleration of the evaporative flow, as coronal closed fields arrest it, will tend to produce an
opposite impulse, reducing the energy coupling into the interior. The actual mechanism of the coupling remains unclear at
present. 相似文献
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