共查询到20条相似文献，搜索用时 31 毫秒
1.
M. S. Wheatland 《Solar physics》2006,236(2):313-324
Solar flare sympathy is the triggering of a flare in one active region by a flare in another. Statistical tests for flare
sympathy have returned varying results. However, existing tests have relied on flaring rates in active regions being constant
in time, or else have attempted to model the rate variation, which is a difficult task. A simple test is described which is
independent of flaring rates. The test generalizes the approach of L. Fritzová-Švestkova, R.C. Chase, and Z. Švestka [Solar Phys.
48, 275, 1976], and examines the distribution of flare coincidences in pairs of active regions as a function of coincidence
interval τ. The test is applied to available soft X-ray and Hα flare event listings. The soft X-ray events exhibit a deficit
of flare coincidences for τ≤;20 min, which is most likely due to an event-selection effect whereby the increased soft X-ray
emission due to one flare prevents a second flare being identified. The Hα events show an excess of flare coincidences for
τ≤; 10 min, suggesting flare sympathy. The number of Hα event pairs occurring within 10 min of one another is higher than
that expected on the basis of random coincidence by a fraction 0.12± 0.02. Nearby active regions (spatial separation <50˚)
show a greater excess of coincidences for τ≤; 10 min than do active regions which are far apart (spatial separation ≥50˚).
However, the active regions which are far apart still show some evidence for an excess of coincidences at very short coincidence
intervals (τ≤; 2 min), which appears to exclude the possibility of a coronal disturbance propagating from one region to another. 相似文献
2.
The ability of magnetic reconnection solutions to explain statistical flare data is discussed. It is assumed that flares occur at well-defined, isolated sites within an active region, determined by the null points and separators of the coronal magnetic field (Craig, 2001). Statistical flare observations then derive from a multiplicity of independent sites, flaring in parallel, that produce events of widely varying output (Wheatland, 2002). Given that the `separator length' at an individual site controls the event frequency and the mean energy release, it is shown that the observed frequency-energy spectrum N(E)can be inverted to yield a source function that relates directly to the distribution of separator lengths. It is also pointed out that, under the parallel flaring model, inferred waiting-time distributions are naturally interpreted as a superposition of individual point processes. Only a modest number of flaring separators is required to mimic a Poisson process. 相似文献
3.
A time-dependent model for the energy of a flaring solar active region is presented based on an existing stochastic jump-transition
model (Wheatland and Glukhov in Astrophys. J.
494, 858, 1998; Wheatland in Astrophys. J.
679, 1621, 2008 and Solar Phys.
255, 211, 2009). The magnetic free energy of an active region is assumed to vary in time due to a prescribed (deterministic) rate of energy
input and prescribed (random) jumps downwards in energy due to flares. The existing model reproduces observed flare statistics,
in particular flare frequency – size and waiting-time distributions, but modeling presented to date has considered only the
time-independent choices of constant energy input and constant flare-transition rates with a power-law distribution in energy.
These choices may be appropriate for a solar active region producing a constant mean rate of flares. However, many solar active
regions exhibit time variation in their flare productivity, as exemplified by NOAA active region (AR) 11029, observed during
October – November 2009 (Wheatland in Astrophys. J.
710, 1324, 2010). Time variation is incorporated into the jump-transition model for two cases: (1) a step change in the rates of flare transitions,
and (2) a step change in the rate of energy supply to the system. Analytic arguments are presented describing the qualitative
behavior of the system in the two cases. In each case the system adjusts by shifting to a new stationary state over a relaxation
time which is estimated analytically. The model exhibits flare-like event statistics. In each case the frequency – energy
distribution is a power law for flare energies less than a time-dependent rollover set by the largest energy the system is
likely to attain at a given time. The rollover is not observed if the mean free energy of the system is sufficiently large.
For Case 1, the model exhibits a double exponential waiting-time distribution, corresponding to flaring at a constant mean
rate during two intervals (before and after the step change), if the average energy of the system is large. For Case 2 the
waiting-time distribution is a simple exponential, again provided the average energy of the system is large. Monte Carlo simulations
of Case 1 are presented which confirm the estimate for the relaxation time and the expected forms of the frequency – energy
and waiting-time distributions. The simulation results provide a qualitative model for observed flare statistics in AR 11029. 相似文献
4.
The NOAA listings of solar flares in cycles 21?–?24, including the GOES soft X-ray magnitudes, enable a simple determination of the number of flares each flaring active region produces over its lifetime. We have studied this measure of flare productivity over the interval 1975?–?2012. The annual averages of flare productivity remained approximately constant during cycles 21 and 22, at about two reported M- or X-flares per region, but then increased significantly in the declining phase of cycle 23 (the years 2004?–?2005). We have confirmed this by using the independent RHESSI flare catalog to check the NOAA events listings where possible. We note that this measure of solar activity does not correlate with the solar cycle. The anomalous peak in flare productivity immediately preceded the long solar minimum between cycles 23 and 24. 相似文献
5.
Yūki Kubo 《Solar physics》2008,248(1):85-98
This article discusses statistical models for the solar flare interval distribution in individual active regions. We analyzed
solar flare data in 55 active regions that are listed in the Geosynchronous Operational Environmental Satellite (GOES) soft X-ray flare catalog for the years from 1981 to 2005. We discuss some problems with a conventional procedure to
derive probability density functions from any data set and propose a new procedure, which uses the maximum likelihood method
and Akaike Information Criterion (AIC) to objectively compare some competing probability density functions. Previous studies
of the solar flare interval distribution in individual active regions only dealt with constant or time-dependent Poisson process
models, and no other models were discussed. We examine three models – exponential, lognormal, and inverse Gaussian – as competing
models for probability density functions in this study. We found that lognormal and inverse Gaussian models are more likely
models than the exponential model for the solar flare interval distribution in individual active regions. The possible solar
flare mechanisms for the distribution models are briefly mentioned. We also briefly investigated the time dependence of probability
density functions of the solar flare interval distribution and found that some active regions show time dependence for lognormal
and inverse Gaussian distribution functions. The results suggest that solar flares do not occur randomly in time; rather,
solar flare intervals appear to be regulated by solar flare mechanisms. Determining a solar flare interval distribution is
an essential step in probabilistic solar flare forecasting methods in space weather research. We briefly mention a probabilistic
solar flare forecasting method as an application of a solar flare interval distribution analysis. The application of our distribution
analysis to a probabilistic solar flare forecasting method is one of the main objectives of this study. 相似文献
6.
A model is presented to explain the observed frequency distribution of flare energies, based on independent flaring at a number of distinct topological structures (separators) within active-region magnetic fields. The model is a modification and generalization of a recent model due to Craig (2001), and reconciles that model with the observed flare waiting-time distribution, and the observed absence of a flare waiting-time versus energy relationship. The basic assumptions of the model are that flares of energy E
2 occur at separators of length
, and that the frequency of flaring at a separator is defined by the Alfvén transit time of the structure. To reproduce the observed distribution of flare energies the model requires a probability distribution P(
)
–1 of separator lengths
within active regions. This prediction of the model is in principle testable. A theoretical origin for this distribution is also discussed. 相似文献
7.
We use Renewal Theory for the estimation and interpretation of the flare rate from the Geostationary Operational Environmental Satellite (GOES) soft X-ray?flare catalogue. It is found that, in addition to the flare rate variability with the solar cycles, a much faster variation occurs. The fast variation on time scales of days and hours down to minute scale appears to be comparable with time intervals between two successive flares (waiting times). The detected fast non-stationarity of the flaring rate is discussed in the framework of the previously published stochastic models of the waiting time dynamics. 相似文献
8.
We present three-dimensional unsteady modeling and numerical simulations of a coronal active region, carried out within the
compressible single-fluid MHD approximation. We focus on AR 9077 on 14 July 2000, and the triggering of the X5.7 GOES X-ray
class “Bastille Day” flare. We simulate only the lower corona, although we include a virtual photosphere and chromosphere
below. The boundary conditions at the base of this layer are set using temperature maps from line intensities and line-of-sight
magnetograms (SOHO/MDI). From the latter, we generate vector magnetograms using the force-free approximation; these vector
magnetograms are then used to produce the boundary condition on the velocity field using a minimum energy principle (Longcope,
Astrophys. J.
612, 1181, 2004). The reconnection process is modeled through a dynamical hyper-resistivity which is activated when the current exceeds a
critical value (Klimas et al., J. Geophys. Res.
109, 2218, 2004). Comparing the time series of X-ray fluxes recorded by GOES with modeled time series of various mean physical variables
such as current density, Poynting energy flux, or radiative loss inside the active region, we can demonstrate that the model
properly captures the evolution of an active region over a day and, in particular, is able to explain the initiation of the
flare at the observed time. 相似文献
9.
Eric Jonas Monica Bobra Vaishaal Shankar J. Todd Hoeksema Benjamin Recht 《Solar physics》2018,293(3):48
The precise physical process that triggers solar flares is not currently understood. Here we attempt to capture the signature of this mechanism in solar-image data of various wavelengths and use these signatures to predict flaring activity. We do this by developing an algorithm that i) automatically generates features in 5.5 TB of image data taken by the Solar Dynamics Observatory of the solar photosphere, chromosphere, transition region, and corona during the time period between May 2010 and May 2014, ii) combines these features with other features based on flaring history and a physical understanding of putative flaring processes, and iii) classifies these features to predict whether a solar active region will flare within a time period of \(T\) hours, where \(T = 2 \mbox{ and }24\). Such an approach may be useful since, at the present time, there are no physical models of flares available for real-time prediction. We find that when optimizing for the True Skill Score (TSS), photospheric vector-magnetic-field data combined with flaring history yields the best performance, and when optimizing for the area under the precision–recall curve, all of the data are helpful. Our model performance yields a TSS of \(0.84 \pm0.03\) and \(0.81 \pm0.03\) in the \(T = 2\)- and 24-hour cases, respectively, and a value of \(0.13 \pm0.07\) and \(0.43 \pm0.08\) for the area under the precision–recall curve in the \(T=2\)- and 24-hour cases, respectively. These relatively high scores are competitive with previous attempts at solar prediction, but our different methodology and extreme care in task design and experimental setup provide an independent confirmation of these results. Given the similar values of algorithm performance across various types of models reported in the literature, we conclude that we can expect a certain baseline predictive capacity using these data. We believe that this is the first attempt to predict solar flares using photospheric vector-magnetic field data as well as multiple wavelengths of image data from the chromosphere, transition region, and corona, and it points the way towards greater data integration across diverse sources in future work. 相似文献
10.
M. S. Wheatland 《Solar physics》2009,255(2):211-227
A Monte Carlo approach to solving a stochastic-jump transition model for active-region energy (Wheatland and Glukhov: Astrophys. J.
494, 858, 1998; Wheatland: Astrophys. J.
679, 1621, 2008) is described. The new method numerically solves the stochastic differential equation describing the model, rather than the
equivalent master equation. This has the advantages of allowing more efficient numerical solution, the modeling of time-dependent
situations, and investigation of details of event statistics. The Monte Carlo approach is illustrated by application to a
Gaussian test case and to the class of flare-like models presented in Wheatland (Astrophys. J.
679, 1621, 2008), which are steady-state models with constant rates of energy supply, and power-law distributed jump transition rates. These
models have two free parameters: an index (δ), which defines the dependence of the jump transition rates on active-region energy, and a nondimensional ratio (
) of total flaring rate to rate of energy supply. For
the nondimensional mean energy
of the active-region satisfies
, resulting in a power-law distribution of flare events over many decades of energy. The Monte Carlo method is used to explore
the behavior of the waiting-time distributions for the flare-like models. The models with δ≠0 are found to have waiting times that depart significantly from simple Poisson behavior when
. The original model from Wheatland and Glukhov (Astrophys. J.
494, 858, 1998), with δ=0 (i.e., no dependence of transition rates on active-region energy), is identified as being most consistent with observed flare statistics. 相似文献
11.
Short-Term Solar Flare Prediction Using Predictor Teams 总被引：1，自引：0，他引：1
A short-term solar flare prediction model is built using predictor teams rather than an individual set of predictors. The information provided by the set of predictors could be redundant. So it is necessary to generate subsets of predictors which can keep the information constant. These subsets are called predictor teams. In the framework of rough set theory, predictor teams are constructed from sequences of the maximum horizontal gradient, the length of neutral line and the number of singular points extracted from SOHO/MDI longitudinal magnetograms. Because of the instability of the decision tree algorithm, prediction models generated by the C4.5 decision tree for different predictor teams are diverse. The flaring sample, which is incorrectly predicted by one model, can be correctly forecasted by another one. So these base prediction models are used to construct an ensemble prediction model of solar flares by the majority voting rule. The experimental results show that the predictor team can keep the distinguishability of the original set, and the ensemble prediction model can obtain better performance than the model based on the individual set of predictors. 相似文献
12.
Solar flares are powered by the energy stored in magnetic fields, so evolutionary information of the magnetic field is important
for short-term prediction of solar flares. However, the existing solar flare prediction models only use the current information
of the active region. A sequential supervised learning method is introduced to add the evolutionary information of the active
region into a prediction model. The maximum horizontal gradient, the length of the neutral line, and the number of singular
points extracted from SOHO/MDI longitudinal magnetograms are used in the model to describe the nonpotentiality and complexity
of the photospheric magnetic field. The evolutionary characteristics of the predictors are analyzed by using autocorrelation
functions and mutual information functions. The analysis results indicate that a flare is influenced by the 3-day photospheric
magnetic field information before flare eruption. A sliding-window method is used to add evolutionary information of the predictors
into machine learning algorithms, then C4.5 decision tree and learning vector quantization are employed to predict the flare
level within 48 hours. Experimental results indicate that the performance of the short-term solar flare prediction model within
the sequential supervised learning framework is significantly improved. 相似文献
13.
Tetsuya Watanabe Alphonse C. Sterling Hugh S. Hudson Louise K. Harra 《Solar physics》2001,201(1):71-91
We report temperature diagnostics derived from helium-like ions of sulphur for an active region NOAA 7978 obtained with Bragg Crystal Spectrometer (BCS) on board the Yohkoh satellite. For the same region we estimate conductive flux downward to the chromosphere by the Coronal Diagnostic Spectrometer (CDS) on board the Solar and Heliospheric Observatory (SOHO) satellite. This region appeared as a region of soft X-ray enhancement in May 1996, underwent a period of enhanced activity coinciding with flux emergence between 6 July and 12 July, and then continued to exist in a nearly flareless state for several solar rotations until November 1996. Energy balance of the non-flaring active region is basically consistent with a model of an arcade of coronal loops having an average loop-top temperature of 4×106 K. Energy from flare activity during a period of flux emergence is comparable to the energy requirements of the non-flaring active region. However, the non-flaring energy is roughly constant for the subsequent solar rotations following the birth of the active region even after the flare activity essentially subsided. Energy partition between flare activity and steady active-region heating thus varies significantly over the lifetime of the active region, and active-region emission cannot always be identified with flaring. 相似文献
14.
Solar flares occur due to the sudden release of energy stored in active-region magnetic fields. To date, the precursors to
flaring are still not fully understood, although there is evidence that flaring is related to changes in the topology or complexity
of an active-region’s magnetic field. Here, the evolution of the magnetic field in active region NOAA 10953 was examined using
Hinode/SOT-SP data over a period of 12 hours leading up to and after a GOES B1.0 flare. A number of magnetic-field properties and
low-order aspects of magnetic-field topology were extracted from two flux regions that exhibited increased Ca ii H emission during the flare. Pre-flare increases in vertical field strength, vertical current density, and inclination angle
of ≈ 8° toward the vertical were observed in flux elements surrounding the primary sunspot. The vertical field strength and
current density subsequently decreased in the post-flare state, with the inclination becoming more horizontal by ≈ 7°. This
behavior of the field vector may provide a physical basis for future flare-forecasting efforts. 相似文献
15.
Homogeneous plane-parallel model atmospheres for solar flares have been constructed to approximately simulate observations of flares. The wings of the Ca II lines have been used to derive flare upper photosphere models, which indicate temperature increases of ～100 K over the temperature distribution in the pre-existing facula at a height of 300 km above τ5000 = 1. In the case of flares covering sunspots the temperature rise seems to occur much higher in the atmosphere. We solve the transfer and statistical equilibrium equations for a three-level hydrogen atom and a five-level calcium atom in order to obtain the chromospheric flare models. The general properties of flares, including n e, N 2, linear thickness, and Lyman continuum intensity are approximately reproduced. We find that with increasing flare importance the height of the upper chromosphere and transition region occur lower in the solar atmosphere, accounting for the factor of 60–600 increase in pressure in these regions relative to the quiet Sun. The Ca II line profiles agree with observations only by assuming a macro-velocity distribution that increases with height. Also the chromospheric parts of flares appear to be highly inhomogeneous. We show that shock and particle heated flare models do not agree with the observations and propose a thermal response model for flares. In particular, it appears that heating in the photosphere is an essential aspect of flares. 相似文献
16.
The `ribbons' of two-ribbon flares show complicated patterns reflecting the linkages of coronal magnetic field lines through
the lower solar atmosphere. We describe the morphology of the EUV ribbons of the July 14, 2000 flare, as seen in SOHO, TRACE,
and Yohkoh data, from this point of view. A successful co-alignment of the TRACE, SOHO/MDI and Yohkoh/HXT data has allowed us to locate the EUV ribbon positions on the underlying field to within ∼ 2′′, and thus to investigate
the relationship between the ribbons and the field, and also the sites of electron precipitation. We have also made a determination
of the longitudinal magnetic flux involved in the flare reconnection event, an important parameter in flare energetic considerations.
There are several respects in which the observations differ from what would be expected in the commonly-adopted models for
flares. Firstly, the flare ribbons differ in fine structure from the (line-of-sight) magnetic field patterns underlying them,
apparently propagating through regions of very weak and probably mixed polarity. Secondly, the ribbons split or bifurcate.
Thirdly, the amount of line-of-sight flux passed over by the ribbons in the negative and positive fields is not equal. Fourthly,
the strongest hard X-ray sources are observed to originate in stronger field regions. Based on a comparison between HXT and
EUV time-profiles we suggest that emission in the EUV ribbons is caused by electron bombardment of the lower atmosphere, supporting
the hypothesis that flare ribbons map out the chromospheric footpoints of magnetic field lines newly linked by reconnection.
We describe the interpretation of our observations within the standard model, and the implications for the distribution of
magnetic fields in this active region. 相似文献
17.
The deduction from solar flare X-ray photon spectroscopic data of the energy-dependent model-independent spectral index is considered as an inverse problem. Using the well-developed regularization approach we analyze the energy dependency of spectral index for a high-resolution energy spectrum provided by Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The regularization technique produces much smoother derivatives while avoiding additional errors typical of finite differences. It is shown that observations imply a spectral index varying significantly with energy, in a way that also varies with time as the flare progresses. The implications of these findings are discussed in the solar flare context. 相似文献
18.
An X17 class (GOES soft X-ray) two-ribbon solar flare on October 28, 2003 is analyzed in order to determine the relationship
between the timing of the impulsive phase of the flare and the magnetic shear change in the flaring region. EUV observations
made by the Transition Region and Coronal Explorer (TRACE) show a clear decrease in the shear of the flare footpoints during the flare. The shear change stopped in the middle
of the impulsive phase. The observations are interpreted in terms of the splitting of the sheared envelope field of the greatly
sheared core rope during the early phase of the flare. We have also investigated the temporal correlation between the EUV
emission from the brightenings observed by TRACE and the hard X-ray (HXR) emission (E > 150 keV) observed by the anticoincidence system (ACS) of the spectrometer SPI on board the ESA INTEGRAL satellite. The
correlation between these two emissions is very good, and the HXR sources (RHESSI) late in the flare are located within the
two EUV ribbons. These observations are favorable to the explanation that the EUV brightenings mainly result from direct bombardment
of the atmosphere by the energetic particles accelerated at the reconnection site, as does the HXR emission. However, if there
is a high temperature (T > 20 MK) HXR source close to the loop top, a contribution of thermal conduction to the EUV brightenings cannot be ruled out. 相似文献
19.
M. M. Woods L. K. Harra S. A. Matthews D. H. Mackay S. Dacie D. M. Long 《Solar physics》2017,292(2):38
On 29 March 2014, NOAA Active Region (AR) 12017 produced an X1 flare that was simultaneously observed by an unprecedented number of observatories. We have investigated the pre-flare period of this flare from 14:00 UT until 19:00 UT using joint observations made by the Interface Region Imaging Spectrometer (IRIS) and the Hinode Extreme Ultraviolet Imaging Spectrometer (EIS). Spectral lines providing coverage of the solar atmosphere from the chromosphere to the corona were analysed to investigate pre-flare activity within the AR. The results of the investigation have revealed evidence of strongly blue-shifted plasma flows, with velocities up to \(200~\mbox{km}\,\mbox{s}^{-1}\), being observed 40 minutes prior to flaring. These flows are located along the filament present in the active region and are both spatially discrete and transient. In order to constrain the possible explanations for this activity, we undertake non-potential magnetic field modelling of the active region. This modelling indicates the existence of a weakly twisted flux rope along the polarity inversion line in the region where a filament and the strong pre-flare flows are observed. We then discuss how these observations relate to the current models of flare triggering. We conclude that the most likely drivers of the observed activity are internal reconnection in the flux rope, early onset of the flare reconnection, or tether-cutting reconnection along the filament. 相似文献
20.
On 10 March 2001 the active region NOAA 9368 produced an unusually impulsive solar flare in close proximity to the solar limb. This flare has previously been studied in great detail, with observations classifying it as a type 1 white-light flare with a very hard spectrum in hard X-rays. The flare was also associated with a type II radio burst and coronal mass ejection. The flare emission characteristics appeared to closely correspond to previous instances of seismic emission from acoustically active flares. Using standard local helioseismic methods, we identified the seismic signatures produced by the flare that, to date, is the least energetic (in soft X-rays) of the flares known to have generated a detectable acoustic transient. Holographic analysis of the flare shows a compact acoustic source strongly correlated with the impulsive hard X-rays, visible continuum, and radio emission. Time?–?distance diagrams of the seismic waves emanating from the flare region also show faint signatures, mainly in the eastern sector of the active region. The strong spatial coincidence between the seismic source and the impulsive visible continuum emission reinforces the theory that a substantial component of the seismic emission seen is a result of sudden heating of the low photosphere associated with the observed visible continuum emission. Furthermore, the low-altitude magnetic loop structure inferred from potential-field extrapolations in the flaring region suggests that there is a significant anti-correlation between the seismicity of a flare and the height of the magnetic loops that conduct the particle beams from the corona. 相似文献