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1.
Bojan Vršnak Manuela Temmer Astrid Veronig Marian Karlický Jun Lin 《Solar physics》2006,234(2):273-299
We analyze the evolution of the flare/postflare-loop system in the two-ribbon flare of November 3, 2003, utilizing multi-wavelength
observations that cover the temperature range from several tens of MK down to 104 K. A non-uniform growth of the loop system enables us to identify analogous patterns in the height–time, h(t), curves measured at different temperatures. The “knees,” “plateaus,” and “bends” in a higher-temperature curve appear after
a certain time delay at lower heights in a lower-temperature curve. We interpret such a shifted replication as a track of
a given set of loops (reconnected field lines) while shrinking and cooling after being released from the reconnection site.
Measurements of the height/time shifts between h(t) curves of different temperatures provide a simultaneous estimate of the shrinkage speed and cooling rate in a given temperature
domain, for a period of almost ten hours after the flare impulsive phase. From the analysis we find the following: (a) Loop
shrinkage is faster at higher temperatures – in the first hour of the loop-system growth, the shrinkage velocity at 5 MK is
20 – 30 km s−1, whereas at 1 MK it amounts to 5 km s−1; (b) Shrinking becomes slower as the flare decays – ten hours after the impulsive phase, the shrinkage velocity at 5 MK becomes
5 km s−1; (c) The cooling rate decreases as the flare decays – in the 5 MK range it is 1 MK min−1 in the first hour of the loop-system growth, whereas ten hours later it decreases to 0.2 MK min−1; (d) During the initial phase of the loop-system growth, the cooling rate is larger at higher temperatures, whereas in the
late phases the cooling rate apparently does not depend on the temperature; (e) A more detailed analysis of shrinking/cooling
around one hour after the impulsive phase reveals a deceleration of the loop shrinkage, amounting to ā ≈ 10 m s−2 in the T < 5 MK range; (f) In the same interval, conductive cooling dominates down to T ≈ 3 MK, whereas radiation becomes dominant below T ≈ 2 MK; (g) A few hours after the impulsive phase, radiation becomes dominant across the whole T < 5 MK range. These findings are compared with results of previous studies and discussed in the framework of relevant models. 相似文献
2.
We present our results of high temporal resolution spectroscopic observation and study in Hα, Ca II, and He I lines for the 2B/M1.9 confined disk flare on September 9, 2001, combining with GOES soft X-ray (SXR) and Yohkoh hard X-ray (HXR) observations. Apparent redshifted and red-asymmetric profiles were observed in the initial phase. The redshift
lasted until the late phase. The derived velocity depends on both the spectral line and the used method. The redshift velocities
computed from the line centers of the observed emission profiles (υ0) are of the order of 10 km s−1 both inside and outside the streak area. However, the velocities determined from the excess profiles by the bisector method
(υ) are larger in the streak (18–50 km s−1). Both υ and the red full widths (RFWs) derived from the excess profiles show temporal variations similar to the HXR light-curve
in the streak area. Moreover, the Hα line wings of nonthermal characteristics, the redshift velocities, and the lifetime of
impulsive broadening suggest that the streak is related to nonthermal electron bombardment. Spectral simulations reveal that
we cannot reproduce the observed profiles in the three lines simultaneously with a set of parameters, indicating that the
flare atmosphere was not homogeneous along the line-of-sight. Most of the observed Hα profiles showed a ‘flat-top’ structure,
implying the flare plasma was optically thick for this line. The electron temperatures (Te) deduced from the line-center intensity of the three lines are similar and estimated to be higher than 7200 K. The obvious
central reversal of the Hα profiles due to absorption of materials in the impulsive phase lasted more than 2 min. However,
the far blue wings of the Ca II profiles in the impulsive phase showed low-intensity emission, which is suggestive of the
existence of large turbulence or macroscopic motion (> 50 km s−1), which is inconsistent with the current flare model. 相似文献
3.
We studied the evolution of a small eruptive flare (GOES class C1) from its onset phase using multi-wavelength observations
that sample the flare atmosphere from the chromosphere to the corona. The main instruments involved were the Coronal Diagnostic
Spectrometer (CDS) aboard SOHO and facilities at the Dunn Solar Tower of the National Solar Observatory/Sacramento Peak. Transition
Region and Coronal Explorer (TRACE) together with Ramaty High-Energy Spectroscopic Imager (RHESSI) also provided images and
spectra for this flare. Hα and TRACE images display two loop systems that outline the pre-reconnection and post-reconnection magnetic field lines and
their topological changes revealing that we are dealing with an eruptive confined flare. RHESSI data do not record any detectable
emission at energies ≥25 keV, and the observed count spectrum can be well fitted with a thermal plus a non-thermal model of
the photon spectrum. A non-thermal electron flux F ≈ 5 × 1010 erg cm−2 s−1 is determined. The reconstructed images show a very compact source whose peak emission moves along the photospheric magnetic
inversion line during the flare. This is probably related to the motion of the reconnection site, hinting at an arcade of
small loops that brightens successively. The analysis of the chromospheric spectra (Ca II K, He I D3 and Hγ, acquired with a four-second temporal cadence) shows the presence of a downward velocity (between 10 and 20 km s−1) in a small region intersected by the spectrograph slit. The region is included in an area that, at the time of the maximum
X-ray emission, shows upward motions at transition region (TR) and coronal levels. For the He I 58.4 and O v 62.97 lines, we determine a velocity of ≈−40 km s−1 while for the Fe XIX 59.22 line a velocity of ≈−80 km s−1 is determined with a two-component fitting. The observations are discussed in the framework of available hydrodynamic simulations
and they are consistent with the scenario outlined by Fisher (1989). No explosive evaporation is expected for a non-thermal
electron beam of the observed characteristics, and no gentle evaporation is allowed without upward chromospheric motion. It
is suggested that the energy of non-thermal electrons can be dissipated to heat the high-density plasma, where possibly the
reconnection occurs. The consequent conductive flux drives the evaporation process in a regime that we can call sub-explosive. 相似文献
4.
In this paper we present a further study of the Ml class flare observed on October 22, 2002. We focus on the SOHO Coronal
Diagnostic Spectrometer (CDS) spectral observations performed during a multi-wavelength campaign with TRACE and ground-based
instruments (VTT, THEMIS). Strong blue-shifts are observed in the CDS coronal lines in flare kernels during the impulsive
phase of this flare. From a careful wavelength calibration we deduce upflows of 140 km/s for the Fe XIX flare emission, with
a pattern of progressively smaller flows at lower temperatures. Large line-widths were observed, especially for the Fe XIX
line, which indicate the existence of turbulent velocities. The strong upflows correspond to full shifts of the line profiles.
These flows are observed at the initial phase of the flare, and correspond to the “explosive evaporation”. The regions of
the blueshifted kernels, a few arc seconds away from the flare onset location, could be explained by the chain reaction of
successive magnetic reconnections of growing emerging field line with higher and higher overlying field. This interpretation
is evidenced by the analysis of the magnetic topology of the active region using a linear force-free-field extrapolation of
THEMIS magnetograms. 相似文献
5.
Brekke P. Kjeldseth-Moe O. Brynildsen N. Maltby P. Haugan S. V. H. Harrison R. A. Thompson W. T. Pike C. D. 《Solar physics》1997,170(1):163-177
EUV spectra obtained with the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO) show significant flows of plasma in active region loops, both at coronal and transition region temperatures. Wavelength shifts in the coronal lines Mgix 368 Å and Mgx 624 Å corresponding to upflows in the plasma reaching velocities of 50 km s-1 have been observed in an active region. Smaller velocities are detected in the coronal lines Fexvi 360 Å and Sixii 520 Å. Flows reaching 100 km s-1 are observed in spectral lines formed at transition region temperatures, i.e., Ov 629 Å and Oiii 599 Å, demonstrating that both the transition region and the corona are clearly dynamic in nature. Some high velocity events show even higher velocities with line profiles corresponding to a velocity dispersion of 300–400 km s-1. Even in the quiet Sun there are velocity fluctuations of 20 km s-1 in transition region lines. Velocities of the magnitude presented in this paper have never previously been observed in coronal lines except in explosive events and flares. Thus, the preliminary results from the CDS spectrometer promise to put constraints on existing models of the flows and energy balance in the solar atmosphere. The present results are compared to previous attempts to observe flows in the corona. 相似文献
6.
Tokio Tsubaki 《Solar physics》1975,43(1):147-175
A technique developed for analysing line profiles with both speed and high accuracy was used to study the physical conditions
of a coronal formation near a quiescent prominence. Detailed analyses of five coronal lines (Fe xiv λ 5303, Fe x λ 6374, Ni xv λ 6702, Fe xv λ 7059, and Fe xi λ 7892) provided total intensities, Doppler width temperatures, ionization temperatures, and velocities.
Dissimilar spatial fluctuations in intensity are obvious for ions grouped according to (low vs high) ionization potentials.
The intensity of the green line shows a local minimum around the observed quiescent prominence; a corresponding but much more
diffuse pattern is visible in the red line intensity.
Large differences are observed in temperatures derived by different means. In particular,
, while
, and
. The differences between
and
are taken as direct evidence of temperature inhomogeneity. One can thus put little significance in T
e
(xi/x). T
D(λ5303) and T
e
(xv/xiv) fluctuate nearly in parallel at each slit height, with a weak local minimum evident around the prominence. The discrepancy
between these two can be removed if a non-thermal turbulent motion of 6–16 km s−1 is assumed. Variations with height of both T
D(λ5303) and T
e
(xv/xiv) suggest that the coronal temperature maximum is located no more than 15000 km above the top of spicules. A negative gradient
of about 6 deg km−1 is found in the height variation of T
D(λ5303).
The height variation of the green line wavelength shows that the majority of coronal material in this region is flowing from
west to east on the Sun, with the highest velocity of 12 km s−1 found at the lowest heights. This motion is in the same sense as that of the nearby coronal rain, as determined both from
the spectra and wavelength-shifted Hα filtergrams. Superposed on the above flow is a systematic velocity field of up to ±5
km s−1. This field similarly reaches maximum amplitudes at lowest heights showing a local maximum around the prominence.
On leave from Institute of Earth Science and Astrophysics, Shiga University, Ohtsu 520, Japan, as 1973–75 National Academy
of Science/National Research Council Senior Post-Doctoral Research Associate at Sacramento Peak Observatory. 相似文献
7.
H. S. Hudson T. N. Woods P. C. Chamberlin L. Fletcher G. Del Zanna L. Didkovsky N. Labrosse D. Graham 《Solar physics》2011,273(1):69-80
The Extreme-ultraviolet Variability Experiment (EVE; see Woods et al., 2009) obtains continuous EUV spectra of the Sun viewed as a star. Its primary objective is the characterization of solar
spectral irradiance, but its sensitivity and stability make it extremely interesting for observations of variability on time
scales down to the limit imposed by its basic 10 s sample interval. In this paper we characterize the Doppler sensitivity
of the EVE data. We find that the 30.4 nm line of He ii has a random Doppler error below 0.001 nm (1 pm, better than 10 km s−1 as a redshift), with ample stability to detect the orbital motion of its satellite, the Solar Dynamics Observatory (SDO). Solar flares also displace the spectrum, both because of Doppler shifts and because of EVE’s optical layout, which
(as with a slitless spectrograph) confuses position and wavelength. As a flare develops, the centroid of the line displays
variations that reflect Doppler shifts and therefore flare dynamics. For the impulsive phase of the flare SOL2010-06-12, we
find the line centroid to have a redshift of 16.8 ± 5.9 km s−1 relative to that of the flare gradual phase (statistical errors only). We find also that high-temperature lines, such as
Fe xxiv 19.2 nm, have well-determined Doppler components for major flares, with decreasing apparent blueshifts as expected from chromospheric
evaporation flows. 相似文献
8.
Synoptic maps of white-light coronal brightness from SOHO/LASCO C2 and distributions of solar wind velocity obtained from
interplanetary scintillation are studied. Regions with velocity V≈300 – 450 km s−1 and increased density N>10 cm−3, typical of the “slow” solar wind originating from the belt and chains of streamers, are shown to exist at Earth’s orbit,
between the fast solar wind flows (with a maximum velocity V
max ≈450 – 800 km s−1). The belt and chains of streamers are the main sources of the “slow” solar wind. As the sources of “slow” solar wind, the
contribution from the chains of streamers may be comparable to that from the streamer belt. 相似文献
9.
Chung-Chieh Cheng 《Solar physics》1980,65(2):283-298
We studied the EUV line spectra of three flare observed with the NRL slit spectrograph on Skylab. The electron densities in the flare transition-zone plasmas are determined from density-sensitive lines of Si iii and O iv. The electron densities in all three flares studied were greatest during the flare maximum with values of the order of 1012 cm–3. The density decreases by a factor of 2 to 3 in the decay phase of the flares. The intensities of EUV lines from the flare chromospheric and transition-zone plasmas all are greatly enhanced. In contrast to lines for Oi, Ci, Feii and other chromospheric ions, the lines of Oiv and Nv and other transition-zone lines are not only enhanced but also very much broadened.Fitting of the N v 1242 Å line with a two-gaussian model shows that for two of the flares studied, there is a red-shifted component in addition to an unshifted component. The shifted component in the N v line profiles is interpreted as due to a dynamic and moving plasma with a bulk motion velocity of 12 km s–1 for one flare and more than 70 km s–1 for the other. The broadened line profiles indicate that there are large turbulent mass motions with random velocities ranging from 30 to 80 km s–1.Ball Corporation. Now with NASA/Marshall Space Flight Center. 相似文献
10.
The EUV observations from the SMM satellite of two sunspots are presented here. These observations show the sunspots (a) to be regions of lower intensity than the surrounding plage, contrary to that found by previous authors, and (b) to have line intensities which vary little over a period of several hours. An upper limit to mass flows of 2km s-1 is derived, indicating a relatively simple energy balance for the chromosphere-corona transition zone with thermal conduction being balanced by radiative losses. Electron densities derived from Niv to Civ line ratios imply electron pressures (log N
eTe) of 15.0 to 15.3. 相似文献
11.
V. N. Melnik A. A. Konovalenko V. V. Dorovskyy H. O. Rucker E. P. Abranin V. N. Lisachenko A. Lecacheux 《Solar physics》2005,231(1-2):143-155
The results of observations of solar decametric drift pair bursts are presented. These observations were carried out during
a Type III burst storm on July 11–21, 2002, with the decameter radio telescope UTR-2, equipped with new back-end facilities.
High time and frequency resolution of the back-end allowed us to obtain new information about the structure and properties
of these bursts. The statistical analysis of more than 700 bursts observed on 13–15 July was performed separately for “forward”
and “reverse” drift pair bursts. Such an extensive amount of these kind of bursts has never been processed before. It should
be pointed out that “forward” and “reverse” drift pair bursts have a set of similar parameters, such as time delay between
the burst elements, duration of an element, and instant bandwidth of an element. Nevertheless some of their parameters are
different. So, the absolute average value of frequency drift rate for “forward” bursts is 0.8 MHz s−1, while for “reverse” ones it is 2 MHz s−1. The obtained functional dependencies “drift rate vs. frequency” and “flux density vs. frequency” were found to be different
from the current knowledge. We also report about the observation of unusual variants of drift pairs, in particular, of “hook”
bursts and bursts with fine time and frequency structure. A possible mechanism of drift pairs generation is proposed, according
to which this emission may originate from the interaction of Langmuir waves with the magnetosonic waves having equal phase
and group velocities. 相似文献
12.
Asta Pellinen-Wannberg Edmond Murad Gudmund Wannberg Assar Westman 《Earth, Moon, and Planets》2004,95(1-4):627-632
High Power Large Aperture (HPLA) radars generally observe very high meteor velocities averaging over 50 km s−1. There are only a few events recorded around 30 km s−1, while meteors at 20 km s−1 or slower are very rare. This is a clear and debated contradiction to specular meteor radar results. A high plasma density
condition contributes, but the dominating phenomenon is the hyperthermal ionization mechanism due to chemical dynamics of
the ionization process. The observed high velocities can be explained in terms of high hyperthermal ionization cross-sections
for collisions between ablated meteoroid metal atoms such as Na and/or Fe and atmospheric species. 相似文献
13.
Based on currently available observations of 28 maser sources in 25 star-forming regions with measured trigonometric parallaxes,
proper motions, and radial velocities, we have constructed the rotation curve of the Galaxy. Taking different distances to
the Galactic center R
0, we have estimated the peculiar velocity of the Sun, the angular velocity of Galactic rotation, and its three derivatives.
For R
0 = 8 kpc, we have found the circular velocity of the Sun to be V
0 = 243 ± 16 km s−1, which corresponds to a revolution period of 202 ± 10 Myr. We have obtained the Oort constants A = 16.9 ± 1.2 km s−1 kpc−1 and B = −13.5 ± 1.4 km s−1 kpc−1. Our simulation of the influence of a spiral density wave has shown that the peculiar velocity of the Sun with respect to
the local standard of rest and the component (V
⊙)LSR depend significantly on the Sun’s phase in the spiral wave. 相似文献
14.
Kenneth P. Dere 《Solar physics》1982,77(1-2):77-93
Extreme ultraviolet spectra of several active regions are presented and analyzed. Spectral intensities of 3 active regions observed with the NRL Skylab XUV spectroheliograph (170–630 Å) are derived. From this data density sensitive line ratios of Mg viii, Si x, S xii, Fe ix, Fe x, Fe xi, Fe xii, Fe xiii, Fe xiv, and Fe xv are examined and typically yield, to within a factor of 2, electron pressures of 1 dyne cm–2 (n
e
T = 6 × 1015 cm–3 K). The differential emission measure of the brightest 35 × 35 portion of an active region is obtained between 1.4 × 104 K and 5 × 106 K from HCO OSO-VI XUV (280–1370 Å) spectra published by Dupree et al. (1973). Stigmatic EUV spectra (1170–1710 Å) obtained by the NRL High Resolution Telescope and Spectrograph (HRTS) are also presented. Doppler velocities as a function of position along the slit are derived in an active region plage and sunspot. The velocities are based on an absolute wavelength scale derived from neutral chromospheric lines and are accurate to ±2 km s–1. Downflows at 105 K are found throughout the plage with typical velocities of 10 km s–1. In the sunspot, downflows are typically 5 to 20 km s–1 over the umbra and zero over the penumbra. In addition localized 90 and 150 km s–1 downflows are found in the umbra in the same 1 × 1 resolution elements which contain the lower velocity downflows. Spectral intensities and velocities in a typical plage 1 resolution element are derived. The velocities are greatest ( 10 km s–1) at 105 K with lower velocities at higher and lower temperatures. The differential emission measure between 1.3 × 104 K and 2 × 106 K is derived and is found to be comparable to that derived from the OSO-VI data. An electron pressure of 1.4 dynes cm–2 (n
e
T = 1.0 × 1016 cm–3 K) is determined from pressure sensitive line ratios of Si iii, O iv, and N iv. From the data presented it is shown that convection plays a major role in determining the structure and dynamics of the active region transition zone and corona. 相似文献
15.
H. Hamedivafa 《Solar physics》2008,250(1):17-29
An improved method of image segmentation is introduced. The object-tracking algorithm, originally developed by Sobotka, Brandt,
and Simon (Astron. Astrophys. 328, 682, 1997) is modified with special attentions on splitting and merging of umbral dots (UDs), definition of the umbral boundary, and
the birth-frames and the death-frames of UDs. By applying the new method of image segmentation and the object-tracking algorithm
on a 67-min series of white-light images of a large pore (Sobotka et al., Astrophys. J.
511, 436, 1999), the physical characteristics of 20 “resolved” UDs with umbral origin were recorded. The most probable lifetime of the UDs
is between 7 and 10 min. Umbral dots show a typical size of about 230 km. Their mean speeds are smaller than 2 km s−1 with a distribution around a value less than 1 km s−1. However, their average velocities are less than 0.8 km s−1. Brighter (fainter) UDs are formed in the brighter (dimmer) region of the pore. There is no correlation between time-averaged
area or time-averaged speeds and lifetimes. Also, the time-averaged peak intensities of UDs do not show any well-defined dependence
on the corresponding time-averaged areas. It seems that there is a relation between average velocities of UDs and their time-averaged
peak intensities, with brighter UDs moving more slowly. 相似文献
16.
An X2.3 class flare was reported on 10 April 2001 in AR 9415. A halo coronal mass ejection (CME) was associated with this flare. The Coronal Diagnostic Spectrometer (CDS) on board the Solar and Heliospheric Observatory (SOHO), which was running in its daily synoptic mode, recorded a very high-velocity ejection of plasma associated with this activity. The spatial scanning and spectral capabilities of CDS allow the measurement of both transverse and line-of-sight velocities. Components of the plasma, as seen in emission from Ov at around 2.5×105 K, reached transverse velocities in excess of 800 km s–1. The nature of the spectral line profiles suggests that a rotational motion of ±350 km s–1 was superimposed upon the general outward expansion of approximately 150 km s–1. The ejection detected using CDS was found to have a constant acceleration and is thought to be a spray of plasma with a helical structure driven by the magnetic topology. 相似文献
17.
The GMRTHI 21 cm-line observations of galaxies in the Eridanus group are presented. The Eridanus group, at a distance of ≈ 23 Mpc, is
a loose group of ≈200 galaxies. The group extends to more than 10 Mpc in projection. The velocity dispersion of the galaxies
in the group is ≈240 km s−1. The galaxies are clustered into different sub-groups. The overall population mix of the group is 30% (E + S0) and 70% (Sp
+ Irr). The observations of 57 Eridanus galaxies were carried out with the GMRT for ≈ 200 h. HI emission was detected from
31 galaxies. The channel rms of ≈ 1 mJy beam−1 was achieved for most of the image-cubes made with 4 h of data. The corresponding HI column density sensitivity (3σ) is ≈
1 × 1020 cm−2 for a velocity-width of ≈ 13.4 km s−1. The 3σ detection limit of HI mass is ≈ 1.2 X 107 Mpd for a line-width of 50 km s−1. Total HI images, HI velocity fields, global HI line profiles, HI mass surface densities, HI disk parameters and HI rotation
curves are presented. The velocity fields are analysed separately for the approaching and the receding sides of the galaxies.
These data will be used to study the HI and the radio continuum properties, the Tully-Fisher relations, the dark matter halos,
and the kinematical and HI lopsidedness in galaxies. 相似文献
18.
Based on spectra taken with a 6-m telescope, we analyzed the abundances of chemical elements in the He-weak stars HD 21699
and HD 217833, estimated their surface magnetic fields (Bs = 4000 and 4500 G, respectively) from the magnetic intensification of spectral lines, and determined their microturbulences
(V
t = 0.80 and 0.75 km s−1, respectively). The low values of V
t show that the stellar atmospheres are stabilized by a magnetic field, which explains the presence of diffusion processes
that lead to chemical anomalies. Helium is strongly underabundant, and its deficiency is −1.50 and −1.81 dex in HD 21699 and
HD 217833, respectively. We used model atmospheres to determine the effective temperatures, T
eff = 16 000 and 15 450 K, and surface gravities, log g = 4.15 and 3.88, for the stars from the Hδ line, implying that they lie on the main sequence near the stars of luminosity
class V. 相似文献
19.
Ionization equilibrium is a useful assumption which allows temperatures and other plasma properties to be deduced from spectral observations. Inherent to this assumption is the premise that the ion stage densities are determined solely by atomic processes which are local functions of the plasma temperature and electron density. However, if the time scale of plasma flow through a temperature gradient is less than the characteristic time scale for an important atomic process, deviations from the ionization stage densities expected for equilibrium will occur which could introduce serious errors into subsequent analyses. In the past few years, significant flow velocities in the upper solar atmosphere have been inferred from observations of emission lines originaing in the transition region (about 104–106 K) and corona. In this paper, three models of the solar atmosphere (quiet Sun, coronal hole, and a network model) are examined to determine if the emission expected from these model atmospheres could be produced from equilibrium ion populations when steady flows of several kilometers per second are assumed. If the flows are quasi-periodic instead of steady, spatial and temporal averaging inherent in the observations may allow for the construction of satisfactory models based on the assumption of ionization equilibrium. Representative emission lines are analysed for the following ions: C iii, iv, O iv, v, vi, Ne vii, viii, Mg ix, x, Si xii, and Fe ix–xiv. Two principle conclusions are drawn. First, only the iron ions are generally in equilibrium for steady flows of 20 km s–1. For carbon and oxygen, ionization equilibrium is not a valid assumption for steady flows as small as 1 km s–1. Second, the three models representing different solar conditions behave in a qualitatively similar manner, implying that these results are not particularly model dependent over the range of temperature gradients and electron densities thus far inferred for the Sun. In view of the flow velocities which have been reported for the Sun, our results strongly suggest caution in using the assumption of ionization equilibrium for interpreting spectral lines produced in the transition region.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
20.
We present an analysis of the evolution of the thermal flare plasma during the 14 July 2000, 10 UT, Bastille Day flare event,
using spacecraft data from Yohkoh/HXT, Yohkoh/SXT, GOES, and TRACE. The spatial structure of this double-ribbon flare consists of a curved arcade with some 100 post-flare
loops which brighten up in a sequential manner from highly-sheared low-lying to less-sheared higher-lying bipolar loops. We
reconstruct an instrument-combined, average differential emission measure distribution dEM(T)/dT that ranges from T=1 MK to 40 MK and peaks at T
0=10.9 MK. We find that the time profiles of the different instrument fluxes peak sequentially over 7 minutes with decreasing
temperatures from T≈30 MK to 1 MK, indicating the systematic cooling of the flare plasma. From these temperature-dependent relative peak times
t
peak(T) we reconstruct the average plasma cooling function T(t) for loops observed near the flare peak time, and find that their temperature decrease is initially controlled by conductive
cooling during the first 188 s, T(t)∼[1+(t/τcond)]−2/7, and then by radiative cooling during the next 592 s, T(t)∼[1−(t/τrad)]3/5. From the radiative cooling phase we infer an average electron density of n
e=4.2×1011 cm−3, which implies a filling factor near 100% for the brightest observed 23 loops with diameters of ∼1.8 Mm that appear simultaneously
over the flare peak time and are fully resolved with TRACE. We reproduce the time delays and fluxes of the observed time profiles
near the flare peak self-consistently with a forward-fitting method of a fully analytical model. The total integrated thermal
energy of this flare amounts to E
thermal=2.6×1031 erg.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1014257826116 相似文献