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1.
Monte Carlo radiative transfer techniques are used to develop a height-dependent spicule model based upon a more realistic configuration than has hitherto been considered. The spicule is represented by a uniform cylinder, of finite length, standing vertically upon a plane chromosphere. The observed, limb-darkened, anisotropic chromospheric flux incident upon the cylinder is incorporated into the transfer calculations.The resulting model is characterized by a random, line broadening velocity of 20 km/sec, with electron temperature increasing from 6 × 103 K at the base to about 1.5 × 104 K at 11500 km above the solar surface. The corresponding values of electron density are 8 × 1011 cm-3 and 4 × 1010 cm-3. Contrast curves of the spicule model against the chromospheric background are computed and indicate that spicules should appear both bright and dark on the disk, depending upon their position with respect to the limb, the spectral frequency of observation and the viewing height.This work is based on a Ph.D. thesis submitted to the Department of Astro-Geophysics, University of Colorado.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
2.
Measurements of the electron density in 16 flares are summarized and discussed. For 13 of them the electron density has been determined by the halfwidth method discussed in Part I of this paper. In the flash phase of all disk flares of importance 1 + and higher the electron density exceeds 1013 cm–3 and increases with the flare importance. In the maximum of large flares the electron density exceeds 3 × 1013 cm–3 and declines to 1013 cm–3 and to lower values in about 20 minutes after the flash phase. In limb flares, i.e. higher than 5000 km above the solar limb, the electron density is lower than 5 × 1012 cm–3. This shows a decrease of the electron density in the flare elements situated in higher parts of the chromosphere. On the other hand, however, at least in some flares the electron density remains fairly constant within a wide range of height in the upper chromosphere and the low corona. 相似文献
3.
The properties of explosive events in the solar transition zone are presented by means of detailed examples and statistical analyses. These events are observed as regions of exceptionally high velocity ( 100 km s–1) in profiles of Civ, formed at 105 K, observed with the High Resolution Telescope and Spectrograph (HRTS). The following average properties have been determined from observations obtained during the third rocket flight of the HRTS: full width at half maximum extent along the slit - 1.6 × 103 km; maximum velocity - 110 km s–1; peak emission measure - 4 × 1041 cm–3; lifetime - 60 s; birthrate - 4 × 10–21 cm–2 s–1 in a coronal hole and 1 × 10–20 cm–2 s–1 in the quiet Sun; mass - 6 × 108 g; and, kinetic energy - 6 × 1022 erg. The 6 examples show that there are considerable variations from these average parameters in individual events. Although small, the events show considerable spatial structure and are not point-like objects. A spatial separation is often detected between the positions of the red and blue shifted components and consequently the profile cannot be explained by turbulence alone. Mass motions in the events appear to be isotropic because the maximum observed velocity does not show any correlation with heliographic latitude. Apparent motions of the 100 km s–1 plasmas during their 60 s lifetime should be detected but none are seen. The spatial frequency of occurrence shows a maximum near latitudes of 40–50°, but otherwise their sites seem to be randomly distributed. There is enough mass in the explosive events that they could make a substantial contribution to the solar wind. It is hard to explain the heating of typical quiet structures by the release of energy in explosive events. 相似文献
4.
O vi ( = 1032 Å) profiles have been measured in and above a filament at the limb, previously analyzed in H i, Mg ii, Ca ii resonance lines (Vial et al., 1979). They are compared to profiles measured at the quiet Sun center and at the quiet Sun limb.Absolute intensities are found to be about 1.55 times larger than above the quiet limb at the same height (3); at the top of the prominence (15 above the limb) one finds a maximum blue shift and a minimum line width. The inferred non-thermal velocity (29 km s–1) is about the same as in cooler lines while the approaching line-of-sight velocity (8 km s–1) is lower than in Ca ii lines.The O vi profile recorded 30 above the limb outside the filament is wider (FWHM = 0.33 Å). It can be interpreted as a coronal emission of O vi ions with a temperature of about 106 K, and a non-thermal velocity (NTV) of 49 km s–1. This NTV is twice the NTV of quiet Sun center O vi profiles. Lower NTV require higher temperatures and densities (as suggested by K-coronameter measurements). Computed emission measures for this high temperature regime agree with determinations from disk intensities of euv lines. 相似文献
5.
The analysis of two active regions on the limb using observations from SOHO-CDS allows us to determine the electron density and temperature distribution of the coronal emission. We find that the active regions have hot cores (3×106 K) with larger cooler (106 K) loop structures extending above the limb. The electron number density, determined using the Si X diagnostic line ratio, is found to be highest in the active region core (greater than 2.3×109 cm–3). Electron number density values are determined for a range of spectral lines from different ions and are found to increase with temperature between 0.8 and 2.5×106 K. These results are consistent with recent models of enhanced heating along the compact core of active regions, where the magnetic field shear is strongest. 相似文献
6.
The Ultraviolet Spectrometer Experiment on the MARINER 10 spacecraft measured the hydrogen Lyman α emmission resonantly scattered in the Venus exosphere at several viewing aspects during the encounter period. Venus encounter occurred at 17:01 GMT on 5 February 1974. Exospheric emissions above the planet's limb were measured and were analyzed with a spherically symmetric, single scattering, two-temperature model. On the sunlit hemisphere the emission profile was represented by an exospheric hydrogen atmosphere with Tc = 275±50 K and nc = 1.5 × 105 cm?3 and a non-thermal contribution represented by TH = 1250±100 K with nH = 500±100 cm?3. The observations of the dark limb showed that the spherically symmetric model used for the sunlit hemisphere was inappropriate for the analysis of the antisolar hemisphere. The density of the non-thermal component had increased at low altitudes, < 12,000 km, and decreased at high altitudes, > 20,000 km, by comparison. We conclude that the non-thermal source is on the sunward side of the planet. Analysis of the dark limb crossing suggests that the exospheric temperature on the dark side is <125 K if the exospheric density remains constant over the planet; upper limits are discussed. An additional source of Lyman α emission, 70 ± 15 R, was detected on the dark side of the planet and is believed to be a planetary albedo in contrast to multiple scattering from the sunlit side. Our analysis of the MARINER 10 data is consistent when applied to the MARINER 5 data. 相似文献
7.
J. P. Vallée 《Astrophysics and Space Science》1987,137(2):217-224
Line observations of the methylidyne (CH) molecule were performed at Algonquin, toward the reflection nebula vdB102. An analysis of the molecular cloud behind vdB102 yielded several envelope parameters, notably a CH column density of 1×1013 cm–2, a microtubulent velocity of 1.4 km s–1, and a total space density of 1300 cm–3. These observed data are consistent with a stationary reflection nebula roughly facing the earth, located on the near side of the surface of a compact molecular cloud. 相似文献
8.
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
9.
J. P. Vallée 《Astrophysics and Space Science》1987,139(1):129-137
Methylidyne (CH) line observations were obtained at Algonquin from the diffuse molecular cloud envelope at G180.9+4.1, sandwiched between the optical H II region S241 and the molecular cloud core at G180.8+4.0. An analysis of these observations yields several of the envelope parameters, notably a CH column density of 2×1013 cm–2, a microturbulent velocity of 2.6 km s–1, and a total space density of 40 cm–3. 相似文献
10.
J.E. Hall 《Planetary and Space Science》1973,21(1):119-131
Electron densities throughout the D- and E-regions of the ionosphere have been measured during two rocket flights from Woomera, Australia; one in the daytime and one at night. The detailed distributions have a height resolution of much better than a km over the majority of the height range which was 66–175 km on the day flight and 83–184 km at night. This resolution has enabled sharp changes in electron density to be observed such as those associated with positive ion changes near 85 km (Reid 1970) and with sporadic-E layers.The detail and large dynamic range in electron density (102 to 3 × 105 cm?3) were achieved by combining the data from an LF radio propagation experiment with those from a probe experiment. The radio equipment allowed measurement of both the phase and amplitude of the wavefield above a ground transmitter. The method of deducing electron density from the phase velocity of the penetrating component of the wavefield is explained in detail. A comparison of the probe current and electron density has shown that the ratio between them varies slowly with height. 相似文献
11.
Profiles of C iii
1909 and Si iii
1892 obtained on and near the limb during the 1976 flight of the University of Hawaii echelle rocket spectrograph were reduced and analyzed to determine electron densities and mass motions. The electron pressure derived (N
eTe 4 × 1015 cm–3) agrees well with that determined by Cook and Nicolas (1979) from ATM data. Nonthermal velocities in the region of formation of Si iii
1892 on the disk were found to be 10–12 km s–1, somewhat lower than the values obtained by Doschek et al. (1976), also from ATM spectra. However, velocities derived at and above the limb were in closer agreement, about 17 km s–1.Geosciences Systems Department, Computer Sciences Corporation, 8728 Colesville Road, Silver Spring, Md. 20910, U.S.A. 相似文献
12.
Jagdev Singh Takashi Sakurai Kiyoshi Ichimoto S. Muneer A. V. Raveendran 《Solar physics》2006,236(2):245-262
With a view to investigate variations in parameters of coronal emission lines over a large range of radial distance from the limb, raster scans were made with sufficiently long exposure times on several days during September – October 2003. An analysis of the data shows that (i) in most of the coronal structures, the FWHM of the Fe xiv 5303 Å line decreases up to 300″±50″, (ii) the FWHM of the Fe x 6374 Å line increases up to about 200″ and then remains unchanged up to about 500″, and (iii) the FWHMs of the Fe xi 7892 Å and Fe xiii 10747 Å lines show an intermediate behaviour with height. The analysis of the data also shows that the ratio of FWHM of 6374 Å to that of 5303 Å increases from 0.93 at the limb to 1.18 at 200″ above the limb. From this and the ratio of intensities of the two lines we infer that the plasma in steady coronal structures at a height of about 200″ has a temperature of about 1.5 MK and a non-thermal velocity around 17 km s?1. The observations also show that non-homogeneous temperatures and non-thermal velocities largely exist in the lower corona up to about 300″±100″ above the limb. Amplitudes of variations in FWHM of different emission lines with height in the coronal loops are similar to those in the diffuse plasma around the coronal loops. 相似文献
13.
New results concerning prominence observations and in particular the prominence–corona transition region (PCTR) are presented. In order to cover a temperature range from 2 × 104 to 7 × 105 K, several emission lines in many different ionization states were observed with SUMER and CDS on board SOHO. EM and DEM were measured through the whole PCTR. We compared the prominence DEM with the DEM from other solar structures (active region, coronal hole and the chromosphere–corona transition region (CCTR)). We notice a displacement of the prominence DEM minimum towards lower temperatures with respect to the minimum of the other structures. Electron density and pressure diagnostics have been made from the observed C III lines. Local electron density and pressure for T ∼ 7 × 104 K are respectively log N
e = 9.30−0.34
+0.30 and 0.0405−0.014
+0.012. Extrapolations over the entire PCTR temperature range are in good agreement with previous SOHO results (Madjarska et al., 1999). We also provide values of electron density and pressure in two different regions of the prominence (center and edge). The Doppler velocity in the PCTR shows a trend to increase with temperature (at least up to 30 km s -1 at T ∼ 7 × 104 K), an indication of important mass flows. A simple morphological model is proposed from density and motion diagnostics. If the prominence is taken as a magnetic flux tube, one can derive an opening of the field lines with increasing temperature. If the prominence is represented as a collection of threads, their number increases with temperature from 20 to 800. Derived filling factors can reach values as low as 10−3 for a layer thickness of the order of 5000 km. The variation of non-thermal velocities is determined for the first time, in the temperature range from 2 × 104 to 7 × 105 K. The quite clear similarity with the CCTR non-thermal velocities would indicate that heating mechanisms in the PCTR could be the same as in the CCTR (wave propagation, turbulence MHD). 相似文献
14.
New results concerning prominence observations and in particular the prominence–corona transition region (PCTR) are presented. In order to cover a temperature range from 2 × 104 to 7 × 105 K, several emission lines in many different ionization states were observed with SUMER and CDS on board SOHO. EM and DEM were measured through the whole PCTR. We compared the prominence DEM with the DEM from other solar structures (active region, coronal hole and the chromosphere–corona transition region (CCTR)). We notice a displacement of the prominence DEM minimum towards lower temperatures with respect to the minimum of the other structures. Electron density and pressure diagnostics have been made from the observed C III lines. Local electron density and pressure for T ∼ 7 × 104 K are respectively log N
e = 9.30−0.34
+0.30 and 0.0405−0.014
+0.012. Extrapolations over the entire PCTR temperature range are in good agreement with previous SOHO results (Madjarska et al., 1999). We also provide values of electron density and pressure in two different regions of the prominence (center and edge). The Doppler velocity in the PCTR shows a trend to increase with temperature (at least up to 30 km s -1 at T ∼ 7 × 104 K), an indication of important mass flows. A simple morphological model is proposed from density and motion diagnostics. If the prominence is taken as a magnetic flux tube, one can derive an opening of the field lines with increasing temperature. If the prominence is represented as a collection of threads, their number increases with temperature from 20 to 800. Derived filling factors can reach values as low as 10−3 for a layer thickness of the order of 5000 km. The variation of non-thermal velocities is determined for the first time, in the temperature range from 2 × 104 to 7 × 105 K. The quite clear similarity with the CCTR non-thermal velocities would indicate that heating mechanisms in the PCTR could be the same as in the CCTR (wave propagation, turbulence MHD). 相似文献
15.
G. M. Simnett S. J. Tappin S. P. Plunkett D. K. Bedford C. J. Eyles O. C. St. Cyr R. A. Howard G. E. Brueckner D. J. Michels J. D. Moses D. Socker K. P. Dere C. M. Korendyke S. E. Paswaters D. Wang R. Schwenn P. Lamy A. Llebaria M. V. Bout 《Solar physics》1997,175(2):685-698
Two coronal mass ejections have been well observed by the LASCO coronagraphs to move out into the interplanetary medium as
disconnected plasmoids. The first, on July 28, 1996, left the Sun above the west limb around 18:00 UT. As it moved out, a
bright V-shaped structure was visible in the C2 coronagraph which moved into the field-of-view of C3 and could be observed
out to beyond 28 solar radii. The derived average velocity in the plane of the sky was 110 ± 5 km s-1 out to 5 solar radii, and above 15 solar radii the velocity was 269 ± 10 km s-1. Thus there is evidence of some acceleration around 6 solar radii. The second event occurred on November 5, 1996 and left
the west limb around 04:00 UT. The event had an average velocity in the plane of the sky of ∼54 km s-1 below 4 R⊙, and it accelerated rapidly around 5 R⊙ up to 310 ± 10 km s-1. In both events the rising plasmoid is connected back to the Sun by a straight, bright ray, which is probably a signature
of a neutral sheet. In the November event there is evidence for multiple plasmoid ejections. The acceleration of the plasmoids
around a projected altitude of 5 solar radii is probably a manifestation of the source surface of the solar wind.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004994214697 相似文献
16.
J. B. Smith Jr. D. M. Speich R. M. Wilson E. Tandberg-Hanssen S. T. Wu 《Solar physics》1977,52(2):379-391
Skylab soft X-ray observations of two lower coronal limb events and corresponding H observations (Skylab and ground-based) are analyzed. We discuss the morphology and evolution of an eruptive prominence occurring on 21 August 1973, beginning (in H) at about 1300 UT and of a surge on 4 December 1973, beginning at about 1758 UT. For the eruptive prominence, measured X-ray flux is used in the determination of line-of-sight temperatures, emission measures, and electron densities. A peak temperature of 8.5 × l06 K and densities to 3.5 × l09 cm-3 are derived. A time-dependent, two-dimensional, single-fluid magnetohydrodynamic computer code has been used to simulate the coronal response to these prominences. We find that the coronal response to the observed eruptive prominence may be simulated with a density-dominated pressure pulse at the base of the corona ( 30000 km above photosphere), while a temperature pulse of short duration will simulate the coronal response to the surge. Approximately 1031 ergs and 1040 particles (or 1016 g) were deposited into the corona during the eruptive prominence event, while about 1029 ergs and 1038 particles (or 1014 g) were injected during the surge event. A shock wave formed ahead of the ejected material at about 70000 km above the photosphere in the eruptive prominence event and had a velocity of 275 km s-1 at 1.5 r
above the limb.Presently at NASA / Marshall Space Flight Center. 相似文献
17.
Spectra of Hα, Hβ and Hδ have been taken under good seeing conditions with the vacuum tower telescope of Sacramento Peak Observatory. Intensity curves are given at various wavelengths in these lines to permit further comparison with a theoretical model. Moreover, considering in each case the range of height in which the lines are almost optically thin and using a few approximations, the following results are derived: between 2000 and 6000 km above the limb the average thermal + turbulent velocity of the atoms is found to increase from 20 km s?1 to 30 km s?1 and the mean number of hydrogen atoms per cm3 in level 2 is given by $$\log n_2 {\text{ = }}4.5{\text{ }} - {\text{ 0}}{\text{.00056(}}z - 2000)$$ z being the altitude above the limb in km. For line profile computations a new interpolation formula is presented; it gives good profiles with a small number of scans, saving microphotometer time. 相似文献
18.
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
19.
A large surge event appearing in AR 5395 was observed at the Yunnan Observatory on March 19, 1989. H spectral profiles of the event are interpreted by using a two-cloud model and the contours of three parameters: excitation temperature, T
exc, microturbulent velocity, V
t
,and column density of hydrogen atoms at the second level, N
0,2, are obtained, respectively. The question about the unique feature of the solution obtained by the fitting method is also discussed. The results show that the surge is composed of some conglomerated materials with higher temperature and density; the mass ejection is probably intermittent. Neither T
exc nor N
0,2 vary with the height over the solar limb but decrease from the center to the periphery of the surge. V
t
varies from 10 to 30 km s-1 and decreases with height. Some other important parameters, such as electron density, n
e
,and electron pressure, P
e
,etc., have also been estimated. In the surge, with N
0,2 about 2.0 × 1012 cm-2 and T
exc about 8500 K on average, we obtained n
e
= 1.80 × 1010 cm-3 and P
e
= 0.023 dyn cm-2. The energy variations of the surge during the ascending phase are estimated. 相似文献
20.
The UCSD solar X-ray instrument on the OSO-7 satellite observes X-ray bursts in the 2–300 keV range with 10.24 s time resolution. Spectra obtained from the proportional counter and scintillation counter are analyzed for the event of November 16, 1971, at 0519 UT in terms of thermal (exponential spectrum) and non-thermal (power law) components. The energy content of the approximately 20 × 106K thermal plasma increased with the 60 s duration hard X-ray burst which entirely preceded the 5 keV soft X-ray maximum. If the hard X-rays arise by thick target bremsstrahlung, the nonthermal electrons above 10 keV have sufficient energy to heat the thermally emitting plasma. In the thin target case the collisional energy transfer from non-thermal electrons suffices if the power law electron spectrum is extrapolated below 10 keV, or if the ambient plasma density exceeds 4 × 1010 cm–3.Formerly at UCSD. 相似文献