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1.
We have obtained spectroscopic observations in coronal emission lines by choosing two lines simultaneously, one [Fe x] 6374 Å and the other [Fe xi] 7892 Å or [Fe xiii] 10747 Å or [Fe xiv] 5303 Å. We found that in 95 per cent of the coronal loops observed in 6374 Å, the FWHM of the emission line increases with height above the limb irrespective of the size, shape and orientation of the loop and that in case of 5303 Å line decreases with height in about 89 per cent of the coronal loops. The FWHM of 7892 Å and 10747 Å emission lines show intermediate behavior. The increase in the FWHM of 6374 Å line with height is the steepest among these four lines. We have also studied the intensity ratio and ratio of FWHM of these lines with respect to those of 6374 Å as a function height above the limb. We found that the intensity ratio of 7892 Å and 10747 Å lines with respect to 6374 Å line increases with height and that of 5303 Å to 6374 Å decreases with height above the limb. This implies that temperature in coronal loops will appear to increase with height in the intensity ratio plots of 7892 Å and 6374 Å; and 10747 Å and 6374 Å whereas it will appear to decrease with height in intensity ratio of 5303 Å to 6374 Å lineversus height plot. These findings are up to a height of about 200 arcsec above the limb. The varying ratios with height indicate that relatively hotter and colder plasma in coronal loops interact with each other. Therefore, the observed increase in FWHM with height above the limb of coronal emission lines associated with plasma at about 1 MK may not be due to increase in non-thermal motions caused by coronal waves but due to interaction with the relatively hotter plasma. These findings also do not support the existing coronal loop models, which predict an increase in temperature of the loop with height above the limb.  相似文献   

2.
Cinematographic observations of the slitless flash spectrum near the D3 helium line were performed in Yurgamysh at the total solar eclipse of September 22, 1968. The intensity distribution of the D3 line was obtained with a height resolution of 44 km within the height interval between –3400 and +1700 km above the limb. The absorption line D3 on the disk near the limb was discovered.  相似文献   

3.
The unresolved corona for three active regions (ARs) above the solar limb is investigated. Intensities measured for ions formed above 1 MK are presented as a function of height above the solar surface. The observed decrease in intensity with altitude is found to be best fit by an exponential. Furthermore, this exponential decrease is approximately the decrease in emission expected for a hydrostatic planar geometry atmosphere, where the scale height temperature is dependent on the dynamics of the AR. For two of the ARs analyzed, we have found that the best-fit temperature derived from the exponential fits is consistent with an isothermal hydrostatic unresolved corona.  相似文献   

4.
Analysis of three spectra of the exosphere of Mercury in the Na-D lines are presented. Spectra were secured with the high-resolution spectrograph (SARG) of the 3.5 M Telescopio Nazionale Galileo (TNG, located on the Roque de los Muchachos, Canaries) on the evenings of August 23 and 24, 2002. Spectra have resolution ; the slit length was 26.7”. The Na column abundances range from 4.3 to with the highest abundances being close to the illuminated limb. Our observations at true anomaly angles (TAA) from 171°to 174°show the traces of the emission lines to be strongly peaked at the illuminated limb, supportive of recent modeling that shows thermal desorption to be a strong factor in determining the distribution of Na about the planet.  相似文献   

5.
A method is presented for the direct measurement of the heights of the radio emission of solar active regions when they are located at the limb in order to reconstruct the vertical structure of the magnetic field in solar active regions. The method involves an analysis of radio source positions in the scans based on high frequency resolution one-dimensional centimeter-wave measurements performed on the RATAN-600 radio telescope. Radio sources are difficult to identify at many frequencies when observed at the limb at zero position angle because of abrupt signal variations at the solar limb. To eliminate edge effects on the scan, special observing periods are used (near vernal and autumnal equinoxes), when the source at the limb is located far from the scan edge because of the large position angle of the Sun. As a result of these observations, the spectra of relative heights are constructed for a number of sources for the period from 2007 through 2012. Source heights are shown to generally increase with wavelength. The height difference between the 5 and 2 cm emission is equal to 5.2 ± 2.0 Mm, and the corresponding height difference between the 8 and 2 cm emission is equal to 9.6 ± 3.0 Mm. It is shown that such characteristics can be obtained for a field generated by a dipole submerged under the photosphere at a depth of 17 Mm irrespective of the possible reduction of relative altitudes to absolute altitudes.  相似文献   

6.
Filtergrams of the limb show the He i D3 chromosphere as a shell which is separated from the limb by a gap. The height of maximum D3 contribution occurs at about 1350 km above the limb and is independent of the intensity of the D3 emission. We interpret this effect as the height to which coronal EUV radiation is capable of penetrating the atmosphere.  相似文献   

7.
Ultraviolet (UV) nightglow data from the SPICAV instrument (SPectroscopy for the Investigation of the Characteristics of the Atmosphere of Venus) onboard the Venus Express spacecraft, currently in orbit around Venus, are presented. In its extended source mode, SPICAV has shown that the Venus nightglow in the UV contains essentially Lyman-α and Nitric Oxide (NO) emissions. In the stellar mode, when the slit of the spectrometer is removed, an emission is also observed at the limb in addition to the stellar spectrum. A forward model allows us to identify this feature as being an NO emission. Due to radiative recombination of N and O atoms produced on the dayside of Venus, and transported to the nightside, NO nightglow provides important constraints to the Solar-to-Anti Solar thermospheric circulation prevailing above 90 km. The forward model presented here allows us to derive the altitude of the peak of emission of the NO layer, found at 113.5±6 km, as well as its scale height, of 3.4±1 km and its brightness. The latter is found to be very variable with emissions between 19 Kilo-Rayleigh (kR) and 540 kR. In addition, the NO nightglow is sometimes very patchy, as we are able to observe two distinct emission zones in the field of view. Finally, systematic extraction of this emission from stellar occultations extends the database of the NO emission already reported elsewhere using limb observations.  相似文献   

8.
Mars Global Surveyor (MGS) visible (solarband bolometer) and thermal infrared (IR) spectral limb observations from the Thermal Emission Spectrometer (TES) support quantitative profile retrievals for dust opacity and particle sizes during the 2001 global dust event on Mars. The current analysis considers the behavior of dust lifted to altitudes above 30 km during the course of this storm; in terms of dust vertical mixing, particle sizes, and global distribution. TES global maps of visible (solarband) limb brightness at 60 km altitude indicate a global-scale, seasonally evolving (over 190-240° solar longitudes, LS) longitudinal corridor of vertically extended dust loading (which may be associated with a retrograde propagating, wavenumber 1 Rossby wave). Spherical radiative transfer analysis of selected limb profiles for TES visible and thermal IR radiances provide quantitative vertical profiles of dust opacity, indicating regional conditions of altitude-increasing dust mixing ratios. Observed infrared spectral dependences and visible-to-infrared opacity ratios of dust scattering over 30-60 km altitudes indicate particle sizes characteristic of lower altitudes (cross-section weighted effective radius, ), during conditions of significant dust transport to these altitudes. Conditions of reduced dust loading at 30-60 km altitudes present smaller dust particle sizes . These observations suggest rapid meridional transport at 30-80 km altitudes, with substantial longitudinal variation, of dust lifted to these altitudes over southern hemisphere atmospheric regions characterized by extraordinary (m/s) vertical advection velocities. By LS=230° dust loading above 50 km altitudes decreased markedly at southern latitudes, with a high altitude (60-80 km) haze of fine (likely) water ice particles appearing over 10°S-40°N latitudes.  相似文献   

9.
Hale region 16898 was observed by the Westerbork Synthesis Radio Telescope at 6 cm and by the Ultraviolet Spectrometer and Polarimeter and the X-Ray Spectrometer on the Solar Maximum Mission satellite. Optical pictures of the same active region were taken at Sacramento Peak, Big Bear, and Meudon Observatories. The radio emission mechanisms are identified by comparing radio data with ultraviolet and soft X-ray data. The height of the radio sources and the magnetic field strength at that height are deduced. A radio source above a large sunspot shows a crescent shaped depression of circular polarization and a high brightness temperature. The emission mechanism is identified as gyroresonance at the second and the third harmonic layers and it is found that the second harmonic layer, where the magnetic field strength is 900 G, must be in the corona. An extended loop-like source connecting the leading and the following part of the active region as well as the sources associated with small spots are mainly due to thermal free-free emission by hot and dense plasma which is also observed in ultraviolet and soft X-ray radiation. The calculated radio brightness temperature, using the physical parameters deduced from the ultraviolet and soft X-ray line intensities, agrees with the observed brightness temperature. The height of the low brightness temperature sources above the small spots is 6000 ± 3000 km and that above the large spot is less than 3000 km: the source above the large spot does not show any shift relative to the sunspot due to the projection effect. Very strong radio emission was found which was associated with the merging of a group of small spots into the large sunspot. In the same day, warm ( 106 K) and dense matter was present above the large spot. Evidence for nonthermal emission is presented.  相似文献   

10.
A line to continuum ratio of the green line equal to 2.1 Å was measured above the West limb at the height p = 1.75 solar radii during the eclipse. The lower limit to the abundance of iron relative to hydrogen obtained from these measurements is 4 × 10–5.  相似文献   

11.
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   

12.
First observations of the full Stokes vector in the upper chromosphere are presented. The He I 10830 Å line, which has been shown to give reliable measurements of the line-of-sight component of the magnetic field vector, has been used for this purpose. It is shown that the difference between the appearance of chromospheric and photospheric magnetic structures observed close to the solar limb is largely due to the difference in height to which they refer and projection effects. The observations do suggest, however, that the magnetic field above sunspot penumbrae is somewhat more vertical in the chromosphere than in the photosphere.The National Optical Astronomy Obervatories are operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation  相似文献   

13.
Niot  J. M.  Noëns  J. C. 《Solar physics》1997,173(1):53-66
A daily survey of cool material evolution in the inner parts of the solar corona is now performed at the Pic-du-Midi observatory with an H imaging coronagraph. The total field of the coronagraph allows the detection of emission regions all around the solar limb, up to 0.6 solar radius above the limb. This survey is devoted to the study of coronal events and mass motions in a large range of spatial and time scales. The observing modes are associated with a set of numerical treatment processes to produce images which are calibrated in intensity relative to the solar brightness. Position angles and height above the solar limb of the coronal features are determined. Methods of calibration, sky brightness subtraction, and detection of events are discussed.  相似文献   

14.
This work investigates a typical coronal mass ejection (CME) observed on 2003 February 18, by various space and ground instruments, in white light, Ha, EUV and X-ray. The Ha and EUV images indicate that the CME started with the eruption of a long filament located near the solar northwest limb. The white light coronal images show that the CME initiated with the rarefaction of a region above the solar limb and followed by the formation of a bright arcade at the boundary of the rarefying region at height 0.46 R(?) above the solar surface. The rarefying process synchronized with the slow rising phase of the eruptive filament, and the CME leading edge was observed to form as the latter started to accelerate. The lower part of the filament brightened in Ha as the filament rose to a certain height and parts of the filament was visible in the GOES X-ray images during the rise. These brightenings imply that the filament may be heated by the magnetic reconnection below the filament in the early stage of the eruption. We suggest that a possible mechanism which leads to the formation of the CME leading edge and cavity is the magnetic reconnection which takes place below the filament after the filament has reached a certain height.  相似文献   

15.
The European Space Agency’s Rosetta spacecraft, en route to a 2014 encounter with comet 67P/Churyumov-Gerasimenko, made a gravity assist swing-by of Mars on 25 February 2007, closest approach being at 01:54 UT. The Alice instrument on board Rosetta, a lightweight far-ultraviolet imaging spectrograph optimized for in situ cometary spectroscopy in the 750-2000 Å spectral band, was used to study the daytime Mars upper atmosphere including emissions from exospheric hydrogen and oxygen. Offset pointing, obtained five hours before closest approach, enabled us to detect and map the H i Lyman-α and Lyman-β emissions from exospheric hydrogen out beyond 30,000 km from the planet’s center. These data are fit with a Chamberlain exospheric model from which we derive the hydrogen density at the 200 km exobase and the H escape flux. The results are comparable to those found from the Ultraviolet Spectrometer experiment on the Mariner 6 and 7 fly-bys of Mars in 1969. Atomic oxygen emission at 1304 Å is detected at altitudes of 400-1000 km above the limb during limb scans shortly after closest approach. However, the derived oxygen scale height is not consistent with recent models of oxygen escape based on the production of suprathermal oxygen atoms by the dissociative recombination of .  相似文献   

16.
Autocorrelation analyses of K-coronameter observations made at Haleakala and Mauna Loa, Hawaii, during 1964–1967 have established average yearly rotation rates of coronal features as a function of latitude and height above the limb. At low latitudes the corona was found to rotate at the same rate as sunspots but at higher latitudes was consistently faster than the underlying photosphere. There were differences as large as 3–4% in the rate at specific latitudes from year to year and between the two hemispheres. In 1967 a nearly constant rotation was found for heights ranging from 1.125 to 2.0 R 0. For 1966 there was a more complicated pattern of height dependence, with the rate generally decreasing with height at low latitudes and increasing at high latitudes.At Hawaii Institute of Geophysics.  相似文献   

17.
Simultaneous X-ray images in hard (20–40 keV) and softer (6.5–15 keV) energy ranges were obtained with the hard X-ray telescope aboard the Hinotori spacecraft of an impulsive solar X-ray burst associated with a flare near the solar west limb.The burst was composed of an impulsive component with a hard spectrum and a thermal component with a peak temperature of 2.8 × 107 K. For about one minute, the impulsive component was predominant even in the softer energy range.The hard X-ray image for the impulsive component is an extended single source elongated along the solar limb, rather steady and extends from the two-ribbon H flare up to 104 km above the limb. The centroid of this source image is located about 10 (7 × 103 km) ± 5 above the neutral line. The corresponding image observed at the softer X-rays is compact and located near the centroid of the hard X-ray image.The source for the thermal component observed in the later phase at the softer X-rays is a compact single source, and it shows a gradual rising motion towards the later phase.  相似文献   

18.
David Wallach  Bruce Hapke 《Icarus》1985,63(3):354-373
The problem of the reflection of light from an optically thick, spherical atmosphere in which the scatterers are distributed exponentially with a scale height small compared to the radius of the planet is discussed. Exact formal solutions are obtained for the single scattered component. Useful approximate analytic solutions, which also include multiply scattered light, are given. The results are applied to the analysis of the Mariner 10 limb and terminator images of Venus. The altitude of the “detached” haze layer discovered by Mariner 10 is at 79–85 km, but in places the haze exists above 100 km. This layer apparently is a stable, planetwide feature which forms at the top of the Pioneer Venus upper haze layer. It was similar in location, scale height, and thickness at the times of the two missions, in contrast to the lower, high-altitude haze which changed dramatically. We discuss two possibilities for the nature of the limb hazes. (1) The lower haze is probably the sulfuric acid cloud and the “detached” layer may be a separate water-ice haze. (2)The “detached” haze layer may not be separate at all, but part of the sulfuric acid haze, and the apparent “gap” at 75–80 km may be the source region of a broadband absorber. The spatial distribution of the strong near-UV absorber, which may be elemental sulfur as first suggested by B. Hapke and R. Nelson (1975, J. Atmos. Sci.32, 1212–1218), is examined in light of our results. Several arguments indicate that there is no nonabsorbing, overlying haze and that the UV absorber extends to the top of the haze 8layer.  相似文献   

19.
Spectroheliograms were obtained in bands centred at 1.2 mm, 0.8 mm and 0.4 mm wavelength during 1969 and 1971. In order to obtain photometrically valid data, a specialized set of reduction techniques was employed, obviating the effects of severe differential attenuation across the disc by atmospheric water vapour and of emission noise from the atmosphere, before taking out the instrumental spread functions of the telescope and detector.Comparison of our maps with those of other observers at 3 mm and 8.6 mm wavelength suggests that the chromospheric brightness temperature increments above active regions show a monotonic increase with increasing height above the photosphere over the normal increase in brightness temperature in the quiet chromosphere. Within the limit of angular resolution of 3 available, no evidence was recorded of normal limb brightening in our three passbands but the presence of isophotes at 50% of the central disc temperature consistently circumscribing the optical limb implies a narrow spike of sub-millimetre brightening close to the limb.  相似文献   

20.
This work investigates the spatial relation between coronal X-ray sources and coherent radio emissions, both generally thought to be signatures of particle acceleration. Two limb events were selected during which the radio emission was well correlated in time with hard X-rays. The radio emissions were of the type of decimetric pulsations as determined from the spectrogram observed by Phoenix-2 of ETH Zurich. The radio positions were measured from observations with the Nançay Radioheliograph between 236 and 432 MHz and compared to the position of the coronal X-ray source imaged with RHESSI. The radio pulsations originated at least 30?–?240 Mm above the coronal hard X-ray source. The altitude of the radio emission increases generally with lower frequency. The average positions at different frequencies are on a line pointing approximately to the coronal hard X-ray source. Thus, the pulsations cannot be caused by electrons trapped in the flare loops, but are consistent with emission from a current sheet above the coronal source.  相似文献   

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