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1.
The temporal association between the kinematic parameters of chromospheric dark features (DF) and the production of radio type-III bursts is investigated during a period of five months. The Doppler shifts inside six different DF are measured by means of the Meudon Multichannel Subtracting Double Pass Spectrograph (MSDP) during periods of some minutes around 24 type-III bursts. The position of the radio bursts has been checked to be associated with the same active region observed by MSDP, by using the Nançay Radioheliograph. It appears that 23 out of 24 bursts take place when the DF is totally or predominantly blue-shifted. In 18 out of 21 cases, a maximum of the outward velocity is observed in the optical image closest in time to the radio burst. The following peculiarities are also shown by the analyzed DF:
- All of them present a lengthened shape, in most cases pointing toward a sunspot: a bright region coinciding with a parasitic polarity is observed in between.
- Horizontal velocities along the DF major axis are often observed, always in a direction opposite to the sunspots.
2.
During a coordinated SMY program, the consecutive formation of two new active centers merging together within AR 2646 was observed from 28 August, to 5 September, 1980. The two preceding spots compressed an inverse polarity spot on 1 September 1980, causing recurrent ejecta of matter with time intervals around 10 min. The observations of the MSDP spectrograph operating in H at the Meudon Solar tower and of the UVSP spectrometer on SMM in the Civ 1548 Å line show that cold and hot material had the same projection, although the upward Civ velocity structure was more extended than the H one. We present evidence that observed contrasts of the H absorbing structure can be interpreted in terms of a dynamic cloud model overlying the chromosphere. H matter follows a magnetic channel with upward velocity around 20–30 km s–1 in the first phase of the event and with downward velocity ( - 40 km s–1) in the second phase. The stored energy is not sufficient to trigger a flare, nor even to propulse matter along the full length of an arch, because of the periodic reorganisation of the magnetic field. 相似文献
3.
N. Mein 《Solar physics》1977,52(2):283-292
In order to precise previous results about wave propagation in the quiet chromosphere (N. Mein and P. Mein, 1976), we study the behaviour of Doppler shifts and intensity fluctuations in 3 lines of Ca ii. We use the same observation as in our previous work, that is to say a sequence of spectra lasting 27 mn, taken at Sacramento Peak Observatory solar tower. Results can be summarized as follows:
- Phase-lag between intensity fluctuations and dopplershifts is always near 90° in the Ca ii lines, even for frequencies as high as 15 mHz, and whatever is the location in the chromospheric network.
- Magneto-acoustic waves propagating vertically in a vertical or horizontal magnetic field could account for the observations only if they were, on one hand reflected in the upper atmosphere, on the other hand propagating with a very high sound or Alfvén speed. The lower limit for the speed (70 km s-1) does not seem to be realistic. Oblique waves could be investigated for better agreement.
4.
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
5.
6.
We analyze the role of weak photospheric flux concentrations that evolve in a filament channel, in the triggering of dynamic
changes in the shape of a filament. The high polarimetric sensitivity of THEMIS allowed us to detect weak flux concentrations
(few Gauss) associated with the filament development. The synoptic instruments (MDI, SOLIS) even if their sensitivity is much
less than THEMIS were useful to follow any subsequent strengthening of these flux concentrations after their identification
in the THEMIS magnetograms. We found that (1) the northern part of the filament develops an Hα barb at the same time that
weak minority polarity elements develop near a plage; (2) a section in the southern part of the Hα filament gradually disappears
and later reforms at the same time that several mixed-polarity magnetic elements appear, then subsequently cancel or spread
away from each other. These changes correspond to increases in EUV emission, as observed by TRACE, EIT, and CDS. This suggests
that the plasma is temporarily heated along the filament spine. An idealized sequence of force-free models of this filament
channel, based on plasma-supporting magnetic dips occurring in the windings of a very weakly twisted flux tube, naturally
explains the evolution of its southern part as being due to changes in the topology of the coronal magnetic field as the photospheric
flux concentrations evolve. 相似文献
7.
Hα observations, using the Multichannel Subtractive Double Pass (MSDP) spectrograph operating on the Meudon Solar Tower, have been made of an active region filament which undergoes a ‘disparition brusque’. The period of observation was from 10 ∶ 45 to 13 ∶ 30 UT on 22 June, 1981. Velocity and intensity fluctuations in Hα were measured. The proper motions of ejecta were followed allowing their trajectories and vector velocities to be determined. To model the dynamics of ejecta several models using thermal or magnetic driving forces are compared. The most promising model explains the motion as the consequence of magnetic stresses acting on an isolated magnetized plasmoïd in a diverging flux tube. 相似文献
8.
The material of Hispanomys decedens (Rodentia, Cricetodontinae) from La Grive-Saint Alban (France) is described in detail for the first time. H. decedens, which is one of the oldest species of the genus, shows the primitive character states that are typical of the Aragonian congeneric species, such as the mesolophs and labial cingula surrounding the upper molar valleys. The detailed examination of the teeth of H. decedens shows that this taxon is a good candidate ancestor for H. aragonensis. 相似文献
9.
Malherbe J. M. Schmieder B. Mein P. Mein N. Van Drielgesztelyi L. Von Uexküll M. 《Solar physics》1998,180(1-2):265-284
Using multi-wavelength observations obtained with the Tenerife telescopes (VTT and GCT) and with the Yohkoh satellite, we observed new emerging flux with an associated arch filament system (AFS) in the chromosphere and bright X-ray loops in the corona. We observed the change of connectivity of the X-ray loop footpoints which may be at the origin of the occurrence of a subflare. Densities, gas and magnetic pressures of cold AFS and hot loops were derived and discussed. The extrapolation of the photospheric magnetic field observed with the GCT in a linear force-free field assumption (constant ) shows that this region, in spite of having roughly a global potential configuration, consists of two systems of arch filaments. We found these two systems best fitted with two sheared magnetic topologies of opposite values of ± 0.1 Mm-1 相似文献
10.