Engineering topics

Simon, G.

Publications and source records attributed to Simon, G..

13 records

NASA NTRS1987

Closed magnetic structures in the chromosphere and in the transition region

Using simultaneous observations of the same solar regions in the lines H-alpha and C IV 1548 A, schematic models of closed magnetic lines have been derived from dynamical constraints. It is concluded that the magnetic loops are closed at higher levels above facular than above nonfacular regions. This result remains valid whatever are the assumed density models and even if the 3-min oscillations are taken into account. The center-to-limb behavior is well predicted by taking into account the relative opacity in the chromosphere and transition region.

Malherbe, J. M.↗

NASA NTRS1987

On the onset of eruptive prominences and coronal transients

During the Maximum Year, preflare and preeruptive phenomena have been observed which give a new idea on the association of eruptive prominences and coronal transients. The propagation of a C IV brightening through a prominence is related to the onset of a MHD wave. It is followed by the activation of the prominence and its eruption some two hours later. A coronal transient is observed above 1.6 R(s). It is argued that the eruption of the prominence is the result of perturbations in the magnetic field configuration initiated by the MHD waves. The consequence would be that more generally the primary initiation of the ruption may happen up to several hours before the rise of the prominence.

Simon, G.↗

NASA NTRS1986

Constraints on filament models deduced from dynamical analysis

The conclusions deduced from simultaneous observations with the Ultra-Violet Spectrometer and Polarimeter (UVSP) on the Solar Maximum Mission satellite, and the Multichannel Subtractive Double Pass (MSPD) spectrographs at Meudon and Pic du Midi observatories are presented. The observations were obtained in 1980 and 1984. All instruments have almost the same field of view and provide intensity and velocity maps at two temperatures. The resolution is approx. 0.5 to 1.5" for H alpha line and 3" for C IV. The high resolution and simultaneity of the two types of observations allows a more accurate description of the flows in prominences as functions of temperature and position. The results put some contraints on the models and show that dynamical aspects must be taken into account.

Simon, G.↗

NASA NTRS1986

Filament eruption connected to protospheric activity

Two cases of activation of filaments that occured in regions of intense magnetic activity was studied. The simultaneous observations from Debrecen Observatory (white light and H alpha filtergram), and from Meudon Observatory (magnetogram, MSDP dopplergram and intensity maps in H alpha) gave a complementary set of data from which can be produced evidence of the influence of the photospheric magnetic field on the destabilization process of the filaments. On June 22, 1980, the eruption of the filament is associated with the motion of pores, which are manifestations of emerging flux knots. On September 3, 1980, the twisting motions in the filament are associated to the birth of a pore in its neighborhood. These observations are discussed.

Simon, G.↗

NASA NTRS1986

Dynamics of solar filaments. VI - Center-to-limb study of H-alpha and C IV velocities in a quiescent filament

The rotation of a stable quiescent filament from near disk center to the limb has been observed. Observations of intensity and velocity were made in H-alpha and C IV, and compared with magnetic field measurements. From the H-alpha observations, it is concluded that the filament is made up of many small scale magnetic features that are not coherently aligned along the neutral line. They are especially convoluted at the apparent 'footpoints'. The measured velocities are of the order of a few kilometers per second in both lines. However, the comparison of the standard deviations of the C IV velocities in and out of the filament as it rotates toward the limb shows that the vertical velocities in the filament are greater than the horizontal velocities. Measurements of velocity do not make it possible to distinguish between the Raadu-Kuperus (1973) or Kippenhahn-Schluter (1957) models for prominences because neither theory is adequately developed for this comparison. However, the observation of the many fine loops brings into question the correctness of either model.

Simon, G.↗

NASA NTRS1985

Dynamics of solar filaments. IV - Structure and mass flow of an active region filament

An active region filament near the center of the solar disk was observed on September 29-30, 1980, with the Multichannel Subtractive Double Pass Spectrograph of the Meudon solar tower and the UV Spectrograph and Polarimeter aboard the SMM satellite. H-alpha and C IV measurements are presently used to study brightness and material velocity in the 10,000 and 100,000 K temperature ranges, and photospheric magnetograms are used to investigate the underlying magnetic field. Attention is given to the constraints imposed on possible filament structures by observations, as well as the expected MHD relationships.

Schmieder, B.↗

NASA NTRS1985

Mass fluxes and magnetic structures in the chromosphere and the transition region - Canopies

Preliminary results of applying a model of canopy-type magnetic lines to account for observed mass fluxes in the chromosphere and transiton region are presented. A set of center-to-limb data obtained in H-alpha and C IV, and to which the model is applied, is reported. The C IV line is assumed to form everywhere at the same height, and the H-alpha formation height is derived by assuming that the absorption coefficient is proportional to the local density. The density ratio between H-alpha and C IV levels is taken to be 100. From the results, it is concluded that the model accounts for the low ratio of radial velocities C IV/H-alpha at r = 0, the increase of H-alpha velocity near the limb, and the general center-to-limb behavior in both lines.

Mein, P.↗

NASA NTRS1984

Flare build-up study - Homologous flares group. I

Solar Maximum Mission observations have been used to study the origin and amount of energy, mechanism of storage and release, and conditions for the occurrence of solar flares, and some results of these studies as they pertain to homologous flares are briefly discussed. It was found that every set of flares produced 'rafales' of homologous flares, i.e., two, three, four, or more flares separated in time by an hour or less. No great changes in macroscopic photospheric patterns were observed during these flaring periods. A quantitative brightness parameter of the relation between homologous flares is defined. Scale changes detected in the dynamic spectrum of flare sites are in good agreement with a theoretical suggestion by Sturrock. Statistical results for different homologous flare active regions show the existence in homologous flaring areas of a 'pivot' of previous filaments interpreted as a signature of an anomaly in the solar rotation.

Martres, M.-J.↗

NASA NTRS1984

Recurrent mass ejections observed in H-alpha and CIV

Time sequences of recurrent mass ejections have been observed during a coordinated SMY program (Sept. 1, 1980 - Sept. 23, 1980 - Oct. 2, 1980). Comparison of the temporal evolution of H-alpha and CIV brightnesses shows a weak phase lag between H-alpha and CIV maxima, in the case of homologous flares, with CIV brightness maxima preceding H-alpha maxima. The analysis of the variation of the ejection velocities is expected to lead to the determination of an energy balance. Such recurrent ejections could be due to periodic energy storage and periodic reorganization of magnetic field as envisaged to occur for flares, but at lower energy levels.

Schmieder, B.↗

NASA NTRS1982

Measurements of solar transition zone velocities and line broadening using the ultraviolet spectrometer and polarimeter on the Solar Maximum Mission

The UVSP instrument on SMM is able to observe solar regions at two wavelengths in the same line with a band-pass of 0.3 A. Intensity and Doppler velocity maps are derived. It is shown that the numerical values are sensitive to the adopted Doppler width and the range of velocities is limited to within 30 km/sec. A method called Double Dopplergram Determination (DDD) is described for deriving both the Doppler width and the velocity (up to 80 km/sec), and the main sources of uncertainties are discussed. To illustrate the method, a set of C IV 1548 A observations is analyzed according to this procedure. The mean C IV Doppler width measured (0.15 A) is comparable to previous determinations. A relation is found between bright regions and down-flows. Large Doppler widths correspond to strong velocity gradients.

Simon, G.↗

NASA NTRS1982

Dynamics of the eruptive prominence of 6 May 1980 and its relationship to the coronal transient

The active prominence of the 6 May 1980 has been observed between 5.23 and 10.22 UT with the Ultraviolet Spectrometer and Polarimeter (UVSP) on board the Solar Maximum Mission (SMM) satellite. Intensities of 1548 A line of CIV and dopplershifts have been derived. A motion of the magnetic tube maintaining the prominence material is noted. This motion is followed by a coronal transient observed with the Coronagraph and Polarimeter (C/P) between 11 and 13 UT. It is suggested that the event is related to a MHD wave induced by a flare occurring behind the solar disk, and a MHD modeling of the perturbation is proposed.

Mein, N.↗

NASA NTRS1982

Mass motions in the solar chromosphere and transition zone

A comparison is made between H-alpha and C IV observations of Active Region 2717 on October 9, 1980. On the basis of this comparison, it is found that upward velocities are present above sunspots in the chromosphere-corona transition zone (20 km/s). The downward velocities are found to be well correlated in both lines. Doppler-shift ratios between C IV and H-alpha levels (approximately 10) are seen to be much smaller than expected from density ratio estimates. The comparison is seen as suggesting that flow lines are probably far from vertical in the transition zone. It is pointed out, however, that this depends on model densities that may not be correct. A simple method for comparing matter flows is presented. The best fit between H-alpha and C IV levels is obtained when C IV Doppler shifts are multiplied by the line intensity to the power 0.5 (approximately) in order to make allowance for density fluctuations.

Mein, P.↗

NASA NTRS1982

About the onsets of closely-consecutive homologous flares

The onsets of closely consecutive homologous flares (CCHF), which are separated by less than 6 hours and most often by about 1 hour, are compared with that of isolated flares (no flare in the region half a day before). Isolated flares appear to be formed of two components, a surging arch and a flaring arch, while a set of CCHF may be composed of consecutive elementary flares or of a series of complex ones. It is shown that the onset of eruptive flare phenomena is not the same for an isolated event and for a member of CCHF (excluding the first) as found in H-alpha and EUV observations, and probably in X-ray observations also. It is suggested that a CCHF set would become a single flare with episodic enhancement of brightness by taking account of the common H-alpha behavior of surging and flaring arches as well as the EUV emission.

Martres, M. J.↗