An evaluation of the possibility of studying flare plasma turbulence using the satellites of Hei line forbidden components

Using the Baranger-Mozer method, we explore the possibility of diagnosing the flare plasma of forbidden Hei lines, that permits the determination of the plasma oscillation frequency and noise level. Examination of the Hei lines observed in solar flare has led us to conclude that:

1. the appearance of satellites of forbidden components in the flares spectrum, due to turbulent electric fields, is the most probable for Hei 3819.606 Å lines;
2. the Baranger-Mozer method is more sensitive to the high-frequency component of turbulent fields than to the low-frequency ones;
3. the upper limit of the turbulent oscillation level in flares is evaluated.

In the spectrum of the solar flare of 26 September, 1963 we detected satellites of the forbidden component of the 3820 Å line and used its relative intensity to derive the level of low-frequency oscillations (～1.5 kVcm^-1).     

The results of statistical analysis of the coronal profiles above the solar active regions

In order to establish some regularities or variations in the distribution of widths and intensities of the coronal line profiles λ 5303 and λ 6374 depending upon the solar activity, a statistical analysis was made for more than 3000 profiles (the data covering the period 1966–1972). The following results obtained:

1. The distribution of coronal line profile widths changes depending upon the solar activity phase.
2. The character of the relation between the intensities and widths varies with variation of the solar activity phase.

     

The effect of solar parameters on seasonal variation of 5893 Å line intensity at Calcutta

The purpose of this paper is to present the correlation of seasonal variation of 5893 Å line intensity with relative sunspot numbers, solar flare numbers and the variable component of 10.7 cm solar flux. A study has been made and the following important results have been obtained.

1. The intensity of 5893 Å line at Calcutta shows periodic variation with different solar parameters during descending part of secondary peak of 21st solar cycle (1984–1985).
2. 5893 Å line intensity of Mt. Abu also shows periodic variation with solar parameters during the period 1965–1968 when there was a peak phase of 20th solar cycle.
3. A possible explanation for such type of variation is also presented.

     

Motions and magnetic fields in filaments

Based on the developed method of jointly using data on the magnetic fields and brightness of filaments and coronal holes (CHs) at various heights in the solar atmosphere as well as on the velocities in the photosphere, we have obtained the following results:

The upward motion of matter is typical of filament channels in the form of bright stripes that often surround the filaments when observed in the HeI 1083 nm line.

The filament channels observed simultaneously in Hα and HeI 1083 nm differ in size, emission characteristics, and other parameters. We conclude that by simultaneously investigating the filament channels in two spectral ranges, we can make progress in understanding the physics of their formation and evolution.

Most of the filaments observed in the HeI 1083 nm line consist of dark knots with different velocity distributions in them. A possible interpretation of these knots is offered.

The height of the small-scale magnetic field distribution near the individual dark knots of filaments in the solar atmosphere varies between 3000 and 20000 km.

The zero surface separating the large-scale magnetic field structures in the corona and calculated in the potential approximation changes the inclination to the solar surface with height and is displaced in one or two days.

The observed formation of a filament in a CH was accompanied by a significant magnetic field variation in the CH region at heights from 0 to 30000 km up to the change of the predominant field sign over the entire CH area. We assume that this occurs at the stage of CH disappearance.

     

Solar flare physics enlivened by TRACE and RHESSI

The Transition Region and Coronal Explorer (TRACE) gave us the highest EUV spatial resolution and the Ramaty High Energy Solar Spectrometric Imager (RHESSI) gave us the highest hard X-ray and gammaray spectral resolution to study solar flares. We review a number of recent highlights obtained from both missions that either enhance or challenge our physical understanding of solar flares, such as:

1. Multi-thermal Diagnostic of 6.7 and 8.0 keV Fe and Ni lines
2. Multi-thermal Conduction Cooling Delays
3. Chromospheric Altitude of Hard X-Ray Emission
4. Evidence for Dipolar Reconnection Current Sheets
5. Footpoint Motion and Reconnection Rate
6. Evidence for Tripolar Magnetic Reconnection
7. Displaced Electron and Ion Acceleration Sources.

     

Some properties of velocity fields in the solar photosphere

Photoelectric measurements of Doppler shifts of various Fraunhofer lines obtained with the Capri magnetograph were analysed. The height dependence of the supergranular and oscillatory motions, as well as the two dimensional structure of these velocity fields is investigated. The most interesting results are the following:

1. The oscillatory and supergranular motions are still clearly present in very deep photospheric layers as detected e.g. by means of the Ci line at 5380.3 Å.
2. Whereas the vertical motions (both of oscillation and supergranulation) increase with height, the horizontal component of the supergranular flow is found to be decreasing slightly.
3. Aperiodic horizontal motions are observed in the photospheric layers, which are probably connected with the process of excitation of the oscillatory field.
4. There is no simple way of describing the oscillatory field in terms of independently oscillating ‘cells’, since the two-dimensional pattern changes its appearance drastically already in a fraction of one oscillation period.
5. The correlation obtained by previous observers between vertical stationary motions, the chromospheric network and magnetic fields in particular is confirmed.

     

Keynote address: Outstanding problems in solar physics

Celebrating the diamond jubilee of the Physics Research Laboratory (PRL) in Ahmedabad, India, we look back over the last six decades in solar physics and contemplate on the ten outstanding problems (or research foci) in solar physics:

1. The solar neutrino problem
2. Structure of the solar interior (helioseismology)
3. The solar magnetic field (dynamo, solar cycle, corona)
4. Hydrodynamics of coronal loops
5. MHD oscillations and waves (coronal seismology)
6. The coronal heating problem
7. Self-organized criticality (from nanoflares to giant flares)
8. Magnetic reconnection processes
9. Particle acceleration processes
10. Coronal mass ejections and coronal dimming

The first two problems have been largely solved recently, while the other eight selected problems are still pending a final solution, and thus remain persistent Challenges for Solar Cycle 24, the theme of this jubilee conference.     

The photospheric network

Spectroheliograms, obtained in certain Fraunhofer lines with the 82-cm solar image at the Kitt Peak National Observatory, show a bright photospheric network having the following properties:

1. It resembles, but does not coincide with, the chromospheric network, the structure of the photospheric network being finer and more delicate than the relatively coarse structure of the chromospheric network.
2. It is exactly cospatial with the network of non-sunspot photospheric magnetic fields.
3. Its visibility in a given photospheric Fraunhofer line is primarily dependent on the states of ionization and excitation from which the line is formed and secondarily dependent on the Zeemansensitivity of the line-being most visible in low-excitation lines of neutral atoms and least visible in high-excitation lines of singly ionized atoms.

We conclude that these magnetic regions of the solar atmosphere are a few hundred degrees hotter than their surroundings, and that they are visible in white light near the limb as photospheric faculae.     

Chromospheric inhomogeneities in sunspot umbrae

The properties of rapidly changing inhomogeneities visible in the H and K lines above sunspot umbrae are described. We find as properties for these ‘Umbral Flashes’:

1. A lifetime of 50 sec. The light curve is asymmetrical, the increase is faster than the decrease in brightness.
2. A diameter ranging from the resolution limit up to 2000 km.
3. A tendency to repeat every 145 sec.
4. A ‘proper motion’ of 40 km/sec generally directed towards the penumbra.
5. A Doppler shift of 6 km/sec.
6. A magnetic field of 2100 G.
7. A decrease in this field of 12 G/sec. This decrease is probably related to the flash motion.
8. At any instant an average of 3–5 flashes in a medium-sized umbra. A weak feature often persists in the umbra after the flash. This post-flash structure initially shows a blue shift, but 100–120 sec after the flash, it shows a rapid red shift just before the flash repeats.

     

Rotational Tomography For 3d Reconstruction Of The White-Light And Euv Corona In The Post-Soho Era

Improving our understanding of the mechanisms that energize the solar wind and heat structures in the solar corona requires the development of empirical methods that can determine the three-dimensional (3D) temperature and density distributions with as much spatial and temporal resolution as possible. This paper reviews the solar rotational tomography (SRT) methods that will be used for 3D reconstruction of the solar corona from data obtained by the next generation of space-based missions such as the Solar and Terrestrial Relations Observatory (STEREO), Solar-B and the Solar Dynamics Observatory (SDO). In the next decade, SRT will undergo rapid advancement on several frontiers of 3D image reconstruction:

1. Electron density reconstruction from white-light coronagraph images.
2. Differential emission measure (DEM) reconstruction from EUV images.
3. Dual-spacecraft (STEREO) observing geometry.
4. Fusion of data from multiple spacecraft with differing instrumentation.
5. Time-dependent estimation methods.

Although the principles described apply to many different wavelength regimes, this paper concentrates on white-light and EUV data. Previous work on all of these subjects is reviewed, and major technical issues and future directions are discussed.     

Evolution of the solar Lyman alpha flux during four consecutive years

Four consecutive years of a quasi-continuous survey of the solar Lα line are presented. Absolute calibration and aging correction are evaluated producing higher quality measurements which are:

-the total Lα flux,

-the central Lα flux,

-the blue wing flux at 0.33 Å from the center,

-the slope of the blue wing at the same location.

Empirical laws are deduced from this large amount of data giving a relation between these different parameters and the flux integrated over the whole line. Furthermore, other empirical laws are obtained between the total Lα flux and two solar activity indices. These relations give a possibility of evaluating the solar Lα flux even when no observation is available and, as previously found by Prinz (1974), show that to a first approximation the solar Lα flux is composed of a quiet and of an active component. The active component changes with the 27 days period; the quiet one with the 11 yr solar cycle.     

On the number of effective integrals in galactic models

Three different numerical techniques are tested to determine the number of integrals of motion in dynamical systems with three degrees of freedom.

1. The computation of the whole set of Lyapunov Characteristic Exponents (LCE).
2. The triple sections in the configurations space.
3. The Stine-Noid box-counting technique.

These methods are applied to a triple oscillator with coupling terms of the third order. Cases are found for which one effective integral besides the Hamiltonian subsists during a very long time. Such orbits display simultaneously chaotic and quasi-periodic motion, according to which coordinates are considered. As an application, the LCE procedure is applied to a triaxial elliptical galaxy model. Contrary to similar 2-dimensional systems, this 3-dimensional one presents noticeable zones in the phase space without any non-classical integral.     

Correlation and spectral analysis of daily solar radio flux

Correlation and spectral analysis of solar radio flux density and sunspot number near the maximum of the sunspot cycle has indicated the existence of

1. long period amplitude modulation of the slowly varying component (SVC) of radio emission
2. coronal storage over a period of the order of three solar rotations
3. fast decay (one solar rotation period or less) of gyromagnetic emissions from radio sources
4. shift in location of chromospheric sources compared to those of either the upper corona or the photosphere.

     

Global solar activity on long time scales

We report the results of the application of our approach to study the behavior of solar activity in the past, where:

When reconstructing the variations of solar activity, geomagnetic parameters, and the interplanetary magnetic field in the past we select a sequence of increasing time scales, which can be naturally represented by the potentials of available observational data. We select a total of four time scales: 150–200 years, 400 years, 1000 years, and 10000 years.

When constructing the series of each successive (in terms of length) time scale we use the data of the previous time scale as reference data.

We abandon, where possible, the series of traditional statistical parameters in favor of the series of physical parameters.

When deriving the relations between any parameters of solar activity, geomagnetic disturbance, and the interplanetary magnetic field, we take into account the differential nature of relations on different time scales. To this end, we use the earlier proposed MSR and DPS methods.

To verify the resulting reconstructions, we use the “principle of witnesses”, which uses independent (in some cases, indirect) information as initial data.

     

Inhomogeneities in the solar atmosphere from the CaII infra-red lines

From a time sequence of high dispersion spectra taken by Evans, the solar fine structures are studied in the Caii infra-red triplet. The Doppler shifts and the intensity fluctuations in different points of the profiles are converted into fluctuations of the model atmosphere. A weighting function method is worked out in that purpose. The theoretical line profiles are computed in non LTE from a program written by Dumont. The results are arranged in two parts:

1. Low temporal frequencies. A three-column model describes the steady field of temperature, microturbulence and radial velocities fluctuations in the photosphere-chromosphere transition zone.
2. Oscillations. The propagation of waves is considered in the three above-mentioned columns. The oscillation amplitudes seem statistically larger in the hot column. The vertical phase velocity is very large, even for frequencies higher than the cut-off frequency of acoustic waves. Velocity and temperature fluctuations are connected by different curves of phase-lags and amplitude ratios suggesting a short relaxation time of the temperature fluctuations in the low chromosphere.

     

On the Hβ, [OIII] lines and continuum variability character in the nucleus of Seyfert galaxy NGC 1275

The radiation fluxes of the NGC 1275 galaxy central region are being observed on the 1.25-m telescope, using a scanning spectrophotometer with the entrance aperture 10″ in three Δλ=80 Å spectral regions: Hβ, 4959+5007 Å [OIII] and continuum. There were 35 nights of observations during 1982–1987. With the time resolution of half an hour 379 measurements were obtained in each spectral region. The analysis of these results shows:

1. The standard deviations of measurements in each spectral region 2–3 times exceed the errors of observations.
2. The radiation flux distribution resembles to normal one only for Hβ line.
3. Two-humps forms of continuum flux distribution curve is like that of radio emission in 8 mm and 2.6 cm wavelengths.
4. Various forms of fluxes distribution curves of Hβ and [OIII] lines permit us to suppose that the location of these lines emission regions near the sources of excitation are different.

     

Nature of variation of Antarctic O3 depletion and its correlation with solar UV radiation

The purpose of this paper is to study the nature of variation of O₃ concentration of Antarctic Survey Stations and its correlation with solar ultraviolet radiation. Solar UV data for the period November 1978 to October 1984 are taken from Solar Geophysical Data Book. In absence of solar UV data for long period, a calibration curve between solar UV radiation and solar flare number (S.F.NO.) is drawn. (A straight line is obtained and correlation coefficient between two variables is 80%). The equation of straight line from least square principle becomes, UV flux = 0.2672 + 2.7578 × 10^?5 × S.F.NO. From this equation UV flux values for long period are calculated from known values of solar flare numbers. O₃ concentration of two Antarctic Survey Stations, Halley Bay (76? S, 27? W) and McMurdo (78? S, 166? E) are considered for analysis and following important results are obtained:

1. Yearly variations of O₃ concentrations and UV radiations are mainly controlled by their October concentrations.
2. Correlation coefficient between O₃ concentration and UV radiation is 62% for the month of October. For the other months it is poor.
3. It is concluded that dramatic decrease of O₃ concentration at Antarctica is independent of solar UV radiation and chemical processes are responsible for special depletion of O₃.

     

Motion of dust particles under the influence of a latitudinally dependent force

The Kelperian motion of dust particles in the solar system is mainly influenced by the electromagnetic and plasma Poynting-Robertson drag. The first force is isotropic while the second one shows latitudinal variations due to the observed differences of the solar wind parameters in the ecliptic plane and over the solar poles. Close to the Sun other effects become important, e.g. sublimation and sputtering, as well as for submicron particles Lorentz scattering has to be taken into account. These forces are very weak for dust grains of moderate size (10–100 µ) not too close (>0.03 AU) to the Sun and are neglected here. Assuming that the general form of the latidudinally dependent force is a series expansion in Legendre polynomials, we have studied the averaged equations of motion for the classical elements and found the first integral of them. The general character of motion is the same as for the classical Poynting-Robertson drag: particles spiral towards the Sun. The new features in the orbital evolution under the latitudinally dependent force as compared with the isotropic Poynting-Robertson drag are:

1. not only the semimajor axisa and the eccentricity ε but also the argument of the perihelion ω varies with time,
2. the rate of change ofa, ε, ω depends on the inclination.

An example of particle trajectories in the phase space of elements is presented.     

Ephemeral active regions in 1970 and 1973

A study of ephemeral active regions (ER) identified on good quality full-disk magnetograms reveals:

1. On the average 373 and 179 ER were present on the Sun in 1970 and 1973 respectively. The number varies with the solar cycle.
2. The median lifetime of ER depends on observation quality and selection rules but is estimated as about 12 hr for our data.
3. The latitude distribution is very broad but not uniform. The distribution peaks near the equator and shows variations similar to distributions of large active regions.
4. The longitude distribution is essentially homogeneous.
5. The spatial orientation of ER is almost random. In 1973 there is a hint of an excess of new cycle orientations at high latitudes.

A comparison of parameters of ER and regular active regions suggests that ER are the small-scale end of a broad spectrum of active regions. The role of ER in the light of present theories of solar activity is investigated but is not yet clear. Heating of the chromosphere and corona may be significantly affected by ER.     

On the latitude migration of polar faculae in the solar activity cycle period: 1970–1978

Coordinates of polar faculae have been measured and processed using daily photoheliograms of the Kislovodsk Station of the Pulkovo observatory with the final goal of studying their latitude distribution during the solar cycles 20–21. The results obtained are as follows:

1. The first polar faculae emerge immediately after the polarity inversion of the solar magnetic field at the latitudes from 40° to 70° with the average ?-55°.
2. The zone of the emergence of polar faculae migrates poleward during the period between the neighbouring polarity inversions of the solar magnetic field. This migration is about 20° for 8 years, which corresponds to a velocity of 0.5 m s^-1.
3. The maximum number of polar faculae was reached at the activity minimum (1975–1976).
4. The last polar faculae were observed in the second half of 1978 at the latitudes from 70° to 80°.