A B S T R A C T S O F F O R T H C O M I N G P A P E R S

I. P. TINDO, B. VALNiCEK, M. A. LIVSHITS, and V. D. IVANOV: Preliminary Interpretation of the Polarization Measurements Performed on 'Intercosmos-4' During Three X-Ray Solar Flares. (Received 2 May, 1972.)

Analysis of the X-ray polarization data at ;~ ~ 0.8 A for three major chromospheric flares shows that during the 'hard ' phase of the flare the X-rays are polarized in the plane, the projection of which on the solar disc is going approximately from the flare region to the center of the disc. Simultaneously performed measurements of the spectral energy distribution have proved that observed X-rays are produced by the bremsstrahlung of the accelerated electrons with the energies in the range 10 + 100 keV. The experimental data are in good agreement with the flare model, which deals with the radial movement of accelerated electrons towards the photosphere, together with the continuous injection of these electrons into the emitting region.

E. N. FRAZIER and J. O. STENFLO : On the Small-Scale Structure of Solar Magnetic Fields. (Received 9 May, 1972.)

The small-scale structure of solar magnetic fields has been studied using simultaneous recordings in the spectral lines Fe I 5250/~ and Fe I 5233/~, obtained with the Kitt Peak multi-channel magneto- graph, We find that more than 90 ~ of the magnetic flux in active regions (excluding the sunspots), observed with a 2.4 by 2.4" aperture, is channelled through narrow filaments. This percentage is even higher in quiet areas. The field lines in a magnetic filament diverge rapidly with height, and part of the flux returns back to the neighbouring photosphere. Therefore the strong fields within a magnetic filament are surrounded by weak fields of the order of a few gauss of the opposite polarity. The field-strength distribution within a filament, including the surrounding opposite-polarity fields, seems to be almost the same for all filaments within a given active or quiet region.

The analysis of a scan made during an imp. 2 flare showed that observations during and after the flare would give a fictitious decrease of the magnetic energy in the region by a factor of 2-3 due to line-profile changes during the flare.

MICHAEL L. SHAW : A Simulation of the Directivity Effect to be Expected in Hard X-Ray Flare. (Re- ceived 26 May, 1972.)

A Monte Carlo technique has been used to predict the relative visibility of solar hard X-ray flares as a function of solar longitude assuming the model of Takakura and Kai to be realistic. Comparison is made with previous statistical studies of observations. A discernible longitudinal variation in the relative visibility of flares is shown to be expected but the probability of flares being visible towards the limb is shown to be higher than had previously been evident.

The effect of the possible downward inclination of the particle beam with respect to the solar sur- face is considered.

J, H. PIDDINGTON: A Model of the Quiet Solar Atmosphere, (Received 14 June, 1972.)

The solar atmosphere may be divided into a number of isolated active components and a quiet residue. On the largest scale the latter is dominated by a general dipole magnetic field of strength 1-2 G; its observable components are flux concentrations in supergranule boundary regions (SBR's), spicules, mottles and polar plumes. The velocity field in the SBR's is discussed. There are continuous gas

ABSTRACTS OF FORTHCOMING PAPERS 485

streaming motions up and down between the photosphere and the corona; spicules may be mainly downward-moving gas.

A unifying model is developed of these various components, as well as the heating mechanism of the whole quiet atmosphere. Highly ordered velocity fields of the cell, together with a gravitational wave, cause a vertical magnetic force tube to collapse below a critical level; the result is an upward eruption of a vortex ring at the Alfv~n velocity. The complex mass velocity pattern may explain spicules, mottles and plumes, as well as unobservable streaming motions.

The quiet atmosphere is divided into regions above SBR's and those above the inner parts of the cells. Hydromagnetic eruptions from the former may account for the entire heat requirement of the atmosphere. The model atmosphere has a chromosphere-corona transition layer which bulges up- wards above the SBR's and so conforms with EUV data. The energy and mass balances in this solar atmosphere are considered, and it is also shown to be consistent with the radio data.

GEORGE L. WITHBROE and YI MING WANG: A Model for the Polar Transition Layer and Corona for November 1967. (Received 16 June, 1972.)

A model for the chromospheric-coronal transition layer and lower corona has been constructed for the south polar region. EUV observations acquired by the Harvard OSO-4 experiment in the fall of 1967 were used in the analysis. The observations can be explained with a simple model consisting of two types of regions. One region has a temperature-density structure similar to that in models developed for typical equatorial quiet areas. The other region has a corona in which the temperature and density are a factor of about 2 lower and the chromospheric-coronal temperature gradient is less steep by a factor of 4.

N. MYKLAND: Relative Umbral Intensity of a Large Sunspot. (Received 28 June, 1972.)

Simultaneous observations of relative umbral intensities in four wavelength regions are presented. In the visual wavelength region the umbral intensities show lower values than given by most authors. By observing the same spot during different seeing conditions the method of correction for stray light is found to be consistent within the accuracy of the method. In addition, a new simple correction method is suggested.

P. ULMSCHNEIDER and W. KALKOFEN: The Effect of Mechanical Waves on Empirical Solar Models. (Received in final form 28 June, 1972.)

Empirical solar models contain the effect of heating due to radiative energy loss from acoustic waves. We estimate here the temperature difference between the radiative equilibrium model and the empiri- cal model. At optical depth zs000 = 0.1 this difference is small, but near the temperature minimum (Ts000 = 10 -4) it reaches between 53 and 83 K. The temperature difference between the equator and the poles caused by a hypothetical difference in the heating is estimated.

Y. UCHII)A, M . D . ALT$CHULER, and G. NEWKIRK. JR. : Flare-Produced Coronal MHD-Fast- Mode Wavefronts and Moreton's Wave Phenomenon. (Received 3 July, 1972.)

The propagation characteristics of MHD fast-mode disturbances, which can emanate from flare regions, are computed for realistic conditions of the solar corona at the times of particular flares. The path of a fast-mode disturbance is determined by the large-scale (global) coronal distributions of magnetic field and density, and can be computed by a general ray-tracing procedure (eikonal equation) adapted to MHD. We use the coronal (electron) density distribution calculated from daily K-corona- meter data, and the coronal magnetic field calculated under the current-free approximation from magnetograph measurements of the photospheric magnetic field. We compare the path and time- development of an M H D fast-mode wavefront emitted from the flare region (as calculated from a realistic model corona for the day of the observed Moreton wave event) with actual observations of

486 ABSTRACTS OF FORTHCOMING PAPERS

the Moreton event, and find that the Moreton wave can be identified with the rapidly moving inter- section of the coronal fast-mode wavefront and the chromosphere (as hypothesized in our previous paper); the directivity (anisotropic propagation), as well as other characteristics of the propagation of the Moreton wave can be successfully explained.

L. A. FRANK and D. A. GURNETT: Direct Observations of Low-Energy Solar Electrons Associated with a Type III Solar Radio Burst. (Received in final form 7 July, 1972.)

A highly anisotropic packet of solar electron intensities was observed on 1971 April 6 with a sensitive electrostatic analyzer array on the Earth-orbiting satellite IMP-6. The anisotropies of intensities at electron energies of several keV were factors >~ 10 favoring the expected direction of the interplanetary magnetic lines of force from the Sun. The directional, differential intensities of solar electrons were determined over the energy range 1 to 40 keV and peak intensities were ~ 10 ~ (cmZ-s-sr-eV) -~ at 2 to 6 keV. This anisotropic packet of solar electrons was detected at the satellite for a period of 4200 s and was soon followed by isotropic intensities for a relatively prolonged period. This impulsive emission was associated with the onsets of an optical flare, soft X-ray emission and a radio noise storm at centimeter wavelengths on the western limb of the Sun. Simultaneous measurements of a type III radio noise burst at kilometric wavelengths with a plasma wave instrument on the same satellite showed that the onsets for detectable noise levels ranged from 500 s at 178 kHz to 2700 s at 31.1 kHz. The corresponding drift rate requires a speed of N 0.15 c for the exciting particles if the emission is at the electron plasma frequency. The corresponding electron energy of ~ 6 keV is in excellent agreement with the above direct observations of the anisotropic electron packet. Further supporting evidence that several-keV solar electrons in the anisotropic packet are associated with the emission of type III radio noise beyond ~ 50 solar radii is provided by their time-of-arrival at Earth and the relative durations of the radio noise and the solar electron packet. Electron intensities at E >~ 45 keV and the isotropic intensities of lower-energy solar electrons are relatively uncorrelated with the measurements of type III radio noise at these low frequencies. The implications of these observations relative to those at higher frequencies, and heliocentric radial distances < 50 solar radii, include apparent deceleration of the exciting electron beam with increasing heliocentric radial distance.

A. GREVE, C. D. McKEITH, and N. E. McKEITH: High Resolution Ultraviolet Solar Spectra in the Region 2765 to 2822 A. (Received 11 July, 1972.)

Wavelengths and identifications of the near ultraviolet solar spectrum are presented. The data were obtained during the rocket flight of an interferometer spectrograph with a spectral resolution of 0.03/~.

P. R. WILSOn: The Cooling of a Sunspot. I: A Carnot Cycle and the Hydromagnetic Interactions. (Received in final form 12 July, 1972.)

A mechanism is proposed to explain the cooling of a sunspot in terms of the detailed interactions between the magnetic field and the convective motions. The mechanism provides that an axially symmetric concentration of magnetic field deforms the normal supergranule cell pattern below the sunspot into a radial outflow of plasma over a region of diameter ~ 60 Mm.

The flow occurs at depths where the magnetic and kinetic energy densities are approximately equal ( ~ 5 Mm) and is described in terms of a Carnot refrigeration cycle. Application of the hydromagnetic equations to a very simple model shows that, because the magnetic field concentration causes the outflow, the field will itself decay in a time short compared with the lifetime of a spot. However, a slightly more sophisticated model does suggest conditions under which this decay is considerably reduced.

Observations of the flux in magnetic knots surrounding a sunspot, together with the outward drift of these knots and associated faculae show how this field decay may be interpreted physically. Further, the recent observation by Sheeley and Bhatnagar (1971) of extra-penumbral velocities directed radially outwards for distances ~ 10 Mm beyond the penumbra"more like the supergranulation than an extension of the Evershed velocity" provides support for the mechanism. The observed drift

ABSTRACTS OF FORTHCOMING PAPERS 487

velocities indicate that the sunspot field should decay in a period of order three hours, which supports the deduction from the restricted solutions but emphasises the need to account for the observed spot lifetimes. This is discussed in a later paper.

1. D. PALMER: Shock Wave Effects in Solar Cosmic Ray Events. (Received in final form 12 July, 1972.)

Two low-energy ( < 1 MeV) solar proton events which display a gradual intensity increase to a maxi- mum near the time of an SSC, followed by an abrupt, large decrease, are interpreted in terms of a population of cosmic rays which are 'swept' ahead of an interplanetary shock wave. A model which describes the variation with time of intensity and anisotropy at the Earth is developed using a Monte Carlo technique which traces the histories of particles released impulsively at the Sun. A good fit to each of the profiles observed at 0.6 to 0.9 MeV proton energies is obtained with a diffusion coefficient K ~ 2 • 10 ~~ cm ~ s -1 and a near perfect shock reflector.

L. D . DE FEITER and C. OE JAGER: Superthermal Plasma Grains and Their Relation to Solar Flares. (Received 17 July, 1972.)

We define superthermal plasma grains as bright points (diameter < 20"), visible on high resolution X-ray heliograms. Flares appear to show a strong tendency to occur at the places of these grains. There are indications that (part of) the hot plasma produced by consecutive flares is accumulated and confined in the superthermal plasma grains, and that with increasing energy content of a grain the probability for a drastic change of its magnetic structure increases, thus reducing the possibility for more flares to occur.

K. HARVEY and J. HARVEY: Observations of Moving Magnetic Features Near Sunspots. (Received 17 July, 1972).

The properties of small ( < 2") moving magnetic features near certain sunspots are studied with several time series of longitudinal magnetograms and Ha filtergrams. We find that the moving magnetic features:

(1) Are associated only with decaying sunspots surrounded entirely or in part by a zone without a permanent vertical magnetic field.

(2) Appear first at or slightly beyond the outer edge of the parent sunspot regardless of the presence or absence of a penumbra.

(3) Move approximately radially outward from sunspots at about 1 km s -1 until they vanish or reach the network.

(4) Appear with both magnetic polarities from sunspots of single polarities but appear with a net flux of the same sign as the parent sunspot.

(5) Transport net flux away from the parent sunspots at the same rates as the flux decay of the sunspots.

(6) Tend to appear in opposite polarity pairs. (7) Appear to carry a total flux away from sunspots several times larger than the total flux of the

sunspots. (8) Produce only a very faint emission in the core of Ha. A model to help understand the observa-

tions is proposed.

P. R. WILSON: The Cooling of a Sunspot. II: Convection Zone Models and the Magnetic Power Supply. (Received in final form 17 July, 1972.)

In order to discuss the detailed interactions between the magnetic and velocity fields below a sunspot, several models of the convection zone are considered. It is suggested that giant convection cells establish a pattern of large superadiabatic gradients near the top and bottom of the zone analogous with the temperature gradients in laboratory convection. These gradients in turn establish their own eddies or cells with dimensions typical of the local scale height. Those at the top correspond to the

488 ABSTRACTS OF FORTHCOMING PAPERS

photospheric granules while overshoot motions from the bottom of the layer may be related to the surface supergranule motions.

The possibility that the surface supergranule motions are due to a counter-cell lying above a thermally driven supergranule cell are discussed and this concept is included on one of the models which may be typical of quiet regions of the convection zone. However, it is suggested that just prior to the appearance of a sunspot, overshoot motions from the deep eddy may extend almost to the top of the convection zone replacing the counter-cell by the motions of the cooling cycle discussed in Paper I.

The magnetic power required by this cycle may be supplied by the upward drift of flux ropes expelled from and amplified by these elongated convection eddies. For a typical sunspot, an upper limit to the power required is 9 x 1038 erg s-L Consideration of all forms of energy emitted from a sunspot and its immediate neighbourhood (including hydromagnetic waves and excess facular radiation) fails to account for 1.1 x 1029 erg s -~ of the flux normally emitted through an equivalent area of the photosphere. Thus if this thermal and kinetic energy is converted to magnetic energy by the expulsion of flux from the convective eddies, the magnetic power requirements of the cooling mechanism may be readily satisfied.

A. K. DUPREE and W. HENZE, JR.: Solar Rotation as Determined from OSO-4 EUV Spectrohelio- grams. (Received 17 July, 1972.)

Spectroheliograms obtained in extreme ultraviolet (EUV) lines and the Lyman continuum are used to determine the rotation rate of the solar chromosphere, transition region, and corona. A cross-correla- tion analysis of the observations indicates the presence of differential rotation through the chromo- sphere and transition region. The rotation rate does not vary with height. The average sidereal rotation rate is given by co(deg day -1) = 13.46-2.99 sinZB where B is the solar latitude. This rate agrees with spectroscopic determinations of the photospheric rotation rate, but is slower by

1 deg day -1 than rates determined from the apparent motion of photospheric magnetic fields and from the brightest points of active regions observed in the EUV. The corona does not clearly show differential rotation as do the chromosphere and transition region.

E. FOSSAT and G. RICORT: Contribution to the Observation of the Photospheric Oscillations. (Re- ceived in final form 20 July, 1972.)

Observations of the 300 s photospheric oscillation on large solar surfaces (up to 5'20" in diameter) using a sodium optical resonance cell seem to show that the power at long horizontal wavelengths is larger than previous results would indicate. In order to get more information about the spatial distri- bution of the energy, a new observational method has been perfected, which will allow us to obtain the spatiotemporal power spectrum.

In some of our observations, a long-period oscillation (about 40 rain) appears, with an amplitude comparable to that of the 300 s oscillation, and which seems to be correlated with the occurrence of chromospheric flares.

C. J. PSU~EK and R. G. TESKE: Core Electron Densities of Coronal Polar Plumes. (Received 20 July, 1972.)

The electron density in the cores of coronal polar plumes that is determined from observations will depend upon the assumed electron density distribution through the plume in a direction normal to its axis. Core electron densities obtained by Saito (1965) and by Newkirk and Harvey (1968) were derived using different assumed electron density profiles, and are not in agreement. We have re- discussed Saito's data using Newkirk and Harvey's electron density profile and find that the disagree- ment persists. Whether this indicates a true variation in electron density in plume cores cannot now be stated. Errors in the electron densities derived here may arise through errors in measuring the angles 0 and c~ which enter into the analysis. While plausible variations in 0 produce no appreciable errors in core electron density, plausible variations in c~ may introduce appreciable errors into the determinations of that quantity.

ABSTRACTS OF FORTHCOMING PAPERS 489

R. E. GUSEINOV" On the Aller's Admixture Radiation Effect During the Compression Process in the Solar Corona and Generation of Coronal Formations. (Received in final form 25 July, 1972.)

The cooling due to the Aller's admixture radiation in the energy balance equation describing the coronal gas condensation is taken into account. It is shown that the compression mechanism does not apply for the explanation of the quiescent prominences formation but is quite suitable for the definite kinds of active prominences and flares of coronal origin.

Two possible variants of magnetic field before and in the process of compression within the coronal element and beyond of it are considered.

J. H. CARVER, B.H. HORTON, G . W . A . LOCKEu and BRYAN ROFE" Ultraviolet Ion Chamber Measurements of the Solar Minimum Brightness Temperature. (Received in final form 26 July, 1972.)

The solar ultraviolet flux in the wavelength bands 1580-1640 A and 1430-1470/~ (FWHM) has been measured using photon ion chambers carried on the satellite WRESAT I (1967-118A). These observa- tions of the integrated ultraviolet flux from the entire disk indicate a value of (4570 ~-50)K for the solar temperature minimum. The results are compared with other estimates of the minimum value of the solar brightness temperature.

D. L. McKENZIE, D. W. DATLOWE, and L. E. PETERSON: Spectral Development of a Solar X-Ray Burst Observed on OSO-7. (Received in final form 1 August, 1972.)

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 1972 November 16, at 0519 UT in terms of thermal (exponential spectrum) and nonthermal (power law) components. The energy content of the approximately 20 • 106 K 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 non- thermal electrons above 10 keV have sufficient energy to heat the thermally emitting plasma. In the thin target case the collisional energy transfer from nonthermal electrons suffices if the power law electron spectrum is extrapolated below 10 keV, or if the ambient plasma density exceeds 4 • 10 ~~ cm-L

PAUL N. SWANSON, FRED L. WEFER, WILLIAM J. DECKER, and JOHN P. HAGEN: Further Evidence for a Complex Limb Structure in the Solar Radial Brightness Distribution at mm Wavelengths. (Received in final form 1 August, 1972.)

A computer program to convolve numerically any azimuthally symmetric, solar radial brightness distribution with standard antenna patterns of small half power beamwidths has been used to find a solar brightness distribution which is a good fit to the eclipse curve obtained during the 1970 March 7 partial solar eclipse with the NRAO 36 ft antenna at 3.5 ram. This brightness distribution is compared with the brightness distribution at 3.2 m m determined by the Pennsylvania State University Radio Astronomy Observatory group during the same eclipse but observed from Mexico where totality occurred. The two brightness distributions are very similar in shape, showing a double peak near the limb, but differing slightly in the positions of the peaks.

R. S. BENSON and J. L. KULANDER: Electron Impact Excitation Rates for Helium. (Received in final form 18 August, 1972.)

Electron impact excitation rates are calculated for all transitions in He ~ and ii between individual terms for n ~< 4. Rates calculated for a large number of different experimental, theoretical and semi- empirical cross sections are compared. The rates are approximately given by the expression A T n exp ( - -c~Eo/kT) over the range 4000 _< T_< 50000K for He ~ and 10 a < T ~ 105K for He II.

490 ABSTRACTS OF FORTHCOMING PAPERS

S. BlSWAS and B. RADHAKRISHNAN: Energetic Solar Particles and Their Relation to Optical Flares. (Received in final form 21 August, 1972.)

It has been recently suggested by several investigators that the accelerated charged particles provide the energy of the optical flare by the ionization loss process. We have examined this mechanism assuming different forms of the spectrum of the accelerated protons at lower chromosphere. The flux and the energy spectrum of protons of energy 0.1-100 MeV have been calculated at successive heights, from 10 ~ to 40 • 10 ~ km from the solar surface taking into account the ionization loss, pitch angle distribution and density distribution of the neutral and ionized hydrogen in the chromosphere and lower corona. Hence the energy spectrum of the protons escaping from the Sun and the amount of energy dissipated in the solar chromosphere are computed. Comparing the calculated results with the observational data on the solar event of 1961 September 28, it is found that the ionization loss of the accelerated protons and heavier nuclei in the solar atmosphere may supply a significant part of the energy of the optical flare assuming that the fraction, f, of magnetic tubes of force extending out of the solar atmosphere is about 1 ~ . The accelerated proton spectrum in the form of power law in kinetic energy seems to be the most appropriate form. In the event of 1961 September 28, best esti- mates are made on this basis of the total number and the energy spectrum of protons at injection, the flux and energy spectrum of escaping protons and the energy dissipated in the solar atmosphere by the accelerated ions. It is found that the possible range of variation of the height of injection level hardly affects the total energy dissipated. The high variability of the intensity of protons released by the Sun is interpreted in terms of the variations of the parameter, f, determined by the configurations of the magnetic field lines.

OIVIND HAUGE: Solar Isotopic Composition and Abundance of Europium. (Received in final form 28 August, 1972.)

High resolution spectra of six photospheric Eu xI lines have been studied using the method of spec- trum synthesizing. The isotope ratio is found to be Eu153/Eu151 = (48 4-6)/(52T 6) and the solar abundance of europium equals log~Eu = 0.7 4- 0.2 in the logeH = 12.00 scale.

CH. V. SASTRY : Observations on the Time and Frequency Structure of Solar Decameter Radio Bursts. (Received in final form 28 August, 1972.)

Solar radio bursts were observed with a 4-channel radiometer and polarization analyser at wavelengths around 12 m. The time and frequency resolutions were 10 ms and 100 kHz respectively. Observations on the duration, time profile and frequency splitting are described.

F. W. J/iGER: Instrumental Polarization Concerning Magnetographic Measurements. (Received in final form 28 August, 1972.)

It is shown in detail in which way magnetographic measurements may be affected by instrumental polarization. To eliminate this influence we propose a combined method of partial compensation and computation practicable successfully with only a moderate expenditure of calculation and instrumen- tal equipment.

I. W. ROXBURGH: The Asymptotic Behavior of the Supersonic Solutions of the Two-Fluid Solar Wind Equations. (Received 1 September, 1972.)

Three different asymptotic branches of the two-fluid equations are found with Veal, m, vra~'*, where, is the inverse distance from the Sun, with (m, n)=(2/7, 2/7), (2/7, 6/7), (4/3, 4/3); other special

solutions are also found but they correspond to special choices of density and temperature at the corona. In all the (4/3, 4/3) solutions, the electron and proton temperatures tend to equality at large distances.