Center-to-limb profiles of the aluminum autoionization lines in the solar spectrum

The rotation of the solar corona has been studied using recurrence properties of the green coronal line (5303 Å) for the interval 1947–1970. Short-lived coronal activity is found to show the same differential rotation as short-lived photospheric magnetic field features. Long-lived recurrences show rigid rotation in the latitude interval ±57°.5. It is proposed that at least part of the variability of rotational properties of the solar atmosphere may be understood as a consequence of coexistence of differential and rigid solar rotation.On leave from Torino University, Italy, as an ESRO-NASA Fellow.     

Some factors affecting the growth and decay of plages

The Mount Wilson coarse array magnetograph data set is analyzed to examine the dependence of growth and decay rates on the tilt angles of the magnetic axes of the regions. It is found that there is a relationship between these quantities which is similar to that found earlier for sunspot groups. Regions near the average tilt angle show larger average (absolute) growth and decay rates. Thepercentage growth and decay rates show minima (in absolute values) at the average tilt angles because the average areas of regions are largest near this angle. This result is similar to that derived earlier for sunspot groups. As in the case of spot groups, this suggests that, for decay, the effect results from the fact that the average tilt angle may represent the simplest subsurface configuration of the flux loop or loops that make up the region. In the case of region growth, it was suggested that the more complicated loop configuration should result in increased magnetic tension in the flux loop, and thus in a slower ascent of the loop to the surface, and thus a slower growth rate. In order to examine this further, the growth and decay rates of plage regions were examined as functions of the magnetic complexity of the regions. In the case of decay, the result was as expected from the model suggested above - that is, the more complex regions decayed more slowly. But for growing regions the effect is the opposite to that expected (more complex regions grow faster, even in terms of percentage growth), so the explanation of the tilt angle effect for growing regions proposed earlier may not be valid.Operated by the Association of Universities for Research in Astronomy, Inc., under Cooperative Agreement with the National Science Foundation.     

Measurement of Kodaikanal white-light images

A program of digitization of the daily white-light solar images from the Kodaikanal station of the Indian Institute of Astrophysics is in progress. A similar set of white-light data from the Mount Wilson Observatory was digitized some years ago. In both cases, areas and positions of individual sunspot umbrae are measured. In this preliminary report, comparisons of these measurements from the two sites are made. It is shown that both area and position measurements are in quite good agreement. The agreement is sufficiently good that it is possible to measure motions and area changes of sunspots from one site to the next, involving time differences from about 12 hours to about 36 hours. This enables us to trace the motions of many more small sunspots than could be done from one site alone. Very small systematic differences in rotation rate between the two sites of about 0.4% are found. A portion of this discrepancy is apparently due to the difference in plate scales between the two sites. Another contributing factor in the difference is the latitude visibility of sunspots. In addition it is suggested that a small, systematic difference in the measured radii at the two sites may contribute a small amount to this discrepancy, but it has not been possible to confirm this hypothesis. It is concluded that in general, when dealing with high precision rotation results of this sort, one must be extremely careful about subtle systematic effects.Operated by the Association of Universities for Research in Astronomy, Inc., under Cooperative Agreement with the National Science Foundation.     

Evidence for a poleward meridional flow on the sun

We define for observational study two subsets of all polar zone filaments, which we call polemost filaments and polar filament bands. The behavior of the mean latitude of both the polemost filaments and the polar filament bands is examined and compared with the evolution of the polar magnetic field over an activity cycle as recently distilled by Howard and LaBonte (1981) from the past 13 years of Mt. Wilson full-disk magnetograms. The magnetic data reveal that the polar magnetic fields are built up and maintained by the episodic arrival of discrete f-polarity regions that originate in active region latitudes and subsequently drift to the poles. After leaving the active-region latitudes, these unipolar f-polarity regions do not spread equatorward even though there is less net flux equatorward; this indicates that the f-polarity regions are carried poleward by a meridional flow, rather than by diffusion. The polar zone filaments are an independent tracer which confirms both the episodic polar field formation and the meridional flow. We find:

1. The mean latitude of the polemost filaments tracks the boundary of the polar field cap and undergoes an equatorward dip during each arrival of additional polar field.
2. Polar filament bands track the boundary latitudes of the unipolar regions, drifting poleward with the regions at about 10 m s^-1.
3. The Mt. Wilson magnetic data, combined with a simple model calculation, show that the filament drift expected from diffusion alone would be slower than observed, and in some cases would be equatorward rather than poleward.
4. The observation that filaments drift poleward along with the magnetic regions shows that fields of both polarities are carried by the meridional flow, as would be expected, rather than only the f-polarity flux which dominates the strength. This leads to the prediction that in the mid-latitudes during intervals between the passage of f-polarity regions, both polarities are present in nearly equal amounts. This prediction is confirmed by the magnetic data.

     

Some observations bearing on the problem of the short-period oscillations

Observations of solar velocity fields made simultaneously at Mount Wilson and at Kitt Peak with the same size aperture (5 arc-sec) and same position on the disk (± 1 arc-sec) are presented. The object is to clarify whether the short-period oscillations (SPO's) previously reported (Howard, 1967), could be caused by local seeing conditions. The time of onset and general character of the SPO's are found to be well correlated for the two sites, a condition that favors a solar origin. However, because correlation in complete detail did not prove possible, some doubt must remain regarding the source of the SPO's.Kitt Peak National Observatory Contribution No. 287.Operated by The Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

Radio and visible-light observations of a coronal arcade transient

We discuss simultaneous visible-light and radio observations of a coronal transient that occurred on 9 April, 1980. Visible-light observations of the transient and the associated erupting prominence were available from the Coronagraph/Polarimeter carried aboard SMM, the P78-1 coronagraph, and from the Haleakala Observatory. Radio observations of the related type III-II-IV bursts were available from the Clark Lake and Culgoora Observatories. The transient was extremely complex; we suggest that an entire coronal arcade rather than just a single loop participated in the event. Type III burst sources observed at the beginning of the event were located along a nearby streamer, which was not disrupted, but was displaced by the outmoving loops. The type II burst showed large tangential motion, but unlike such sources usually do, it had no related herringbone structure. A moving type IV burst source can be associated with the most dense feature of the white-light transient.     

Transient brightenings of interconnecting loops

We discuss three different kinds of dynamic events related to interconnecting loops observed in soft X-rays aboard Skylab: (1) A newly born transequatorial loop that was either emerging from subphotospheric layers or gradually filled in with hot plasma. (2) Large-scale twists of interconnecting loops which never relax, and often only form, after the loop brightenings. (3) Three events where the loop that later interconnected two active regions had been visible long before one of the interconnecting regions was born. Several impacts this observation might have upon our understanding of the process of flux emergence are suggested.     

Saturn's rings: Particle size distributions for thin layer models

The small physical thickness of Saturn's rings requires that radio occultation observations be interpreted using scattering models with limited amounts of multiple scatter. A new model in which the possible order of near-forward scatter is strictly limited allows for the small physical thickness, and can be used to relate Voyager 1 observations of 3.6-and 13-cm wavelength microwave scatter from Saturn's rings to the ring particle size distribution function n(a), for particles with radius 0.001 ≤ a ≤ 20 m. This limited-scatter model yields solutions for particle size distribution functions for eight regions in Saturn's rings, which exhibit approximately inverse-cubic power-law behavior, with large-size cutoffs in particle radius ranging from about 5 m in ring C to about 10 m in parts of ring A. The power-law index is about 3.1 in ring C, about 2.8 in the Cassini division, and increases systematically with radial location in ring A from 2.7 at 2.10R_s to slightly more than 3.0 at 2.24R_s. Corresponding mass densities are 32–43 kg/m² in ring C, 188 kg/m² in the Cassini division, and 244–344 kg/m² in ring A, under the assumption that the material density of the particles is 0.9 g/cm³. These values are a factor of 1 to 2 lower than first-order mass loading estimates derived from resonance phenomena. In view of the uncertainties in the measurements and in the linear density wave model, and the strong arguments for icy particles with specific gravity not greater than about 1, we interpret this discrepancy as being indicative of possible differences in the regions studied, or systematic errors in the interpretation of the scattering results, the density wave phenomena, or some combination of the above.     

Nanophase magnetite in matrix of anomalous EL3 chondrite Northwest Africa (NWA) 8785

NWA 8785 is a remarkable EL3 chondrite with a high abundance (~34 vol%) of an Fe-rich matrix. This is the highest matrix abundance known among enstatite chondrites (ECs) and more similar to the matrix abundances in some carbonaceous and Rumuruti chondrites. X-ray diffraction and TEM data indicate that the fine-grained portion of the NWA 8785 matrix consists of nanoscale magnetite mixed with a noncrystalline silicate material and submicron-sized enstatite and plagioclase grains. This is the first report of magnetite nanoparticles in an EL3. The Si content of the metal (0.7 wt%), presence of ferroan alabandite, and its O isotopic composition indicate NWA 8785 is EL3-related. Having more abundant matrix than in other ECs, and that the matrix is rich in magnetite nanoparticles, which are not present in any other EC, suggest classification as an EL3 anomalous. Although we cannot completely exclude any of the mechanisms or environments for formation of the magnetite, we find a secondary origin to be the most compelling. We suggest that the magnetite formed due to hydrothermal activity in the meteorite parent body. Although ECs are relatively dry and likely formed within the nebular snow line, ices may have drifted inward from just beyond the snow line to the region where the EL chondrites were accreting, or more likely the snow line migrated inward during the early evolution of the solar system. This may have resulted in the condensation of ices and provided an ice-rich region for accretion of the EL3 parent body. Thus, the EL3 parent body may have had hydrothermal activity and if Earth formed near the EC accretion zone, similar bodies may have contributed to the Earth's water supply. NWA 8785 greatly extends the range of known characteristics of ECs and EC parent body processes.