Engineering topics

Hildner, E.

Publications and source records attributed to Hildner, E..

36 records · Page 2

NASA NTRS1978

Forerunners - Outer rims of solar coronal transients

The large loop or blob-like transient events viewed in the white-light corona are rimmed by broad regions where the density is slightly enhanced above the pretransient corona. Every one of the Skylab events studied for which sufficiently good Skylab coronagraph coverage is available shows this effect. The upper boundaries of these 'forerunners' blend gradually into the background corona 1-2 solar radii above the transient's leading edges. In any single event, the coronal mass enhancement represented by the forerunner comprises up to 25% of the total excess mass present in the coronagraph's field of view and includes a much larger volume of the corona than previously attributed to the underlying transient. A forerunner without an accompanying transient has not yet been seen. Clearly, forerunners must be reckoned with in any proposed models of discrete outward coronal mass motions, because they indicate the presence of disturbed corona far ahead of the denser portions of the event.

Jackson, B. V.↗

NASA NTRS1978

Prompt solar proton events and coronal mass ejections

Data from the HAO white-light coronagraph and the X-ray telescope on Skylab have been used to investigate the coronal manifestations of 18 prompt solar proton events observed on the IMP 7 spacecraft during the Skylab period. Evidence is found that a mass-ejection event is a necessary condition for the occurrence of a prompt proton event. Mass-ejection events can be observed directly in the white-light coronagraph when they occur near the limb and inferred from the presence of a long-decay X-ray event when they occur on the disk. It is suggested that: (1) the occurrence of mass-ejection events facilitates the escape of protons - whether accelerated at low or high altitudes - to the interplanetary medium; and (2) there may exist a proton acceleration region above or around the outward moving ejecta far above the flare site.

Kahler, S. W.↗

NASA NTRS1977

Coronal mass-ejections-kinematics of the 19 December 1973 event

A detailed description of the observed kinematics of the coronal disturbance of December 19, 1973, is presented along with inferences about the temperatures, densities, magnetic fields, and electric currents within the event. This disturbance consisted of the eruption of a previously quiescent prominence, an associated ejection of coronal material, and the destruction of a large coronal streamer. Observations of the prominence and the corona with a scanning spectroheliometer and a white-light coronagraph aboard Skylab before, during, and after the prominence eruption are discussed, and the temperature and density in the eruptive prominence are traced as the prominence rose to a height of 3 solar radii over 7 hr. The results obtained are shown to reinforce previous arguments that the material comprising the bulk of the mass ejected from the corona in transient events arises from the low corona rather than from the eruptive prominence, which may accompany the coronal mass ejection.

Schmahl, E.↗

NASA NTRS1977

Noncompressive density enhancements in the solar wind

When the bulk flow speed is nearly constant or falling, high densities are sometimes observed in the solar wind. These densities do not appear to be generated in interplanetary space. It is noted that the magnetic field is not enhanced within these events, and that the proton and/or electron temperatures are low, varying in opposition to the density. About 1/3 of these density events contains interplanetary magnetic field reversals, some of which are noisy and do not qualify as sector boundaries. It is estimated that the average event contains approximately 10 to the 16th g of material and 2.6 x 10 to the 31st ergs, so that aggregated events, when they are common, make a negligible contribution to the total mass and energy budget of the solar wind at 1 AU. It is suggested that there may be an association between density enhancements and solar coronal mass ejection events.

Gosling, J. T.↗

NASA NTRS1977

Mass ejections from the solar corona into interplanetary space

Results obtained from analysis of Skylab coronagraph images of mass ejections from the solar corona are reviewed which demonstrate the importance of mass-ejection coronal transients to the interplanetary medium and which support the belief that magnetic forces are the primary mechanism driving mass ejections from the corona. Observations of 13 large ejection events are examined which indicate that coronal mass ejections contribute a nonnegligible fraction of the mass flux from the sun, especially toward the heliographic equator near the maximum of a solar activity cycle. It is shown that observed loop-shaped transients were associated with regions of increased magnetic field and with separations of unipolar field regions, that the forces driving the transients outward acted to great heights long after the onsets of the events, and that the behavior of the ejecta was magnetically controlled. It is concluded that mass ejections from the corona contributed at least 3% of the mass flux from the sun during the Skylab era and that the most common loop-shaped ejections are magnetically driven through the corona.

Hildner, E.↗

NASA NTRS1977

Mass ejections from the solar corona into interplanetary space

Data are presented that show that during the Skylab era, mass ejections from the solar corona probably contributed at least 3% of the mass flux from the sun. The frequency of the transients is expected to increase with overall activity in the solar cycle, so more than 10% of the sun's mass efflux will be in the form of ejections at solar cycle maximum.

Hildner, E.↗

NASA NTRS1976

Expansion of an X-ray coronal arch into the outer corona

An asymmetric expanding arch photographed in the inner corona with an X-ray telescope on August 13, 1973, is identified as the source of the mass ejected in a white-light transient in the outer corona. The morphology, angular position, estimated mass, and apparent rate of upward acceleration of the lower coronal arch are similar to those of the arch seen passing through the outer corona. The mass of material removed from the lower corona is estimated to be 2 by 10 to the 15th power g, and the upward motion is consistent with a constant acceleration of 12.5 m/sec per sec between 1.3 and 5 solar radii.

Rust, D. M.↗

NASA NTRS1976

The speeds of coronal mass ejection events

Results are presented for a systematic study of ejection speeds for the mass-ejection events observed with the white-light coronagraph aboard Skylab. At least 66 such events (most of them not associated with flares) were observed during the Skylab mission. Direct measurements of the displacements of the leading edges of the observed disturbances yield ejection speeds ranging from less than 100 to greater than 1200 km/s, with the average being close to 470 (+ or - 50) km/s; seventy percent of the events are found to have speeds exceeding the escape velocity at 6 solar radii. It is shown that the speeds are loosely correlated with the type of H-alpha activity associated with the mass ejections and that events associated with flares usually have speeds greater than those of events associated with eruptive prominences. Despite their poor quality, statistics indicate that the fastest mass-ejection events tend to produce type II-IV burst pairs, while single type II or type IV bursts tend to be associated with events of intermediate speed.

Gosling, J. T.↗

NASA NTRS1976

Initial results from the High Altitude Observatory white light coronagraph on Skylab - A progress report

Frequent periodic observations by the white-light coronagraph allow an examination of coronal variations over a broad range of temporal scales. Examples of the slowest and most rapid variations are presented. An example of extremely slow coronal variations is the gradual evolution - to a large equatorial streamer - in association with a marked decrease in solar activity, as the total magnetic flux in one hemisphere decreased. Another example is given of a long-lived quasi-stable coronal streamer, apparently associated with a stable filament channel; comparison of this streamer with coronal potential-magnetic-field computations show little correlation. Some results on coronal transients - the most rapid variations observed - are summarized. Characteristic masses and energies involved in mass-ejection transients, their temporal and spatial distributions, their associations with surface phenomena and possible interplanetary signatures, and their role in coronal evolution are briefly noted.

Macqueen, R. M.↗

NASA NTRS1976

Frequency of coronal transients and solar activity

The white light coronagraph aboard Skylab observed at least 110 coronal transients during 227 days of observations. It is shown that these transients occurred preferentially at longitudes where the sunspot number and the area times brightness index of calcium plages were high. The number of transients observed to arise from each of four quadrants in heliographic longitude, rotation by rotation, was strongly correlated with the average value of these measures of solar activity. From this it is inferred that coronal transients occur more commonly where magnetic fields are stronger, more complex, and varying more rapidly.

Hildner, E.↗

NASA NTRS1975

The sources of material comprising a mass ejection coronal transient

The origin of the material ejected during a white-light coronal transient on August 26 and 27, 1973, is investigated using simultaneous observations of a slowly ascending prominence and the more rapid accompanying coronal transient. Nearly identical simultaneous images of the prominence were obtained over a six-hour period in the H-alpha and He II (304 A) emission lines; contemporaneous Skylab coronograph observations over approximately 1.5 hours showed that the mass-ejection coronal transient rose above the ascending prominence. Based on analysis of these observations, it is concluded that: (1) the bulk of the ejected material originated in the lower corona, despite the lack of an observed depletion there; (2) the material in the transient was at coronal temperature and was visible in polarized radiation due to Thomson scattering of photospheric light by free electrons; and (3) the total event was far larger, more energetic, and longer lasting than would have been inferred from the prominence observations alone.

Hildner, E.↗

NASA NTRS1975

A search for forward scattering of sunlight from lunar libration clouds

Data obtained with the white-light coronagraph on Skylab are analyzed to determine the radiance of forward scattered sunlight from particles in lunar libration regions. It is found that the libration regions could not be distinguished against the solar K + F coronal background, and upper limits are determined for the libration cloud radiance as well as density enhancements in the libration region. The actual spatial density enhancement is calculated on the basis of previous observations by Roach (1975). The radiance contrast of a possible model libration cloud is calculated with respect to the K- and F-corona/zodiacal-light background and is found to be a maximum in the vicinity of a solar elongation angle of the order of 30 deg.

Munro, R. H.↗

NASA NTRS1975

Evidence for downflow following a coronal transient

On 11 September 1973 a peculiar prominence was observed. The prominence displayed strong (approximately 50 km per sec) systematic motions toward and away from the observer. The unusual spectrographic appearance of the prominence might have been due to downflowing material lifted into the corona during an earlier coronal transient.

Hildner, E.↗

NASA NTRS1975

The large coronal transient of 10 June 1973. I - Observational description

Ground-based and Skylab coronagraph observations are used to trace a coronal loop transient from its inception near the surface to a distance of 5 solar radii. Events in the lower solar atmosphere associated with this feature are outlined chronologically, and its physical appearance is described. The densities, mass, and energy of the transient are estimated, its shape is determined, and its typical and atypical characteristics are noted. It is inferred that this transient was caused by the emergence of an active region. It is shown that it was not immediately preceded by a flare and that the material at its leading edge did not decelerate appreciably, even at approximately 5 solar radii.

Hildner, E.↗

NASA NTRS1975

Direct observations of a flare related coronal and solar wind disturbance

Numerous mass ejections from the sun have been detected with orbiting coronagraphs. Here for the first time we document and discuss the direct association of a coronagraph observed mass ejection, which followed a 2B flare, with a large interplanetary shock wave disturbance observed at 1 AU. Estimates of the mass and energy content of the coronal disturbance are in reasonably good agreement with estimates of the mass and energy content of the solar wind disturbance at 1 AU. The energy estimates as well as the transit time of the disturbance are also in good agreement with numerical models of shock wave propagation in the solar wind.

Gosling, J. T.↗

NASA NTRS1974

Mass ejections from the sun - A view from Skylab

More than 30 instances of sudden mass ejections from the sun were observed with the white light coronagraph experiment aboard Skylab during the first 118 days of the mission. Typically, these ejections appear as large magnetic loops rooted at the sun, yet expanding outward through the solar corona at speeds of the order of 400 km/sec. The loops always appear to retain their magnetic connection to the sun. Eighteen of these ejections were associated with active and eruptive prominences and surges; only three ejections appear to have been flare initiated. Associations with ground-detected metric wavelength type 2 and 4 radio bursts occur for about 30% of these events; however, ground-detected type 2 and 4 radio bursts originating near the limb are almost invariably accompanied by coronagraph-observed ejections. Pressure or MHD waves run out ahead of the transient material ejecta; at times these waves can be detected by their effects on nearby coronal structures.

Gosling, J. T.↗

NASA NTRS1974

The solar corona as seen from Skylab

The white light coronagraph (WLC) experiment of the Skylab/ATM obtained an unprecedented series of observations of the solar corona from 1.5 to 6 solar radii for approximately eight and one-half months. Coronal evolution and disruptions seen by the WLC occur on many different time scales. Some illustrative examples will be shown. The characteristics of mass ejection coronal transients - as we presently know them - will be given. These include: the greater than expected frequency of occurrence; the correlation with solar activity; the quantity of mass and energy contained in a transient; etc.

Hildner, E.↗

NASA NTRS1974

The outer solar corona as observed from Skylab - Preliminary results

The white-light coronagraph experiment has made frequent, periodic observations of the solar corona from 1.5 to 6.0 solar radii during the Skylab mission, and these observations will permit the determination of the three-dimensional extent of coronal forms. There are several time scales on which visual changes in coronal structures occur, ranging from approximately one-half rotation to less than hours. A number of events corresponding to the shortest time scale - coronal transients - cause major restructuring of the corona.

Macqueen, R. M.↗