Engineering topics

Martin, Sara F.

Publications and source records attributed to Martin, Sara F..

11 records

NASA NTRS1994

Material ejection

This paper reviews the major discussions and conclusions of the Flares 22 Workshop concerning the physical processes involved in mass ejecta events, with an emphasis on large-scale phenomena, especially Coronal Mass Ejections (CMEs). New insights have been gained from recent data obtained from the Solar Maximum Mission (SMM) and Yohkoh spacecraft and from several new ground-based radio and optical instruments, as well as from theoretical advances concerning the origins, driving mechanisms and long-term evolution of CMEs.

Webb, David F.↗

NASA NTRS1990

Elementary bipoles of active regions and ephemeral active regions

The general properties of elementary bipoles (EBs), the class of moving magnetic features identified by Frazier (1972) as building blocks of new solar active regions, are described, and variations in their characteristics are illustrated with extensive videomagnetograms obtained at Big Bear Solar Observatory during 1984-1989. Consideration is given to ephemeral active regions consisting of EBs with only one positive and one negative pole, multiple-pole ephemeral regions, reversed-polarity EBs, interactions among EBs and adjacent magnetic features, and the EBs of small and medium active regions. The detection of EBs prior to the appearance of arch filaments confirms the relationship found by Frazier.

Martin, Sara F.↗

NASA NTRS1990

Conditions for the formation of prominences as inferred from optical observations

It is suggested that three conditions, if dynamically maintained for a sufficient period of time, will result in the formation of a solar prominence. These conditions are the presence of a coronal arcade that connects the magnetic fields on opposite sides of a prominence; the existence of a long-term (hours to days) converging flow of small patches of opposite-polarity magnetic flux toward a common-polarity inversion zone; and the cancellation of encountered patches of magnetic flux of opposite polarity at a photospheric polarity inversion boundary.

Martin, Sara F.↗

NASA NTRS1989

Mass motions associated with solar flares

Mass motions are a principal means by which components of solar flares can be distinguished. Typical patterns of mass motions in H-alpha are described for chromospheric flare ribbons, remote chromospheric flare patches, flare loops, flaring arches, surges, erupting filaments and some expanding coronal features. Interrelationships between these phenomena are discussed and illustrations of each are presented.

Martin, Sara F.↗

NASA NTRS1989

Flaring arches. II - Events in the arch system of 6/7 November, 1980

A characterization is developed for the 57,000-km long arch-shaped coronal structure of November 6, 1980, which became the site, first, of 13 quasi-periodic X-ray brightenings, and then of a series of 17 flaring arches. A comparison of H-alpha, O V, and X-ray data for the SB arch has qualitatively confirmed that a hot conduction front producing X-rays in the least dense plasma is first present, and is followed by a decelerating, denser plasma bulk in O V, with an eventual, still-further-decelerating very dense plasma becoming visible in H-alpha emission.

Svestka, Zdenek↗

NASA NTRS1989

The footpoints of giant arches

H-alpha photographs are presented, which show chromospheric footpoints of the giant post-flare arches discovered by the Hard X-ray Imaging Spectrometer on the SMM satellite. The photographs display chromospheric signatures associated with five sequential giant arch events observed during November 6-10, 1980. The sets of footpoints at both ends of the arches have very slow brightness variations correlated in time with the brightness variations of the X-ray arches. The identifications of the two sets of footpoints is confirmed by current-free modeling of the coronal magnetic field (Kopp and Poletto, 1989). Possible explanations for the giant arch phenomenon are discussed.

Martin, Sara F.↗

NASA NTRS1988

Long-term evolution of a high-latitude active region

The decay phase of one of the largest active regions of solar cycle 22 that developed by the end of June 1987 is studied. Migration of the magnetic fields northward, poleward, and equatorward is shown to lead to the apparent rotation of the magnetic axis of the region. The sunspot motions and pattern of evolution of the magnetic fields noted provide evidence for the existence of a large-scale velocity field within the active region.

Marquette, William H.↗

NASA NTRS1988

The identification and interaction of network, intranetwork, and ephemeral-region magnetic fields

Network magnetic fields are described as the dynamic product of the merging and cancelling of intranetwork fields, ephemeral regions, and the remnants of active regions. The similarities of these phenomena with solar magnetic features are pointed out. The intranetwork magnetic fields are characterized by the flow of successive fragments in approximately radial patterns away from their apparent source sites.

Martin, Sara F.↗

NASA NTRS1987

Multi-thermal observations of newly formed loops in a dynamic flare

The dynamic flare of November 6, 1980 (max at about 15:26 UT) developed a rich system of growing loops which could be followed in H-alpha for 1.5 hr. Throughout the flare, these loops, near the limb, were seen in emission against the disk. Theoretical computations of deviations from LTE populations for a hydrogen atom reveal that this requires electron densities in the loops close to, or in excess of 10 to the 12th/cu cm. From measured widths of higher Balmer lines the density at the tops of the loops was found to be 4 x 10 to the 12th/cu cm if no nonthermal motions were present, or 5 x 10 to the 11th/cu cm for a turbulent velocity of about 12 km/s. It is now general knowledge that flare loops are initially observed in X-rays and become visible in H-alpha only after cooling. For such a high density, a loop would cool through radiation from 10 to the 7th to 10 to the 4th K within a few minutes so that the dense H-alpha loops should have heights very close to the heights of the X-ray loops. This, however, contradicts the observations obtained by the HXIS and FCS instruments on board SMM which show the X-ray loops at much higher altitudes than the loops in H-alpha. Therefore, it is suggested that the density must have been significantly lower when the loops were formed, and that the flare loops were apparently both shrinking and increasing in density while cooling.

Svestka, Zdenek F.↗

NASA NTRS1986

Recent observations of the formation of filaments

Two examples of the formation of small filaments in H alpha are described and illustrated. In both cases, the formation is seen to be the spontaneous appearance of strands of absorbing mass that evolve from no previous structure. The initial development of the filaments appears to consist of the accumulation of these absorptive strands along approximately parallel paths in a channel between large-scale, opposite polarity magnetic fields on either side of the filaments. The strands exhibit continuous changes in shape and degree of absorption which can be due to successive condensations resulting in new strands, mass motions within the strands, and outflow of the mass from the strands. For at least several hours before the formation of both filaments, small-scale fragments of opposite polarity, line-of-sight magnetic flux adjacent to or immediately below the filaments, and at the ends of the filaments, were cancelling. This type of magnetic flux disappearance continued during the development of the filaments and is commonly observed in association with established filaments. Cancellation is interpreted as an important evolutionary change in the magnetic field that can lead to configurations suitable for the formation of filaments.

Martin, Sara F.↗

NASA NTRS1986

Small-scale eruptive filaments on the quiet sun

A study of a little known class of eruptive events on the quiet sun was conducted. All of 61 small-scale eruptive filamentary structures were identified in a systematic survey of 32 days of H alpha time-lapse films of the quiet sun acquired at Big Bear Solar Observatory. When fully developed, these structures have an average length of 15 arc seconds before eruption. They appear to be the small-scale analog of large-scale eruptive filaments observed against the disk. At the observed rate of 1.9 small-scale eruptive features per field of view per average 7.0 hour day, the rate of occurence of these events on the sun were estimated to be greater than 600 per 24 hour day.. The average duration of the eruptive phase was 26 minutes while the average lifetime from formation through eruption was 70 minutes. A majority of the small-scale filamentary sturctures were spatially related to cancelling magnetic features in line-of-sight photospheric magnetograms. Similar to large-scale filaments, the small-scale filamentary structures sometimes divided opposite polarity cancelling fragments but often had one or both ends terminating at a cancellation site. Their high numbers appear to reflect the much greater flux on the quiet sun. From their characteristics, evolution, and relationship to photospheric magnetic flux, it was concluded that the structures described are small-scale eruptive filaments and are a subset of all filaments.

Hermans, Linda M.↗