Streaming Magnetic Features near Sunspots

Vrabec, Dale

doi:10.1017/s0074180900069102

Cited by 30 publications

(6 citation statements)

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“…Strous (1994) and Strous and Zwaan (1999) described elementary bipoles as seen in magnetograms and continuum images, and Hα images taken with the Lockheed SOUP filter at the Swedish Solar Observatory. They called them flux emergence events and showed small magnetic features (Figure 2) with the similar sizes and the flow patterns as discussed independently by Vrabec (1974) and Martin (1990). Another independent observation was by Bernasconi et al (2002) who described features they named Moving Dipolar Features (MDFs) as seen in magnetograms from a balloon born observatory, "The Flare Genesis Experiment."…”

Section: Elementary Bipoles and Associated Featuressupporting

confidence: 67%

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Observational Evidence of Shallow Origins for the Magnetic Fields of Solar Cycles

Martin

2018

Front. Astron. Space Sci.

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Observational evidence for the origin of active region magnetic fields has been sought from published information on extended solar cycles, statistical distributions of active regions and ephemeral regions, helioseismology results, positional relationships to supergranules, and fine-scale magnetic structure of active regions and their sunspots during their growth. Statistical distributions of areas of ephemeral and active regions blend together to reveal a single power law. The shape of the size distribution in latitude of all active regions is independent of time during the solar cycle, yielding further evidence that active regions of all sizes belong to the same population. Elementary bipoles, identified also by other names, appear to be the building blocks of active regions; sunspots form from elementary bipoles and are therefore deduced to develop from the photosphere downward, consistent with helioseismic detection of downflows to 3-4 Mm below sunspots as well as long-observed downflows from chromospheric/coronal arch filaments into sunspots from their earliest appearance. Time-distance helioseismology has been effective in revealing flows related to sunspots to depths of 20 Mm. Ring diagram analysis shows a statistically significant preference for upflows to precede major active region emergence and downflows after flux emergence but both are often observed together or not detected. From deep-focus helioseismic techniques for seeking magnetic flux below the photosphere prior major active regions, there is evidence of acoustic travel-time perturbation signatures rising in the limited range of depths of 42-75 Mm but these have not been verified or found at more shallow depths by helioseismic holographic techniques. The development of active regions from clusters of elementary bipoles appears to be the same irrespective of how much flux an active region eventually develops. This property would be consistent with the magnetic fields of large active regions being generated in the same way and close the same depth as small active regions in a shallow zone below the photosphere. All evidence considered together, understanding the origins of the magnetic fields of solar cycles boils down to learning how and where elementary bipoles are generated beneath the photosphere.

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Section: Elementary Bipoles and Associated Featuressupporting

confidence: 67%

“…The earliest paper on elementary bipoles was by Vrabec (1974) who called them MMI for "moving magnetic features-inward. (toward a sunspot)."…”

Section: Elementary Bipoles and Associated Featuresmentioning

confidence: 99%

Observational Evidence of Shallow Origins for the Magnetic Fields of Solar Cycles

Martin

2018

Front. Astron. Space Sci.

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“…However, if one in tends to study their movements and evolutionary changes, considerably better data are needed. By far the most effective method for both detecting and observing MFO has proven to be the transformation of magnet ograms into time-lapse movies (Vrabec, 1971;Harvey andSchoolman, 1972), but these require large numbers of magnetograms and longer time coverage. For example, a recent movie of MFO prepared from observations made by Chapman (1973) with the Aerospace spectroheliograph reveals many interesting details regarding the fine structure, polarities, and patterns of flow of MMF's as well as the manner in which they first appear, subsequently change, interact, or finally disappear.…”

Section: Appendix Observational and Instrumental Aspectsmentioning

confidence: 99%

“…As was stated previously, one of the most outstanding needs of MMF research is to obtain continuous, synoptic magnetic field observations over extended intervals of many days so that the complete evolutionary history of MFO and MFI, as they relate to the evolutionary development of sunspots, can be observed. Ultimately, such observations will come from space observatories, but it should be realized that it is also feasible to obtain continuous solar data with a suitable network of groundbased observatories distributed in longitude, or from a single installation at a suf ficiently high latitude Rogers, 1970).…”

Section: Appendix Observational and Instrumental Aspectsmentioning

confidence: 99%

Streaming Magnetic Features near Sunspots

Vrabec

1974

Symp. - Int. Astron. Union

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Observations prompted by Sheeley's discovery of outflowing CN bright points from sunspots have established that there occur small moving magnetic features (MMF's) near sunspots. These MMF's exhibit a highly ordered pattern of movement directly related to the associated sunspot. The observations are consistent with the concept of magnetic flux outflow (MFO), a process whereby net magnetic flux of the same polarity as the sunspot is transferred from a decaying sunspot to the surrounding magnetic network. Small magnetic flux concentrations are apparently convected outward by a velocity cell centered on the sunspot. Doppler spectroheliograms have provided evidence for such systematic outward velocities extending as far as 10000 to 20000 km beyond the outer edge of the penumbra of some sunspots, which is comparable to the extent of MFO. While MFO is best observed by means of time-lapse movies of the magnetic fields, it is also manifested morphologically on individual magnetograms by features that resemble moats (or bays) and wreaths around only those sunspots where MFO is present. Two examples of magnetic features streaming toward and into rapidly forming sunspots are described, providing evidence for the occurrence of magnetic flux inflow (MFI) associated with the growth phase of sunspot development. It is, therefore, likely that MFI and MFO are basic aspects of the evolutionary development of sunspots. Observational and instrumental aspects relevant to the investigation of MMF's are described in the Appendix.

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“…The structures surrounding the spot possess low LOS magnetic field components and evolve moving away (Vrabec 1974). The penumbra-pore interaction always occurs such that the penumbra seemingly 'feeds' the pore with magnetic flux.…”

Section: Results On Temporal Evolutionmentioning

confidence: 99%