Synoptic IPS and Yohkoh soft X‐ray observations

Hick, P. P.; Jackson, B. V.; Rappoport, S. A.; Woan, G.; Slater, G. L.; Strong, K. T.; Uchida, Yutaka

doi:10.1029/95gl00011

Cited by 30 publications

(17 citation statements)

References 6 publications

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“…Radially aligned structures have been observed in the inner heliosphere by Helios in situ plasma measurements (Thieme, Schwenn, & Marsch 1989;Thieme, Marsch, & Schwenn 1990). When Yohkoh soft X-ray synoptic maps were correlated with IPS (interplanetary scintillation measurements that reflect density fluctuations) maps based on measurements beyond 0.5 AU by the Mullard Radio Astronomy Observatory in Cambridge, England, a better match was found for the active regions than the heliospheric current sheet (Hick et al 1995). The heliospheric current sheet is not detected by the Cambridge array because the enhanced density fluctuations associated with the heliospheric current sheet span an angular size of only a few degrees (Woo et al 1995a;Habbal et al 1997), which is smaller than the spatial resolution of the Cambridge array.…”

Section: Discussionmentioning

confidence: 99%

Imprint of the Sun on the Solar Wind

Woo

Habbal

1999

The Astrophysical Journal

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Observations of the inner corona in polarized brightness by the Mauna Loa Mk III K-coronameter at 1.15 R , and soft X-rays by Yohkoh at 1.03 R , are combined with 1995 Ulysses radio occultation measurements of the solar wind to demonstrate that the signatures of the coronal hole boundary, active regions, and bright points are present in the heliocentric distance range of 20-30 R , . The existence of these signatures in the brightness of the corona (observed by ranging measurements) and the contrast of the small-scale raylike structures comprising the corona (observed by Doppler scintillation measurements) at such distances can readily be accounted for by open field lines rooted within the complex magnetic structures of the quiet Sun, active regions, and bright points. Hence, with the exception of the small volume of interplanetary space occupied by the heliospheric current sheet that evolves from coronal streamers within a few solar radii of the Sun, small-scale raylike structures carry the imprint of the different density structures of the solar disk approximately radially into the heliosphere.

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Section: Discussionmentioning

confidence: 99%

Imprint of the Sun on the Solar Wind

Woo

Habbal

1999

The Astrophysical Journal

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“…This observation suggests that magnetically-driven outward flows from active regions may contribute to the global coronal structure or even to the slow, dense component of the solar wind [e.g., Hick et al, 1995]. Such a mechanism may also be of general interest for stellar mass loss.…”

Section: Expanding Active-region Loopsmentioning

confidence: 99%

Soft X-Ray Signatures of Coronal Ejections

Hudson

Webb

2013

Geophysical Monograph Series

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We have a new view of the time behavior of the inner solar corona via the extensive soft X-ray observations of Yohkoh. These show many forms of expansion of coronal material, ranging from highly collimated structures (jets) to large-scale evacuations ("dimmings") of the diffuse corona. We review these effects, emphasizing those probably related to CMEs, and present a preliminary classification scheme of the large-scale ejections seen in soft X-rays. The new observations bring clarity and focus to the well-established scenario of filament channel -+ CME -+ X-ray arcade. The associated Xray brightening typically occurs in a close temporal relationship with the ejection as inferred from the dimming, but the location of the ejected mass may be displaced from the region of strongest brightening. The soft X-ray observations thus far have shown no clear example of the familiar three-part structure of CMEs as seen in white-light coronal images.

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“…That the finest filamentary structures emanate from the active region (factor of 3-6 smaller than in the polar coronal hole) is consistent with expectations based on heat transport and photospheric flux bundle packing considerations (Golub & Pasachoff 1997, p. 202 2005) are smaller, having higher frequency break points than those observed here, indicating that the smallest scale evolves with radial distance. Since the levels of the power spectrum of the Doppler fluctuations covering both filamentary structures (steeper power law) and convected turbulence (shallower power law) rise and fall together (Pätzold et al 1996;Woo & Habbal 1997b), turbulence inhomogeneities associated with active regions also have the steepest gradients, which explains why enhanced intensity scintillation is correlated with active regions (Hick et al 1995). The steepest density gradients of filamentary structures and convected turbulence are a consequence of the strength and complexity of the magnetic field in active regions.…”

Section: Radio Observations and Resultsmentioning

confidence: 99%

Ultra-fine-Scale Filamentary Structures in the Outer Corona and the Solar Magnetic Field

Woo

2006

ApJ

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Filamentary structures following magnetic field lines pervade the Sun's atmosphere and offer us insight into the solar magnetic field. Radio propagation measurements have shown that the smallest filamentary structures in the solar corona are more than 2 orders of magnitude finer than those seen in solar imaging. Here we use radio Doppler measurements to characterize their transverse density gradient and determine their finest scale in the outer corona at 20-30 R , where open magnetic fields prevail. Filamentary structures overlying active regions have the steepest gradient and finest scale, while those overlying coronal holes have the shallowest gradient and least finest scale. Their organization by the underlying corona implies that these subresolution structures extend radially from the entire Sun, confirming that they trace the coronal magnetic field responsible for the radial expansion of the solar wind. That they are rooted all over the Sun elucidates the association between the magnetic field of the photosphere and that of the corona, as revealed by the similarity between the power spectra of the photospheric field and the coronal density fluctuations. This association along with the persistence of filamentary structures far from the Sun demonstrate that subresolution magnetic fields must play an important role not only in magnetic coupling of the photosphere and corona, but also in coronal heating and solar wind acceleration through the process of small-scale magnetic reconnection. They also explain why current widely used theoretical models that extrapolate photospheric magnetic fields into the corona do not predict the correct source of the solar wind.

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Synoptic IPS and Yohkoh soft X‐ray observations

Cited by 30 publications

References 6 publications

Imprint of the Sun on the Solar Wind

Imprint of the Sun on the Solar Wind

Soft X-Ray Signatures of Coronal Ejections

Ultra-fine-Scale Filamentary Structures in the Outer Corona and the Solar Magnetic Field

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