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Belenko, I. A.

doi:10.1023/a:1010372926629

Cited by 15 publications

(11 citation statements)

References 10 publications

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“…From previous publications (Harvey et al, 1982;DeForest et al, 1997;Wilhelm, 2000;Belenko, 2001) we know that the magnetic flux in coro- There is a clear trend for the loop height to decrease with Bz |Bz| , the correlation coefficient between these two quantities being r c = −0.87. Interestingly the loop length is not so strongly correlated (r c = −0.57), mainly because of CH3 and CH6, which have anomalously long loops (but not strikingly high ones).…”

Section: What Magnetic Features Are Responsible For Coronal Holes?mentioning

confidence: 77%

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Similarities and Differences between Coronal Holes and the Quiet Sun: Are Loop Statistics the Key?

Wiegelmann

Solanki

2004

Sol Phys

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Abstract. Coronal holes (CH) emit significantly less at coronal temperatures than quiet Sun regions (QS), but can hardly be distinguished in most chromospheric and lower transition region lines. A key quantity for the understanding of this phenomenon is the magnetic field. We use data from SOHO/MDI to reconstruct the magnetic field in coronal holes and the quiet Sun with the help of a potential magnetic model. Starting from a regular grid on the solar surface we then trace field lines, which provide the overall geometry of the 3D magnetic field structure.We distinguish between open and closed field lines, with the closed field lines being assumed to represent magnetic loops. We then try to compute some properties of coronal loops. The loops in the CH are found to be on average flatter than in the QS. High and long closed loops are extremely rare, whereas short and low-lying loops are almost as abundant in coronal holes as in the quiet Sun. When interpreted in the light of loop scaling laws this result suggests an explanation for the relatively strong chromospheric and transition region emission (many low-lying, short loops), but the weak coronal emission (few high and long loops) in coronal holes. In spite of this contrast our calculations also suggest that a significant fraction of the cool emission in CHs comes from the open flux regions. Despite these insights provided by the magnetic field line statistics further work is needed to obtain a definite answer to the question if loop statistics explain the differences between coronal holes and the quiet Sun.

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Section: What Magnetic Features Are Responsible For Coronal Holes?mentioning

confidence: 77%

“…The magnetic field strength in the photosphere beneath coronal holes has been measured by several authors, (e.g., Levine 1977, Bohlin and Sheeley 1978, Harvey et al 1982, DeForest et al 1997, Belenko 2001. The magnetic flux in coronal holes clearly shows a dominant polarity.…”

Section: Introductionmentioning

confidence: 85%

Similarities and Differences between Coronal Holes and the Quiet Sun: Are Loop Statistics the Key?

Wiegelmann

Solanki

2004

Sol Phys

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“…The number of non-polar coronal holes increases during the rising phase of the solar cycle (Belenko 2001). Locations of individual coronal holes change significantly on the solar disk every day.…”

Section: Analysis and Resultsmentioning

confidence: 99%

“…The smaller details are represented by the harmonics of higher order. The harmonic coefficients for 1904-1984Carrington rotations (1996-2001 from the Wilcox Solar Observatory were used.…”

Section: Analysis and Resultsmentioning

confidence: 99%

Coronal holes and the solar polar field reversal

Bilenko¹

2002

A&A

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Abstract.The relationship between the solar polar magnetic field reversal and coronal hole evolution is investigated for the time interval from 1996 to 2001. The distribution of coronal holes shows some evolutionary changes in relation to the polarity reversals, and these changes appear to be coordinated with changes in the global magnetic field structure, suggesting that the polar reversal originates from global processes. There are periods when the character of the coronal hole distribution on the solar disk changes significantly, indicating that the magnetic field structure changes. These can be interpreted as periods of rearrangement of the multipole magnetic field structure. It is found that the evolution of the geometric structure of the photospheric magnetic field during these periods is not characterized by a continuous transition from one dominant structure to another, but by relatively sudden rearrangement of the dominant geometrical structure of the magnetic field. These coronal holes and photospheric magnetic field rearrangements coincide with the polar photospheric magnetic field strength variations. The minimum phase of the solar cycle is dominated by the dipole component of the global solar magnetic field. The zonal magnetic field structure and zonal non-polar coronal hole distribution existed at that time. The sectorial magnetic field structure appears when the polar field strength reaches 0.7 of its maximum value in the corresponding hemisphere. This structure was established at different times in each hemisphere. In the north hemisphere it has existed since November 1998 and in the south hemisphere it has existed since October 1997. The rearrangement from one configuration to another occurs during a short time period, about 1 ÷ 2 solar rotations. The coronal hole number and area evolution indicates a redistribution of positive-polarity and negative-polarity photospheric magnetic fields inside these longitudinal sectors, which reflects the solar polar field reversal.

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“…A detailed analysis of high-resolution magnetograms shows that network magnetic elements within the coronal holes are predominately of the same polarity. The ratio of areas occupied by opposite polarities is 1:4 within the coronal holes, while it is about 1:1 in quiet regions (Varsik et al 1999;Belenko 2001). In regions of mixed polarities, a lot of field lines do not rise high into the corona as they connect the nearby patches of opposite polarity, whereas in the regions of predominant polarity most of the field lines reach high altitude (Fig.…”

Section: Introductionmentioning

confidence: 96%

On the dynamic nature of the prolate solar chromosphere: jet formation

Filippov¹,

Koutchmy²,

Vilinga³

2007

A&A

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Context. In "cool" spectral lines, the smoothed upper edge of the solar chromosphere is prolate in the South-North direction at the epoch of minimum solar activity and nearly spherically symmetric at the maximum phase. We attribute the effect to the dynamical nature of the upper chromosphere, which consists of a large number of small jet-like structures ascending into the corona. We could not resolve the source region of an individual jetlet, although similar but larger structures are visible, especially in EUV coronal lines. Aims. We consider the problem of the formation of an individual jet above the limb, assuming that a large number of jet-like events is responsible for the prolate solar upper chromosphere. We then assume that spicules, being the cool part of the phenomenon, behave similarly, and we will mainly concentrate the analysis on the magnetic origin of the event.Methods. Image processing is used to reveal the displacement of magnetic field tubes filled with coronal plasma and jet formation due to field aligned motion above the null point created in the corona by the emerging magnetic bipole. Results. The growth of the bipole leads to a reconnection of the field lines and to a specific plasma motion in the vicinity of the null point that results in a plasma flow along the spine line of the 3D null. We assume that similar but smaller processes could happen very often at a smaller scale in the chromosphere, near emerging magnetic ephemeral regions, forming numerous jetlets in the upper chromosphere. As the field aligned motion is guided by the magnetic field, at the epoch of low activity the large-scale structure of the polar magnetic field and the one of the quiet equatorial region is sufficiently different to explain the prolateness of the chromosphere.

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Cited by 15 publications

References 10 publications

Similarities and Differences between Coronal Holes and the Quiet Sun: Are Loop Statistics the Key?

Similarities and Differences between Coronal Holes and the Quiet Sun: Are Loop Statistics the Key?

Coronal holes and the solar polar field reversal

On the dynamic nature of the prolate solar chromosphere: jet formation

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