Coronal holes

Altschuler, Martin D.; Trotter, Dorothy E.; Orrall, F. Q.

doi:10.1007/bf00165276

Cited by 133 publications

(47 citation statements)

References 9 publications

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“…The plasma temperature and density in CHs is low compared to their surroundings, and thus they appear as dark areas in the corona (Munro and Withbroe, 1972;Cranmer, 2009). They can be observed in space-based X-ray (Wilcox, 1968;Altschuler, Trotter, and Orrall, 1972;Hundhausen, 1972) and EUV images (Newkirk, 1967;Tousey, Sandlin, and Purcell, 1968;Del Zanna and Bromage, 1999). More recent studies on the outflow dynamics and Doppler shifts of coronal holes improved the understanding of CHs being the source of the fast solar wind (Hassler et al, 1999;Peter and Judge, 1999;Xia, Marsch, and Curdt, 2003;Aiouaz, Peter, and Lemaire, 2005).…”

Section: Introductionmentioning

confidence: 99%

Real-Time Solar Wind Prediction Based on SDO/AIA Coronal Hole Data

et al. 2015

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We present an empirical model based on the visible area covered by coronal holes close to the central meridian in order to predict the solar wind speed at 1 AU with a lead time up to four days in advance with a 1-h time resolution. Linear prediction functions are used to relate coronal hole areas to solar wind speed. The function parameters are automatically adapted by using the information from the previous 3 Carrington Rotations. Thus the algorithm automatically reacts on the changes of the solar wind speed during different phases of the solar cycle. The adaptive algorithm has been applied to and tested on SDO/AIA-193Å observations and ACE measurements during the years 2011 − 2013, covering 41 Carrington Rotations. The solar wind speed arrival time is delayed and needs on average 4.02 ± 0.5 days to reach Earth. The algorithm produces good predictions for the 156 solar wind high speed streams peak amplitudes with correlation coefficients of cc ≈ 0.60. For 80% of the peaks, the predicted arrival matches within a time window of 0.5 days of the ACE in situ measurements. The same algorithm, using linear predictions, was also applied to predict the magnetic field strength from coronal hole areas but did not give reliable predictions (cc ≈ 0.2).

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Section: Introductionmentioning

confidence: 99%

Real-Time Solar Wind Prediction Based on SDO/AIA Coronal Hole Data

et al. 2015

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“…Furthermore, different transient phenomena with origin at the solar surface produce disturbances to the steady SW. An example of these SW "transient structures" is the phenomenon of fast transient streams of plasma from coronal holes (Altschuler, Trotter, and Orrall, 1972) or interplanetary coronal mass ejections (ICMEs), which have a magnetic topology radically different from the steady SW (e.g., Dasso et al, 2005b). These composite structures (which can contain several smaller sub-structures such as shock waves, plasma sheaths, etc.)…”

Section: Introductionmentioning

confidence: 99%

Characterization of the Turbulent Magnetic Integral Length in the Solar Wind: From 0.3 to 5 Astronomical Units

et al. 2014

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The solar wind is a structured and complex system, in which the fields vary strongly over a wide range of spatial and temporal scales. As an example, the turbulent activity in the wind affects the evolution in the heliosphere of the integral turbulent scale or correlation length [λ], usually associated with the breakpoint in the turbulent-energy spectrum that separates the inertial range from the injection range. This large variability of the fields demands a statistical description of the solar wind. In this work, we study the probability distribution function (PDF) of the magnetic autocorrelation lengths observed in the solar wind at different distances from the Sun. We use observations from Helios, ACE, and Ulysses spacecraft. We distinguish between the usual solar wind and one of its transient components (Interplanetary Coronal Mass Ejections, ICMEs), and study also solar wind samples with low and high proton beta [β p ]. We find that in the last 3 regimes the PDF of λ is a log-normal function, consistent with the multiplicative and non-linear processes that take place in the solar wind, the initial λ (before the Alfvénic point) being larger in ICMEs.

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“…According to current understanding coronal holes differ from the normal quiet Sun mainly through the structure of the magnetic field, with the field lines being mainly closed in the normal quiet Sun and open above coronal holes (e.g. Altschuler et al 1972). Hot gas is trapped in closed loops, but is able to escape along the open field lines.…”

Section: Introductionmentioning

confidence: 99%

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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Coronal holes

Cited by 133 publications

References 9 publications

Real-Time Solar Wind Prediction Based on SDO/AIA Coronal Hole Data

Real-Time Solar Wind Prediction Based on SDO/AIA Coronal Hole Data

Characterization of the Turbulent Magnetic Integral Length in the Solar Wind: From 0.3 to 5 Astronomical Units

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

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