Photospheric magnetic structure of coronal holes

Hofmeister, Stefan J.; Utz, D.; Heinemann, Stephan G.; Veronig, Astrid; Temmer, Manuela

doi:10.1051/0004-6361/201935918

Cited by 43 publications

(42 citation statements)

References 36 publications

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“…The strength of the photospheric magnetic field underlying the CHs is distributed around 2.9 ± 1.9 G which is in agreement with most results found in the literature and shows that CHs are mostly covered by low magnetic field. v) We confirm previous studies (Hofmeister et al, 2017;Heinemann et al, 2018b;Hofmeister et al, 2019) that the magnetic configuration of CHs is highly dependent on the abundance and field strength of the small unipolar magnetic elements (flux tubes), which only cover a small fraction of the CH area.…”

Section: Discussionsupporting

confidence: 90%

“…When interpreting such parameters a relative comparison should be preferred rather than relying on absolute values. Hofmeister et al (2019) showed that the photospheric magnetic field underlying CHs can be divided into 3 categories: ≈ 22 ± 4% of the signed magnetic flux is contributed by a slightly unbalanced background field. ≈ 5.0 ± 0.1% come from small scale unipolar magnetic elements (flux tubes, FTs) nearly symmetrically distributed over both polarities and which are associated with the super-, meso-, and granular motion of the photosphere.…”

Section: Analysis Of the Underlying Photospheric Magnetic Fieldmentioning

confidence: 99%

“…This evolutionary process seems to be governed especially by interchange reconnection (Wang and Sheeley, 2004;Madjarska, Doyle, and van Driel-Gesztelyi, 2004;Krista, Gallagher, and Bloomfield, 2011;Ma et al, 2014;Kong et al, 2018) and flux emergence (Cranmer, 2009, and the references therein). Hofmeister et al (2017), Hofmeister et al (2019), and Heinemann et al (2018b) found that the abundance of the strong unipolar magnetic elements (flux tubes) is what defines the magnetic configuration of a CH. Notwithstanding that they cover only a small fraction of the CH area they contribute a major part of the total signed magnetic flux of the CH.…”

Section: Distribution Over Chs Of Solar Cycle 24mentioning

confidence: 99%

“…Our results are in better agreement with the study of Heinemann et al (2018b) who found values of r A ≤ 5% and r = 48 to 71%. The recent study by Hofmeister et al (2019) found that these strong FTs have lifetimes larger that those of supergranular cells essentially making them the fundamental building blocks of CHs, and they are not governed by the photospheric network motion.…”

Section: Distribution Over Chs Of Solar Cycle 24mentioning

confidence: 99%

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Statistical Analysis and Catalog of Non-polar Coronal Holes Covering the SDO-Era Using CATCH

et al. 2019

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Coronal holes are usually defined as dark structures seen in the extreme ultraviolet and X-ray spectrum which are generally associated with open magnetic fields. Deriving reliably the coronal hole boundary is of high interest, as its area, underlying magnetic field, and other properties give important hints as regards high speed solar wind acceleration processes and compression regions arriving at Earth. In this study we present a new threshold-based extraction method, which incorporates the intensity gradient along the coronal hole boundary, which is implemented as a user-friendly SSW-IDL GUI. The Collection of Analysis Tools for Coronal Holes (CATCH) enables the user to download data, perform guided coronal hole extraction and analyze the underlying photospheric magnetic field. We use CATCH to analyze non-polar coronal holes during the SDO-era, based on 193 Å filtergrams taken by the Atmospheric Imaging Assembly (AIA) and magnetograms taken by the Heliospheric and Magnetic Imager (HMI), both on board the Solar Dynamics Observatory (SDO). Between 2010 and 2019 we investigate 707 coronal holes that are located close to the central meridian. We find coronal holes distributed across latitudes of about ± 60 • , for which we derive sizes between 1.6 × 10 9 and 1.8 × 10 11 km 2. The absolute value of the mean signed magnetic field strength tends towards an average of 2.9 ± 1.9 G. As far as the abundance and size of coronal holes is concerned, we find no distinct trend towards the northern or southern hemisphere. We find that variations in local and global conditions may significantly change Electronic supplementary material The online version of this article (

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Section: Discussionsupporting

confidence: 90%

Section: Analysis Of the Underlying Photospheric Magnetic Fieldmentioning

confidence: 99%

Section: Distribution Over Chs Of Solar Cycle 24mentioning

confidence: 99%

Section: Distribution Over Chs Of Solar Cycle 24mentioning

confidence: 99%

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Statistical Analysis and Catalog of Non-polar Coronal Holes Covering the SDO-Era Using CATCH

et al. 2019

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“…The total area covered by long-lived magnetic elements with lifetimes > 4 days is strongly correlated with the unbalanced magnetic flux of CHs (cc = 0.99). These magnetic elements account for ≈ 68% of the unbalanced "open" magnetic flux of CHs at typical coverages of about 3% of the total CH area (Hofmeister et al, 2019;Heinemann et al, 2019). Heinemann et al (2018a,b) investigated a long-lived low-latitude CH observed by the Solar Dynamics Observatory (SDO) and Solar Terrestrial Relations Observatory (STEREO) spacecraft over ten solar rotations from February 2012 to October 2012 (see Figure 7).…”

Section: Introductionmentioning

confidence: 99%

Differential Emission Measure Plasma Diagnostics of a Long-Lived Coronal Hole

et al. 2020

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We use Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) data to reconstruct the plasma properties from differential emission measure (DEM) analysis for a previously studied long-lived, low-latitude coronal hole (CH) over its lifetime of ten solar rotations. We initially obtain a non-isothermal DEM distribution with a dominant component centered around 0.9 MK and a secondary smaller component at 1.5-2.0 MK. We find that deconvolving the data with the instrument point spread function (PSF) to account for long-range scattered light reduces the secondary hot component. Using the 2012 Venus transit and a 2013 lunar eclipse to test the efficiency of this deconvolution, significant amounts of residual stray light are found for the occulted areas. Accounting for this stray light in the error budget of the different AIA filters further reduces the secondary hot emission, yielding CH DEM distributions that are close to isothermal with the main contribution centered around 0.9 MK. Based on these DEMs, we analyze the evolution of the emission measure (EM), density, and averaged temperature during the CH's lifetime. We find that once the CH is clearly observed in EUV images, the bulk of the CH plasma reveals a quite constant state, i.e. temperature and density reveal no major changes, whereas the total CH area and the photospheric magnetic fine structure inside the CH show a distinct evolutionary pattern. These findings suggest that CH plasma properties are mostly "set" at the CH formation or/and that all CHs have similar plasma properties.

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