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

Abstract

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 (

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

“…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).…”

Reconstructing Coronal Hole Areas With EUHFORIA and Adapted WSA Model: Optimizing the Model Parameters

“…Any instrument (in this case AIA) suffers inevitable depletions (e.g., decreasing sensitivity, aging filters, and others), distortion of optical system, and scattered light to name just a few. But in the context of this study, especially regarding the CH detection, we do not believe that these uncertainties introduce significant errors, as each CH was manually tuned to account for such instrumental and observational changes (see for more details Heinemann et al, ). For the case of large CHs we have only one point so the relation between coverage and area remains inconclusive.…”

“…The CH boundaries were extracted using catch (Heinemann et al, 2019), an intensity threshold algorithm that is modulated by the intensity gradient along the CHs boundary. The SSW-IDL-written GUI enables the user to optimize the threshold used for the CH extraction by considering the average intensity profile at the Journal of Geophysical Research: Space Physics 10.1029/2019JA027173 boundary to find the highest gradient.…”

“…The lower and upper bounds present a significantly overestimated and underestimated threshold for the extraction. For further information on the algorithm, we refer to Heinemann et al (2019). Line-of-sight effects can introduce errors in the boundary extraction of the CH with CATCH; however, these errors are of the order of 2 to 8 arcseconds.…”

“…To do that, we selected a sample of 15 CHs located around the central meridian of the solar disk as viewed from Earth, but at different latitudes (see section ). Using CATCH (Collection of Analysis Tools for Coronal Holes; Heinemann et al, ), we extracted the boundaries of these CHs based on their appearance in EUV filtergrams at 193 Å (section ). We reconstructed their areas with EUHFORIA, by varying the paired values for the heights of the source surface and the inner boundary of the SCS model, in order to find optimal values that produce a better match between modeled and observed CH areas (section ).…”