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Register a new userIs the Polar Region Different from the Quiet Region of the Sun?
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Observations of the polar region of the Sun are critically important for understanding the solar dynamo and the acceleration of solar wind. We carried out precise magnetic observations on both the North polar region and the quiet Sun at the East limb with the Spectro-Polarimeter of the Solar Optical Telescope aboard Hinode to characterize the polar region with respect to the quiet Sun. The average area and the total magnetic flux of the kG magnetic concentrations in the polar region appear to be larger than those of the quiet Sun. The magnetic field vectors classified as vertical in the quiet Sun have symmetric histograms around zero in the strengths, showing balanced positive and negative flux, while the histogram in the North polar region is clearly asymmetric, showing a predominance of the negative polarity. The total magnetic flux of the polar region is larger than that of the quiet Sun. In contrast, the histogram of the horizontal magnetic fields is exactly the same between the polar region and the quiet Sun. This is consistent with the idea that a local dynamo process is responsible for the horizontal magnetic fields. A high-resolution potential field extrapolation shows that the majority of magnetic field lines from the kG-patches in the polar region are open with a fanning-out structure very low in the atmosphere, while in the quiet Sun, almost all the field lines are closed.
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Element abundance ratios of magnesium to neon (Mg/Ne) and neon to oxygen (Ne/O) in the transition region of the quiet Sun have been derived by re-assessing previously published data from the Coronal Diagnostic Spectrometer on board the Solar and Heliospheric Observatory in the light of new atomic data. The quiet Sun Mg/Ne ratio is important for assessing the effect of magnetic activity on the mechanism of the first ionization potential (FIP) effect, while the Ne/O ratio can be used to infer the solar photospheric abundance of neon, which can not be measured directly. The average Mg/Ne ratio is found to be $0.52pm 0.11$, which applies over the temperature region 0.2--0.7~MK, and is consistent with the earlier study. The Ne/O ratio is, however, about 40% larger, taking the value $0.24pm 0.05$ that applies to the temperature range 0.08--0.40~MK. The increase is mostly due to changes in ionization and recombination rates that affect the equilibrium ionization balance. If the Ne/O ratio is interpreted as reflecting the photospheric ratio, then the photospheric neon abundance is $8.08pm 0.09$ or $8.15pm 0.10$ (on a logarithmic scale for which hydrogen is 12), according to whether the oxygen abundances of M.~Asplund et al. or E.~Caffau et al. are used. The updated photospheric neon abundance implies a Mg/Ne FIP bias for the quiet Sun of $1.6pm 0.6$.
We studied the dynamics of the solar atmosphere in the region of a large quiet-Sun filament, which erupted on 21 October 2010. The filament eruption started at its northern end and disappeared from the H$alpha$ line-core filtergrams line within a few hours. The very fast motions of the northern leg were recorded in ultraviolet light by AIA. We aim to study a wide range of available datasets describing the dynamics of the solar atmosphere for five days around the filament eruption. This interval covers three days of the filament evolution, one day before the filament growth and one day after the eruption. We search for possible triggers that lead to the eruption of the filament. The surface velocity field in the region of the filament were measured by means of time-distance helioseismology and coherent structure tracking. The apparent velocities in the higher atmosphere were estimated by tracking the features in the 30.4 nm AIA observations. To capture the evolution of the magnetic field, we extrapolated the photospheric line-of-sight magnetograms and also computed the decay index of the magnetic field. We found that photospheric velocity fields showed some peculiarities. Before the filament activation, we observed a temporal increase of the converging flows towards the filaments spine. In addition, the mean squared velocity increased temporarily before the activation and peaked just before it, followed by a steep decrease. We further see an increase in the average shear of the zonal flow component in the filaments region, followed by a steep decrease. The photospheric l.o.s. magnetic field shows a persistent increase of induction eastward from the filament spine. The decay index of the magnetic field at heights around 10 Mm shows a value larger than critical at the connecting point of the northern filament end.
Rapid Blue- and Red-shifted Excursions (RBEs and RREs) are likely to be the on-disk counterparts of Type II spicules. Recently, heating signatures from RBEs/RREs have been detected in IRIS slit-jaw images dominated by transition-region lines around network patches. Additionally, signatures of Type II spicules have been observed in AIA diagnostics. The full-disk, ever-present nature of the AIA diagnostics should provide us with sufficient statistics to directly determine how important RBEs and RREs are to the heating of the transition region and corona. We find, with high statistical significance, that at least 11% of the low-coronal brightenings detected in a quiet-Sun region in 304, can be attributed to either RBEs or RREs as observed in Halpha, and a 6% match of 171 detected events to RBEs or RREs with very similar statistics for both types of Halpha features. We took a statistical approach that allows for noisy detections in the coronal channels and provides us with a lower, but statistical significant, bound. Further, we consider matches based on overlapping features in both time and space, and find strong visual indications of further correspondence between coronal events and co-evolving but non-overlapping, RBEs and RREs.
This work reviews our understanding of the magnetic fields observed in the quiet Sun. The subject has undergone a major change during the last decade (quiet revolution), and it will remain changing since the techniques of diagnostic employed so far are known to be severely biased. Keeping these caveats in mind, our work covers the main observational properties of the quiet Sun magnetic fields: magnetic field strengths, unsigned magnetic flux densities, magnetic field inclinations, as well as the temporal evolution on short time-scales (loop emergence), and long time-scales (solar cycle). We also summarize the main theoretical ideas put forward to explain the origin of the quiet Sun magnetism. A final prospective section points out various areas of solar physics where the quiet Sun magnetism may have an important physical role to play (chromospheric and coronal structure, solar wind acceleration, and solar elemental abundances).
The cluster formed by active regions (ARs) NOAA 11121 and 11123, approximately located on the solar central meridian on 11 November 2010, is of great scientific interest. This complex was the site of violent flux emergence and the source of a series of Earth-directed events on the same day. The onset of the events was nearly simultaneously observed by the Atmospheric Imaging Assembly (AIA) telescope aboard the Solar Dynamics Observatory (SDO) and the Extreme-Ultraviolet Imagers (EUVI) on the Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) suite of telescopes onboard the Solar-Terrestrial Relations Observatory (STEREO) twin spacecraft. The progression of these events in the low corona was tracked by the Large Angle Spectroscopic Coronagraphs (LASCO) onboard the Solar and Heliospheric Observatory (SOHO) and the SECCHI/COR coronagraphs on STEREO. SDO and SOHO imagers provided data from the Earths perspective, whilst the STEREO twin instruments procured images from the orthogonal directions. This spatial configuration of spacecraft allowed optimum simultaneous observations of the AR cluster and the coronal mass ejections that originated in it. Quadrature coronal observations provided by STEREO revealed a notably large amount of ejective events compared to those detected from Earths perspective. Furthermore, joint observations by SDO/AIA and STEREO/SECCHI EUVI of the source region indicate that all events classified by GOES as X-ray flares had an ejective coronal counterpart in quadrature observations. These results have direct impact on current space weather forecasting because of the probable missing alarms when there is a lack of solar observations in a view direction perpendicular to the Sun-Earth line.
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