Solar X-ray jets are evidently made by a burst of reconnection of closed magnetic field in a jet's base with ambient "open" field 1, 2 . In the widely-accepted version of the "emergingflux" model, that reconnection occurs at a current sheet between the open field and emerging closed field and also makes a compact hot brightening that is usually observed at the edge of the jet's base 1, 3 . Here we report on high-resolution X-ray and EUV observations of 20 randomly-selected X-ray jets in polar coronal holes. In each jet, contrary to the emergingflux model, a miniature version of the filament eruptions that initiate coronal mass ejections (CMEs) 4-7 drives the jet-producing reconnection, and the compact hot brightening is made by internal reconnection of the legs of the minifilament-carrying erupting closed field, analogous to solar flares of larger-scale eruptions. Previous observations have found that some jets are driven by base-field eruptions [8][9][10]12 , but only one such study, of only one jet, provisionally questioned the emerging-flux model 13 . Our observations support the view that solar filament eruptions are made by a fundamental explosive magnetic process that occurs on a vast range of scales, from the biggest CME/flare eruptions down to X-ray jets, and perhaps down to 1 even smaller jets that are candidates for powering coronal heating 10,14, 15 . A picture similar to that suggested by our observations was drawn before, inferred from different observations and based on a different origin of the erupting minifilament flux rope 11 (see Methods). Solar X-Ray jets are imaged from space in the ∼0.2-2.0 keV range. They are dynamic (upward velocities ∼200 km s −1 ), long (∼5×10 4 km), narrow (8×10 3 km), and transient (lifetimes To assess observationally the production of X-ray jets, we analysed 20 jets (Extended Data Table 1) in the solar polar regions using X-ray images from the X-ray telescope (XRT) on the Hinode satellite 22 , which detects a broad temperature range of coronal plasmas hotter than about These images clearly show a dark feature, similar to a small-scale solar chromospheric filament (hereafter, "minifilament"), moving upward and laterally, starting from ∼22:06 UT. Its velocity is ∼ 40 km s −1 between 22:07 UT and ∼22:10 UT, when it reaches the apex of the illuminated arched base of the X-ray jet. After 22:10 UT, the minifilament is expelled in the spire of an EUV jet that is the counterpart to the XRT jet. In EUV the jet has both emission and absorption components, with the minifilament evolving into part of the jet. Significantly however, the JBP, both in soft X-rays and in EUV, is at the location from where the minifilament erupted. Thus the JBP is the analog to the commonly-observed solar flare arcade forming in the wake of larger-scale filament 3 eruptions; such flare arcades are made by internal reconnection (i.e., reconnection occurring on the inside of the closed driving field 24 ) of the legs of the erupting closed field of a filament. This is not consistent with the JBP result...

examining many X-ray jets in Hinode/XRT coronal X-ray movies of the polar coronal holes, we found that there is a dichotomy of polar X-ray jets. About two thirds fit the standard reconnection picture for coronal jets, and about one third are another type. We present observations indicating that the non-standard jets are counterparts of erupting-loop Hα macrospicules, jets in which the jet-base magnetic arch undergoes a miniature version of the blowout eruptions that produce major CMEs. From the coronal X-ray movies we present in detail two typical standard X-ray jets and two typical blowout X-ray jets that were also caught in He II 304 Å snapshots from STEREO/EUVI. The distinguishing features of blowout X-ray jets are (1) X-ray brightening inside the base arch in addition to the outside bright point that standard jets have, (2) blowout eruption of the base arch's core field, often carrying a filament of cool (T ~10 4-10 5 K) plasma, and (3) an extra jet-spire strand rooted close to the bright point. We present cartoons showing how reconnection during blowout eruption of the base arch could produce the observed features of blowout X-ray jets. We infer that (1) the standardjet/blowout-jet dichotomy of coronal jets results from the dichotomy of base arches that do not have and base arches that do have enough shear and twist to erupt open, and (2) there is a large class of spicules that are standard jets and a comparably large class of spicules that are blowout jets.

Solar flares produce radiation which can have an almost immediate effect on the near-Earth environment, making it crucial to forecast flares in order to mitigate their negative effects. The number of published approaches to flare forecasting using photospheric magnetic field observations has proliferated, with varying claims about how well each works. Because of the different analysis techniques and data sets used, it is essentially impossible to compare the results from the literature. This problem is exacerbated by the low event rates of large solar flares. The challenges of forecasting rare events have long been recognized in the meteorology community, but have yet to be fully acknowledged by the space weather community. During the interagency workshop on "all clear" forecasts held in Boulder, CO in 2009, the performance of a number of existing algorithms was compared on common data sets, specifically line-of-sight magnetic field and continuum intensity images from MDI, with consistent definitions of what constitutes an event. We demonstrate the importance of making such systematic comparisons, and of using standard verification statistics to determine what constitutes a good prediction scheme. When a comparison was made in this fashion, no one method clearly outperformed all others, which may in part be due to the strong correlations among the parameters used by different methods to characterize an active region. For M-class flares and above, the set of methods tends towards a weakly positive skill score (as measured with several distinct metrics), with no participating method proving substantially better than climatological forecasts.

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A large fraction of major flares occur in active regions that exhibit a configuration. The formation and disintegration of configurations is very important in understanding the evolution of photospheric magnetic fields. In this paper we study the relationship between the change in spot structures and associated major flares. We present a new observational result that part of penumbral segments in the outer spot structure decay rapidly after major flares; meanwhile, the neighboring umbral cores and/or inner penumbral regions become darker. Using whitelight (WL) observations from the Transition Region and Coronal Explorer (TRACE ), we study the short-term evolution of spots associated with seven major flares, including six X-class flares and one M-class flare. The rapid changes, which can be identified in the time profiles of WL mean intensity are permanent, not transient, and thus are not due to flare emission. The co-aligned magnetic field observations obtained with the Michelson Doppler Imager (MDI) show substantial changes in the longitudinal magnetic field associated with the decaying penumbrae and darkened central areas. For two events for which vector magnetograms were available, we find that the transverse field associated with the penumbral decay areas decreased while it increased in the central darkened regions. Both events also show an increase in the magnetic shear after the flares. For all the events, we find that the locations of penumbral decay are related to flare emission and are connected by prominent TRACE postflare loops. To explain these observations, we propose a reconnection picture in which the two components of a spot become strongly connected after the flare. The penumbral fields change from a highly inclined to a more vertical configuration, which leads to penumbral decay. The umbral core and inner penumbral region become darker as a result of increasing longitudinal and transverse magnetic field components.

We present observations of eruptive events in an active region adjacent to an on-disk coronal hole on 2012 June 30, primarily using data from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA), SDO/Helioseismic and Magnetic Imager (HMI), and STEREO-B. One eruption is of a large-scale (∼100″) filament that is typical of other eruptions, showing slow-rise onset followed by a faster-rise motion starting as flare emissions begin. It also shows an “EUV crinkle” emission pattern, resulting from magnetic reconnections between the exploding filament-carrying field and surrounding field. Many EUV jets, some of which are surges, sprays and/or X-ray jets, also occur in localized areas of the active region. We examine in detail two relatively energetic ones, accompanied by GOES M1 and C1 flares, and a weaker one without a GOES signature. All three jets resulted from small-scale (∼20″) filament eruptions consistent with a slow rise followed by a fast rise occurring with flare-like jet-bright-point brightenings. The two more-energetic jets showed crinkle patters, but the third jet did not, perhaps due to its weakness. Thus all three jets were consistent with formation via erupting minifilaments, analogous to large-scale filament eruptions and to X-ray jets in polar coronal holes. Several other energetic jets occurred in a nearby portion of the active region; while their behavior was also consistent with their source being minifilament eruptions, we could not confirm this because their onsets were hidden from our view. Magnetic flux cancelation and emergence are candidates for having triggered the minifilament eruptions.

We study a series of X-ray-bright, rapidly-evolving active-region coronal jets outside the leading sunspot of AR 12259, using Hinode/XRT, SDO/AIA and HMI, and IRIS data. The detailed evolution of such rapidly evolving "violent" jets remained a mystery after our previous investigation of active region jets , Paper 1). The jets we investigate here erupt from three localized subregions, each containing a rapidly evolving (positive) minority-polarity magnetic-flux patch bathed in a (majority) negative-polarity magnetic-flux background. At least several of the jets begin with eruptions of what appear to be thin (thickness < ∼ 2 ′′ ) miniature-filament (minifilament) "strands" from a magnetic neutral line where magnetic flux cancelation is ongoing, consistent with the magnetic configuration presented for coronal-hole jets in Sterling et al. (2015). Some jets strands are difficult/impossible to detect, perhaps due to, e.g. their thinness, obscuration by surrounding bright or dark features, or the absence of erupting cool-material minifilaments in those jets. Tracing in detail the flux evolution in one of the subregions, we find bursts of strong jetting occurring only during times of strong flux cancelation. Averaged over seven jetting episodes, the cancelation rate was ∼1.5×1019 Mx hr −1 . An average flux of ∼5×10 18 Mx canceled prior to each episode, arguably building up ∼10 28 -10 29 ergs of free magnetic energy per jet. From these and previous observations, we infer that flux cancelation is the fundamental process responsible for the pre-eruption buildup and triggering of at least many jets in active regions, quiet regions, and coronal holes.

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