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1.
As the observational signature of the footprints of solar magnetic field lines open into the heliosphere, coronal holes provide a critical measure of the structure and evolution of these lines. Using a combination of Solar and Heliospheric Observatory/Extreme ultraviolet Imaging Telescope (SOHO/EIT), Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA), and Solar Terrestrial Relations Observatory/Extreme Ultraviolet Imager (STEREO/EUVI A/B) extreme ultraviolet (EUV) observations spanning 1996?–?2015 (nearly two solar cycles), coronal holes are automatically detected and characterized. Coronal hole area distributions show distinct behavior in latitude, defining the domain of polar and low-latitude coronal holes. The northern and southern polar regions show a clear asymmetry, with a lag between hemispheres in the appearance and disappearance of polar coronal holes.  相似文献   

2.
We carry out an analysis of the mass that is evacuated from three coronal dimming regions observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. The three events are unambiguously identified with white-light coronal mass ejections (CMEs) that are associated in turn with surface activity of diverse nature: an impulsive (M-class) flare, a weak (B-class) flare, and a filament eruption without a flare. The use of three AIA coronal passbands allows applying a differential emission measure technique to define the dimming regions and identify their evacuated mass through the analysis of the electronic density depletion associated with the eruptions. The temporal evolution of the mass loss from the three dimmings can be approximated by an exponential equation followed by a linear fit. We determine the mass of the associated CMEs from COR2 data. The results show that the evacuated masses from the low corona represent a considerable amount of the CME mass. We also find that plasma is still being evacuated from the low corona at the time when the CMEs reach the COR2 field of view. The temporal evolution of the angular width of the CMEs, of the dimming regions in the low corona, and of the flux registered by GOES in soft X-rays are all in close relation with the behavior of mass evacuation from the low corona. We discuss the implications of our findings toward a better understanding of the temporal evolution of several parameters associated with the analyzed dimmings and CMEs.  相似文献   

3.
In Fall 2008 NASA selected a large international consortium to produce a comprehensive automated feature-recognition system for the Solar Dynamics Observatory (SDO). The SDO data that we consider are all of the Atmospheric Imaging Assembly (AIA) images plus surface magnetic-field images from the Helioseismic and Magnetic Imager (HMI). We produce robust, very efficient, professionally coded software modules that can keep up with the SDO data stream and detect, trace, and analyze numerous phenomena, including flares, sigmoids, filaments, coronal dimmings, polarity inversion lines, sunspots, X-ray bright points, active regions, coronal holes, EIT waves, coronal mass ejections (CMEs), coronal oscillations, and jets. We also track the emergence and evolution of magnetic elements down to the smallest detectable features and will provide at least four full-disk, nonlinear, force-free magnetic field extrapolations per day. The detection of CMEs and filaments is accomplished with Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph (LASCO) and ground-based Hα data, respectively. A?completely new software element is a trainable feature-detection module based on a generalized image-classification algorithm. Such a trainable module can be used to find features that have not yet been discovered (as, for example, sigmoids were in the pre-Yohkoh era). Our codes will produce entries in the Heliophysics Events Knowledgebase (HEK) as well as produce complete catalogs for results that are too numerous for inclusion in the HEK, such as the X-ray bright-point metadata. This will permit users to locate data on individual events as well as carry out statistical studies on large numbers of events, using the interface provided by the Virtual Solar Observatory. The operations concept for our computer vision system is that the data will be analyzed in near real time as soon as they arrive at the SDO Joint Science Operations Center and have undergone basic processing. This will allow the system to produce timely space-weather alerts and to guide the selection and production of quicklook images and movies, in addition to its prime mission of enabling solar science. We briefly describe the complex and unique data-processing pipeline, consisting of the hardware and control software required to handle the SDO data stream and accommodate the computer-vision modules, which has been set up at the Lockheed-Martin Space Astrophysics Laboratory (LMSAL), with an identical copy at the Smithsonian Astrophysical Observatory (SAO).  相似文献   

4.
Coronal mass ejections (CMEs) are considered as one of the driving sources of space weather. They are usually associated with many physical phenomena, e.g. flares, coronal dimmings, and sigmoids. To detect these phenomena, traditional supervised-learning methods assumed that at most one event occurred in a CME; therefore each CME instance is associated with a single label and the phenomenon is processed in isolation. This simplifying assumption does not fit well, as CMEs might have multiple events simultaneously. We propose to detect multiple CME-associated events by multi-label learning methods. With the data available from the Atmospheric Imaging Assembly (AIA) and the Large Angle and Spectrometric Coronagraph (LASCO), texture features representing the events are extracted from all of the associated and not-associated CMEs and converted into feature vectors for multi-label learning use. Then a function is learned to predict the proper label sets for CMEs, such that eight events, i.e. coronal dimming, coronal hole, coronal jet, coronal wave, filament, filament eruption, flare, and sigmoid, are detected explicitly. To test the proposed detection algorithm, we adopt the four-fold cross-validation strategy on a set of 551 labeled CMEs from AIA. Experimental results demonstrate the good performance of the multi-label classification methods in terms of test error.  相似文献   

5.
Coronal holes (CHs) are regions of open magnetic field lines in the solar corona and the source of the fast solar wind. Understanding the evolution of coronal holes is critical for solar magnetism as well as for accurate space weather forecasts. We study the extreme ultraviolet (EUV) synoptic maps at three wavelengths (195 Å/193 Å, 171 Å and 304 Å) measured by the Solar and Heliospheric Observatory/Extreme Ultraviolet Imaging Telescope (SOHO/EIT) and the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) instruments. The two datasets are first homogenized by scaling the SDO/AIA data to the SOHO/EIT level by means of histogram equalization. We then develop a novel automated method to identify CHs from these homogenized maps by determining the intensity threshold of CH regions separately for each synoptic map. This is done by identifying the best location and size of an image segment, which optimally contains portions of coronal holes and the surrounding quiet Sun allowing us to detect the momentary intensity threshold. Our method is thus able to adjust itself to the changing scale size of coronal holes and to temporally varying intensities. To make full use of the information in the three wavelengths we construct a composite CH distribution, which is more robust than distributions based on one wavelength. Using the composite CH dataset we discuss the temporal evolution of CHs during the Solar Cycles 23 and 24.  相似文献   

6.
In our previous articles (Chertok et al. in Solar Phys. 282, 175, 2013; Chertok et al. in Solar Phys. 290, 627, 2015), we presented a preliminary tool for the early diagnostics of the geoeffectiveness of solar eruptions based on the estimate of the total unsigned line-of-sight photospheric magnetic flux in accompanying extreme ultraviolet (EUV) arcades and dimmings. This tool was based on the analysis of eruptions observed during 1996?–?2005 with the Extreme-ultraviolet Imaging Telescope (EIT) and the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO). Empirical relationships were obtained to estimate the probable importance of upcoming space weather disturbances caused by an eruption, which just occurred, without data on the associated coronal mass ejections. In particular, it was possible to estimate the intensity of a non-recurrent geomagnetic storm (GMS) and Forbush decrease (FD), as well as their onset and peak times. After 2010?–?2011, data on solar eruptions are obtained with the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We use relatively short intervals of overlapping EIT–AIA and MDI–HMI detailed observations, and additionally, a number of large eruptions over the next five years with the 12-hour cadence EIT images to adapt the SOHO diagnostic tool to SDO data. We show that the adopted brightness thresholds select practically the same areas of arcades and dimmings from the EIT 195 Å and AIA 193 Å image, with a cross-calibration factor of 3.6?–?5.8 (5.0?–?8.2) for the AIA exposure time of 2.0 s (2.9 s). We also find that for the same photospheric areas, the MDI line-of-sight magnetic flux systematically exceeds the HMI flux by a factor of 1.4. Based on these results, the empirical diagnostic relationships obtained from SOHO data are adjusted to SDO instruments. Examples of a post-diagnostics based on SDO data are presented. As before, the tool is applicable to non-recurrent GMSs and FDs caused by nearly central eruptions from active regions, provided that the southern component of the interplanetary magnetic field near the Earth is predominantly negative, which is not predicted by this tool.  相似文献   

7.
Variations in the propagation of globally propagating disturbances (commonly called “EIT waves”) through the low solar corona offer a unique opportunity to probe the plasma parameters of the solar atmosphere. Here, high-cadence observations of two “EIT wave” events taken using the Atmospheric Imaging Assembly (AIA) instrument onboard the Solar Dynamics Observatory (SDO) are combined with spectroscopic measurements from the Extreme ultraviolet Imaging Spectrometer (EIS) onboard the Hinode spacecraft and used to examine the variability of the quiet coronal magnetic-field strength. The combination of pulse kinematics from SDO/AIA and plasma density from Hinode/EIS is used to show that the magnetic-field strength is in the range ≈?2?–?6 G in the quiet corona. The magnetic-field estimates are then used to determine the height of the pulse, allowing a direct comparison with theoretical values obtained from magnetic-field measurements from the Helioseismic and Magnetic Imager (HMI) onboard SDO using global-scale PFSS and local-scale extrapolations. While local-scale extrapolations predict heights inconsistent with prior measurements, the agreement between observations and the PFSS model indicates that “EIT waves” are a global phenomenon influenced by global-scale magnetic field.  相似文献   

8.
Measurements of magnetic fields and electric currents in the pre-eruptive corona are crucial to the study of solar eruptive phenomena, like flares and coronal mass ejections (CMEs). However, spectro-polarimetric measurements of certain photospheric lines permit a determination of the vector magnetic field only at the photosphere. Therefore, there is considerable interest in accurate modeling of the solar coronal magnetic field using photospheric vector magnetograms as boundary data. In this work, we model the coronal magnetic field above multiple active regions with the help of a potential field and a nonlinear force-free field (NLFFF) extrapolation code over the full solar disk using Helioseismic and Magnetic Imager (SDO/HMI) data as boundary conditions. We compare projections of the resulting magnetic field lines with full-disk coronal images from the Atmospheric Imaging Assembly (SDO/AIA) for both models. This study has found that the NLFFF model reconstructs the magnetic configuration closer to observation than the potential field model for full-disk magnetic field extrapolation. We conclude that many of the trans-equatorial loops connecting the two solar hemispheres are current-free.  相似文献   

9.
We present a study of the origin of coronal mass ejections (CMEs) that were not accompanied by obvious low coronal signatures (LCSs) and yet were responsible for appreciable disturbances at 1 AU. These CMEs characteristically start slowly. In several examples, extreme ultraviolet (EUV) images taken by the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory reveal coronal dimming and a post-eruption arcade when we make difference images with long enough temporal separations, which are commensurate with the slow initial development of the CME. Data from the EUV imager and COR coronagraphs of the Sun Earth Connection Coronal and Heliospheric Investigation onboard the Solar Terrestrial Relations Observatory, which provide limb views of Earth-bound CMEs, greatly help us limit the time interval in which the CME forms and undergoes initial acceleration. For other CMEs, we find similar dimming, although only with lower confidence as to its link to the CME. It is noted that even these unclear events result in unambiguous flux rope signatures in in situ data at 1 AU. There is a tendency that the CME source regions are located near coronal holes or open field regions. This may have implications for both the initiation of the stealthy CME in the corona and its outcome in the heliosphere.  相似文献   

10.
Wei Liu  Leon Ofman 《Solar physics》2014,289(9):3233-3277
Global extreme-ultraviolet (EUV) waves are spectacular traveling disturbances in the solar corona associated with energetic eruptions such as coronal mass ejections (CMEs) and flares. Over the past 15 years, observations from three generations of space-borne EUV telescopes have shaped our understanding of this phenomenon and at the same time led to controversy about its physical nature. Since its launch in 2010, the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) has observed more than 210 global EUV waves in exquisite detail, thanks to its high spatio–temporal resolution and full-disk, wide-temperature coverage. A combination of statistical analysis of this large sample, more than 30 detailed case studies, and data-driven MHD modeling, has been leading their physical interpretations to a convergence, favoring a bimodal composition of an outer, fast-mode magnetosonic wave component and an inner, non-wave CME component. Adding to this multifaceted picture, AIA has also discovered new EUV wave and wave-like phenomena associated with various eruptions, including quasi-periodic fast propagating (QFP) wave trains, magnetic Kelvin–Helmholtz instabilities (KHI) in the corona and associated nonlinear waves, and a variety of mini-EUV waves. Seismological applications using such waves are now being actively pursued, especially for the global corona. We review such advances in EUV wave research focusing on recent SDO/AIA observations, their seismological applications, related data-analysis techniques, and numerical and analytical models.  相似文献   

11.
It is generally accepted that transient coronal holes (TCHs, dimmings) correspond to the magnetic footpoints of CMEs that remain rooted in the Sun as the CME expands out into the interplanetary space. However, the observation that the average intensity of the 12 May 1997 dimmings recover to their pre-eruption intensity in SOHO/EIT data within 48 hours, whilst suprathermal unidirectional electron heat fluxes are observed at 1 AU in the related ICME more than 70 hours after the eruption, leads us to question why and how the dimmings disappear whilst the magnetic connectivity is maintained. We also examine two other CME-related dimming events: 13 May 2005 and 6 July 2006. We study the morphology of the dimmings and how they recover. We find that, far from exhibiting a uniform intensity, dimmings observed in SOHO/EIT data have a deep central core and a more shallow extended dimming area. The dimmings recover not only by shrinking of their outer boundaries but also by internal brightenings. We quantitatively demonstrate that the model developed by Fisk and Schwadron (Astrophys. J. 560, 425, 2001) of interchange reconnections between “open” magnetic field and small coronal loops is a strong candidate for the mechanism facilitating the recovery of the dimmings. This process disperses the concentration of  “open” magnetic field (forming the dimming) out into the surrounding quiet Sun, thus recovering the intensity of the dimmings whilst still maintaining the magnetic connectivity to the Sun. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.  相似文献   

12.
Observations of the solar full-disk were carried out by the Atmo- spheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) with the Fe IX 171 Å line on 16th October 2010. The obtained high-quality data permit us to elaborate on the coronal loop oscillations. It is found that a major flare of GOES (Geostationary Operational Environmental Satellite) class M2.9 occurred in the active region NOAA 1112 during this period, which triggered a number of coronal loops on the solar surface to oscillate. Among them, there are two coronal loops exhibiting oscillations with different physical features. The oscillation of the coronal loop located at W492/S170 is a simple harmonic oscillation with a period of 385s, which abides by the oscillating equation of x = 2.2 sin[2π/385(t–768)], while the other located at W559/S142 is a damping oscillation with a period of 449s, and the oscillating equation is expressed by x = 24.8e - 2π/343 t sin[2π/449(t–1128)], where t is the observational time in units of second.  相似文献   

13.
The continuous stream of data available from the Atmospheric Imaging Assembly (AIA) telescopes onboard the Solar Dynamics Observatory (SDO) spacecraft has allowed a deeper understanding of the Sun. However, the sheer volume of data has necessitated the development of automated techniques to identify and analyse various phenomena. In this article, we describe the Coronal Pulse Identification and Tracking Algorithm (CorPITA) for the identification and analysis of coronal “EIT waves”. CorPITA uses an intensity-profile technique to identify the propagating pulse, tracking it throughout its evolution before returning estimates of its kinematics. The algorithm is applied here to a data set from February 2011, allowing its capabilities to be examined and critiqued. This algorithm forms part of the SDO Feature Finding Team initiative and will be implemented as part of the Heliophysics Event Knowledgebase (HEK). This is the first fully automated algorithm to identify and track the propagating “EIT wave” rather than any associated phenomenon and will allow a deeper understanding of this controversial phenomenon.  相似文献   

14.
Coronal dimmings are often present on both sides of erupting magnetic configurations. It has been suggested that dimmings mark the location of the footpoints of ejected flux ropes and, thus, their magnetic flux can be used as a proxy for the flux involved in the ejection. If so, this quantity can be compared to the flux in the associated interplanetary magnetic cloud to find clues about the origin of the ejected flux rope. In the context of this physical interpretation, we analyze the event, flare, and coronal mass ejection (CME) that occurred in active region 10486 on 28 October 2003. The CME on this day is associated with large-scale dimmings, located on either side of the main flaring region. We combine SOHO/Extreme Ultraviolet Imaging Telescope data and Michelson Doppler Imager magnetic maps to identify and measure the flux in the dimming regions. We model the associated cloud and compute its magnetic flux using in situ observations from the Magnetometer Instrument and the Solar Wind Electron Proton Alpha Monitor aboard the Advance Composition Explorer. We find that the magnetic fluxes of the dimmings and magnetic cloud are incompatible, in contrast to what has been found in previous studies. We conclude that, in certain cases, especially in large-scale events and eruptions that occur in regions that are not isolated from other flux concentrations, the interpretation of dimmings requires a deeper analysis of the global magnetic configuration, since at least a fraction of the dimmed regions is formed by reconnection between the erupting field and the surrounding magnetic structures.  相似文献   

15.
On 13 June 2010, an eruptive event occurred near the solar limb. It included a small filament eruption and the onset of a relatively narrow coronal mass ejection (CME) surrounded by an extreme ultraviolet (EUV) wave front recorded by the Solar Dynamics Observatory’s (SDO) Atmospheric Imaging Assembly (AIA) at high cadence. The ejection was accompanied by a GOES M1.0 soft X-ray flare and a Type-II radio burst; high-resolution dynamic spectra of the latter were obtained by the Appareil de Routine pour le Traitement et l’Enregistrement Magnetique de l’Information Spectral (ARTEMIS IV) radio spectrograph. The combined observations enabled a study of the evolution of the ejecta and the EUV wave front and its relationship with the coronal shock manifesting itself as metric Type-II burst. By introducing a novel technique, which deduces a proxy of the EUV compression ratio from AIA imaging data and compares it with the compression ratio deduced from the band-split of the Type-II metric radio burst, we are able to infer the potential source locations of the radio emission of the shock on that AIA images. Our results indicate that the expansion of the CME ejecta is the source for both EUV and radio shock emissions. Early in the CME expansion phase, the Type-II burst seems to originate in the sheath region between the EUV bubble and the EUV shock front in both radial and lateral directions. This suggests that both the nose and the flanks of the expanding bubble could have driven the shock.  相似文献   

16.
We demonstrate that study of the evolving magnetic nature of coronal dimming regions can be used to probe the large-scale magnetic structure involved in the eruption of a coronal mass ejection (CME). We analyse the intensity evolution of coronal dimming regions using 195 Å data from the Extreme ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO). We measure the magnetic flux, using data from the SOHO/Michelson Doppler Imager (MDI), in the regions that seem most likely to be related to plasma removal. Then, we compare these magnetic flux measurements to the flux in the associated magnetic cloud (MC). Here, we present our analysis of the well-studied event on 12 May 1997 that took place just after solar minimum in a simple magnetic configuration. We present a synthesis of results already published and propose that driven “interchange reconnection” between the expanding CME structure with ‘`open’' field lines of the northern coronal hole region led to the asymmetric temporal and spatial evolution of the two main dimming regions, associated with this event. As a result of this reconnection process, we find the southern-most dimming region to be the principal foot-point of the MC. The magnetic flux from this dimming region and that of the MC are found to be in close agreement within the same order of magnitude, 1021 Mx.  相似文献   

17.
Coronal dimming can be considered to be a disk signature of front-side coronal mass ejections (CMEs) (Thompson et al.: 2000, Geophys. Res. Lett. 27, 1431). The study of the magnetic connectivity associated with coronal dimming can shed new light on the magnetic nature of CMEs. In this study, four major flare-CME events on 14 July 2000, 28 October 2003, 7 November 2004, and 15 January 2005 are analyzed. They were all halo CMEs associated with major flare activity in complex active regions (ARs) and produced severe space weather consequences. To explore the magnetic connectivity of these CMEs, global potential-field extrapolations based on the composite synoptic magnetograms from the Michelson Doppler Imager onboard the Solar and Heliospheric Observatory are constructed, and their association with coronal dimming is revealed by the Extreme ultraviolet Imaging Telescope. It is found that each flare-CME event involved interaction of more than ten sets of magnetic-loop systems. These loop systems occupied over 50% of all identified loop systems in the visible hemisphere and covered a wide range of solar longitudes and latitudes. We categorize the loop systems as active-region loops (ARLs), AR-interconnecting loops (ARILs) including transequatorial loops (TLs), and long arcades (LAs) straddling filament channels. A recurring pattern, the saddle-field configuration (SFC), consisting of ARILs, is found to be present in all four major flare-CME events. The magnetic connectivity revealed by this work implies that intercoupling and interaction of multiple flux-loop systems are required for a major CME. For comparison, a simple flare-CME event of 12 May 1997 with a relatively simple magnetic configuration is chosen. Even for this simple flare-CME event, we find that multiple flux-loop systems are also present.  相似文献   

18.
Some quiet-Sun days observed by the Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO) during the time interval in 2010?–?2017 were used to continue our previous analyses reported by Didkovsky and Gurman (Solar Phys.289, 153, 2014a) and Didkovsky, Wieman, and Korogodina (Solar Phys.292, 32, 2017). The analysis consists of determining and comparing spatial spectral ratios (spectral densities over some time interval) from spatial (segmentation-cell length) power spectra. The ratios were compared using modeled compatible spatial frequencies for spectra from the Extreme ultraviolet Imaging Telescope (EIT) on-board the Solar and Heliospheric Observatory (SOHO) and from AIA images. With the new AIA data added to the EIT data we analyzed previously, the whole time interval from 1996 to 2017 reported here is approximately the length of two “standard” solar cycles (SC). The spectral ratios of segmentation-cell dimension structures show a significant and steady increase with no detected indication of SC-related returns to the values that characterize the SC minima. This increase in spatial power at high spatial frequencies is interpreted as a dissipation of medium-size EUV network structures to smaller-size structures in the transition region. Each of the latest ratio changes for 2010 through 2017 spectra calculated for a number of consecutive short-term intervals has been converted into monthly mean ratio (MMR) changes. The MMR values demonstrate variable sign and magnitudes, thus confirming the solar nature of the changes. These changes do not follow a “typical” trend of instrumental degradation or a long-term activity profile from the He?ii (30.4 nm) irradiance measured by the Extreme ultraviolet Spectrophotometer (ESP) either. The ESP is a channel of the Extreme ultraviolet Variability Experiment (EVE) on-board SDO.  相似文献   

19.
Studies of the onset of Earth-directed coronal mass ejections (CMEs) rely on solar disk observations where CME structures are difficult to disentangle because of the diversity and transient character of the phenomena involved. Dimmings and coronal waves are among the best evidence of the large-scale reorganization of coronal magnetic fields associated with the onset of CMEs. The physical mechanism behind EIT waves is still unclear: they are considered as MHD waves and/or as a consequence of plasma compression on the extending border of a dimming. In this paper, we address the problem of automatically detecting and analyzing EIT waves and dimmings in EUV images. This paper presents a “proof of principle” that automated detection of EIT wave and dimmings is indeed possible. At the current stage of work, the method can unambiguously detect dimmings and EIT waves when applied on a typical test-case event. Moreover, we propose a way to extract these events from the data, and determine such parameters as life time, depth, area and volume of dimmings for future catalogs. For EIT waves we unambiguously define, in near solar minimum conditions, the eruption center, the front of EIT wave and its propagation velocity. In addition, we show that the presented methods yield new insights about the geometrical shape of dimmings and the connection with the EIT wave front properties, and the apparent angular rotation of the EIT wave under study.  相似文献   

20.
Explosive events appear as broad non-Gaussian wings in the line profiles of small transition-region phenomena. Images from the Solar Dynamics Observatory (SDO) give a first view of the plasma dynamics at the sites of explosive events seen simultaneously in O?vi spectra of a region of quiet Sun, taken with the ultraviolet spectrometer Solar Ultraviolet Measurements of Emitted Radiation (SUMER) onboard the Solar and Heliospheric Observatory (SOHO). Distinct event bursts were seen either at the junction of supergranular network cells or near emerging flux. Three are described in the context of their surrounding transition region (304 Å) and coronal (171 Å) activity. One showed plasma ejections from an isolated pair of sites, with a time lag of 50 seconds between events. At the site where the later explosive event was seen, the extreme ultraviolet (EUV) images show a hot core surrounded by a small, expanding ring of chromospheric emission, which we interpret as a “splash.” The second explosive-event burst was related to flux cancellation, inferred from Helioseismic and Magnetic Imager (HMI) magnetograms, and a coronal dimming surrounded by a ring of bright EUV emission with explosive events at positions where the spectrometer slit crossed the bright ring. The third series of events occurred at the base of a slow, small coronal mass ejection (mini-CME). All events studied here imply jet-like flows probably triggered by magnetic reconnection at supergranular junctions. Events come from sites close to the footpoints of jets seen in Atmospheric Imaging Assembly (AIA) images, and possibly from the landing site of high-velocity flows. They are not caused by rapid rotation in spicules.  相似文献   

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