Satellite Sunspots Research Articles

A New Small Satellite Sunspot Triggering Recurrent Standard and Blowout Coronal Jets

Abstract In this paper, we report a detailed analysis of recurrent jets originated from a location with emerging, canceling, and converging negative magnetic field at the east edge of NOAA active region AR11166 from 2011 March 9 to 10. The event presented several interesting features. First, a satellite sunspot appeared and collided with a pre-existing opposite polarity magnetic field and caused a recurrent solar jet event. Second, the evolution of the jets showed blowout-like nature and standard characteristics. Third, the satellite sunspot exhibited a motion toward the southeast of AR11166 and merged with the emerging flux near the opposite polarity sunspot penumbra, which afterward, due to flux convergence and cancellation episodes, caused recurrent jets. Fourth, three of the blowout jets associated with coronal mass ejections (CMEs), were observed from the field of view of the Solar Terrestrial Relations Observatory. Fifth, almost all the blowout jet eruptions were accompanied with flares or with more intense brightening in the jet base region, while almost standard jets did not manifest such obvious features during eruptions. The most important feature, the blowout jets, were inclined to faster and larger scales than the standard jets. The standard jets instead were inclined to be relatively longer-lasting. The obvious shearing and twisting motions of the magnetic field may be interpreted as due to the shearing and twisting motions for a blowout jet eruption. The statistical results show that ~30% of the blowout jets directly developed into CMEs. This suggests that the blowout jets and CMEs should have a close relationship.

High-resolution He i 10830 Å Narrowband Imaging for an M-class Flare. II. Multiple Hot Channels: Their Origin and Destination

Abstract In this paper, we report our second-part result for the M1.8 class flare on 2012 July 5, with an emphasis on the initiation process for the flare-associated filament eruption. The data set consists of high-resolution narrowband images in He i 10830 Å and broadband images in TiO 7057 Å taken at Big Bear Solar Observatory with the 1.6 m aperture Goode Solar Telescope. EUV images in different passbands observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory are used to distinguish hot plasma from cool plasma structures during the flare process. High-resolution 10830 Å images clearly show that, below the horizontal fibrils, which correspond to the filament’s spine in full-disk Hα images, a sheared arch filament system (AFS) lies across the penumbra and surrounding satellite sunspots, between which continuous shearing motion is observed. Before the eruption, three microflares occurred successively and were followed by the appearance of three EUV hot channels. Two hot channels erupted, producing two flaring sites and two major peaks in GOES soft X-ray light curves; however, one hot channel’s eruption failed. The 10830 Å imaging enables us to trace the first two hot channels to their very early stage, which is signified by the rising of the AFS after the first two precursors. Continuous flux emergence and localized flare-associated cancellation are observed under the AFS. In addition, EUV ejections were observed during the formation of the EUV hot channels. These observations support the fact that the hot channels are the result of magnetic reconnections during precursors.

The Eruption of a Small-scale Emerging Flux Rope as the Driver of an M-class Flare and of a Coronal Mass Ejection

Abstract Solar flares and coronal mass ejections are the most powerful explosions in the Sun. They are major sources of potentially destructive space weather conditions. However, the possible causes of their initiation remain controversial. Using high-resolution data observed by the New Solar Telescope of Big Bear Solar Observaotry, supplemented by Solar Dynamics Observatory observations, we present unusual observations of a small-scale emerging flux rope near a large sunspot, whose eruption produced an M-class flare and a coronal mass ejection. The presence of the small-scale flux rope was indicated by static nonlinear force-free field extrapolation as well as data-driven magnetohydrodynamics modeling of the dynamic evolution of the coronal three-dimensional magnetic field. During the emergence of the flux rope, rotation of satellite sunspots at the footpoints of the flux rope was observed. Meanwhile, the Lorentz force, magnetic energy, vertical current, and transverse fields were increasing during this phase. The free energy from the magnetic flux emergence and twisting magnetic fields is sufficient to power the M-class flare. These observations present, for the first time, the complete process, from the emergence of the small-scale flux rope, to the production of solar eruptions.

Horizontal flow fields observed in Hinode G-band images

The flare-prolific active region NOAA 10930 offered both a developing delta-spot and a decaying satellite sunspot of opposite polarity. The objective of this study is to characterize the photometric decay of the satellite sunspot and the evolution of photospheric and chromospheric horizontal proper motions in its surroundings. We apply the local correlation tracking technique to a 16-hour time-series of Hinode G-band and CaIIH images and study the horizontal proper motions in the vicinity of the satellite sunspot on 2006 December 7. Decorrelation times were computed to measure the lifetime of solar features in intensity and flow maps. We observed shear flows in the dominant umbral cores of the satellite sunspot. These flows vanished once the penumbra had disappeared. This slow penumbral decay had an average rate of 152Mm2/day over an 11-hour period. Typical lifetimes of intensity features derived from an autocorrelation analysis are 3-5min for granulation, 25-35min for G-band bright points, and up to 200-235min for penumbrae, umbrae, and pores. Long-lived intensity features (i.e., the dominant umbral cores) are not related to long-lived flow features in the northern part of the sunspot, where flux removal, slowly decaying penumbrae, and persistent horizontal flows of up to 1 km/s contribute to the erosion of the sunspot. Finally, the restructuring of magnetic field topology was responsible for a homologous M2.0 flare, which shared many characteristics with an X6.5 flare on the previous day. Notwithstanding the prominent role of delta-spots in flaring, we conclude based on the decomposition of the satellite sunspot, the evolution of the surrounding flow fields, and the timing of the M2.0 flare that the vanishing magnetic flux in the decaying satellite sunspot played an instrumental role in triggering the homologous M2.0 flare and the eruption of a small Halpha filament.

Multiwavelength Study of the M8.9/3B Solar Flare from AR NOAA 10960

We present a multi-wavelength analysis of a long duration white-light solar flare (M8.9/3B) event that occurred on 4 June 2007 from NOAA AR 10960. The flare was observed by several spaceborne instruments, namely SOHO/MDI, Hinode/SOT, TRACE and STEREO/SECCHI. The flare was initiated near a small, positive-polarity, satellite sunspot at the centre of the AR, surrounded by opposite-polarity field regions. MDI images of the AR show considerable amount of changes in a small positive-polarity sunspot of delta configuration during the flare event. SOT/G-band (4305 A) images of the sunspot also suggest the rapid evolution of the positive-polarity sunspot with highly twisted penumbral filaments before the flare event, which were oriented in the counterclockwise direction. It shows the change in orientation and also remarkable disappearance of twisted penumbral filaments (~35-40%) and enhancement in umbral area (~45-50%) during the decay phase of the flare. TRACE and SECCHI observations reveal the successive activations of two helical twisted structures associated with this sunspot, and the corresponding brightening in the chromosphere as observed by the time-sequence images of SOT/Ca II H line (3968 A). The secondary-helical twisted structure is found to be associated with the M8.9 flare event. The brightening starts 6-7 min prior to the flare maximum with the appearance of secondary helical-twisted structure. The flare intensity maximizes as this structure moves away from the AR. This twisted flux-tube associated with the flare triggering, is found to be failed in eruption. The location of the flare is found to coincide with the activation site of the helical twisted structures. We conclude that the activations of successive helical twists in the magnetic flux tubes/ropes plays a crucial role in the energy build-up process and triggering of M-class solar flare without a CME.

Observations of Hαsurges and ultraviolet jets above satellite sunspots

Aims To know more about the physical origin of surges and jets, we investigated seven successive surge events, which occurred above the satellite sunspots of active region NOAA 10720 on 2005 January 15. Methods. Using data from the Transition Region and Coronal Explorer (TRACE), Big Bear Solar Observatory (BBSO) and Solar and Heliospheric Observatory (SOHO), we present a detailed study of the surges and their relations with the associated small arch filament, UV jets, flares and photospheric longitudinal magnetic fields. Results. The seven H-alpha surges we studied repeatedly occurred where the photospheric longitudinal fluxes of opposite magnetic polarities emerged, converged and were canceled by each other. Correspondingly, a small satellite spot emerged, decayed and disappeared during a period of about 2 hours in the white-light observations. In morphology, all surges displayed almost linear ejective structures. Their dynamic properties, such as the transverse velocity, projected maximum length and lifetime, varied in wide ranges. They are 30 -200 km s(-1), 38 000-220 000 km and from several to tens of minutes, respectively. Correspondingly, the intensities of their correlated microflares were different too. The surges of major velocities or maximum lengths seemed to be accompanied by processes of more energy release. Prior to these surge events, a small H-alpha arch filament connecting the opposite flux elements was found at the base region. Instead of erupting completely, it gradually disappeared during the surges. Its role in the surge activities is very like a bipolar flux, which contained the cool plasma and reconnected with the ambient magnetic fields. In 1600 angstrom, three surge events exhibited the composite structures of bright jets and nearby small flaring loops, which provides direct evidence of magnetic reconnection origin of the surges. A careful comparison revealed that the ends of the arch filament, the UV jets and the small flaring loops just corresponded to the interacting longitudinal fluxes in the photosphere. Conclusions. These observational results support the magnetic reconnection model of surges and jets.

Magnetohydrodynamic theories of solar flares

Our current understanding of the MHD of the flare process is summarised, with some emphasis on processes which produce strong impulsive electric fields and current filamentation. As an introduction, a description of the two main types of flare (i.e., simple-loop and two-ribbon) is given, together with an account of the two branches of reconnection theory (tearing modes and the Petschek-Sonnerup mechanism). Modern numerical experiments of reconnection suggest impulsive bursty acceleration of particles in many small regions of width a hundred kilometres or less. This is followed by a discussion of the eruptive instability thought to initiate a large flare and of the reconnection process of energy release. Finally, the role of emerging flux and horizontally moving satellite sunspots is discussed briefly.

Flares and changing magnetic fields

An observational study of maps of the longitudinal component of the photospheric fields in flaring active regions leads to the following conclusions: (1) The broad-wing Hα kernels characteristic of the impulsive phase of flares occur within 10″ of neutral lines encircling features of isolated magnetic polarity (‘satellite sunspots’). (2) Photospheric field changes intimately associated with several importance 1 flares and one importance 2B flare are confined to satellite sunspots, which are small (10″ diam). They often correspond to spot pores in white-light photographs. (3) The field at these features appears to strengthen in the half hour just before the flares. During the flares the growth is reversed, the field drops and then recovers to its previous level. (4) The magnetic flux through flare-associated features changes by about 4 × 1019 Mx in a day. The features are the same as the ‘Structures Magnetiques Evolutives’ of Martres et al. (1968a). (5) An upper limit of 1021 Mx is set for the total flux change through McMath Regions 10381 and 10385 as the result of the 2B flare of 24 October, 1969. (6) Large spots in the regions investigated did not evince flux changes or large proper motions at flare time. (7) The results are taken to imply that the initial instability of a flare occurs at a neutral point, but the magnetic energy lost cannot yet be related to the total energy of the subsequent flare. (8) No unusual velocities are observed in the photosphere at flare time.

Chromospheric explosions and satellite sunspots

Observations of the longitudinal component of the photospheric magnetic fields near sunspots imply that surges and Ellerman bombs occur at neutral points in the magnetic fields (i.e. |B|=0) in the chromosphere. The neutral points appear above satellite sunspots, which are defined as polarity reversals (in B||) near the edges of large-spot penumbrae. A series of magnetograph observations shows a point of satellite polarity vanishing during a period of almost continuous surge activity. The lost magnetic energy is comparable to the energy release evidenced by the surge.