Article

Formation Process of a Light Bridge Revealed with the Hinode Solar Optical Telescope

Publications- Astronomical Society of Japan (Impact Factor: 2.44). 10/2007;
Source: arXiv

ABSTRACT The Solar Optical Telescope (SOT) aboard HINODE successfully and continuously observed a formation process of a light bridge in a matured sunspot of the NOAA active region 10923 for several days with high spatial resolution. During its formation, many umbral dots were observed emerging from the leading edges of penumbral filaments, and intruding into the umbra rapidly. The precursor of the light bridge formation was also identified as the relatively slow inward motion of the umbral dots which emerged not near the penumbra, but inside the umbra. The spectro-polarimeter on SOT provided physical conditions in the photosphere around the umbral dots and the light bridges. We found the light bridges and the umbral dots had significantly weaker magnetic fields associated with upflows relative to the core of the umbra, which implies that there was hot gas with weak field strength penetrating from subphotosphere to near the visible surface inside those structures. There needs to be a mechanism to drive the inward motion of the hot gas along the light bridges. We suggest that the emergence and the inward motion are triggered by a buoyant penumbral flux tube as well as the subphotospheric flow crossing the sunspot.

0 Bookmarks
 · 
70 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We examine the buildup to and onset of an active region filament confined eruption of 2010 May 12, using EUV imaging data from the Solar Dynamics Observatory (SDO) Atmospheric Imaging Array and line-of-sight magnetic data from the SDO Helioseismic and Magnetic Imager. Over the hour preceding eruption the filament undergoes a slow rise averaging ~3 km s–1, with a step-like trajectory. Accompanying a final rise step ~20 minutes prior to eruption is a transient preflare brightening, occurring on loops rooted near the site where magnetic field had canceled over the previous 20 hr. Flow-type motions of the filament are relatively smooth with speeds ~50 km s–1 prior to the preflare brightening and appear more helical, with speeds ~50-100 km s–1, after that brightening. After a final plateau in the filament's rise, its rapid eruption begins, and concurrently an outer shell "cocoon" of the filament material increases in emission in hot EUV lines, consistent with heating in a newly formed magnetic flux rope. The main flare brightenings start ~5 minutes after eruption onset. The main flare arcade begins between the legs of an envelope-arcade loop that is nearly orthogonal to the filament, suggesting that the flare results from reconnection among the legs of that loop. This progress of events is broadly consistent with flux cancellation leading to formation of a helical flux rope that subsequently erupts due to onset of a magnetic instability and/or runaway tether cutting.
    The Astrophysical Journal Letters 03/2011; 731(1):L3. · 6.35 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We observe an erupting jet feature in a solar polar coronal hole, using data from Hinode/Solar Optical Telescope (SOT), Extreme Ultraviolet Imaging Spectrometer (EIS), and X-Ray Telescope (XRT), with supplemental data from STEREO/EUVI. From extreme-ultraviolet (EUV) and soft X-ray (SXR) images we identify the erupting feature as a blowout coronal jet: in SXRs it is a jet with a bright base, and in EUV it appears as an eruption of relatively cool (~50,000 K) material of horizontal size scale ~30'' originating from the base of the SXR jet. In SOT Ca II H images, the most pronounced analog is a pair of thin (~1'') ejections at the locations of either of the two legs of the erupting EUV jet. These Ca II features eventually rise beyond 45'', leaving the SOT field of view, and have an appearance similar to standard spicules except that they are much taller. They have velocities similar to that of "type II" spicules, ~100 km s–1, and they appear to have spicule-like substructures splitting off from them with horizontal velocity ~50 km s–1, similar to the velocities of splitting spicules measured by Sterling et al. Motions of splitting features and of other substructures suggest that the macroscopic EUV jet is spinning or unwinding as it is ejected. This and earlier work suggest that a subpopulation of Ca II type II spicules are the Ca II manifestation of portions of larger scale erupting magnetic jets. A different subpopulation of type II spicules could be blowout jets occurring on a much smaller horizontal size scale than the event we observe here.
    The Astrophysical Journal 10/2010; 722(2):1644. · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We examine solar spicules using high-cadence Ca II data of the north pole coronal hole region, using the Solar Optical Telescope (SOT) on the Hinode spacecraft. The features we observe are referred to as "Type II" spicules by De Pontieu et al. in 2007. By convolving the images with the inverse-point-spread function for the SOT Ca II filter, we are able to investigate the roots of some spicules on the solar disk, and the evolution of some spicules after they are ejected from the solar surface. We find that the source regions of at least some of the spicules correspond to locations of apparent-fast-moving (~few × 10 km s-1), transient (few 100 s), Ca II brightenings on the disk. Frequently the spicules occur when these brightenings appear to collide and disappear. After ejection, when seen above the limb, many of the spicules fade by expanding laterally (i.e., roughly transverse to their motion away from the solar surface), splitting into two or more spicule "strands," and the spicules then fade without showing any downward motion. Photospheric/chromospheric acoustic shocks alone likely cannot explain the high velocities (~100 km s-1) of the spicules. If the Ca II brightenings represent magnetic elements, then reconnection among those elements may be a candidate to explain the spicules. Alternatively, many of the spicules could be small-scale magnetic eruptions, analogous to coronal mass ejections, and the apparent fast motions of the Ca II brightenings could be analogs of flare loops heated by magnetic reconnection in these eruptions.
    The Astrophysical Journal Letters 05/2010; 714(1). · 6.35 Impact Factor

Full-text (2 Sources)

View
3 Downloads
Available from
Jul 17, 2014