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Register a new userInitial Helioseismic Observations by Hinode/SOT
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Results from initial helioseismic observations by Solar Optical Telescope onboard Hinode are reported. It has been demonstrated that intensity oscillation data from Broadband Filter Imager can be used for various helioseismic analyses. The k-omega power spectra, as well as corresponding time-distance cross-correlation function that promises high-resolution time-distance analysis below 6-Mm travelling distance, were obtained for G-band and CaII-H data. Subsurface supergranular patterns have been observed from our first time-distance analysis. The results show that the solar oscillation spectrum is extended to much higher frequencies and wavenumbers, and the time-distance diagram is extended to much shorter travel distances and times than they were observed before, thus revealing great potential for high-resolution helioseismic observations from Hinode.
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Aims. We study the coherency of solar spicules intensity oscillations with increasing height above the solar limb in quiet Sun, active Sun and active region using observations from HINODE/SOT. Existence of coherency up to transition region strengthens the theory of the coronal heating and solar wind through energy transport and photospheric oscillations. Methods. Using time sequences from the HINODE/SOT in Ca II H line, we investigate oscillations found in intensity profiles at different heights above the solar limb. We use the Fourier and wavelet analysis to measure dominant frequency peaks of intensity at the heights, and phase difference between oscillations at two certain heights, to find evidence for the coherency of the oscillations. Finally, we can calculate the energy and the mass transported by spicules providing energy equilibrium, according to density values of spicules at different heights. To extend this work, we can also consider coherent oscillations at different latitudes and suggest to study of oscillations which may be obtained from observations of other satellites.
We present observations of a precursory signature that would be helpful for understanding the formation process of sunspot penumbrae. The Hinode Solar Optical Telescope successfully captured the entire evolution of a sunspot from the pore to a large well-developed sunspot with penumbra in an emerging flux region appeared in NOAA Active Region 11039. We found an annular zone (width 3-5) surrounding the umbra (pore) in Ca II H images before the penumbra is formed around the umbra. The penumbra was developed as if to fill the annular zone. The annular zone shows weak magnetogram signals, meaning less magnetic flux or highly inclined fields there. Pre-existing ambient magnetic field islands were moved to be distributed at the outer edge of the annular zone and did not come into the zone. There is no strong systematic flow patterns in the zone, but we occasionally observed small magnetic flux patches streaming out. The observations indicate that the annular zone is different from sunspot moat flow region and that it represents the structure in the chromosphere. We conclude that the annular zone reflects the formation of a magnetic canopy overlying the region surrounding the umbra at the chromospheric level, much before the formation of the penumbra at the photospheric level. The magnetic field structure in the chromosphere needs to be considered in the formation process of the penumbrae.
The Solar Optical Telescope onboard Hinode revealed the fine-scale structure of the Evershed flow and its relation to the filamentary structures of the sunspot penumbra. The Evershed flow is confined in narrow channels with nearly horizontal magnetic fields, embedded in a deep layer of the penumbral atmosphere. It is a dynamic phenomenon with flow velocity close to the photospheric sound speed. Individual flow channels are associated with tiny upflows of hot gas (sources) at the inner end and downflows (sinks) at the outer end. SOT/Hinode also discovered ``twisting motions of penumbral filaments, which may be attributed to the convective nature of the Evershed flow. The Evershed effect may be understood as a natural consequence of thermal convection under a strong, inclined magnetic field. Current penumbral models are discussed in the lights of these new Hinode observations.
We investigated four major solar flare events that occurred in active regions NOAA 10930 (December 13 and 14, 2006) and NOAA 11158 (February 13 and 15, 2011) by using data observed by the Solar Optical Telescope (SOT) onboard the Hinode satellite. To reveal the trigger mechanism of solar flares, we analyzed the spatio-temporal correlation between the detailed magnetic field structure and the emission image of the Ca H line at the central part of flaring regions for several hours prior to the onset of flares. We observed in all the flare events that the magnetic shear angle in the flaring regions exceeded 70 degrees, as well as that characteristic magnetic disturbances developed at the centers of flaring regions in the pre-flare phase. These magnetic disturbances can be classified into two groups depending on the structure of their magnetic polarity inversion lines; the so-called Opposite-Polarity and Reversed-Shear magnetic field recently proposed by our group, although the magnetic disturbance in one event of the four samples is too subtle to clearly recognize the detailed structure. The result suggests that some major solar flares are triggered by rather small magnetic disturbances. We also show that the critical size of the flare-trigger field varies among flare events and briefly discuss how the flare-trigger process depends on the evolution of active regions.
We present the first simultaneous observations of chromospheric anemone jets in solar active regions with Hinode SOT Ca II H broadband filetergram and Ca II K spetroheliogram on the Domeless Solar Telescope (DST) at Hida Observatory. During the coordinated observation, 9 chromospheric anemone jets were simultaneously observed with the two instruments. These observations revealed three important features, i.e.: (1) the jets are generated in the lower chromosphere, (2) the length and lifetime of the jets are 0.4-5 Mm and 40-320 sec, (3) the apparent velocity of the jets with Hinode SOT are 3-24 km/s, while Ca II K3 component at the jets show blueshifts (in 5 events) in the range of 2- 6 km/s. The chromospheric anemone jets are associated with mixed polarity regions which are either small emerging flux regions or moving magnetic features. It is found that the Ca II K line often show red or blue asymmetry in K2/K1 component: the footpoint of the jets associated with emerging flux regions often show redshift (2-16 km/s), while the one with moving magnetic features show blueshift (around 5 km/s). Detailed analysis of magnetic evolution of the jet foaming regions revealed that the reconnection rate (or canceling rate) of the total magnetic flux at the footpoint of the jets are of order of 10^{16} Mx/s, and the resulting magnetic energy release rate (1.1-10) x 10^{24} erg/s, with the total energy release (1-13) x 10^{26} erg for the duration of the magnetic cancellations, 130s. These are comparable to the estimated total energy, 10^{26} erg, in a single chromospheric anemone jet. An observation-based physical model of the jet is presented. The relation between chromospheric anemone jets and Ellerman bombs is discussed.
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