29 research outputs found
Interaction between a fast rotating sunspot and ephemeral regions as the origin of the major solar event on 2006 December 13
The major solar event on 2006 December 13 is characterized by the
approximately simultaneous occurrence of a heap of hot ejecta, a great
two-ribbon flare and an extended Earth-directed coronal mass ejection. We
examine the magnetic field and sunspot evolution in active region NOAA AR
10930, the source region of the event, while it transited the solar disk centre
from Dec. 10 to Dec. 13. We find that the obvious changes in the active region
associated with the event are the development of magnetic shear, the appearance
of ephemeral regions and fast rotation of a smaller sunspot. Around the area of
the magnetic neutral line of the active region, interaction between the fast
rotating sunspot and the ephemeral regions triggers continual brightening and
finally the major flare. It is indicative that only after the sunspot rotates
up to 200 does the major event take place. The sunspot rotates at
least 240 about its centre, the largest sunspot rotation angle which
has been reported.Comment: 4 pages, 6 figures, ApJ Letters inpres
The Horizontal Component of Photospheric Plasma Flows During the Emergence of Active Regions on the Sun
The dynamics of horizontal plasma flows during the first hours of the
emergence of active region magnetic flux in the solar photosphere have been
analyzed using SOHO/MDI data. Four active regions emerging near the solar limb
have been considered. It has been found that extended regions of Doppler
velocities with different signs are formed in the first hours of the magnetic
flux emergence in the horizontal velocity field. The flows observed are
directly connected with the emerging magnetic flux; they form at the beginning
of the emergence of active regions and are present for a few hours. The Doppler
velocities of flows observed increase gradually and reach their peak values
4-12 hours after the start of the magnetic flux emergence. The peak values of
the mean (inside the +/-500 m/s isolines) and maximum Doppler velocities are
800-970 m/s and 1410-1700 m/s, respectively. The Doppler velocities observed
substantially exceed the separation velocities of the photospheric magnetic
flux outer boundaries. The asymmetry was detected between velocity structures
of leading and following polarities. Doppler velocity structures located in a
region of leading magnetic polarity are more powerful and exist longer than
those in regions of following polarity. The Doppler velocity asymmetry between
the velocity structures of opposite sign reaches its peak values soon after the
emergence begins and then gradually drops within 7-12 hours. The peak values of
asymmetry for the mean and maximal Doppler velocities reach 240-460 m/s and
710-940 m/s, respectively. An interpretation of the observable flow of
photospheric plasma is given.Comment: 20 pages, 10 figures, 3 tables. The results of article were presented
at the ESPM-13 (12-16 September 2011, Rhodes, Greece, Abstract Book p. 102,
P.4.12,
http://astro.academyofathens.gr/espm13/documents/ESPM13_abstract_programme_book.pdf
The Relationship Between Plasma Flow Doppler Velocities and Magnetic Field Parameters During the Emergence of Active Regions at the Solar Photospheric Level
A statistical study has been carried out of the relationship between plasma
flow Doppler velocities and magnetic field parameters during the emergence of
active regions at the solar photospheric level with data acquired by the
Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory
(SOHO). We have investigated 224 emerging active regions with different spatial
scales and positions on the solar disc. The following relationships for the
first hours of the emergence of active regions have been analysed: i) of peak
negative Doppler velocities with the position of the emerging active regions on
the solar disc; ii) of peak plasma upflow and downflow Doppler velocities with
the magnetic flux growth rate and magnetic field strength for the active
regions emerging near the solar disc centre (the vertical component of plasma
flows); iii) of peak positive and negative Doppler velocities with the magnetic
flux growth rate and magnetic field strength for the active regions emerging
near the limb (the horizontal component of plasma flows); iv) of the magnetic
flux growth rate with the density of emerging magnetic flux; v) of the Doppler
velocities and magnetic field parameters for the first hours of the appearance
of active regions with the total unsigned magnetic flux at the maximum of their
development.Comment: 14 pages, 8 figures. The results of article were presented at the
ESPM-13 (12-16 September 2011, Rhodes, Greece, Abstract Book p. 102-103,
P.4.13,
http://astro.academyofathens.gr/espm13/documents/ESPM13_abstract_programme_book.pdf
Investigations of the MnI 539.47 nm and MnI 542.04 nm lines in solar plages
We observed the MnI 539.47 nm and 542.04nm line profiles in the quiet photosphere and plage regions in 1998 and 2001, and measured the full widths at half maximum, equivalent widths and depths of these profiles. The relative changes of the MnI 539.47 nm line parameters, normalized to the values obtained for quiet photosphere, as a function of magnetic field strength in plages is analyzed. We found, for plage region observed in 1998, that both the equivalent width and the depth of the line profile decrease with increasing strength of magnetic filed in plage at a rate of 9x10−4 /Gauss, but the full width at half maximum does not show any significant regular changes. Based on these results, the variations of the MnI 539.47 nm spectral line in solar flux with activity cycle could be explained by the variation of solar surface coverage with plages. For observations in 2001, the equivalent width and the depth of this line profile also decrease with increasing strength of magnetic filed in plage, but there are significant differences in the behavior of line parameters in comparison with the 1998 values. Comparison of changes of the MnI 539.47 nm line parameters with the parameters of the MnI 542.04 nm line in 1998 shows a clear discrepancy between them. On the contrary, in 2001 the full widths at half maximum and the equivalent widths of these two lines behaved in a similar fashion.