624 research outputs found
Properties of Solar Ephemeral Regions at the Emergence Stage
For the first time, we statistically study the properties of ephemeral
regions (ERs) and quantitatively determine their parameters at the emergence
stage based on a sample of 2988 ERs observed by the \emph{Solar Dynamics
Observatory}. During the emergence process, there are three kinds of kinematic
performances, i.e., separation of dipolar patches, shift of ER's magnetic
centroid, and rotation of ER's axis. The average emergence duration, flux
emergence rate, separation velocity, shift velocity, and angular speed are 49.3
min, 2.6 10 Mx s, 1.1 km s, 0.9 km s, and
0\degr.6 min, respectively. At the end of emergence, the mean magnetic
flux, separation distance, shift distance, and rotation angle are 9.3
10 Mx, 4.7 Mm, 1.1 Mm, and 12\degr.9, respectively. We also find that
the higher the ER magnetic flux is, (1) the longer the emergence lasts, (2) the
higher the flux emergence rate is, (3) the further the two polarities separate,
(4) the lower the separation velocity is, (5) the larger the shift distance is,
(6) the slower the ER shifts, and (7) the lower the rotation speed is. However,
the rotation angle seems not to depend on the magnetic flux. Not only at the
start time, but also at the end time, the ERs are randomly oriented in both the
northern and the southern hemispheres. Besides, neither the anticlockwise
rotated ERs, nor the clockwise rotated ones dominate the northern or the
southern hemisphere.Comment: 25 pages, 12 figures; accepted for publication in Ap
Self-cancellation of ephemeral regions in the quiet Sun
With the observations from the Helioseismic and Magnetic Imager aboard the
Solar Dynamics Observatory, we statistically investigate the ephemeral regions
(ERs) in the quiet Sun. We find that there are two types of ERs: normal ERs
(NERs) and self-cancelled ERs (SERs). Each NER emerges and grows with
separation of its opposite polarity patches which will cancel or coalesce with
other surrounding magnetic flux. Each SER also emerges and grows and its
dipolar patches separate at first, but a part of magnetic flux of the SER will
move together and cancel gradually, which is described with the term
"self-cancellation" by us. We identify 2988 ERs among which there are 190 SERs,
about 6.4% of the ERs. The mean value of self-cancellation fraction of SERs is
62.5%, and the total self-cancelled flux of SERs is 9.8% of the total ER flux.
Our results also reveal that the higher the ER magnetic flux is, (i) the easier
the performance of ER self-cancellation is, (ii) the smaller the
self-cancellation fraction is, and (iii) the more the self-cancelled flux is.
We think that the self-cancellation of SERs is caused by the submergence of
magnetic loops connecting the dipolar patches, without magnetic energy release.Comment: 6 pages, 4 figures, accepted for publication in ApJ
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