Moving Magnetic Features

1
Moving Magnetic Features

• Jun Zhang
• National Astronomical Observatories
• Chinese Academy of Sciences

2

• Using data recorded by the Michelson Doppler
  Imager (MDI) instrument on the Solar and
  Heliospheric Observatory (SOHO), we have traced
  42 pairs of opposite magnetic polarity moving
  magnetic features (MMFs)in active region NOAA
  8375.

3

The horizontal velocity of MMFs ranges from 0.1
km s-1 to 0.7 km s-1, and on average, the
velocity of an MMF pair decreases significantly
(from 0.6 km s-1 to 0.35 km s-1)with increasing
distance from the MMF's birth place. In contrast,
the decrease of the average velocity far less
obviously (from0.5 km s-1 to 0.4 km -1) with
increasing distance from the sunspot.
4
This result suggests that the change in MMF flow
speed does not reflect the radial structure of
the moat flow, but rather is intrinsic to the
evolution of the MMF pairs.The vertical velocity
indicates that the elements of MMF pairs with
polarity opposite to that of the sunspot support
a downflow (Doppler redshift) of about 100 m s-1.
The average Doppler shift difference between
negative and positive elements is around 150 m
s-1.

5

• These observational results confirm the model
  that MMF pairs are part of a U-loop emanating
  from the sunspot's magnetic canopy. According to
  this model the downflow is caused by the Evershed
  flow returning below the solar surface.

6

• The horizontal velocity of MMF elements is
  plotted versus relative distance from MMF birth
  place.

7
Left SOHO/MDI longitudinal magnetograms showing
the northern part of the sunspot of AR NOAA 8375
. A box at0113 UT outlines the field-of view of
the following magnetograms.Three arrows denote a
negative element of an MMF pair Right
corresponding MDI Dopplergrams. White patches
show downflow, and black patches, upflows. Three
arrows point to the Dopplershift of the negative
element.
8

Upper panel histogram showing the Doppler shift
of the individual MMFs Lower panel histogram
showing the difference of the Doppler shift
between negative and positive MMF elements.
9
Sketch of a possible explanation of the creation(
upper frame) and motion (lower frame) of MMF pairs
10
Detailed sketch showing the relationship among an
umbra, a penumbra,an MMF pair and a canopy base.
11
(No Transcript)
12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
(No Transcript)
27
(No Transcript)