High-latitude activity and its relationship to the mid-latitude solar activity.

1
High-latitude activity and its relationship to
the mid-latitude solar activity. Elena E.
Benevolenskaya J. Todd Hoeksema Stanford
University
Abstract. The high-latitude activity at
photosphere and corona, and their relation to the
mid-latitude activity in cycle 23 using the
Extreme Ultraviolet (EUV) coronal observation
have been explored using the MDI magnetic
synoptic maps available on the SOHO web page with
a new calibration and EIT synoptic maps. The EIT
synoptic maps of EUV images in three lines Fe and
in one line He II (171A, 195A, 284A and 304A)
are obtained for period June 1996 - May 2006
(CR1911-CR2042) from the full disk EIT images.
They are represented by values of the line
intensity centered on the central meridian and
can be directly compared with magnetic synoptic
maps (MDI maps). It was found that the solar
cycle dependence of the EUV polar corona occurs
because of the large-scale topology of the solar
corona and its relationship with the mid-latitude
magnetic flux. It is seen more pronounced on the
rising phase of the solar cycle due to the
connectivity of the coronal structures extended
from the mid-latitude to the high-latitude. But,
after the solar cycle maximum the EUV polar
corona shows a less dependence of the
mid-latitude corona. In the polar regions the
absent of the correlation of the unsigned
magnetic flux and EUV corona occurs not only due
to the effect of projection. But it tells about
the numerous emerging bi-polar and unipolar
regions inside the polar region which does not
contribute to the brightness of the EUV corona.
Really, during the solar minimum when the polar
magnetic field reaches its maximum and number of
unipolar magnetic regions of strong magnetic
field increases, but we observe dimming and
coronal holes instead of the bright EUV corona.
Mid-latitude and high-latitude magnetic fields.
Magnetic elements
Zonal Structure of the Solar cycle 23
Polar magnetic field, its reversals
Figure 6. Synoptic frames of magnetic field. Left
image ?t0 hours, middle image ?t14 hours,
right image?t25 hours
The hourly averaged (50 images inside 1 hour) MDI
images were transformed to the Carrington
coordinate system. As a result, the magnetic
frames centered on the central meridian from -40o
to 40o in longitude stepped 0.1o and in sin
latitude with resolution equals 0.001 of sin
latitude are obtained. The area of the magnetic
frames is about 1.735 1011 km2,and area of each
pixel equals 8.45 105 km2.
Example for two magnetic element in Mid latitude
Figure 3. Polar magnetic field (at 55o) from
Wilcox Solar Observatory. North hemisphere Is
marked by the blue color, South hemisphere is
marked by the red color.
?t 2 years
End of reversal at 55o in South
Start of reversal at 55o in South
Time of polar magnetic field reversals
L. Svalgaard And E. W. Cliver, ApJ, 2007
Figure 8. Left panels Displacement of the
magnetic element in longitude and in Latitude.
Right panel Area of magnetic element with B
lt-10 G.
Figure 7. Left panels Displacement of the
magnetic element in longitude and in Latitude.
Right panel Area of magnetic element with B
gt10 G.
two sets of activity waves
Dynamics of the small-scale magnetic field which
forms the streamers or surges is very
complicated. Near the pole we did not observe
continually latitudinal motion for individual
magnetic elements and it may be related to slow
down of the meridional circulation (Raouafi,
Harvey, 2007).
Examples for magnetic elements in High latitude
(about 80o)
Durrant and Wilson (2003) found time of reversals
using The Kitt Peak data CR1975 2 in North and
CR1981 1 in South. MDI data confirmed this
results.
Figure1. A) Sunspot area as a function of time
from June 1996 to May 2006 (Carrington rotations
from 1911 to 2042) Axisymmetrical distributions
as a function of latitude and time for B) EUV
flux in Fe XII and C) He II lines D) Unsigned
magnetic flux 0 20G, MDI (old calibration). E)
B- component of the magnetic field, in the
blue-red color map is -1G 1G, MDI (old
calibration)
What contributes these uncertainties? Line of
sight component? Radial field approximation?
Space scale of the averaged magnetic field?
Figure 9. Left panels Displacement of the
magnetic short-lived element in longitude and in
Latitude. Right panel Area of magnetic element
with B gt10 G.
Figure 10. Left panels Displacement of the
long-lived magnetic element in longitude and
in Latitude. Right panel Area of magnetic
element with B gt10 G.
Conclusions

• The zonal or axisymmetrical structure of the
  solar cycle reveals the transport of the magnetic
  flux from the mid to high latitude.
• Migration of the zonal neutral line defines the
  reversal of the magnetic field during the solar
  cycle.
• The transport of the magnetic energy is a complex
  process related to the surface, subsurface and
  coronal processes.

Figure 5. The total MDI unsigned magnetic flux
of the radial field component in the latitude
zones from 78o to 88o in Northern (solid line)
and Southern Hemispheres (dash lines) b) The
relative positive polarity parts of magnetic flux
in Northern (solid line) and Southern (dash line)
hemispheres c) The total signed magnetic flux.
The polar magnetic field reversal was in CR1975
2 (March 2001) in the North and in CR1980 2
(September 2001) in South.
Figure 2. Left image YOHKOH Soft X-ray image,
right panel topolgy of the Magnetic field during
the rising phase of the Sun. Foot-points of the
giants loops Forms the high-latitude activity
waves.