Emergence of Small-Scale Magnetic Loops in the Quiet Sun Internetwork

1
Emergence of Small-Scale Magnetic Loops in the
Quiet Sun Internetwork
R. Centeno, H Socas-Navarro, B. Lites, M.
Kubo High Altitude Observatory (NCAR), Boulder CO
80301, USA
Z. Frank, R. Shine, T. Tarbell, A. Title Lockheed
Martin Space and Astrophysics Laboratory, Palo
Alto, CA, USA
K. Ichimoto, S. Tsuneta, Y. Katsukawa, Y.
Suematsu National Astronomical Observatory of
Japan, Tokyo, Japan
T. Shimizu Japan Aerospace Exploration Agency,
Tokyo, Japan
S. Nagata Kwasan and Hida Observatories, Kyoto
University, Japan
The Astrophysical Journal, Volume 666, Issue 2,
pp. L137-L140.
Presented by Angelo P. Verdoni Center for
Solar-Terrestrial Research Fall 2007
2
Introduction

• Presented in this paper is clear evidence of the
  emergence and temporal
• evolution of a small-scale InterNetwork (IN)
  magnetic loop in the quiet Sun
• photosphere.
• The nature of InterNetwork (IN) magnetic fields
  is currently a hot topic of
• debate
• Strong kG field strengths associated with small
  filling factorsa
• Predominance of weak magnetic fields (300 500
  G)b
• Litesc , using the Advanced Stokes Polarimeter
  (ASP), reports Horizontal
• Internetwork Fields (HIFs) with typical sizes of
  1 and lifetimes of 5
• minutes, suggesting small magnetic loops are
  being advected towards the
• surface by the upward motion of the plasma inside
  the granule.
• Measurement of the full topology of a magnetic
  loop requires accurate 2-D
• spectropolarimetric maps of the four Stokes
  parameters, with high S/N ratio
• ( 10-3 continuum intensity), high spatial
  resolution and good consistent
• seeing conditions. The Spectro-Polarimetr (SP) of
  the Solar Optical
• Telescope (SOT) on board Hinoded meets all of
  these requirements.

3
Observations Hinode SP/SOT
Figures taken from http//solarb.msfc.nasa.gov/do
cuments/Tarbell_SolarB.pdf
4
Observations
5
Magnetic Flux Density and Field Topology

• To quantify the magnetic flux density and its
  topology, full Stokes LTE inversions ( using
  LILIAe ) of pixels with non-negligible linear or
  circular polarization signals.
• LTE inversions should give reliable magnetic
  flux density values. However, some of the signals
  are marginally above noise level.
• By adjusting various parameters ( one example,
  keeping field height constant or allowing linear
  variation in height ) different values of the
  flux density were calculated. So, the apparent
  transverse and longitudinal flux densities were
  computed from the integrated polarization
  signalsf and the LTE inversione was used to
  determine the field topology (which remained
  consistently independent of parameter variation).

6
Magnetic Flux Density and Field Topology

• Figure shows ( for the 4 X 4 region ) the
  time sequence of the longitudinal and transverse
  flux density ( 1st and 2nd row respectively ).
  The bottom row shows the field orientation with
  color-coded pixels representing inclination
  values and arrows representing the direction of
  positive polarity.

7
Magnetic Flux Density and Field Topology

• t 0, barely any magnetic signal present in the
  granular region centered at approximately
  (1,2)
• t 2 min, new concentration of mostly
  horizontal ( transverse ) flux density appears.
  The field is parallel to the surface and azimuth
  makes angle 60 degrees with E-W direction
• t 4 min, magnetic feature has stretched in
  the linear direction. Magnetic poles now
  apparent.
• t 6 min, transverse flux is not detectable
  with vertical dipoles visibly drifting towards
  granule boundary.

8
Magnetic Flux Density and Field Topology

• Due to the azimuth ambiguity there are two
  possible topology configurations for the magnetic
  loop seen at t 6 min.

9
Conclusions

• Observational evidence is presented of an
  emergent magnetic loop
• structure at quiet sun disk center. The flux
  emerges within granular region
• showing strong horizontal magnetic signal flanked
  by traces of two vertical
• opposite polarities.
• This event brings 1017 Mx of apparent
  longitudinal magnetic flux and
• does not seem to have any major influence on the
  shape of the underlying
• granulation pattern. In agreement with
  simulationsg where small scale
• magnetic loop structures with less than 1018 Mx
  of longitudinal flux are not
• sufficiently buoyant to rise coherently against
  the granulation, and produce
• no visible disturbances.
• The convective motions carry the vertical
  magnetic flux towards the
• intergranular lanes, where it stays confined for
  longer times. This could
• explain why transverse magnetic flux (observed at
  disk center) is in general
• co-spatial with granules while longitudinal flux
  tends to be concentrated in
• the intergranular lanes.

10
References

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