The fine structure of the quiet solar atmosphere

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The fine structure of the quiet solar atmosphere

• Georgia Tsiropoula
• Kostas Tziotziou

National Observatory of Athens Institute for
Space Applications and Remote Sensing, Greece
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The chromospheric network outlined by mottles

• Mottles outline the network boundaries in the
  chromosphere
• There are typically about 30 mottles per network
  cell at any one time
• The cause of mottles is not known yet with
  certainty.
• Mottles are very important structures because
  they are considered as
• a) the disk counterpart of spicules
• b) the principal channels through which mass
  and energy is supplied from the lower layers to
  the corona and the solar wind

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Spicules observed at the limb

• Mottles (or spicules) are jets of plasma with
  lifetimes of 5 minutes, heights of
  5,000-10,000km, diameters of 500-1000 km, speeds
  of 20-30 km/s and temperatures of 10,000?

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Observations

• Performed with the Multichannel Subtractive
  Double Pass (MSDP) spectrograph
• Provides spectra from which two dimensional
  intensity and velocity images at different
  wavelengths within a line can be constructed
• 50 cm refractor (Pic du Midi Observatory,
  Pyrénées)
• THEMIS (Observatorio del Teide, Tenerife)

Mein P. AA 381, 271, 2002
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Ha observations of a rosette with MSDP (50 cm
refractor of the Pic du Midi Observatory)
Tsiropoula, Alissandrakis and Schmieder AA 271,
574, 1993
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Method of computation

• Use of the Cloud model
• optically thin structures
• constant source function S

• Initial parameters
• ?0
• ??D 0.3 Å
• tmax 1
• S 0.1550.159(P1-C1)/C1

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Cloud velocities as a function of time along the
axe of a mottleTsiropoula, Alissandrakis and
Schmieder AA 290, 285, 1994
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Ha observations of a chain of mottles with MSDP
on THEMIS
Tziotziou, Tsiropoula and Mein AA 402, 361,
(2003)
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Intensity and velocity in different wavelengths
Intensity ?a
Intensity ?a0.48 Å
Intensity ?a-0.48 Å
Doppler ?a0.48 Å
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Cloud velocities as a function of time along the
axe of a mottle
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A model for the velocity variations based on
reconnection
Squeezing of opposite polarity fields
Reconnection of magnetic fields
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MDI continuum images MDI magnetograms
H. Potts (Glasgow University, 2006)
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Other parameters calculated from the following
relations
Tsiropoula and Schmieder, AA, 324, 1183, 1997
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Mass flux from fine structures

• Upward mass flux depends on
• fraction f of the solar surface covered by fine
  structures at any moment (f 0.05, total number
  of mottles 4x105)
• the mass density ? (2.2 10-13 g cm-3)
• the axial velocity ?a (?a ?LOS/cos?, ?45o)

• Assuming that at any given moment
• only half of the mottles show upward motion
• only half of the material flows upwards

thus most of the mass does fall down!
Mass outflow from the solar corona 3 10-11 g
cm-2 s-1
Tsiropoula Tziotziou AA 424, 279, 2004
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Detailed energy flux from fine structures
During the reconnection phase fluxes released
from each event
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Energy flux from fine structures

• Global energy flux terms estimated assuming
• lifetime of mottles 300 s
• (duration of outflow-downflow of 150 s)
• the area of each event
• birthrate of events (1333 events/s)

14 of the needed energy flux (3 105 ergs cm-2
s-1)
Energy flux provided for heating of corona
B15 G
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Conclusions

• Several parameters describing mottles can be
  obtained from MSDP
• Ha spectra
• There are strong indications that mottles are
  driven by magnetic
• reconnection
• Mass outflow from mottles two orders of
  magnitude larger than that
• needed for the mass balance of the solar
  corona
• Most of the mass returns back explaining the
  downflows in the network
• boundaries observed in the EUV lines
• Energy outflow from mottles accounts for 14 of
  the energy budget
• of the solar corona (underestimated)
• May be the corona is in fact heated by a wide
  variety of mechanisms
• that each accounts for some of the required
  heating rate.
• MSDP powerful instrument providing high spatial
  and temporal
• resolution spectra in various lines
• THEMIS with its vector magnetogram will help in
  giving a definitive
• answer on the role of the magnetic field in
  the formation of mottles