Measurements of significant plasma flows in the regions of blinkers with SOHOCDS

1
Measurements of significant plasma flows in the
regions of blinkers with SOHO/CDS
K. Steed1 and G. Del Zanna1
UCL Department of Space and Climate
Physics Mullard Space Science Laboratory
ABSTRACT In this study, the results from previous
research into how the temperatures and densities
of blinkers vary with time are confirmed. We also
use SOHO/CDS and rastering to do the first
2-dimensional imaging of the velocities of plasma
flows in blinkers which are found to be very
dynamic.

• INTRODUCTION
• Blinkers are small, explosive events, located in
  the transition region and observed as
  brightenings everywhere on the Sun. A number of
  blinkers located within 200 of the disk centre
  were studied, and we present here, one example of
  a blinker observed between 0740 and 0750 UT
  on 25th February 2001.

Density 3.74e10
Density 1.74e10

• The blinker is observed at its maximum intensity
  by SOHO/CDS/NIS in a raster taken at 0746 UT.
  It is identified in the transition region EUV
  emission lines, O III and O V, as a cluster of
  bright pixels however it is not seen in the
  cooler, chromospheric line, He I or the hotter,
  coronal line, Mg IX.

Density 2.63e10
Density 1.82e10

• Plots of the ratios of the intensities of
  different oxygen (EUV) emission lines over the
  duration of the blinker provide an indication of
  how temperature varies with time within the
  blinker.
• These ratios are flat, suggesting that blinkers
  are not temperature events.

• Electron density is measured using O IV emission
  lines measured using CDS. This analysis allows
  us to determine whether blinkers are caused by
  density enhancements or changes in the transition
  region filling factor.

• The density of the blinker is calculated, using
  the CHIANTI atomic database (Dere et al., 1997,
  Landi et al., 2006), from the ratios of the
  intensities of each of four O IV emission lines
  detected (identified as a (553.3 Å), b (554.0
  Å), c (554.5 Å) and d (555.2 Å)) with a fifth
  O IV emission line formed at 625.8 Å. This
  calculates a value for the density of the blinker
  resulting from each of these emission line
  ratios.

• A comparison of the values for the density
  calculated from each of the O IV emission line
  ratios indicates that electron density is
  constant within the blinker.

• Most previous research into blinkers has been
  conducted using SOHO/SUMER where the slit was
  fixed. Using SOHO/CDS, which enables us to
  raster, means we are able to do 2D imaging of the
  velocities and directions of plasma flows in the
  regions of blinkers.

• In the presence of the strongest blinkers, large
  velocity flows are seen to be sustained for a
  longer period, sometimes existing this way for
  longer than five minutes.

• Very dynamic plasma flows in the regions of
  blinkers are observed, with adjacent upflows and
  downflows exceeding 50 km/s. This value is much
  greater than previously published values, also
  obtained using SOHO/CDS, which are in the region
  of 10 20 km/s (Gallagher et al., 1999), and
  values obtained using the high resolution
  spectroscopic instrument SOHO/SUMER, which were
  even smaller (Teriaca et al., 2001).

• CONCLUSIONS
• Blinkers are only visible in atomic emission
  lines formed at transition region temperatures (
  105 K), confirming the source region of these
  types of events.
• The ratios of the intensities of different
  oxygen emission lines in a blinker are flat,
  indicating that the temperature of a blinker does
  not vary with time. This confirms the results of
  previous research (Harrison et al., 1997), which
  concluded that blinkers are not temperature
  events.
• The values for the electron density obtained for
  the blinkers in this study are found to be very
  similar to each other. The O IV emission line
  intensity ratios are flat, and this confirms the
  results of previous research (Teriaca et al.,
  2001) which concluded that the electron density
  is constant in a blinker, since I a ne2. This
  lends strength to the theory that blinkers are
  caused by an increase in the transition region
  filling factor, rather than density enhancements.
• Significant plasma flows have been identified in
  blinkers, and these may be important for
  ultimately understanding the cause of these
  events.

REFERENCES Dere, K. P., Landi, E., Mason, H. E.,
Monsignori Fossi, B. C., and Young, P. R (1997),
CHIANTI An Atomic Database for Emission Lines,
A AS, 125, 149 - 173 Gallagher, P.T, Phillips,
K. J. H., Harra-Murnion, L. K., Baudin, F., and
Keenan, F. P. (1999), Transient Events in the EUV
Transition Region and Chromosphere, A A, 348,
251 - 260 Harrison, R. A., Lang, J., Brooks, D.
H., and Innes, D. E. (1999), A Study of Extreme
Ultraviolet Blinker Activity, A A, 351, 1115
1132 Landi, E., Del Zanna, G., Young, P. R.,
Dere, K. P., Mason, H. E., and Landini, M.
(2006), CHIANTI An Atomic Database for Emission
Lines. VII. New Data for X-Rays and Other
Improvements, ApJS, 162, 261 - 280 Teriaca, L.,
Madjarska, M. S., and Doyle, J. G. (2001),
Electron Density Variations During Ultraviolet
Transient Events, Sol. Phys., 200, 1-2, 91 -114

• Mullard Space Science Laboratory, University
  College London,
• Holmbury St. Mary, Dorking, RH5 6NT, UK.

ks3_at_mssl.ucl.ac.uk