OBSERVATIONS OF POLAR PLUMES
WITH THE SUMER INSTRUMENT ON SOHO
D. M. Hassler¹, K. Wilhelm²,
P. Lemaire³, U. Schühle²
(1) High Altitude Observatory/NCAR, Boulder, CO
(Now at Southwest Research Institute, Boulder, CO);
(2) Max-Planck-Institut für Aeronomie, Katlenburg-Lindau, Germany;
(3) Institut d'Astrophysique Spatiale, Orsay, France
(Solar Physics, 175, 375)
ABSTRACT
We present new observations of O VI 1032 Å line profiles in
polar plumes, and inter-plume regions, on the disk and above the
limb in the north coronal hole obtained with the SUMER (Solar
Ultraviolet Measurements of Emitted Radiation) instrument on the
SOHO (Solar and Heliospheric Observatory) spacecraft. On 22
May 1996, a 5 x 5 arcmin spectroheliogram was scanned above the
north polar coronal hole with the entrance slit extending from 1.03
to 1.33 solar radii with 1.5 arcsec spatial resolution and 0.040 Å per
pixel spectral resolution in the wavelength range 1020-1040 Å .
Detailed plume structure in O VI 1032 Å can be seen extending
beyond 1.3 solar radii, with intensities in the plume regions 10-50%
brighter, but line widths 10-15% narrower, than the inter-plume
regions. Possible explanations for this observed anti-correlation
between line width and intensity in the plume and inter-plume
regions are discussed.
FIGURE CAPTIONS
Figure 2:
The first part of the sequence used the 0.3 x 120
arcsecond slit to make two raster images or spectroheliograms (16 x
2 arcmin²) with 1.5 arcsecond steps extending ± 8 arcminutes from
central meridian, shown in the bottom half of the figure. (The scale
is 1.5 arcsec/pixel along the x-axis and 1 arcsec/pixel along the y-
axis) In these raster images, one can see narrow jets or
macrospicules originating from bright points near the limb and
extending 30-60 arcseconds above the limb on both the east and
west side of central meridian. The second part of the sequence,
using the 1 x 300 arcsecond slit, extending from 30 arcseconds
above the limb out to 1.33 solar radii, obtained a single raster image
or spectroheliogram extending ± 5 arcminutes from central meridian,
shown in the top half of the figure. One can see in this image, along
with the larger scale plume structures, two small jets or
macrospicules near central meridian which appear to originate from
bright points at the limb in the lower images and extend 15-20
arcseconds into this upper image.
Figure 3:
The corresponding SOHO/EIT image in FeXII at 195
Å taken at 02:06 UT May 22 shown for reference. As can be seen
in the figure, the polar coronal holes in both the north and south
extend far enough onto the disk (toward low latitudes) to permit
unambiguous line-of-sight observations above the limb without risk
of contamination from foreground or background structures.
(Courtesy of the EIT Consortium)
Figure 7:
An image of the O VI 1032 Å line intensity and line
width (assuming a single Gaussian profile) as a function of height
and position above the limb obtained during the raster scan on May
22, 1996. The most notable feature is the striking anti-correlation
between line intensity and line width near central meridian.
