TY - CONF
T1 - Dissertation Talk: The Impact of Sunspots on Modelling Coronal UV Observations
AU - Morgan, H.
AU - Habbal, Shadia Rifai
PY - 2005/5/1
Y1 - 2005/5/1
N2 - Existing model studies of O VI 1032 and 1037 A spectral lines from
UVCS/SOHO observations often conclude that O5+ ions in coronal streamers
have no significant outflow velocity at heights below 3 Rs, and large
increases above this height. These observations were modelled with a
typical O VI quiet Sun disk spectrum, and the subsequent results were
interpreted as an indication of different flows arising from closed and
open magnetic field regions within streamers. Given that the O VI solar
disk spectrum emitted from sunspots is very different from the spectrum
emitted from the quiet Sun or coronal holes, we show how the inclusion
of a contribution from sunspots in the incident disk radiation, which
excites the coronal O5+ ions, has a significant impact on the intensity
and intensity ratio of the coronal O VI spectral lines. Such a result
has important implications for the calculation of the outflow velocity
of O5+ ions in streamers. Through the analysis of UVCS observations of a
solar maximum active region streamer with a large sunspot cluster at its
base, we show how the inclusion of a 3% contribution from sunspots in
the modelled quiet disk spectrum allows agreement between the observed
and modeled intensity ratios at lower heights with non-zero outflow
velocities. Such a result cannot be achieved with a standard quiet Sun
disk spectrum. Taking the sunspot contribution into account yields O5+
ions with an outflow velocity of about 80 km/s at a height of 3 Rs,
increasing linearly to 260 km/s at a height of 8 Rs. These results imply
that the presence of sunspots on the solar disk concurrent with streamer
observations requires a revision of published results.
AB - Existing model studies of O VI 1032 and 1037 A spectral lines from
UVCS/SOHO observations often conclude that O5+ ions in coronal streamers
have no significant outflow velocity at heights below 3 Rs, and large
increases above this height. These observations were modelled with a
typical O VI quiet Sun disk spectrum, and the subsequent results were
interpreted as an indication of different flows arising from closed and
open magnetic field regions within streamers. Given that the O VI solar
disk spectrum emitted from sunspots is very different from the spectrum
emitted from the quiet Sun or coronal holes, we show how the inclusion
of a contribution from sunspots in the incident disk radiation, which
excites the coronal O5+ ions, has a significant impact on the intensity
and intensity ratio of the coronal O VI spectral lines. Such a result
has important implications for the calculation of the outflow velocity
of O5+ ions in streamers. Through the analysis of UVCS observations of a
solar maximum active region streamer with a large sunspot cluster at its
base, we show how the inclusion of a 3% contribution from sunspots in
the modelled quiet disk spectrum allows agreement between the observed
and modeled intensity ratios at lower heights with non-zero outflow
velocities. Such a result cannot be achieved with a standard quiet Sun
disk spectrum. Taking the sunspot contribution into account yields O5+
ions with an outflow velocity of about 80 km/s at a height of 3 Rs,
increasing linearly to 260 km/s at a height of 8 Rs. These results imply
that the presence of sunspots on the solar disk concurrent with streamer
observations requires a revision of published results.
UR - http://hdl.handle.net/2160/10572
M3 - Abstract
SP - 1
ER -