27,540 research outputs found
On The Doppler Velocity of Emission Line Profiles Formed in the "Coronal Contraflow" that is the Chromosphere-Corona Mass Cycle
This analysis begins to explore the complex chromosphere-corona mass cycle
using a blend of imaging and spectroscopic diagnostics. Single Gaussian fits to
hot emission line profiles (formed above 1MK) at the base of coronal loop
structures indicate material blue-shifts of 5-10km/s while cool emission line
profiles (formed below 1MK) yield red-shifts of a similar magnitude -
indicating, to zeroth order, that a temperature-dependent bifurcating flow
exists on coronal structures. Image sequences of the same region reveal weakly
emitting upward propagating disturbances in both hot and cool emission with
apparent speeds of 50-150km/s. Spectroscopic observations indicate that these
propagating disturbances produce a weak emission component in the blue wing at
commensurate speed, but that they contribute only a few percent to the
(ensemble) emission line profile in a single spatio-temporal resolution
element. Subsequent analysis of imaging data shows material "draining" slowly
(~10km/s) out of the corona, but only in the cooler passbands. We interpret the
draining as the return-flow of coronal material at the end of the complex
chromosphere-corona mass cycle. Further, we suggest that the efficient
radiative cooling of the draining material produces a significant contribution
to the red wing of cool emission lines that is ultimately responsible for their
systematic red-shift as derived from a single Gaussian fit when compared to
those formed in hotter (conductively dominated) domains. The presence of
counter-streaming flows complicates the line profiles, their interpretation,
and asymmetry diagnoses, but allows a different physical picture of the lower
corona to develop.Comment: 7 pages, 5 color figures. Accepted to Appear Ap
Quasi-period outflows observed by the X-Ray Telescope onboard Hinode in the boundary of an active region
Persistent outflows have recently been detected at boundaries of some active
regions. Although these outflows are suggested to be possible sources of the
slow solar wind, the nature of these outflows is poorly understood. Through an
analysis of an image sequence obtained by the X-Ray Telescope onboard the
Hinode spacecraft, we found that quasi-period outflows are present in the
boundary of an active region. The flows are observed to occur intermittently,
often with a period of 5-10 minutes. The projected flow speed can reach more
than 200 km/s, while its distribution peaks around 50 km/s. This sporadic
high-speed outflow may play an important role in the mass loading process of
the slow solar wind. Our results may imply that the outflow of the slow solar
wind in the boundary of the active region is intermittent and quasi-periodic in
nature.Comment: 5 figures, accepted by RA
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