123 research outputs found
Relationship between earth-directed solar eruptions and magnetic clouds at 1AU: A brief review
We review relationships between coronal mass ejections (CMEs), EIT post
eruption arcades, and the coronal neutral line associated with global magnetic
field and magnetic clouds near the Earth. Our previous findings indicate that
the orientation of a halo CME elongation may correspond to the orientation of
the underlyig flux rope. Here we revisit these preliminary reports by comparing
orientation angles of elongated LASCO CMEs, both full and partial halos, to the
post eruption arcades. Based on 100 analysed events, it was found that the
overwhelming majority of halo CMEs are elongated in the direction of the axial
field of the post eruptio arcades. Moreover, this conclusion also holds for
partial halo CMEs as well as for events that originate further from the disk
center. This suggests that the projection effect does not drastically change
the appearance of full and partial halos and their imagesstill bear reliable
information about the underlying magnetic fields. We also compared orientations
of the erupted fields near the Sun and in the interplanetary space and found
that the local tiltof the coronal neutral line at 2.5 solar radii is well
correlated with the magnetic cloud axis measured near the Earth. We suggest
that the heliospheric magnetic fields significantly affect the propagating
ejecta. Sometimes, the ejecta may even rotate so that its axis locally aligns
itself with the heliospheric current sheet.Comment: 12 pages; 8 figure
Active Region Moss: Doppler Shifts from Hinode/EIS Observations
Studying the Doppler shifts and the temperature dependence of Doppler shifts
in moss regions can help us understand the heating processes in the core of the
active regions. In this paper we have used an active region observation
recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) onboard Hinode
on 12-Dec-2007 to measure the Doppler shifts in the moss regions. We have
distinguished the moss regions from the rest of the active region by defining a
low density cut-off as derived by Tripathi et al. (2010). We have carried out a
very careful analysis of the EIS wavelength calibration based on the method
described in Young et al. (2012). For spectral lines having maximum sensitivity
between log T = 5.85 and log T = 6.25 K, we find that the velocity distribution
peaks at around 0 km/s with an estimated error of 4-5 km/s. The width of the
distribution decreases with temperature. The mean of the distribution shows a
blue shift which increases with increasing temperature and the distribution
also shows asymmetries towards blue-shift. Comparing these results with
observables predicted from different coronal heating models, we find that these
results are consistent with both steady and impulsive heating scenarios.
However, the fact that there are a significant number of pixels showing
velocity amplitudes that exceed the uncertainty of 5 km s is suggestive
of impulsive heating. Clearly, further observational constraints are needed to
distinguish between these two heating scenarios.Comment: 21 pages (single column), 7 figures, Accepted for Publication in The
Astrophysical Journa
- …