4,240 research outputs found
Spatiotemporal organization of energy release events in the quiet solar corona
Using data from STEREO and SOHO spacecraft, we show that temporal
organization of energy release events in the quiet solar corona is close to
random, in contrast to the clustered behavior of flaring times in solar active
regions. The locations of the quiet-Sun events follow the meso- and
supergranulation pattern of the underling photosphere. Together with earlier
reports of the scale-free event size statistics, our findings suggest that
quiet solar regions responsible for bulk coronal heating operate in a driven
self-organized critical state, possibly involving long-range Alfv\'{e}nic
interactions.Comment: 5 pages, 4 figures, 1 tabl
Heating of the solar corona by the resonant absorption of Alfven waves
An improved method for calculating the resonance absorption heating rate is discussed and the results are compared with observations in the solar corona. The primary conclusion to be drawn from these calculations is that to the level of the approximation adopted, the observations of the heating rate and nonthermal line broadening in the solar corona are consistent with heating by the resonance absorption mechanism
Slow magnetosonic waves and fast flows in active region loops
Recent EUV spectroscopic observations indicate that slow magnetosonic waves
are present in active region (AR) loops. Some of the spectral data were also
interpreted as evidence of fast (~100-300 km/s) quasi-periodic flows. We have
performed three-dimensional magnetohydrodynamic (3D MHD) modeling of a bipolar
AR that contains impulsively generated waves and flows in coronal loops. The
model AR is initiated with a dipole magnetic field and gravitationally
stratified density, with an upflow driven steadily or periodically in localized
regions at the footpoints of magnetic loops. The resulting flows along the
magnetic field lines of the AR produce higher density loops compared to the
surrounding plasma by injection of material into the flux-tubes and the
establishment of siphon flow. We find that the impulsive onset of flows with
subsonic speeds result in the excitation of damped slow magnetosonic waves that
propagate along the loops and coupled nonlinearly driven fast mode waves. The
phase speed of the slow magnetosonic waves is close to the coronal sound speed.
When the amplitude of the driving pulses is increased we find that slow
shock-like wave trains are produced. When the upflows are driven periodically,
undamped oscillations are produced with periods determined by the periodicity
of the upflows. Based on the results of the 3D MHD model we suggest that the
observed slow magnetosonic waves and persistent upflows may be produced by the
same impulsive events at the bases of ARs.Comment: Accepted for publication in The Astrophysical Journa
Image-Optimized Coronal Magnetic Field Models
We have reported previously on a new method we are developing for using
image-based information to improve global coronal magnetic field models. In
that work we presented early tests of the method which proved its capability to
improve global models based on flawed synoptic magnetograms, given excellent
constraints on the field in the model volume. In this follow-up paper we
present the results of similar tests given field constraints of a nature that
could realistically be obtained from quality white-light coronagraph images of
the lower corona. We pay particular attention to difficulties associated with
the line-of-sight projection of features outside of the assumed coronagraph
image plane, and the effect on the outcome of the optimization of errors in
localization of constraints. We find that substantial improvement in the model
field can be achieved with this type of constraints, even when magnetic
features in the images are located outside of the image plane
- …