98 research outputs found
On The Possible Mechanism Of Energy Dissipation In Shock-Wave Fronts Driven Ahead Of Coronal Mass Ejections
Analysis of Mark 4 and LASCO C2, C3 coronagraph data shows that, at the
distance R from the center of the Sun, the thickness of a
CME-generated shock-wave front () may be of order of the proton mean
free path. This means that the energy dissipation mechanism in the shock front
at these distances is collisional. A new discontinuity (thickness ) is observed to appear in the anterior part of the front at R. Within the limits of experimental error, the thickness
0.1-0.2 R does not vary with distance and is
determined by the spatial resolution of the LASCO C3 instrument. At the initial
stage of formation, the discontinuity on the scale of has rather
small amplitude and exists simultaneously with the front having thickness
. The relative amplitude of the discontinuity gradually increases
with distance, and the brightness profile behind it becomes even. Such
transformations may be associated with the transition from a collisional shock
wave to a collisionless one.Comment: 3 figure
Study of the mechanism for solar wind formation
Observations of the corona and solar wind are analyzed and compared with generalized results derived from laboratory-scale experiments. It was shown that a thermal pressure gradient can make a major contribution to a precipitating plasma of the solar wind emanating from coronal holes. It is found that the divergence Phi = (R/R sub solar radius)f of the magnetic field lines, originating from coronal holes, is one of the factors governing solar wind velocity at Earth orbit (R= 1 AU). A decrease in the velocity V sub R = 1 AU from approx = 750 mk/sec down to approx = 450 km/sec may be attributable to an increase in superradial divergence f from approx = 7-9 to 20. The plasma energy flux density F at the base of the coronal holes representing the sources of the solar wind with V sub R=1AE = (450 to 750) km/sec, remains nearly constant, being F approx = (1.4 +/- 0.3) x 10 to the 6th power x ergs/sq cm/sec for the period 1973-1975
Comment on "CAWSES November 7-8, 2004, superstorm: Complex solar and interplanetary features in the post-solar maximum phase" by B. T. Tsurutani, E. Echer, F. L. Guarnieri, and J. U. Kozyra
Recently Tsurutani et al., (2008) (Paper 1) analyzed the complex
interplanetary structures during 7 to 8 November, 2004 to identify their
properties as well as resultant geomagnetic effects and the solar origins.
Besides mentioned paper by Gopalswamy et al., (2006) the solar and
interplanetary sources of geomagnetic storm on 7-10 November, 2004 have also
been discussed in details in series of other papers. Some conclusions of these
works essentially differ from conclusions of the Paper 1 but have not been
discussed by authors of Paper 1. In this comment we would like to discuss some
of these distinctions.Comment: Submitted for publication in Geophysical Research Letter
Coronal Shock Waves, EUV Waves, and Their Relation to CMEs. III. Shock-Associated CME/EUV Wave in an Event with a Two-Component EUV Transient
On 17 January 2010, STEREO-B observed in extreme ultraviolet (EUV) and white
light a large-scale dome-shaped expanding coronal transient with perfectly
connected off-limb and on-disk signatures. Veronig et al. (2010, ApJL 716, 57)
concluded that the dome was formed by a weak shock wave. We have revealed two
EUV components, one of which corresponded to this transient. All of its
properties found from EUV, white light, and a metric type II burst match
expectations for a freely expanding coronal shock wave including correspondence
to the fast-mode speed distribution, while the transient sweeping over the
solar surface had a speed typical of EUV waves. The shock wave was presumably
excited by an abrupt filament eruption. Both a weak shock approximation and a
power-law fit match kinematics of the transient near the Sun. Moreover, the
power-law fit matches expansion of the CME leading edge up to 24 solar radii.
The second, quasi-stationary EUV component near the dimming was presumably
associated with a stretched CME structure; no indications of opening magnetic
fields have been detected far from the eruption region.Comment: 18 pages, 10 figures. Solar Physics, published online. The final
publication is available at http://www.springerlink.co
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