1,270 research outputs found
Evolution of Alfv\'enic fluctuations inside an interplanetary coronal mass ejection and their contributions to local plasma heating: Joint observations from 1.0 AU to 5.4 AU
Directly tracking an interplanetary coronal mass ejection (ICME) by widely
separated spacecrafts is a great challenge. However, such an event could
provide us a good opportunity to study the evolution of embedded Alfv\'enic
fluctuations (AFs) inside ICME and their contributions to local plasma heating
directly. In this study, an ICME observed by Wind at 1.0 au on March 4-6 1998
is tracked to the location of Ulysess at 5.4 au. AFs are commonly found inside
the ICME at 1.0 au, with an occurrence rate of 21.7% and at broadband
frequencies from 4 to 5 Hz. When the ICME
propagates to 5.4 au, the Aflv\'enicity decreases significantly, and AFs are
rare and only found at few localized frequencies with the occurrence rate
decreasing to 3.0%. At the same time, the magnetic field intensity at the
AF-rich region has an extra magnetic dissipation except ICME expansion effect.
The energetics of the ICME at different radial distance is also investigated
here. Under similar magnetic field intensity situations at 1.0 au, the
turbulence cascade rate at the AF-rich region is much larger than the value at
the AF-lack region. Moreover, it can maintain as the decrease of magnetic field
intensity if there is lack of AFs. However, when there exists many AFs, it
reduces significantly as the AFs disappear. The turbulence cascade dissipation
rate within the ICME is inferred to be 1622.3 ,
which satisfies the requirement of local ICME plasma heating rate, 1653.2
. We suggest that AF dissipation is responsible for
extra magnetic dissipation and local plasma heating inside ICME.Comment: 15 pages, 3 figures, 1 tabl
Study on 2015 June 22 Forbush decrease with the muon telescope in Antarctic
By the end of 2014, a cosmic ray muon telescope was installed at Zhongshan
Station in Antarctic and has been continuously collecting data since then. It
is the first surface muon telescope to be built in Antarctic. In June 2015,
five CMEs were ejected towards the Earth initiating a big large Forbush
decrease (FD) event. We conduct a comprehensive study of the galactic cosmic
ray intensity fluctuations during the FD using the data from cosmic ray
detectors of multiple stations (Zhongshan, McMurdo, South Polar and Nagoya) and
he solar wind measurements from ACE and WIND. A pre-increase before the shock
arrival was observed. Distinct differences exist in the timelines of the
galactic cosmic ray recorded by the neutron monitors and the muon telescopes.
FD onset for Zhongshan muon telescope is delayed (2.5h) with respect to SSC
onset. This FD had a profile of four-step decrease. The traditional one- or
two-step classification of FDs was inadequate to explain this FD.Comment: 10 pages,6 figure
Kinetic Properties of an Interplanetary Shock Propagating inside a Coronal Mass Ejection
We investigate the kinetic properties of a typical fast-mode shock inside an
interplanetary coronal mass ejection (ICME) observed on 1998 August 6 at 1 AU,
including particle distributions and wave analysis with the in situ
measurements from Wind. Key results are obtained concerning the shock and the
shock-ICME interaction at kinetic scales: (1) gyrating ions, which may provide
energy dissipation at the shock in addition to wave-particle interactions, are
observed around the shock ramp; (2) despite the enhanced proton temperature
anisotropy of the shocked plasma, the low plasma beta inside the ICME
constrains the shocked plasma under the thresholds of the ion cyclotron and
mirror-mode instabilities; (3) whistler heat flux instabilities, which can
pitch--angle scatter halo electrons through a cyclotron resonance, are observed
around the shock, and can explain the disappearance of bidirectional electrons
inside the ICME together with normal betatron acceleration; (4) whistler waves
near the shock are likely associated with the whistler heat flux instabilities
excited at the shock ramp, which is consistent with the result that the waves
may originate from the shock ramp; (5) the whistlers share a similar
characteristic with the shocklet whistlers observed by Wilson et al, providing
possible evidence that the shock is decaying because of the strong magnetic
field inside the ICME.Comment: Published in ApJ
Satistical Study of the Interplanetary Coronal Mass Ejections from 1996 to 2014
In this work, we establish an ICME list from 1996 to 2014 based on the
in-situ observations from the WIND and ACE satellites. Based on this ICME list,
we extend the statistical analysis of the ICMEs to the solar maximum phase of
solar cycle 24th. The analysis of the annual variations of the properties of
ICMEs show that the number of ICMEs, the number of shocks, the percentage of
ICMEs drove shocks, the magnetic field and plasma properties of ICMEs are well
correlated with the solar cycle variation. The number of MCs do not show any
correlation with sunspot number. But, the percentage of the MCs in ICMEs show
good anti-correlation with the sunspot number. By comparison the parameters of
MCs with None-MC ICMEs, we found that the MCs are stronger than the None-MC
ICMEs . In addition, we compare the parameters of ICMEs with and without
shocks. It is found that the ICMEs with shocks are much stronger than the ICME
without shocks. Meanwhile, we discuss the distribution of the magnetic field
and solar wind plasmas parameters of the sheath regions of ICMEs at first time.
We find that the magnetic field and solar wind velocity in the sheath region
are higher than them in the ejecta of ICMEs from statistical point of view.Comment: 8 Pages, 10 figure
Multi-spacecraft Observations of the Coronal and Interplanetary Evolution of a Solar Eruption Associated with Two Active Regions
We investigate the coronal and interplanetary evolution of a coronal mass
ejection (CME) launched on 2010 September 4 from a source region linking two
active regions (ARs) 11101 and 11103, using extreme ultraviolet imaging,
magnetogram, white-light and in situ observations from SDO, STEREO, SOHO, VEX
and Wind. A potential-field source-surface model is employed to examine the
configuration of the coronal magnetic field surrounding the source region. The
graduated cylindrical shell model and a triangulation method are applied to
determine the kinematics of the CME in the corona and interplanetary space.
From the remote sensing and in situ observations we obtain some key results:
(1) the CME was deflected in both the eastward and southward directions in the
low corona by the magnetic pressure from the two ARs and possibly interacted
with another ejection, which caused that the CME arrived at VEX that was
longitudinally distant from the source region; (2) although VEX was closer to
the Sun, the observed and derived CME arrival times at VEX are not earlier than
those at Wind, which suggests the importance of determining both the frontal
shape and propagation direction of the CME in interplanetary space; (3) the
ICME was compressed in the radial direction while the longitudinal transverse
size was extended.Comment: 20 pages, 9 figures, 1 table; accepted by Ap
Propagation and Interaction Properties of Successive Coronal Mass Ejections in Relation to a Complex Type II Radio Burst
We examine the propagation and interaction properties of three successive
coronal mass ejections (CMEs) from 2001 November 21-22, with a focus on their
connection with the behaviors of the associated long-duration complex type II
radio burst. In combination with coronagraph and multi-point in situ
observations, the long-duration type II burst provides key features for
resolving the propagation and interaction complexities of the three CMEs. The
two CMEs from November 22 interacted first and then overtook the November 21
CME at a distance of about 0.85 AU from the Sun. The time scale for the shock
originally driven by the last CME to propagate through the preceding two CMEs
is estimated to be about 14 and 6 hr, respectively. We present a simple
analytical model without any free parameters to characterize the whole
Sun-to-Earth propagation of the shock, which shows a remarkable consistency
with all the available data and MHD simulations even out to the distance of
Ulysses (2.34 AU). The coordination of in situ measurements at the Earth and
Ulysses, which were separated by about in latitude, gives
important clues for the understanding of shock structure and the interpretation
of in situ signatures. The results also indicate means to increase
geo-effectiveness with multiple CMEs, which can be considered as another
manifestation of the "perfect storm" scenario proposed by [liu14a] although the
current case is not "super" in the same sense as the 2012 July 23 event.Comment: Accepted for publication in Ap
Dynamically Expanded CNN Array for Video Coding
Video coding is a critical step in all popular methods of streaming video.
Marked progress has been made in video quality, compression, and computational
efficiency. Recently, there has been an interest in finding ways to apply
techniques form the fast-progressing field of machine learning to further
improve video coding.
We present a method that uses convolutional neural networks to help refine
the output of various standard coding methods. The novelty of our approach is
to train multiple different sets of network parameters, with each set
corresponding to a specific, short segment of video. The array of network
parameter sets expands dynamically to match a video of any length. We show that
our method can improve the quality and compression efficiency of standard video
codecs.Comment: 3 pages, 2 figure
Geometry, Kinematics and Heliospheric Impact of a Large CME-driven Shock in 2017 September
A powerful coronal mass ejection (CME) occurred on 2017 September 10 near the
end of the declining phase of the historically weak solar cycle 24. We obtain
new insights concerning the geometry and kinematics of CME-driven shocks in
relation to their heliospheric impacts from the optimal, multi-spacecraft
observations of the eruption. The shock, which together with the CME driver can
be tracked from the early stage to the outer corona, shows a large oblate
structure produced by the vast expansion of the ejecta. The expansion speeds of
the shock along the radial and lateral directions are much larger than the
translational speed of the shock center, all of which increase during the flare
rise phase, peak slightly after the flare maximum and then decrease. The near
simultaneous arrival of the CME-driven shock at the Earth and Mars, which are
separated by 156.6 in longitude, is consistent with the dominance of
expansion over translation observed near the Sun. The shock decayed and failed
to reach STEREO A around the backward direction. Comparison between ENLIL MHD
simulations and the multi-point in situ measurements indicates that the shock
expansion near the Sun is crucial for determining the arrival or non-arrival
and space weather impact at certain heliospheric locations. The large shock
geometry and kinematics have to be taken into account and properly treated for
accurate predictions of the arrival time and space weather impact of CMEs.Comment: Accepted for publication in Ap
A Solar Eruption with Relatively Strong Geo-effectiveness Originating from Active Region Peripheral Diffusive Polarities
We report the observations of a moderate but relatively intense geo-effective
solar eruption on 2015 November 4 from the peripheral diffusive polarities of
active region 12443. We use space-borne Solar Dynamics Observatory and ACE
observations. EUV images identified helical pattern along a filament channel
and we regard this channel as flux-rope structure. Flow velocity derived from
tracked magnetograms infers converging motion along the polarity inversion line
beneath the filament channel. An associated magnetic cancellation process was
detected in the converging region. Further, the pre-eruptive EUV brightening
was observed in the converging region, the most intense part of which appeared
in the magnetic cancellation region. These observations imply that the
converging and cancelling flux probably contributed to the formation of the
helical magnetic fields associated with the flux rope. A filament-height
estimation method suggests that the middle part of the filament probably lies
at a low altitude and was consistent with the initial place of the eruption. A
thick current channel associated with the flux rope is also determined. For a
expanding thick current channel, the critical height of the decay index for
torus instability lies in the range of 37 - 47 Mm. Southward magnetic fields in
the sheath and the ejecta induced a geomagnetic storm with a Dst global minimum
of ~-90 nT.Comment: Accepted for publication in Ap
A CME-driven shock analysis of the 14-Dec-2006 SEP event
Observations of the interplanetary shock provide us with strong evidence of
particle acceleration to multi-MeV energies, even up to GeV energy, in a solar
flare or coronal mass ejection (CME). Diffusive shock acceleration is an
efficient mechanism for particle acceleration. For investigating the shock
structure, the energy injection and energy spectrum of a CME-driven shock, we
perform dynamical Monte Carlo simulation of the 14-Dec-2006 CME-driven shock
using an anisotropic scattering law. The simulated results of the shock fine
structure, particle injection, and energy spectrum are presented. We find that
our simulation results give a good fit to the observations from multiple
spacecraft.Comment: 14 pages, 8 figures, 1 tables. Accepted by RA
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