35 research outputs found
Reconstructing solar wind inhomogeneous structures from stereoscopic observations in white-light: Small transients along the Sun-Earth line
The Heliospheric Imagers (HI) on board the two spacecraft of the Solar
Terrestrial Relations Observatory (STEREO) provided white-light images of
transients in the solar wind from dual perspectives from 2007 to 2014. In this
paper, we develop a new method to identify and locate the transients
automatically from simultaneous images from the two inner telescopes, known as
HI-1, based on a correlation analysis. Correlation coefficient (cc) maps along
the Sun-Earth line are constructed for the period from 1 Jan 2010 to 28 Feb
2011. From the maps, transients propagating along the Sun-Earth line are
identified, and a 27-day periodic pattern is revealed, especially for
small-scale transients. Such a periodicity in the transient pattern is
consistent with the rotation of the Sun's global magnetic structure and the
periodic crossing of the streamer structures and slow solar wind across the
Sun-Earth line, and this substantiates the reliability of our method and the
high degree of association between the small-scale transients of the slow solar
wind and the coronal streamers. Besides, it is suggested by the cc map that
small-scale transients along the Sun-Earth line are more frequent than
large-scale transients by a factor of at least 2, and that they quickly
diffused into background solar wind within about 40 Rs in terms of the
signal-to-noise ratio of white-light emissions. The method provides a new tool
to reconstruct inhomogeneous structures in the heliosphere from multiple
perspectives.Comment: 24 pages, 9 figures, to be published on Journal of Geophysical
Research - Space Physic
Three-dimensional Reconstruction of Coronal Mass Ejections by CORAR Technique through Different Stereoscopic Angle of STEREO Twin Spacecraft
Recently, we developed the Correlation-Aided Reconstruction (CORAR) method to
reconstruct solar wind inhomogeneous structures, or transients, using dual-view
white-light images (Li et al. 2020; Li et al. 2018). This method is proved to
be useful for studying the morphological and dynamical properties of transients
like blobs and coronal mass ejection (CME), but the accuracy of reconstruction
may be affected by the separation angle between the two spacecraft (Lyu et al.
2020). Based on the dual-view CME events from the Heliospheric Imager CME Join
Catalogue (HIJoinCAT) in the HELCATS (Heliospheric Cataloguing, Analysis and
Techniques Service) project, we study the quality of the CME reconstruction by
the CORAR method under different STEREO stereoscopic angles. We find that when
the separation angle of spacecraft is around 150{\deg}, most CME events can be
well reconstructed. If the collinear effect is considered, the optimal
separation angle should locate between 120{\deg} and 150{\deg}. Compared with
the CME direction given in the Heliospheric Imager Geometrical Catalogue
(HIGeoCAT) from HELCATS, the CME parameters obtained by the CORAR method are
reasonable. However, the CORAR-obtained directions have deviations towards the
meridian plane in longitude, and towards the equatorial plane in latitude. An
empirical formula is proposed to correct these deviations. This study provides
the basis for the spacecraft configuration of our recently proposed Solar Ring
mission concept (Wang et al. 2020b).Comment: 18 pages, 9 figure
On the Propagation of a Geoeffective Coronal Mass Ejection during March 15 -- 17, 2015
The largest geomagnetic storm so far in the solar cycle 24 was produced by a
fast coronal mass ejection (CME) originating on 2015 March 15. It was an
initially west-oriented CME and expected to only cause a weak geomagnetic
disturbance. Why did this CME finally cause such a large geomagnetic storm? We
try to find some clues by investigating its propagation from the Sun to 1 AU.
First, we reconstruct the CME's kinematic properties in the corona from the
SOHO and SDO imaging data with the aid of the graduated cylindrical shell (GCS)
model. It is suggested that the CME propagated to the west
away from the Sun-Earth line with a speed of
about 817 km s before leaving the field of view of the SOHO/LASCO C3
camera. A magnetic cloud (MC) corresponding to this CME was measured in-situ by
the Wind spacecraft two days later. By applying two MC reconstruction methods,
we infer the configuration of the MC as well as some kinematic information,
which implies that the CME possibly experienced an eastward deflection on its
way to 1 AU. However, due to the lack of observations from the STEREO
spacecraft, the CME's kinematic evolution in interplanetary space is not clear.
In order to fill this gap, we utilize numerical MHD simulation, drag-based CME
propagation model (DBM) and the model for CME deflection in interplanetary
space (DIPS) to recover the propagation process, especially the trajectory, of
the CME from to 1 AU. It is suggested that the trajectory of the CME
was deflected toward the Earth by about , consistent with the
implication from the MC reconstruction at 1 AU. This eastward deflection
probably contributed to the CME's unexpected geoeffectiveness by pushing the
center of the initially west-oriented CME closer to the Earth.Comment: 10 pages, 5 figures, 1 table, accepted by JGR - Space Physic