Unveiling the Journey of a Highly Inclined CME: Insights from the March 13, 2012 Event with 110^∘ Longitudinal Separation
arxiv(2024)
Abstract
A fast and wide Coronal Mass Ejection (CME) erupted from the Sun on
2012-03-13. Its interplanetary counterpart was detected in situ two days later
by STEREO-A and near-Earth spacecraft. We suggest that at 1 au the CME extended
at least 110^∘ in longitude, with Earth crossing its east flank and
STEREO-A crossing its west flank. Despite their separation, measurements from
both positions showed very similar in situ CME signatures. The solar source
region where the CME erupted was surrounded by three coronal holes (CHs). Their
locations with respect to the CME launch site were east (negative polarity),
southwest (positive polarity) and west (positive polarity). The solar magnetic
field polarity of the area covered by each CH matches that observed at 1 au in
situ. Suprathermal electrons at each location showed mixed signatures with only
some intervals presenting clear counterstreaming flows as the CME transits both
locations. The strahl population coming from the shortest magnetic connection
of the structure to the Sun showed more intensity. The study presents important
findings regarding the in situ measured CME on 2012-03-15, detected at a
longitudinal separation of 110^∘ in the ecliptic plane despite its
initial inclination being around 45^∘ when erupted. This suggests that
the CME may have deformed and/or rotated, allowing it to be observed near its
legs with spacecraft at a separation angle greater than 100^∘. The CME
structure interacted with high-speed streams generated by the surrounding CHs.
The piled-up plasma in the sheath region exhibited an unexpected correlation in
magnetic field strength despite the large separation in longitude. In situ
observations reveal that at both locations there was a flank encounter, where
the spacecraft crossed the first part of the CME, then encountered ambient
solar wind, and finally passed near the legs of the structure.
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