14 research outputs found
Simulating Interactions Between Coronal Mass Ejections
Coronal mass ejections (CMEs) launch large amounts of plasma and magnetic fields into the interplanetary medium. Under the right initial conditions, this ejecta can reach Earth and cause issues with electronic devices. As such, we would like to have an accurate model that depicts how these CMEs propagate as they leave the sun. By using fluid dynamics and one-minute resolution in-situ solar wind data, we sought to simulate CME plasma propagation with analytical and numerical models. Because the interstellar medium contains other material and other events happen on the sun simultaneously, CMEs can interact with each other and other ejecta, which can cause them to change, so in order to have an accurate simulation we considered these interactions in our model. For our model, we made the assumption that the plasma was an ideal fluid, was super-alfvenic, and we employed an injection radius of 10 R⦿
Numerical simulations of ICME-ICME interactions
We present hydrodynamical simulations of interacting Coronal Mass Ejections
in the Interplanetary medium (ICMEs). In these events, two consecutive CMEs are
launched from the Sun in similar directions within an interval of time of a few
hours. In our numerical model, we assume that the ambient solar wind is
characterized by its velocity and mass-loss rate. Then, the CMEs are generated
when the flow velocity and mass-loss rate suddenly change, with respect to the
ambient solar wind conditions during two intervals of time, which correspond to
the durations of the CMEs. After their interaction, a merged region is formed
and evolve as a single structure into the interplanetary medium. In this work,
we are interested in the general morphology of this merged region, which
depends on the initial parameters of the ambient solar wind and each of the
CMEs involved. In order to understand this morphology, we have performed a
parametric study in which we characterize the effects of the initial parameters
variations on the density and velocity profiles at 1 AU, using as reference the
well-documented event of July 25th, 2004. Based on this parametrization we were
able to reproduce with a high accuracy the observed profiles. Then, we apply
the parametrization results to the interaction events of May 23, 2010; August
1, 2010; and November 9, 2012. With this approach and using values for the
input parameters within the CME observational errors, our simulated profiles
reproduce the main features observed at 1 AU. Even though we do not take into
account the magnetic field, our models give a physical insight into the
propagation and interaction of ICMEs
Space, time and velocity association of successive coronal mass ejections
Our aim is to investigate the possible physical association between
consecutive coronal mass ejections (CMEs). Through a statistical study of the
main characteristics of 27761 CMEs observed by SOHO/LASCO during the past 20
years. We found the waiting time (WT) or time elapsed between two consecutive
CMEs is hrs for 59\% and hrs for 97\% of the events, and the CME
WTs follow a Pareto Type IV statistical distribution. The difference of the
position-angle of a considerable population of consecutive CME pairs is less
than , indicating the possibility that their source locations are in
the same region. The difference between the speed of trailing and leading
consecutive CMEs follows a generalized Student t-distribution. The fact that
the WT and the speed difference have heavy-tailed distributions along with a
detrended fluctuation analysis shows that the CME process has a long-range
dependence. As a consequence of the long-range dependence, we found a small but
significative difference between the speed of consecutive CMEs, with the speed
of the trailing CME being higher than the speed of the leading CME. The
difference is largest for WTs 10 hrs,
and it is more evident during the ascending and descending phases of the solar
cycle. We suggest that this difference may be caused by a drag force acting
over CMEs closely related in space and time
The Closest View of a Fast Coronal Mass Ejection: How Faulty Assumptions near Perihelion Lead to Unrealistic Interpretations of PSP/WISPR Observations
We report on the closest view of a coronal mass ejection observed by the
Parker Solar Probe (PSP)/Wide-field Imager for {Parker} Solar PRobe (WISPR)
instrument on September 05, 2022, when PSP was traversing from a distance of
15.3~to~13.5~R from the Sun. The CME leading edge and an arc-shaped
{\emph{concave-up} structure near the core} was tracked in WISPR~field of view
using the polar coordinate system, for the first time. Using the impact
distance on Thomson surface, we measured average speeds of CME leading edge and
concave-up structure as 2500~~270\,km\,s and
400~~70\,km\,s with a deceleration of
20~m~s for the later. {The use of the plane-of-sky approach
yielded an unrealistic speed of more than three times of this estimate.} We
also used single viewpoint STEREO/COR-2A images to fit the Graduated
Cylindrical Shell (GCS) model to the CME while incorporating the source region
location from EUI of Solar Orbiter and estimated a 3D speed of
2700\,km\,s. We conclude that this CME exhibits the highest
speed during the ascending phase of solar cycle 25. This places it in the
category of extreme speed CMEs, which account for only 0.15\% of all CMEs
listed in the CDAW CME catalog.Comment: 13 Pages, 6 Figures; Accepted in The Astrophysical Journal Letter
A prominence eruption from the Sun to the Parker Solar Probe with multi-spacecraft observations
In the early hours of 2021 April 25, the Solar Probe Cup on board Parker Solar Probe registered the passage of a solar wind structure characterized by a clear and constant He2+/H+ density ratio above 6% during three hours. The He2+ contribution remained present but fainting and intermittent within a twelve-hour window. Solar Orbiter and Parker Solar Probe were in nearly perfect quadrature, allowing for optimal observing configuration in which the material impacting the Parker Solar Probe was in the Solar Orbiter plane of the sky and visible off the limb. In this work, we report the journey of the helium-enriched plasma structure from the Sun to the Parker Solar Probe by combining multi-spacecraft remote-sensing and in situ measurements. We identify an erupting prominence as the likely source, behind the Sun relative to the Earth, but visible to multiple instruments on both the Solar-Terrestrial Relations Observatory-A and Solar Orbiter. The associated CME was also observed by coronagraphs and heliospheric imagers from both spacecrafts before reaching the Parker Solar Probe at 46 R⊙, 8 h after the spacecraft registered a crossing of the heliospheric current sheet. Except for extraordinary helium enhancement, the CME showed ordinary plasma signatures and a complex magnetic field with an overall strength enhancement. The images from the Wide-field Imager for Solar Probe (WISPR) aboard Parker Solar Probe show a structure entering the field of view a few hours before the in situ crossing, followed by repetitive transient structures that may be the result of flying through the CME body. We believe this to be the first example of a CME being imaged by WISPR directly before and during being detected in situ. This study highlights the potential of combining the Parker Solar Probe in situ measurements in the inner heliosphere with simultaneous remote-sensing observations in (near) quadrature from other spacecrafts
The Temperature, Electron, and Pressure Characteristics of Switchbacks: Parker Solar Probe Observations
Parker Solar Probe (PSP) observes unexpectedly prevalent switchbacks, which
are rapid magnetic field reversals that last from seconds to hours, in the
inner heliosphere, posing new challenges to understanding their nature, origin,
and evolution. In this work, we investigate the thermal states, electron pitch
angle distributions, and pressure signatures of both inside and outside
switchbacks, separating a switchback into spike, transition region (TR), and
quiet period (QP). Based on our analysis, we find that the proton temperature
anisotropies in TRs seem to show an intermediate state between spike and QP
plasmas. The proton temperatures are more enhanced in spike than in TR and QP,
but the alpha temperatures and alpha-to-proton temperature ratios show the
opposite trends, implying that the preferential heating mechanisms of protons
and alphas are competing in different regions of switchbacks. Moreover, our
results suggest that the electron integrated intensities are almost the same
across the switchbacks but the electron pitch angle distributions are more
isotropic inside than outside switchbacks, implying switchbacks are intact
structures but strong scattering of electrons happens inside switchbacks. In
addition, the examination of pressures reveals that the total pressures are
comparable through a switchback, confirming switchbacks are pressure-balanced
structures. These characteristics could further our understanding of ion
heating, electron scattering, and the structure of switchbacks.Comment: submitted to Ap
Parker Solar Probe Observations of High Plasma Beta Solar Wind from Streamer Belt
In general, slow solar wind from the streamer belt forms a high plasma beta
equatorial plasma sheet around the heliospheric current sheet (HCS) crossing,
namely the heliospheric plasma sheet (HPS). Current Parker Solar Probe (PSP)
observations show that the HCS crossings near the Sun could be full or partial
current sheet crossing (PCS), and they share some common features but also have
different properties. In this work, using the PSP observations from encounters
4 to 10, we identify streamer belt solar wind from enhancements in plasma beta,
and we further use electron pitch angle distributions to separate it into HPS
solar wind that around the full HCS crossings and PCS solar wind that in the
vicinity of PCS crossings. Based on our analysis, we find that the PCS solar
wind has different characteristics as compared with HPS solar wind: a) PCS
solar wind could be non-pressure-balanced structures rather than magnetic
holes, and the total pressure enhancement mainly results from the less reduced
magnetic pressure; b) some of the PCS solar wind are mirror unstable; c) PCS
solar wind is dominated by very low helium abundance but varied alpha-proton
differential speed. We suggest the PCS solar wind could originate from coronal
loops deep inside the streamer belt, and it is pristine solar wind that still
actively interacts with ambient solar wind, thus it is valuable for further
investigations on the heating and acceleration of slow solar wind
The Structure and Origin of Switchbacks: Parker Solar Probe Observations
Switchbacks are rapid magnetic field reversals that last from seconds to
hours. Current Parker Solar Probe (PSP) observations pose many open questions
in regards to the nature of switchbacks. For example, are they stable as they
propagate through the inner heliosphere, and how are they formed? In this work,
we aim to investigate the structure and origin of switchbacks. In order to
study the stability of switchbacks, we suppose the small scale current sheets
therein may work to braid and stabilize the switchbacks. Thus, we use the
partial variance of increments method to identify the small scale current
sheets, and then compare their distributions in switchbacks. With more than one
thousand switchbacks identified with PSP observations in seven encounters, we
find many more current sheets inside than outside switchbacks, indicating that
these micro-structures should work to stabilize the S-shape structures of
switchbacks. Additionally, with the helium measurements, we study the
variations of helium abundance ratios and alpha-proton differential speeds to
trace switchbacks to their origins. We find both helium-rich and helium-poor
populations in switchbacks, implying the switchbacks could originate from both
closed and open magnetic field regions in the Sun. Moreover, we observe that
the alpha-proton differential speeds also show complex variations as compared
to the local Alfv\'en speed. The joint distributions of both parameters show
that low helium abundance together with low differential speed is the dominant
state in switchbacks. The presence of small scale current sheets in switchbacks
along with the helium features are in line with the hypothesis that switchbacks
could originate from the Sun via interchange reconnection process. However,
other formation mechanisms are not excluded