13 research outputs found
Evolution of the Radial Size and Expansion of Coronal Mass Ejections Investigated by Combining Remote and In-Situ Observations
A fundamental property of coronal mass ejections (CMEs) is their radial
expansion, which determines the increase in the CME radial size and the
decrease in the CME magnetic field strength as the CME propagates. CME radial
expansion can be investigated either by using remote observations or by in-situ
measurements based on multiple spacecraft in radial conjunction. However, there
have been only few case studies combining both remote and in-situ observations.
It is therefore unknown if the radial expansion estimated remotely in the
corona is consistent with that estimated locally in the heliosphere. To address
this question, we first select 22 CME events between the years 2010 and 2013,
which were well observed by coronagraphs and by two or three spacecraft in
radial conjunction. We use the graduated cylindrical shell model to estimate
the radial size, radial expansion speed, and a measure of the dimensionless
expansion parameter of CMEs in the corona. The same parameters and two
additional measures of the radial-size increase and magnetic-field-strength
decrease with heliocentric distance of CMEs based on in-situ measurements are
also calculated. For most of the events, the CME radial size estimated by
remote observations is inconsistent with the in-situ estimates. We further
statistically analyze the correlations of these expansion parameters estimated
using remote and in-situ observations, and discuss the potential reasons for
the inconsistencies and their implications for the CME space weather
forecasting.Comment: Accepted by Ap
Multi-Spacecraft Observations of the Evolution of Interplanetary Coronal Mass Ejections Between 0.3 and 2.2 AU: Conjunctions with the Juno Spacecraft
We present a catalogue of 35 interplanetary coronal mass ejections (ICMEs)
observed by the Juno spacecraft and at least one other spacecraft during its
cruise phase to Jupiter. We identify events observed by MESSENGER, Venus
Express, Wind, and STEREO with magnetic features that can be matched
unambiguously with those observed by Juno. A multi-spacecraft study of ICME
properties between 0.3 and 2.2 AU is conducted: we firstly investigate the
global expansion by tracking the variation in magnetic field strength with
increasing heliocentric distance of individual ICME events, finding significant
variability in magnetic field relationships for individual events in comparison
with statistical trends. With the availability of plasma data at 1 AU, the
local expansion at 1 AU can be compared with global expansion rates between 1
AU and Juno. Despite following expected trends, the local and global expansion
rates are only weakly correlated. Finally, for those events with clearly
identifiable magnetic flux ropes, we investigate the orientation of the flux
rope axis as they propagate; we find that 64% of events displayed a decrease in
inclination with increasing heliocentric distance, and 40% of events undergo a
significant change in orientation as they propagate towards Juno. The
multi-spacecraft catalogue produced in this study provides a valuable link
between ICME observations in the inner heliosphere and beyond 1 AU, thereby
improving our understanding of ICME evolution
Observations of Extreme ICME Ram Pressure Compressing Mercury's Dayside Magnetosphere to the Surface
Mercury's magnetosphere is known to be affected by enhanced ram pressures and
magnetic fields inside interplanetary coronal mass ejections (ICMEs). Here we
report detailed observations of an ICME compressing Mercury's dayside
magnetosphere to the surface. A fast CME launched from the Sun on November 29
2013 impacted first MESSENGER, which was orbiting Mercury, on November 30 and
later STEREO-A near 1 AU on December 1. Following the ICME impact, MESSENGER
remained in the solar wind as the spacecraft traveled inwards and northwards
towards Mercury's surface until it reached and passed its closest approach to
the planet (at 371 km altitude) without crossing into the magnetosphere. The
magnetospheric crossing finally occurred 1 minute before reaching the planet's
nightside at 400 km altitude and 84N latitude, indicating the lack of
dayside magnetosphere on this orbit. In addition, the peak magnetic field
measured by MESSENGER at this time was 40% above the values measured in the
orbits just prior to and after the ICME, a consequence of the magnetospheric
compression. Using both a proxy method at Mercury and measurements at STEREO-A,
we show that the extremely high ram pressure associated with this ICME was more
than high enough to collapse Mercury's weak magnetosphere. As a consequence,
the ICME plasma likely interacted with Mercury's surface, evidenced by enhanced
sodium ions in the exosphere. The collapse of Mercury's dayside magnetosphere
has important implications for the habitability of close-in exoplanets around M
dwarf stars, as such events may significantly contribute to planetary
atmospheric loss in these systems
Work-Life Balance Starts with Proper Deadlines and Exemplary Agencies
Diversity, equity and inclusion (DEI) programs can only be implemented
successfully if proper work-life balance is possible in Heliophysics (and in
STEM field in general). One of the core issues stems from the culture of
"work-above-life" associated with mission concepts, development, and
implementation but also the expectations that seem to originate from numerous
announcements from NASA (and other agencies). The benefits of work-life balance
are well documented; however, the entire system surrounding research in
Heliophysics hinders or discourages proper work-life balance. For example,
there does not seem to be attention paid by NASA Headquarters (HQ) on the
timing of their announcements regarding how it will be perceived by
researchers, and how the timing may promote a culture where work trumps
personal life. The same is true for remarks by NASA HQ program officers during
panels or informal discussions, where seemingly innocuous comments may give a
perception that work is expected after "normal" work hours. In addition, we are
calling for work-life balance plans and implementation to be one of the
criteria used for down-selection and confirmation of missions (Key Decision
Points: KDP-B, KDP-C).Comment: White paper submitted to the Decadal Survey for Solar and Space
Physics (Heliophysics) 2024-2033; 6 page
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Mixing Interstellar Clouds Surrounding the Sun
On its journey through the Galaxy, the Sun passes through diverse regions of the interstellar medium. High-resolution spectroscopic measurements of interstellar absorption lines in spectra of nearby stars show absorption components from more than a dozen warm partially ionized clouds within 15 pc of the Sun. The two nearest clouds—the Local Interstellar Cloud (LIC) and Galactic (G) cloud—move toward each other. Their bulk heliocentric velocities can be compared with the interstellar neutral helium flow velocity obtained from space-based experiments. We combine recent results from Ulysses, IBEX, and STEREO observations to find a more accurate estimate of the velocity and temperature of the very local interstellar medium. We find that, contrary to the widespread viewpoint that the Sun resides inside the LIC, the locally observed velocity of the interstellar neutral helium is consistent with a linear combination of the velocities of the LIC and G cloud, but not with either of these two velocities. This finding shows that the Sun travels through a mixed-cloud interstellar medium composed of material from both these clouds. Interactions between these clouds explain the substantially higher density of the interstellar hydrogen near the Sun and toward stars located within the interaction region of these two clouds. The observed asymmetry of the interstellar helium distribution function also supports this interaction. The structure and equilibrium in this region require further studies using in situ and telescopic observations.
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New Observations Needed to Advance Our Understanding of Coronal Mass Ejections
Coronal mass ejections (CMEs) are large eruptions from the Sun that propagate
through the heliosphere after launch. Observational studies of these transient
phenomena are usually based on 2D images of the Sun, corona, and heliosphere
(remote-sensing data), as well as magnetic field, plasma, and particle samples
along a 1D spacecraft trajectory (in-situ data). Given the large scales
involved and the 3D nature of CMEs, such measurements are generally
insufficient to build a comprehensive picture, especially in terms of local
variations and overall geometry of the whole structure. This White Paper aims
to address this issue by identifying the data sets and observational priorities
that are needed to effectively advance our current understanding of the
structure and evolution of CMEs, in both the remote-sensing and in-situ
regimes. It also provides an outlook of possible missions and instruments that
may yield significant improvements into the subject.Comment: White Paper submitted to the Heliophysics 2024-2033 Decadal Survey, 9
pages, 4 figure
Redefining flux ropes in heliophysics
Magnetic flux ropes manifest as twisted bundles of magnetic field lines. They carry significant amounts of solar mass in the heliosphere. This paper underlines the need to advance our understanding of the fundamental physics of heliospheric flux ropes and provides the motivation to significantly improve the status quo of flux rope research through novel and requisite approaches. It briefly discusses the current understanding of flux rope formation and evolution, and summarizes the strategies that have been undertaken to understand the dynamics of heliospheric structures. The challenges and recommendations put forward to address them are expected to broaden the in-depth knowledge of our nearest star, its dynamics, and its role in its region of influence, the heliosphere.Fil: Nieves Chinchilla, Teresa. National Aeronautics and Space Administration; Estados UnidosFil: Pal, Sanchita. George Mason University. School Of Physics. Astronomy And Computational Sciences; Estados Unidos. National Aeronautics and Space Administration; Estados UnidosFil: Salman, Tarik M.. George Mason University. School Of Physics. Astronomy And Computational Sciences; Estados Unidos. National Aeronautics and Space Administration; Estados UnidosFil: Carcaboso, Fernando. Catholic University Of America; Estados Unidos. National Aeronautics and Space Administration; Estados UnidosFil: Guidoni, Silvina E.. American University. College Of Arts & Sciences. Physics Departament.; Estados Unidos. National Aeronautics and Space Administration; Estados UnidosFil: Cremades Fernandez, Maria Hebe. Consejo Nacional de Investigaciones CientÃficas y Técnicas; Argentina. Universidad de Mendoza. Facultad de Ingenieria; ArgentinaFil: Narock, Ayris. National Aeronautics and Space Administration; Estados UnidosFil: Balmaceda, Laura Antonia. George Mason University. School Of Physics. Astronomy And Computational Sciences; Estados Unidos. National Aeronautics and Space Administration; Estados Unidos. Consejo Nacional de Investigaciones CientÃficas y Técnicas; ArgentinaFil: Lynch, Benjamin J.. University of California at Berkeley; Estados UnidosFil: Al Haddad, Nada. University Of New Hampshire; Estados UnidosFil: RodrÃguez GarcÃa, Laura. Universidad de Alcalá; EspañaFil: Narock, Thomas W.. Goucher College; Estados UnidosFil: Dos Santos, Luiz F. G.. Shell Global Solutions; Estados UnidosFil: Regnault, Florian. University Of New Hampshire; Estados UnidosFil: Kay, Christina. Catholic University Of America; Estados Unidos. National Aeronautics and Space Administration; Estados UnidosFil: Winslow, Réka M.. University Of New Hampshire; Estados UnidosFil: Palmerio, Erika. Predictive Science Inc.; Estados UnidosFil: Davies, Emma E.. University Of New Hampshire; Estados UnidosFil: Scolini, Camilla. University Of New Hampshire; Estados UnidosFil: Weiss, Andreas J.. National Aeronautics and Space Administration; Estados UnidosFil: Alzate, Nathalia. National Aeronautics and Space Administration; Estados UnidosFil: Jeunon, Mariana. Catholic University Of America; Estados Unidos. National Aeronautics and Space Administration; Estados UnidosFil: Pujadas, Roger. Universidad Politécnica de Catalunya; España. National Aeronautics and Space Administration; Estados Unido
On the importance of investigating CME complexity evolution during interplanetary propagation
This perspective paper brings to light the need for comprehensive studies on the evolution of interplanetary coronal mass ejection (ICME) complexity during propagation. To date, few studies of ICME complexity exist. Here, we define ICME complexity and associated changes in complexity, describe recent works and their limitations, and outline key science questions that need to be tackled. Fundamental research on ICME complexity changes from the solar corona to 1 AU and beyond is critical to our physical understanding of the evolution and interaction of transients in the inner heliosphere. Furthermore, a comprehensive understanding of such changes is required to understand the space weather impact of ICMEs at different heliospheric locations and to improve on predictive space weather models
Characteristic Scales of Complexity and Coherence within Interplanetary Coronal Mass Ejections: Insights from Spacecraft Swarms in Global Heliospheric Simulations
Many aspects of the 3D structure and evolution of interplanetary coronal mass ejections (ICMEs) remain unexplained. Here, we investigate two main topics: (1) the coherence scale of magnetic fields inside ICMEs, and (2) the dynamic nature of ICME magnetic complexity. We simulate ICMEs interacting with different solar winds using the linear force-free spheromak model incorporated into the EUHFORIA model. We place a swarm of ∼20,000 spacecraft in the 3D simulation domain and characterize ICME magnetic complexity and coherence at each spacecraft based on the simulated time series. Our simulations suggest that ICMEs retain a lower complexity and higher coherence along their magnetic axis, but that a characterization of their global complexity requires crossings along both the axial and perpendicular directions. For an ICME of initial half angular width of 45° that does not interact with other large-scale solar wind structures, global complexity can be characterized by as little as 7–12 spacecraft separated by 25°, but the minimum number of spacecraft rises to 50–65 (separated by 10°) if interactions occur. Without interactions, ICME coherence extends for 45°, 20°–30°, 15°–30°, and 0°–10° for B , B _ϕ , B _θ , and B _r , respectively. Coherence is also lower in the ICME west flank compared to the east flank due to Parker spiral effects. Moreover, coherence is reduced by a factor of 3–6 by interactions with solar wind structures. Our findings help constrain some of the critical scales that control the evolution of ICMEs and aid in the planning of future dedicated multispacecraft missions
Characterizing Interplanetary Coronal Mass Ejection-related Forbush Decreases at Mercury Using MESSENGER Observations: Identification of a One- or Two-step Structure
The large-scale magnetic structure of interplanetary coronal mass ejections (ICMEs) has been shown to cause decreases in the galactic cosmic ray (GCR) flux measured in situ by spacecraft, known as Forbush decreases (Fds). We use measurements of the GCR count rate obtained by NASA’s MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft during its orbital phase around Mercury to identify such Fds related to the passage of ICMEs and characterize their structure. Of the 42 ICMEs with corresponding high-quality GCR data, 79% are associated with a Fd. Thus, a total of 33 ICME-related Fds were identified, 24 of which (73%) have a two-step structure. We use a superposed epoch analysis to build an average Fd profile at MESSENGER and find that despite the variability of individual events, a two-step structure is produced and is directly linked with the magnetic boundaries of the ICME. By using results from previous studies at Earth and Mars, we also address whether two-step Fds are more commonly observed closer to the Sun; we found that, although likely, this is not conclusive when comparing to the wide range of results of previous studies conducted at Earth. Finally, we find that the percentage decrease in GCR flux of the Fd is greater at MESSENGER on average than at Earth and Mars, decreasing with increasing heliocentric distance. The relationship between the percentage decrease and maximum hourly decrease is also in agreement with previous studies, and follows trends relating to the expansion of ICMEs as they propagate through the heliosphere