Solar Source Regions Research Articles

Dependence of coronal mass ejections on the morphology and toroidal flux of their source magnetic flux ropes

Context. Coronal mass ejections (CMEs) stand as intense eruptions of magnetized plasma from the Sun, and they play a pivotal role in driving significant changes of the heliospheric environment. Deducing the properties of CMEs from their progenitors in solar source regions is crucial for space weather forecasting. Aims. The primary objective of this paper is to establish a connection between CMEs and their progenitors in solar source regions, enabling us to infer the magnetic structures of CMEs before their full development. Methods. We created a dataset comprising a magnetic flux rope series with varying projection shapes (S-, Z-, and toroid-shaped), sizes, and toroidal fluxes using the Regularized Biot-Savart Laws (RBSL). These flux ropes were inserted into solar quiet regions with the aim of imitating the eruptions of quiescent filaments. Thereafter, we simulated the propagation of these flux ropes from the solar surface to a distance of 25 R⊙ with our global coronal magnetohydrodynamic (MHD) model COCONUT. Results. Our parametric survey revealed significant impacts of source flux ropes on the consequent CMEs. Regarding the flux-rope morphology, we find that the projection shape (e.g., sigmoid or torus) can influence the magnetic structures of CMEs at 20 R⊙, albeit with minimal impacts on the propagation speed. However, these impacts diminish as source flux ropes become fat. In terms of toroidal flux, our simulation results demonstrate a pronounced correlation with the propagation speed of CMEs as well as the successfulness in erupting. Conclusions. This work builds the bridge between the CMEs in the outer corona and their progenitors in solar source regions. Our parametric survey suggests that the projection shape, cross-section radius, and toroidal flux of source flux ropes are crucial parameters in predicting magnetic structures and the propagation speed of CMEs, providing valuable insights for space weather prediction. On the one hand, the conclusion drawn here could be instructive in identifying the high-risk eruptions with the potential to induce stronger geomagnetic effects (Bz and propagation speed). On the other hand, our findings hold practical significance for refining the parameter settings of launched CMEs at 21.5 R⊙ in heliospheric simulations, such as with EUHFORIA, based on observations for their progenitors in solar source regions.

The origin of interplanetary switchbacks in reconnection at chromospheric network boundaries

There is renewed interest in heliospheric physics following the recent exploration of the pristine solar wind by the Parker Solar Probe. Magnetic switchback structures are frequently observed in the inner heliosphere, but there are open questions about their origin. Many researchers are investigating the statistical properties of switchbacks and their relationships with wave modes, stream types and solar activity, but the sources of switchbacks remain elusive. Here we report that interplanetary switchbacks originate from magnetic reconnection on the Sun that occurs at chromospheric network boundaries and launch solar jet flows. We link in situ interplanetary measurements and remote-sensing solar observations to establish a connection between interplanetary switchbacks and their solar source region, featuring solar jets, chromospheric network boundaries and photospheric magnetic field evolution. Our findings suggest that joint observations of switchbacks and solar jets provide a better estimate of the contribution of magnetic reconnection to coronal heating and solar wind acceleration.

Radial evolution of the accuracy of ballistic solar wind backmapping

Context. Solar wind backmapping is a technique employed to connect in situ measurements of heliospheric plasma structures to their origin near the Sun. The most widely used method is ballistic mapping, which neglects the effects of solar wind acceleration and corotation and instead models the solar wind as a constant radial outflow whose speed is determined by measurements in the heliosphere. This results in plasma parcel streamlines that form an Archimedean spiral (the Parker spiral) when viewed in the solar corotating frame. This simplified approach assumes that the effects of solar wind acceleration and corotation compensate for each other in the deviation of the source longitude. Most backmapping techniques so far considered magnetic connectivity from a heliocentric distance of 1 au to the Sun. Aims. We quantify the angular deviation between different backmapping methods that depends on the location of the radial probe and on the variation in the solar wind speed with radial distance. We assess these differences depending on source longitude and solar wind propagation time. Methods. We estimated backmapping source longitudes and travel times using (1) the ballistic approximation (constant speed), (2) a physically justified method using the empirically constrained acceleration profile Iso-poly, derived from Parker solar wind equations and also a model of solar wind tangential flows that accounts for corotational effects. We compared the differences across mapped heliocentric distances and for different asymptotic solar wind speeds. Results. The ballistic method results in a Carrington longitude of the source with a maximum deviation of 4″ below 3 au compared to the physics-based mapping method taken as reference. However, the travel time especially for the slow solar wind could be underestimated by 1.5 days at 1 au compared to non-constant speed profile. This time latency may lead to an association of incorrect solar source regions with given in situ measurements. Neglecting corotational effects and accounting for acceleration alone causes a large systematic shift in the backmapped source longitude. Conclusions. Incorporating both acceleration and corotational effects leads to a more physics-based representation of the plasma trajectories through the heliosphere compared to the ballistic assumption. This approach accurately assesses the travel time and provides a more realistic estimate of the longitudinal separation between a plasma parcel measured in situ and its source region. Nonetheless, it requires knowledge of the radial density and Alfvén speed profiles to compute the tangential flow. Therefore, we propose a compromise for computing the source longitude that employs the commonly used ballistic approach and the travel times computed from the derived radial acceleration speed profile. Moreover, we conclude that this approach remains valid at all radial distances we studied and is not limited to data obtained at 1 au.

SPICE connection mosaics to link the Sun’s surface and the heliosphere

Aims. We present an analysis of the first connection mosaic made by the SPICE instrument on board the ESA/NASA Solar Orbiter mission on March 2, 2022. The data will be used to map coronal composition that will be compared with in-situ measurements taken by SWA/HIS to establish the coronal origin of the solar wind plasma observed at Solar Orbiter. The SPICE spectral lines were chosen to have varying sensitivity to the first ionization potential (FIP) effect, and therefore the radiances of the spectral lines will vary significantly depending on whether the elemental composition is coronal or photospheric. We investigate the link between the behavior of sulfur and the hypothesis that Alfvén waves drive FIP fractionation above the chromosphere. Methods. We performed temperature diagnostics using line ratios and emission measure (EM) loci, and computed relative FIP biases using three different approaches (two-line ratio (2LR), ratios of linear combinations of spectral lines (LCR), and differential emission measure (DEM) inversion) in order to perform composition diagnostics in the corona. We then compared the SPICE composition analysis and EUI data of the potential solar wind source regions to the SWA/HIS data products. Results. Radiance maps were extracted from SPICE spectral data cubes, with values matching previous observations. We find isothermal plasma of around log T = 5.8 for the AR loops targeted, and that higher FIP-bias values are present at the footpoints of the coronal loops associated with two ARs. Comparing the results with the SWA/HIS data products encourages us to think that Solar Orbiter was connected to a source of slow solar wind during this observation campaign. We demonstrate FIP fractionation in observations of the upper chromosphere and transition region, emphasized by the behavior of the intermediate-FIP element sulfur.

Spatial Relationship between CMEs and Prominence Eruptions during SC 24 and SC 25

During their propagation, coronal mass ejections (CMEs) and prominences sometimes display a nonradial motion. During the years after the solar minimum, the CME central position angle tended to be offset closer to the equator compared to that of the associated prominence eruptions (PE). No such effect was observed during solar maximum. The purpose of this paper is to investigate the latitudinal offsets of CMEs with respect to their source regions. We study 256 events from SC 24 and SC 25, listed in the Coordinate Data Analysis Workshop Data Center. We analyzed the CMES radial offset from the associated PEs by comparing their latitudes in the plane of the sky. This work is an extension of the previous work by Gopalswamy et al., but with an independent data set. We have confirmed the systematic equatorward offset of CME from the solar source region for the rising phase of Solar Cycle 25. Our analysis of the relation between CME linear speed and PE-CME latitudinal offset indicated that the velocities of the deflected CMEs are mainly in the range of 200 and 800 km s−1. In this study, we compared the nonradial offsets for the rising and decay phases of SC 24 and our analysis has shown that during the decay phase more events deflected toward the pole can be observed. The observed variation is attributed to the presence of a substantial number of low-latitude coronal holes during the decay phase and to the influence from nearby active regions.

Unveiling the journey of a highly inclined CME

Context. A fast (∼2000 km s−1) and wide (> 110°) coronal mass ejection (CME) erupted from the Sun on March 13, 2012. Its interplanetary counterpart was detected in situ two days later by STEREO-A and near-Earth spacecraft, such as ACE, Wind, and Cluster. 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. Aims. The aim of this work is to understand the propagation and evolution of the CME and its interaction with the surrounding CHs, to explain the similarities and differences between the observations at each spacecraft, and report what one of the most longitudinal expanded CME structures measured in situ would be. Methods. Known properties of the large-scale structures from a variety of catalogues and previous studies were used to have a better overview of this particular event. In addition, multipoint observations were used to reconstruct the 3D geometry of the CME and determine the context of the solar and heliospheric conditions before the CME eruption and during its propagation. The graduated cylindrical shell model (GCS) was used to reproduce the orientation, size and speed of the structure with a simple geometry. Also, the Drag-Based Model (DBM) was utilised to understand the conditions of the interplanetary medium better in terms of the drag undergone by the structure while propagating in different directions. Finally, a comparative analysis of the different regions of the structure through the different observatories was carried out in order to directly compare the in situ plasma and magnetic field properties at each location. Results. The study presents important findings regarding the in situ measured CME on March 15, 2012, detected at a longitudinal separation of 110° in the ecliptic plane despite its initial inclination being around 45° when erupted (March 13). 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. Conclusions. A scenario covering all evidence is proposed for both locations with a general view of the whole structure and solar wind conditions. Also, the study shows the necessity of having multipoint observations of large-scale structures in the heliosphere.

Coronal Magnetic Field Extrapolation and Topological Analysis of Fine-scale Structures during Solar Flare Precursors

Magnetic field plays an important role in various solar eruption phenomena. The formation and evolution of the characteristic magnetic field topology in solar eruptions are critical problems that will ultimately help us understand the origin of these eruptions in the solar source regions. With the development of advanced techniques and instruments, observations with higher resolutions in different wavelengths and fields of view have provided more quantitative information for finer structures. It is therefore essential to improve the method with which we study the magnetic field topology in the solar source regions by taking advantage of high-resolution observations. In this study, we employ a nonlinear force-free field extrapolation method based on a nonuniform grid setting for an M-class flare eruption event (SOL2015-06-22T17:39) with embedded vector magnetograms from the Solar Dynamics Observatory (SDO) and the Goode Solar Telescope (GST). The extrapolation results for which the nonuniform embedded magnetogram for the bottom boundary was employed are obtained by maintaining the native resolutions of the corresponding GST and SDO magnetograms. We compare the field line connectivity with the simultaneous GST/Hα and SDO/Atmospheric Imaging Assembly observations for these fine-scale structures, which are associated with precursor brightenings. Then we perform a topological analysis of the field line connectivity corresponding to fine-scale magnetic field structures based on the extrapolation results. The analysis results indicate that when we combine the high-resolution GST magnetogram with a larger magnetogram from the SDO, the derived magnetic field topology is consistent with a scenario of magnetic reconnection among sheared field lines across the main polarity inversion line during solar flare precursors.

Magnetic flux rope structures associated with filament channels: Two case studies

We report on two case studies regarding the magnetic flux rope (MFR) structure of coronal mass ejections (CMEs) near the Sun and at 1 au. The event is a stealth streamer blow-out CME on 2011 March 25 from AR11176 showing a typical three-part bubble-like flux rope structure. No apparent eruptive signatures (e.g., two-ribbon flare, and post-eruption arcade (PEA)) were detected in the solar disk images; but a faint eruptive prominence (EP) was seen at the limb in STEREO EUV images along with a few confined flares before the eruption. The second event is a CME on 2018 August 20 originating from a quiescent filament region with clear two-ribbon flare and PEA observed; and the prolonged CME acceleration coincides with the GOES X-ray flare light curve and reconnected (RC) flux (Gopalswamy et al., 2022). In both cases, a well-defined magnetic cloud (MC) is detected at 1 au after ∼5 days. The two MCs have similar magnetic field magnitude and poloidal flux, however, the RC fluxes estimated from the associated solar source regions are significantly different. Our detailed analysis suggests the following. 1) The two events share a similar kinematic pattern consisting of a slow-rise phase and a main acceleration phase. 2) In the first case, the RC flux of the associated trigger flare at AR11176 is much smaller than the MC poloidal flux at 1au, and a significant amount of poloidal flux has been added through reconnection during the eruption. 3) Both cases show that the post-eruption flux rope has a lower twist at the core and a higher twist at the edge of the flux rope. In addition, we find that the MCs may deviate from a force-free state at the edge of flux rope. A non-force-free, varying-twist Gold-Hoyle (GH) model provides a better fit to the boundaries of the flux rope than the Lundquist (LQ) fit.

Scope and limitations of ad hoc neural network reconstructions of solar wind parameters

Context.Solar wind properties are determined by the conditions of their solar source region and transport history. Solar wind parameters, such as proton speed, proton density, proton temperature, magnetic field strength, and the charge state composition of oxygen, are used as proxies to investigate the solar source region of the solar wind. The solar source region of the solar wind is relevant to both the interaction of this latter with the Earth’s magnetosphere and to our understanding of the underlying plasma processes, but the effect of the transport history of the wind is also important. The transport and conditions in the solar source region affect several solar wind parameters simultaneously. Therefore, the typically considered solar wind properties (e.g., proton density and oxygen charge-state composition) carry redundant information. Here, we are interested in exploring this redundancy.Aims.The observed redundancy could be caused by a set of hidden variables that determine the solar wind properties. We test this assumption by determining how well a (arbitrary, non-linear) function of four of the selected solar wind parameters can model the fifth solar wind parameter. If such a function provided a perfect model, then this solar wind parameter would be uniquely determined from hidden variables of the other four parameters and would therefore be redundant. If no reconstruction were possible, this parameter would be likely to contain information unique to the parameters evaluated here. In addition, isolating redundant or unique information contained in these properties guides requirements for in situ measurements and development of computer models. Sufficiently accurate measurements are necessary to understand the solar wind and its origin, to meaningfully classify solar wind types, and to predict space weather effects.Methods.We employed a neural network as a function approximator to model unknown, arbitrary, non-linear relations between the considered solar wind parameters. This approach is not designed to reconstruct the temporal structure of the observations. Instead a time-stable model is assumed and each point of measurement is treated separately. This approach is applied to solar wind data from the Advanced Composition Explorer (ACE). The neural network reconstructions are evaluated in comparison to observations, and the resulting reconstruction accuracies for each reconstructed solar wind parameter are compared while differentiating between different solar wind conditions (i.e., different solar wind types) and between different phases in the solar activity cycle. Therein, solar wind types are identified according to two solar-wind classification schemes based on proton plasma properties.Results.Within the limits defined by the measurement uncertainties, the proton density and proton temperature can be reconstructed well. Each parameter was evaluated with multiple criteria. Overall proton speed was the parameter with the most accurate reconstruction, while the oxygen charge-state ratio and magnetic field strength were most difficult to recover. We also analysed the results for different solar wind types separately and found that the reconstruction is most difficult for solar wind streams preceding and following stream interfaces.Conclusions.For all considered solar wind parameters, but in particular the proton density, proton temperature, and the oxygen charge-state ratio, parameter reconstruction is hindered by measurement uncertainties. The proton speed, while being one of the easiest to measure, also seems to carry the highest degree of redundancy with the combination of the four other solar wind parameters. Nevertheless, the reconstruction accuracy for the proton speed is limited by the large measurement uncertainties on the respective input parameters. The reconstruction accuracy of sector reversal plasma is noticeably lower than that of streamer belt or coronal hole plasma. We suspect that this is a result of the effect of stream interaction regions, which strongly influence the proton plasma properties and are typically assigned to sector reversal plasma. The fact that the oxygen charge-state ratio –a non-transport-affected property– is difficult to reconstruct may imply that recovering source-specific information from the transport-affected proton plasma properties is challenging. This underlines the importance of measuring the heavy ion charge-state composition.

Repeated Type III Burst Groups Associated with a B-Class Flare and a Narrow-Width CME

We have analysed a solar event from 27 September 2021, which included a small GOES B-class flare, a compact and narrow-width CME, and radio type III bursts that appeared in groups. The long-duration, repeated metric type III burst emission indicates continuous electron acceleration at high altitudes. The flaring active region was surrounded by strong magnetic fields and large-scale loops, which guided the outflow of the CME plasmoid and hence the narrow, bullet-like appearance of the CME. Radio imaging and EUV observations confirmed the direction of particle propagation and the depletion of matter from the solar source region. We observed V-shaped type III burst emission lanes, which also explain the field configuration and suggest a possible location for repeated reconnection that occurred at a constant altitude.

Ensemble Forecasts of Solar Wind Connectivity to 1 Rs Using ADAPT‐WSA

AbstractThe solar wind which arrives at any location in the solar system is, in principle, relatable to the outflow of solar plasma from a single source location. This source location, itself usually being part of a larger coronal hole, is traceable to 1 RS along the Sun's magnetic field, in which the entire path from 1 RS to a location in the heliosphere is referred to as the solar wind connectivity. While not directly measurable, the connectivity between the near‐Earth solar wind is of particular importance to space weather. The solar wind solar source region can be obtained by leveraging near‐sun magnetic field models and a model of the interplanetary solar wind. In this article, we present a method for making an ensemble forecast of the connectivity presented as a probability distribution obtained from a weighted collection of individual forecasts from the combined Air Force Data Assimilative Photospheric Flux Transport‐Wang Sheeley Arge (ADAPT‐WSA) model. The ADAPT model derives the photospheric magnetic field from synchronic magnetogram data, using flux transport physics and ongoing data assimilation processes. The WSA model uses a coupled set of potential field type models to derive the coronal magnetic field, and an empirical relationship to derive the terminal solar wind speed observed at Earth. Our method produces an arbitrary 2D probability distribution capable of reflecting complex source configurations with minimal assumptions about the distribution structure, prepared in a computationally efficient manner.

The Crucial Role of Perpendicular Diffusion in the Longitude Distribution of >10 MeV Solar Energetic Protons

Gradual solar proton events are thought to consist of solar components originating near the Sun and interplanetary components associated with interplanetary shocks, and the role of interplanetary shocks is considered to be crucial in supplying particles to regions that are not magnetically connected to the solar source region. We calculate the ratios of the peak intensities for the four energy channels (13–16, 20–25, 32–40, and 40–64 MeV) and compare the ratios observed by multiple spacecraft at different locations. We often find that the ratio of peak intensities observed at different locations in the same event remains almost constant as the energy varies. In other words, the ratio of peak intensities from the different energy channels remains almost constant as the position of the spacecraft changes. The phenomenon implies that in many gradual events, energetic particles observed at different locations are mainly composed of solar components that undergo perpendicular diffusion in both the vicinity of the Sun and the interplanetary space, and that perpendicular diffusion is the main factor enabling energetic particles to be observed in regions without magnetic connection to the solar source region.

The Origin of Extremely Nonradial Solar Wind Outflows

The origin of nonradial solar wind flows and their effect on space weather are poorly understood. Here we present a detailed investigation of 12 nonradial solar wind events during solar cycles 23–24, covering the period 1995–2017. In all these events the azimuthal flow angles of the solar wind exceed 6° as measured at the L1 Lagrangian point of the Sun–Earth system, for periods of 24 hr. In addition, all the events were selected during periods when coronal mass ejections (CMEs) and/or corotating interaction regions (CIRs) were absent. For most of the events, the near-Earth solar wind density was <5 cm−3 for periods exceeding 24 hr, similar to the well-known “solar wind disappearance events” wherein near-Earth solar wind densities dropped by two orders of magnitude for periods exceeding 24 hr. The solar source regions determined for all the cases were found to be associated with active region–coronal hole (AR–CH) pairs located around the central meridian. Further, the dynamical evolution of the source regions, studied using both the Extreme-ultraviolet Imaging Telescope and the Michelson Doppler Imager, showed a clear reduction in the CH area accompanied by the emergence of new magnetic flux regions. This dynamic evolution in the AR–CH source regions eventually disturbed the stable CH configurations, thereby giving rise to the extremely nonradial solar wind outflows. We discuss, based on our results, a possible causative mechanism for the origin of these highly nonradial flows that were not associated with either CMEs or CIRs.

An Analytical Model of Turbulence in Parker Spiral Geometry and Associated Magnetic Field Line Lengths

Understanding the magnetic connections from the Sun to interplanetary space is crucial for linking in situ particle observations with the solar source regions of the particles. A simple connection along the large-scale Parker spiral magnetic field is made complex by the turbulent random walk of field lines. In this paper, we present the first analytical model of heliospheric magnetic fields where the dominant 2D component of the turbulence is transverse to the Parker spiral. The 2D wave field is supplemented with a minor wave field component that has asymptotic slab geometry at small and large heliocentric distances. We show that turbulence spreads field lines from a small source region at the Sun to a 60° heliolongitudinal and heliolatitudinal range at 1 au, with a standard deviation of the angular spread of the field lines of 14°. Small source regions map to an intermittent range of longitudes and latitudes at 1 au, consistent with dropouts in solar energetic particle intensities. The lengths of the field lines are significantly extended from the nominal Parker spiral length of 1.17 au up to 1.6 au, with field lines from sources at and behind the west limb considerably longer than those closer to the solar disk center. We discuss the implications of our findings for understanding charged particle propagation and the importance of understanding the turbulence properties close to the Sun.

Tracking magnetic flux and helicity from the Sun to Earth

Aims.We analyze the complete chain of effects – from the Sun to Earth – caused by a solar eruptive event in order to better understand the dynamic evolution of magnetic-field-related quantities in interplanetary space, in particular that of magnetic flux and helicity.Methods.We study a series of connected events – a confined C4.5 flare, a flare-less filament eruption, and a double-peak M-class flare – that originated in NOAA active region (AR) 12891 on late 2021 November 1 and early 2021 November 2. We deduce the magnetic structure of AR 12891 using stereoscopy and nonlinear force-free (NLFF) magnetic field modeling, allowing us to identify a coronal flux rope and to estimate its axial flux and helicity. Additionally, we compute reconnection fluxes based on flare ribbon and coronal dimming signatures from remote sensing imagery. Comparison to corresponding quantities for the associated magnetic cloud (MC) deduced from in situ measurements from Solar Orbiter and near-Earth spacecraft allows us to draw conclusions on the evolution of the associated interplanetary coronal mass ejection (CME). The latter analysis is aided by the application of geometric fitting techniques (graduated cylindrical shell modeling; GCS) and interplanetary propagation models (drag-based ensemble modeling; DBEM) to the interplanetary CME.Results.NLFF modeling suggests the magnetic structure of the host AR was in the form of a left-handed (negative-helicity) flux rope reaching altitudes of 8−10 Mm above photospheric levels, which is in close agreement with the corresponding stereoscopic estimate. GCS and DBEM modeling suggest that the ejected flux rope propagated in a self-similar expanding manner through interplanetary space. Comparison of magnetic fluxes and helicities processed by magnetic reconnection in the solar source region and the respective budgets of the MC indicate a considerable contribution from the eruptive process, though the pre-eruptive budgets also appear to be relevant.

Periodic Solar Wind Structures Observed in Measurements of Elemental and Ionic Composition in situ at L1

Mesoscale periodic structures observed in solar wind plasma serve as an important diagnostic tool for constraining the processes that govern the formation of the solar wind. These structures have been observed in situ and in remote data as fluctuations in proton and electron density. However, only two events of this type have been reported regarding the elemental and ionic composition. Composition measurements are especially important in gaining an understanding of the origin of the solar wind as the composition is frozen into the plasma at the Sun and does not evolve as it advects through the heliosphere. Here, we present the analysis of four events containing mesoscale periodic solar wind structure during which the Iron and Magnesium number density data, measured by the Solar Wind Ion Composition Spectrometer (SWICS) on board the Advanced Composition Explorer spacecraft, are validated at statistically significant count levels. We use a spectral analysis method specifically designed to extract periodic signals from astrophysical time series and apply it to the SWICS 12 minute native resolution data set. We find variations in the relative abundance of elements with low first ionization potential, mass dependencies, and charge state during time intervals in which mesoscale periodic structures are observed. These variations are linked to temporal or spatial variations in solar source regions and put constraints on the solar wind formation mechanisms that produce them. Techniques presented here are relevant for future, higher-resolution studies of data from new instruments such as Solar Orbiter’s Heavy Ion Sensor.

Alpha–Proton Differential Flow of the Young Solar Wind: Parker Solar Probe Observations

Abstract The velocity of alpha particles relative to protons can vary depending on the solar wind type and distance from the Sun. Measurements from the previous spacecraft provided the alpha–proton differential velocities down to 0.3 au. The Parker Solar Probe (PSP) now enables insights into differential flows of the newly accelerated solar wind closer to the Sun for the first time. Here we study the difference between proton and alpha bulk velocities near PSP perihelia of encounters 3–7 when the core solar wind is in the field of view of the Solar Probe Analyzer for Ions instrument. As previously reported at larger heliospheric distances, the alpha–proton differential speed observed by PSP is greater for fast wind than the slow solar wind. We compare PSP observations with various spacecraft measurements and present the radial and temporal evolution of the alpha–proton differential speed. The differential flow decreases as the solar wind propagates from the Sun, consistent with previous observations. While Helios showed a small radial dependence of differential flow for the slow solar wind, PSP clearly showed this dependency for the young slow solar wind down to 0.09 au. Our analysis shows that the alpha–proton differential speed’s magnitude is mainly below the local Alfvén speed. Moreover, alpha particles usually move faster than protons close to the Sun. The PSP crossed the Alfvén surface during its eighth encounter and may cross it in future encounters, enabling us to investigate the differential flow very close to the solar wind acceleration source region for the first time.

Investigation of two coronal mass ejections from circular ribbon source region:Origin, Sun-Earth propagation and Geoeffectiveness

In this article, we compare the properties of two coronal mass ejections (CMEs) that show similar source region characteristics but different evolutionary behaviors in the later phases. We discuss the two events in terms of their near-Sun characteristics, interplanetary evolution and geoeffectiveness. We carefully analyzed the initiation and propagation parameters of these events to establish the precise CME-interplanetary CME (ICME) connection and their near-Earth consequences. The first event is associated with poor geomagnetic storm disturbance index (Dst ≈-20 nT) while the second event is associated with an intense geomagnetic storm of DST ≈-119 nT. The configuration of the sunspots in the active regions and their evolution are observed by Helioseismic and Magnetic Imager (HMI). For source region imaging, we rely on data obtained from Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO) and Hα filtergrams from the Solar Tower Telescope at Aryabhatta Research Institute of Observational Sciences (ARIES). For both the CMEs, flux rope eruptions from the source region triggered flares of similar intensities (≈M1). At the solar source region of the eruptions,we observed a circular ribbon flare (CRF) for both cases, suggesting fan-spine magnetic configuration in the active region corona. The multi-channel SDO observations confirm that the eruptive flares and subsequent CMEs were intimately related to the filament eruption. Within the Large Angle and Spectrometric Coronograph (LASCO) field of view (FOV) thetwo CMEs propagated with linear speeds of 671 and 631 km s−1, respectively. These CMEs were tracked up to the Earth by Solar Terrestrial Relations Observatory (STEREO) instruments. We find that the source region evolution of CMEs, guided by the large-scale coronal magnetic field configuration, along with near-Sun propagation characteristics, such as CME-CME interactions, played important roles in deciding the evolution of CMEs in the interplanetary medium and subsequently their geoeffectiveness.

Proton Beam Abundance Variations and Their Relation to Alpha Particle Properties

Abstract Less abundant but still dynamically important solar wind components are the proton beam and alpha particles, which usually contribute similarly to the total ion momentum. The main characteristics of alpha particles are determined by the solar wind source region, but the origin of the proton beam and its properties are still not fully explained. We use the plasma data measured in situ on the path from 0.3 to 1 au (Helios 1 and 2) and focus on the proton beam development with an increasing radial distance as well as on the connection between the proton beam and alpha particle properties. We found that the proton beam relative abundance increases with increasing distance from the Sun in the collisionally young streams. Among the mechanisms suggested for beam creation, we have identified the wave–particle interactions with obliquely propagating Alfvén modes being consistent with observations. As the solar wind streams get collisionally older, the proton beam decay gradually dominates and the beam abundance is reduced. In search for responsible mechanisms, we found that the content of alpha particles is correlated with the proton beam abundance, and this effect is more pronounced in the fast solar wind streams during the solar maximum. We suggest that Coulomb collisions are the main agent leading to merging of the proton beam and core. We are also showing that the variations of the proton beam abundance are correlated with a decrease of the alpha particle velocity in order to maintain the total momentum balance in the solar wind frame.

The Structural Connection between Coronal Mass Ejection Flux Ropes near the Sun and at 1 au

Abstract We have performed the first comprehensive statistical analysis comparing flux rope (FR) structures of coronal mass ejections (CMEs) near the Sun and at 1 au, using Solar and Heliospheric Observatory and Solar Terrestrial Relations Observatory measurements for the two full solar cycles 23 and 24. This study aims to investigate the physical connection of 102 magnetic FRs among solar source regions, CMEs in the extended corona, and magnetic clouds (MCs) near Earth. Our main results are as follows: (1) We confirmed that the hemispheric-helicity rule holds true for ∼87% of our 102 events. For the 13 events that do not follow this rule, the FR axis directions and helicity signs can be inferred from soft X-ray and extreme ultraviolet images and magnetogram data in the source regions (e.g., coronal arcade skews, Fe xii stalks, sigmoids, and magnetic tongues). (2) Around 25% of the 102 events have rotations &gt;40° between the MC and CME-FR axial orientations. (3) For ∼56% of these rotational events, the FR rotations occurred within the COR2 field of view, which can be predicted from the CME tilts obtained from FR fitting models. In addition, we found that for 89% of the 19 stealth CMEs under study, we were able to use coronal neutral line locations and tilts to predict the FR helicity and its axial direction in the MCs. The above results should help improve the prediction of FR structures in situ. We discuss their implications on space weather forecasts.