Suprathermal and energetic electrons as probes of interplanetary magnetic field topology

La tesis “Suprathermal and Energetic Electrons as Probes of Interplanetary Magnetic Field Topology” escrita por D. Fernando Carcaboso Morales y supervisada por Dr. Raúl Gómez Herrero y Dr. Javier Rodríguez-Pacheco Martín, contemplada dentro del campo de conocimiento de la física del Sistema Solar, viento solar, utiliza distintas metodologías aplicadas al estudio de los electrones supratérmicos y energéticos para inferir varias topologías y propiedades del campo magnético interplanetario. Gran parte del trabajo se centra en dos de las distribuciones más comunes de los electrones supratérmicos: la bidireccionalidad y la isotropía. Éstas son analizadas durante el tránsito de eyecciones coronales de masa interplanetarias, así como en parte del Ciclo Solar 24. También, recoge un estudio de la variabilidad de la anisotropía de los electrones supratérmicos, atendiendo a su dependencia con la energía observada, el grado de actividad solar y la latitud heliomagnética, y hace una comparativa con la propagación de partículas energéticas solares de caracter impulsivo. Además, utiliza modelos desarrollados previamente para el estudio de las estructuras interplanetarias denominadas “nubes magnéticas” y añade actualizaciones reduciendo su número de parámetros libres. Por otro lado, propone un nuevo modelo sencillo para interpretar la propagación de electrones energéticos emisores de radio bursts de Tipo III desde distintos observadores. Por último, adjunta catálogos de periodos largos que presentan isotropía y bidirecionalidad en los electrones supratérmicos, así como de estructuras de cuerdas de flujo, observados por la misión STEREO

Characterisation of suprathermal electron pitch-angle distributions: Bidirectional and isotropic periods in solar wind

Context. Suprathermal electron pitch-angle distributions (PADs) contain substantial information about the magnetic topology of the solar wind. Their characterisation and quantification allow us to automatically identify periods showing certain characteristics. Aims. This work presents a robust automatic method for the identification and statistical study of two different types of PADs: bidirectional suprathermal electrons (BDE, often associated with closed magnetic structures) and isotropic (likely corresponding to solar-detached magnetic field lines or highly scattered electrons). Methods. Spherical harmonics were fitted to the observed suprathermal PADs of the 119&-193 eV energy channel of STEREO/SWEA from March 2007 to July 2014, and they were characterised using signal processing analysis in order to identify periods of isotropic and bidirectional PADs. The characterisation has been validated by comparing the results obtained here with those of previous studies. Results. Interplanetary coronal mass ejections (ICMEs) present longer BDE periods inside the magnetic obstacles. A significant amount of BDE remain after the end of the ICME. Isotropic PADs are found in the sheath of the ICMEs, and at the post-ICME region likely due to the erosion of the magnetic field lines. Both isotropy and BDE are solar-cycle dependent. The isotropy observed by STEREO shows a nearly annual periodicity, which requires further investigation. There is also a correspondence between the number of ICMEs observed and the percentage of time showing BDE. Conclusions. A method to characterise PADs has been presented and applied to the automatic identification of two relevant distributions that are commonly observed in the solar wind, such as BDE and isotropy. Four catalogues (STEREO-A and STEREO-B for isotropic and BDE periods of at least 10 min) based on this identification are provided for future applications.Agencia Estatal de Investigació

The Solar Orbiter Science Activity Plan: translating solar and heliospheric physics questions into action

Solar Orbiter is the first space mission observing the solar plasma both in situ and remotely, from a close distance, in and out of the ecliptic. The ultimate goal is to understand how the Sun produces and controls the heliosphere, filling the Solar System and driving the planetary environments. With six remote-sensing and four in-situ instrument suites, the coordination and planning of the operations are essential to address the following four top-level science questions: (1) What drives the solar wind and where does the coronal magnetic field originate?; (2) How do solar transients drive heliospheric variability?; (3) How do solar eruptions produce energetic particle radiation that fills the heliosphere?; (4) How does the solar dynamo work and drive connections between the Sun and the heliosphere? Maximising the mission"s science return requires considering the characteristics of each orbit, including the relative position of the spacecraft to Earth (a ecting downlink rates), trajectory events (such as gravitational assist manoeuvres), and the phase of the solar activity cycle. Furthermore, since each orbit"s science telemetry will be downloaded over the course of the following orbit, science operations must be planned at mission level, rather than at the level of individual orbits. It is important to explore the way in which those science questions are translated into an actual plan of observations that fits into the mission, thus ensuring that no opportunities are missed. First, the overarching goals are broken down into specific, answerable questions along with the required observations and the so-called Science Activity Plan (SAP) is developed to achieve this. The SAP groups objectives that require similar observations into Solar Orbiter Observing Plans (SOOPs), resulting in a strategic, top-level view of the optimal opportunities for science observations during the mission lifetime. This allows for all four mission goals to be addressed. In this paper, we introduce Solar Orbiter"s SAP through a series of examples and the strategy being followed.Agencia Estatal de Investigació

CME-HSS Interaction and Characteristics Tracked from Sun to Earth

In a thorough study, we investigate the origin of a remarkable plasma and magnetic field configuration observed in situ on June 22, 2011, near L1, which appears to be a magnetic ejecta (ME) and a shock signature engulfed by a solar wind high-speed stream (HSS). We identify the signatures as an Earth-directed coronal mass ejection (CME), associated with a C7.7 flare on June 21, 2011, and its interaction with a HSS, which emanates from a coronal hole (CH) close to the launch site of the CME. The results indicate that the major interaction between the CME and the HSS starts at a height of 1.3 R⊙ up to 3 R⊙. Over that distance range, the CME undergoes a strong north-eastward deflection of at least 30∘ due to the open magnetic field configuration of the CH. We perform a comprehensive analysis for the CME–HSS event using multi-viewpoint data (from the Solar TErrestrial RElations Observatories, the Solar and Heliospheric Observatory and the Solar Dynamics Observatory), and combined modeling efforts (nonlinear force-free field modeling, Graduated Cylindrical Shell CME modeling, and the Forecasting a CME’s Altered Trajectory – ForeCAT model). We aim at better understanding its early evolution and interaction process as well as its interplanetary propagation and related in situ signatures, and finally the resulting impact on the Earth’s magnetosphere

Evidence of a complex structure within the 2013 August 19 coronal mass ejection: Radial and longitudinal evolution in the inner heliosphere

Context. Late on 2013 August 19, a coronal mass ejection (CME) erupted from an active region located near the far-side central meridian from Earth’s perspective. The event and its accompanying shock were remotely observed by the STEREO-A, STEREO-B, and SOHO spacecraft. The interplanetary counterpart (ICME) was intercepted by MESSENGER near 0.3 au and by both STEREO-A and STEREO-B near 1 au, which were separated from each other by 78° in heliolongitude. Aims. The main objective of this study is to follow the radial and longitudinal evolution of the ICME throughout the inner heliosphere and to examine possible scenarios for the different magnetic flux-rope configuration observed on the solar disk and measured in situ at the locations of MESSENGER and STEREO-A, separated by 15° in heliolongitude, and at STEREO-B, which detected the ICME flank. Methods. Solar disk observations are used to estimate the “magnetic flux-rope type”, namely, the magnetic helicity, axis orientation, and axial magnetic field direction of the flux rope. The graduated cylindrical shell model is used to reconstruct the CME in the corona. The analysis of in situ data, specifically the plasma and magnetic field, is used to estimate the global interplanetary shock geometry and to derive the magnetic flux-rope type at different in situ locations, which is compared to the type estimated from solar disk observations. The elliptical cylindrical analytical model is used for the in situ magnetic flux-rope reconstruction. Results. Based on the CME geometry and on the spacecraft configuration, we find that the magnetic flux-rope structure detected at STEREO-B belongs to the same ICME detected at MESSENGER and STEREO-A. The opposite helicity deduced at STEREO-B might be due to that fact that it intercepted one of the legs of the structure far from the flux-rope axis, in contrast to STEREO-A and MESSENGER, which were crossing through the core of the magnetic flux rope. The different flux-rope orientations measured at MESSENGER and STEREO-A probably arise because the two spacecraft measure a curved, highly distorted, and rather complex magnetic flux-rope topology. The ICME may have suffered additional distortion in its evolution in the inner heliosphere, such as the west flank propagating faster than the east flank when arriving near 1 au. Conclusions. This work illustrates how a wide, curved, highly distorted, and rather complex CME showed different orientations as observed on the solar disk and measured in situ at 0.3 au and near 1 au. Furthermore, the work shows how the ambient conditions can significantly affect the expansion and propagation of the CME and ICME, introducing additional irregularities to the already asymmetric eruption. The study also manifests how these complex structures cannot be directly reconstructed with the currently available models and that multi-point analysis is of the utmost importance in such complex events.Agencia Estatal de Investigació

The first widespread solar energetic particle event observed by Solar Orbiter on 2020 November 29

Context. On 2020 November 29, the first widespread solar energetic particle (SEP) event of solar cycle 25 was observed at four widely separated locations in the inner (.1 AU) heliosphere. Relativistic electrons as well as protons with energies >50 MeV were observed by Solar Orbiter (SolO), Parker Solar Probe, the Solar Terrestrial Relations Observatory (STEREO)-A and multiple near-Earth spacecraft. The SEP event was associated with an M4.4 class X-ray flare and accompanied by a coronal mass ejection and an extreme ultraviolet (EUV) wave as well as a type II radio burst and multiple type III radio bursts. Aims. We present multi-spacecraft particle observations and place them in context with source observations from remote sensing instruments and discuss how such observations may further our understanding of particle acceleration and transport in this widespread event. Methods. Velocity dispersion analysis (VDA) and time shift analysis (TSA) were used to infer the particle release times at the Sun. Solar wind plasma and magnetic field measurements were examined to identify structures that influence the properties of the energetic particles such as their intensity. Pitch angle distributions and first-order anisotropies were analyzed in order to characterize the particle propagation in the interplanetary medium. Results. We find that during the 2020 November 29 SEP event, particles spread over more than 230◦ in longitude close to 1 AU. The particle onset delays observed at the different spacecraft are larger as the flare–footpoint angle increases and are consistent with those from previous STEREO observations. Comparing the timing when the EUV wave intersects the estimated magnetic footpoints of each spacecraft with particle release times from TSA and VDA, we conclude that a simple scenario where the particle release is only determined by the EUV wave propagation is unlikely for this event. Observations of anisotropic particle distributions at SolO, Wind, and STEREO-A do not rule out that particles are injected over a wide longitudinal range close to the Sun. However, the low values of the first-order anisotropy observed by near-Earth spacecraft suggest that diffusive propagation processes are likely involved.Agencia Estatal de Investigació

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

First year of energetic particle measurements in the inner heliosphere with Solar Orbiter's Energetic Particle Detector

Context. Solar Orbiter strives to unveil how the Sun controls and shapes the heliosphere and fills it with energetic particle radiation. To this end, its Energetic Particle Detector (EPD) has now been in operation, providing excellent data, for just over a year. Aims. EPD measures suprathermal and energetic particles in the energy range from a few keV up to (near-) relativistic energies (few MeV for electrons and about 500 MeV nuc−1 for ions). We present an overview of the initial results from the first year of operations and we provide a first assessment of issues and limitations. In addition, we present areas where EPD excels and provides opportunities for significant scientific progress in understanding how our Sun shapes the heliosphere. Methods. We used the solar particle events observed by Solar Orbiter on 21 July and between 10 and 11 December 2020 to discuss the capabilities, along with updates and open issues related to EPD on Solar Orbiter. We also give some words of caution and caveats related to the use of EPD-derived data. Results. During this first year of operations of the Solar Orbiter mission, EPD has recorded several particle events at distances between 0.5 and 1 au from the Sun. We present dynamic and time-averaged energy spectra for ions that were measured with a combination of all four EPD sensors, namely: the SupraThermal Electron and Proton sensor (STEP), the Electron Proton Telescope (EPT), the Suprathermal Ion Spectrograph (SIS), and the High-Energy Telescope (HET) as well as the associated energy spectra for electrons measured with STEP and EPT. We illustrate the capabilities of the EPD suite using the 10 and 11 December 2020 solar particle event. This event showed an enrichment of heavy ions as well as 3He, for which we also present dynamic spectra measured with SIS. The high anisotropy of electrons at the onset of the event and its temporal evolution is also shown using data from these sensors. We discuss the ongoing in-flight calibration and a few open instrumental issues using data from the 21 July and the 10 and 11 December 2020 events and give guidelines and examples for the usage of the EPD data. We explain how spacecraft operations may affect EPD data and we present a list of such time periods in the appendix. A list of the most significant particle enhancements as observed by EPT during this first year is also provided.Ministerio de Economía y CompetitividadAgencia Estatal de Investigació

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