Aims. We present a systematic study of the timing and duration of the release processes of near-relativistic (NR; >50 keV) electrons in the low corona. Methods. We analyze seven well-observed events ...using in situ measurements by both the ACE and Wind spacecraft and context electromagnetic observations in soft X-rays, radio, hard X-rays and white light. We make use of velocity dispersion analysis to estimate the release time of the first arriving electrons and compare with the results obtained by using a simulation-based approach, taking interplanetary transport effects into account to unfold the NR electron release time history from in situ measurements. Results. The NR electrons observed in interplanetary space appear to be released during either short (<30 min) or long (>2 h) periods. The observation of NR electron events showing beamed pitch-angle distributions (PADs) during several hours is the clearest observational signature of sustained release in the corona. On the other hand, the in situ observation of PADs isotropizing in less than a couple of hours is a clear signature of a prompt release of electrons in the low corona. Short release episodes appear to originate in solar flares, in coincidence with the timing of the observed type III radio bursts. Magnetic connectivity plays an important role. Only type III radio bursts reaching the local plasma line measured at 1 AU are found to be related with an associated release episode in the low corona. Other type III bursts may also have a release of NR electrons associated with them, but these electrons do not reach L1. Long release episodes appear associated with signatures of long acceleration processes in the low corona (long decay of the soft X-ray emission, type IV radio bursts, and time-extended microwave emission). Type II radio bursts are reported for most of the events and do not provide a clear discrimination between short and long release timescales.
A Multi‐Purpose Heliophysics L4 Mission Posner, A.; Arge, C. N.; Staub, J. ...
Space Weather,
September 2021, 2021-09-00, 20210901, Letnik:
19, Številka:
9
Journal Article
Recenzirano
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The Earth‐Sun Lagrangian point 4 is a meta‐stable location at 1 AU from the Sun, 60° ahead of Earth's orbit. It has an uninterrupted view of the solar photosphere centered on W60, the Earth's nominal ...magnetic field connection to the Sun. Such a mission on its own would serve as a solar remote sensing observatory that would oversee the entire solar radiation hemisphere with significant relevance for protecting Moon and Mars explorers from radiation exposure. In combination with appropriately planned observatories at L1 and L5, the three spacecraft would provide 300° longitude coverage of photospheric magnetic field structure, and allow continuous viewing of both solar poles, with >3.6° elevation. Ideally, the L4 and L5 missions would orbit the Sun with a 7.2° inclination out of the heliographic equator, 14.5° out of the ecliptic plane. We discuss the impact of extending solar magnetic field observations in both longitude and latitude to improve global solar wind modeling and, with the development of local helioseismology, the potential for long‐term solar activity forecasting. Such a mission would provide a unique opportunity for interplanetary and interstellar dust science. It would significantly add to reliability of operational observations on fast coronal mass ejections directed at Earth and for human Mars explorers on their round‐trip journey. The L4 mission concept is technically feasible, and is scientifically compelling.
Plain Language Summary
This work describes the advantages of placing a spacecraft at a point 60° ahead of Earth in its orbit, which offers advantages for viewing areas on the surface of the Sun that hold critical clues about solar ionizing radiation that may affect astronauts on/at the moon or on the way to and from Mars. We describe that a combination of missions ahead and behind the Earth in its orbit would provide additional benefits, even more so if injected in an orbital plane that is tilted by ∼14°. Solar remote sensing observations from these platforms would significantly improve models of the magnetic field and solar wind of the Sun and in the inner solar system, by covering more solar surface area in longitude, but also of the polar regions. This would help us better understand when solar eruptions affect the Earth's magnetosphere. Other benefits, including long‐term advance forecasting of solar activity and the understanding of dust populations in the near‐Sun environment are also discussed. An analysis of launch capabilities shows that such a mission concept, even launching both suggested missions together, is feasible.
Key Points
First thorough analysis of advantages of Earth‐Sun L4 location as observation platform, and combination of L4/L5 at moderate inclination
The L4 view of solar radiation hemisphere is ideal for forecasting/warning Earth‐Moon system and Mars journey of solar energetic particles
Combination of L4/L5 observations would boost inner‐heliosphere solar wind modeling and validation, and long‐term solar activity forecasting
We present observations of energetic particle flux increases up to 1 MeV at 1 AU, which cannot be associated with ordinary mechanisms of particle acceleration, such as acceleration at shocks or at ...the Sun. Such unusual energetic particle events very likely have a local origin. Multi-spacecraft observations show that numerous cases of energetic particle flux enhancements and spikes correspond to passages of spacecraft through areas filled with magnetic islands with a typical width ∼0.01-0.001AU that experience dynamical merging or and contraction. The presence of magnetic islands inside magnetically confined cavities in the solar wind may lead to local particle energization, especially in the case when the particles have already been pre-accelerated to keV energies, for example, at shocks or due to magnetic reconnection at the heliospheric current sheet. We consider different magnetic configurations that provide favourable conditions for both the appearance of small-scale magnetic islands and their confinement.
ABSTRACT During the interval 2012 March 7-11 the geospace experienced a barrage of intense space weather phenomena including the second largest geomagnetic storm of solar cycle 24 so far. Significant ...ultra-low-frequency wave enhancements and relativistic-electron dropouts in the radiation belts, as well as strong energetic-electron injection events in the magnetosphere were observed. These phenomena were ultimately associated with two ultra-fast (>2000 km s−1) coronal mass ejections (CMEs), linked to two X-class flares launched on early 2012 March 7. Given that both powerful events originated from solar active region NOAA 11429 and their onsets were separated by less than an hour, the analysis of the two events and the determination of solar causes and geospace effects are rather challenging. Using satellite data from a flotilla of solar, heliospheric and magnetospheric missions a synergistic Sun-to-Earth study of diverse observational solar, interplanetary and magnetospheric data sets was performed. It was found that only the second CME was Earth-directed. Using a novel method, we estimated its near-Sun magnetic field at 13 R to be in the range 0.01, 0.16 G. Steep radial fall-offs of the near-Sun CME magnetic field are required to match the magnetic fields of the corresponding interplanetary CME (ICME) at 1 AU. Perturbed upstream solar-wind conditions, as resulting from the shock associated with the Earth-directed CME, offer a decent description of its kinematics. The magnetospheric compression caused by the arrival at 1 AU of the shock associated with the ICME was a key factor for radiation-belt dynamics.
The Integrated Science Investigation of the Sun (IS IS) instrument suite on the Parker Solar Probe (PSP) spacecraft is making in situ observations of energetic ions and electrons closer to the Sun ...than any previous mission. Using data collected during its first two orbits, which reached perihelion distances of 0.17 au, we have searched for -rich solar energetic particle (SEP) events under very quiet solar minimum conditions. On 2019-110-111 (April 20-21), -rich SEPs were observed at energies near 1 MeV nucleon-1 in association with energetic protons, heavy ions, and electrons. This activity was also detected by the Ultra-Low-Energy Isotope Spectrometer and the Electron, Proton, and Alpha Monitor instruments on the Advanced Composition Explorer (ACE) spacecraft located near Earth, 0.99 au from the Sun. At that time, PSP and ACE were both magnetically connected to locations near the west limb of the Sun. Remote sensing measurements showed the presence of type III radio bursts and also helical jets from this region of the Sun. This combination of observations is commonly associated with -rich SEP acceleration on the Sun. AR 12738, which was located at Carrington coordinates from which numerous X-ray flares were observed over a period of more than 6 months, was identified as the source of the -rich events. This region was also the source of several other SEP events detected at PSP or ACE. Aside from the period in 2019 April, IS IS did not observe any other -rich SEPs during orbits 1 and 2.
Solar energetic particles (SEPs) detected in space are statistically associated with flares and coronal mass ejections (CMEs). But it is not clear how these processes actually contribute to the ...acceleration and transport of the particles. The present work addresses the question why flares accompanied by intense soft X-ray bursts may not produce SEPs detected by observations with the GOES spacecraft. We consider all X-class X-ray bursts between 1996 and 2006 from the western solar hemisphere. 21 out of 69 have no signature in GOES proton intensities above 10 MeV, despite being significant accelerators of electrons, as shown by their radio emission at cm wavelengths. The majority (11/20) has no type III radio bursts from electron beams escaping towards interplanetary space during the impulsive flare phase. Together with other radio properties, this indicates that the electrons accelerated during the impulsive flare phase remain confined in the low corona. This occurs in flares with and without a CME. Although GOES saw no protons above 10 MeV at geosynchronous orbit, energetic particles were detected in some (4/11) confined events at Lagrangian point L1 aboard ACE or SoHO. These events have, besides the confined microwave emission, dm-m wave type II and type IV bursts indicating an independent accelerator in the corona. Three of them are accompanied by CMEs. We conclude that the principal reason why major solar flares in the western hemisphere are not associated with SEPs is the confinement of particles accelerated in the impulsive phase. A coronal shock wave or the restructuring of the magnetically stressed corona, indicated by the type II and IV bursts, can explain the detection of SEPs when flare-accelerated particles do not reach open magnetic field lines. But the mere presence of these radio signatures, especially of a metric type II burst, is not a sufficient condition for a major SEP event.
The Solar Terrestrial Relations Observatory (STEREO) recordings provide an unprecedented opportunity to study the evolution of solar energetic particle (SEP) events from different observation points ...in the heliosphere, allowing one to identify the effects of the properties of the interplanetary magnetic field (IMF) and solar wind structures on the interplanetary transport and acceleration of SEPs. Two catalogues based on STEREO recordings, have been compiled as a part of the SEPServer project, a three-year collaborative effort of eleven European partners funded under the Seventh Framework Programme of the European Union (FP7/SPACE). In particular, two instruments on board STEREO have been used to identify all SEP events observed within the descending phase of solar cycle 23 and the rising phase of solar cycle 24 from 2007 to 2012, namely: the Low Energy Telescope (LET) and the Solar Electron Proton Telescope (SEPT). A scan of STEREO/LET protons within the energy range 6–10 MeV has been performed for each of the two STEREO spacecraft. We have tracked all enhancements that have been observed above the background level of this particular channel and cross-checked with available lists of interplanetary coronal mass ejections (ICMEs), stream interaction regions (SIRs), and shocks, as well as with the reported events in literature. Furthermore, parallel scanning of the STEREO near relativistic electrons has been performed in order to pinpoint the presence (or absence) of an electron event in the energy range of 55–85 keV, for all of the aforementioned proton events included in our lists. We provide the onset and peak time as well as the peak value of all events for both protons and electrons, the relevant solar associations in terms of electromagnetic emissions, soft and hard X-rays (SXRs and HXRs). Finally, a subset of events with clear recordings at both STEREO spacecraft is presented together with the parent solar events of these multispacecraft SEP events.
SEPServer is a three-year collaborative project funded by the seventh framework programme (FP7-SPACE) of the European Union. The objective of the project is to provide access to state-of-the-art ...observations and analysis tools for the scientific community on solar energetic particle (SEP) events and related electromagnetic (EM) emissions. The project will eventually lead to better understanding of the particle acceleration and transport processes at the Sun and in the inner heliosphere. These processes lead to SEP events that form one of the key elements of space weather. In this paper we present the first results from the systematic analysis work performed on the following datasets: SOHO/ERNE, SOHO/EPHIN, ACE/EPAM, Wind/WAVES and GOES X-rays. A catalogue of SEP events at 1 AU, with complete coverage over solar cycle 23, based on high-energy ( similar to 68-MeV) protons from SOHO/ERNE and electron recordings of the events by SOHO/EPHIN and ACE/EPAM are presented. A total of 115 energetic particle events have been identified and analysed using velocity dispersion analysis (VDA) for protons and time-shifting analysis (TSA) for electrons and protons in order to infer the SEP release times at the Sun. EM observations during the times of the SEP event onset have been gathered and compared to the release time estimates of particles. Data from those events that occurred during the European day-time, i.e., those that also have observations from ground-based observatories included in SEPServer, are listed and a preliminary analysis of their associations is presented. We find that VDA results for protons can be a useful tool for the analysis of proton release times, but if the derived proton path length is out of a range of 1 AU < s3 AU, the result of the analysis may be compromised, as indicated by the anti-correlation of the derived path length and release time delay from the associated X-ray flare. The average path length derived from VDA is about 1.9 times the nominal length of the spiral magnetic field line. This implies that the path length of first-arriving MeV to deka-MeV protons is affected by interplanetary scattering. TSA of near-relativistic electrons results in a release time that shows significant scatter with respect to the EM emissions but with a trend of being delayed more with increasing distance between the flare and the nominal footpoint of the Earth-connected field line.
We report observations of solar energetic particles obtained by the HI-SCALE and COSPIN/LET instruments onboard Ulysses during the period of isolated but intense solar activity in 2006 December, in ...the declining phase of the solar activity cycle. We present measurements of particle intensities and also discuss observations of particle anisotropies and composition in selected energy ranges. Active Region 10930 produced a series of major solar flares with the strongest one (X9.0) recorded on December 5 after it rotated into view on the solar east limb. Located over the South Pole of the Sun, at >72 deg S heliographic latitude and 2.8 AU radial distance, Ulysses provided unique measurements for assessing the nature of particle propagation to high latitudes under near-minimum solar activity conditions, in a relatively undisturbed heliosphere. The observations seem to exclude the possibility that magnetic field lines originating at low latitudes reached Ulysses, suggesting either that the energetic particles observed as large solar energetic particle (SEP) events over the South Pole of the Sun in 2006 December were released when propagating coronal waves reached high-latitude field lines connected to Ulysses, or underwent perpendicular diffusion. We also discuss comparisons with energetic particle data acquired by the STEREO and Advanced Composition Explorer in the ecliptic plane near 1 AU during this period.
In the absence of solar activity, Co-rotating Interaction Regions (CIRs) are a prevailing source of energetic ions observed near 1AU. The combination of observations by near-Earth space observatories ...and the twin STEREO spacecraft offers an excellent platform for multi-point studies of CIRs. The analysis of CIR events during Carrington rotations 2067–2082 provides evidence that CIR-associated energetic ions frequently show significant differences, particularly at sub-MeV energies. We found discrepancies in the structures observed by different spacecraft which cannot always be attributed to the latitudinal separation or to changes in the coronal hole which generates the high-speed stream. We present several cases where these differences are linked to the presence of Interplanetary Coronal Mass Ejections (ICMEs) or small-scale interplanetary transients in the vicinity of or embedded within the CIR. Evidence of the possible role of ICME-CIR interactions as sources of temporal variations in the CIR-associated ion increases are presented and discussed.
► Multi-s/c observations of CIRs are presented for Carrington rotations 2067–2082. ► Events showing evolution during co-rotation from STEREO B to STEREO A are analyzed. ► Transients/ICMEs near or embedded within the CIR are a source of temporal evolution. ► This interaction could favor the formation of shocks and thus enhance ion acceleration.
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