Solar energetic particle time series analysis with Python

Solar Energetic Particles (SEPs) are charged particles accelerated within the solar atmosphere or the interplanetary space by explosive phenomena such as solar flares or Coronal Mass Ejections (CMEs). Once injected into the interplanetary space, they can propagate towards Earth, causing space weather related phenomena. For their analysis, interplanetary in situ measurements of charged particles are key. The recently expanded spacecraft fleet in the heliosphere not only provides much-needed additional vantage points, but also increases the variety of missions and instruments for which data loading and processing tools are needed. This manuscript introduces a series of Python functions that will enable the scientific community to download, load, and visualize charged particle measurements of the current space missions that are especially relevant to particle research as time series or dynamic spectra. In addition, further analytical functionality is provided that allows the determination of SEP onset times as well as their inferred injection times. The full workflow, which is intended to be run within Jupyter Notebooks and can also be approachable for Python laymen, will be presented with scientific examples. All functions are written in Python, with the source code publicly available at GitHub under a permissive license. Where appropriate, available Python libraries are used, and their application is described.</p

Multipoint Observations of the June 2012 Interacting Interplanetary Flux Ropes

We report a detailed analysis of interplanetary flux ropes observed at Venus and subsequently at Earth's Lagrange L1 point between June 15 and 17, 2012. The observation points were separated by about 0.28 AU in radial distance and 5 degrees in heliographic longitude at this time. The flux ropes were associated with three coronal mass ejections (CMEs) that erupted from the Sun on June 12-14, 2012 (SOL2012-06-12, SOL2012-06-13, and SOL2012-06-14). We examine the CME-CME interactions using in-situ observations from the almost radially aligned spacecraft at Venus and Earth, as well as using heliospheric modeling and imagery. The June 14 CME reached the June 13 CME near the orbit of Venus and significant interaction occurred before they both reached Earth. The shock driven by the June 14 CME propagated through the June 13 CME and the two CMEs coalesced, creating the signatures of one large, coherent flux rope at L1. We discuss the origin of the strong interplanetary magnetic fields related to this sequence of events, the complexity of interpreting solar wind observations in the case of multiple interacting CMEs, and the coherence of the flux ropes at different observation points.Peer reviewe

Imprints of long-term solar variability on cosmic rays and terrestrial archives

Abstract Galactic cosmic rays (GCRs) arriving at Earth, interact with nuclei of atmospheric gases leading to the production of cosmogenic radionuclides. The latter, following a series of processes, are eventually stored in terrestrial archives such as ice cores and tree rings. The information that can be collected, traces back millions of years. Since the solar activity has a large impact on GCRs, via modulation processes in the heliosphere, one can gain knowledge about the solar activity in the past using the cosmogenic radionuclide records. The primary goal of our study is to reconstruct the solar activity in the past combining all the available information from different cosmogenic radionuclides and databases obtained from different locations on Earth. The principle idea is that, using terrestrial archives and existing models of radionuclide production, the GCR flux can be reconstructed over the past millennia. Thereafter, the solar activity, after applying a model correlating the GCR flux to different solar parameters, can be reconstructed. To achieve this it was necessary to develop an empirical model reconstructing the tilt angle of the Heliospheric Current Sheet (HCS), one of the important heliospheric factors influencing cosmic ray propagation inside the heliosphere. The HCS tilt has been traced with observations since 1976. Following, a semi-empirical model of GCR modulation in the heliosphere was developed using measurements and reconstructions of the heliospheric parameters that play a major role in the modulation processes. In particular these are the open solar magnetic flux, the solar magnetic polarity and the HCS tilt angle. With this model the cosmic ray variability on Earth in millennial time scales was reconstructed and used as an input parameter in existing models, calculating the production and deposition of the cosmogenic radionuclides ¹⁴C and ¹⁰Be. The results were then compared with the data aiming to achieve the best fit that will lead to best reconstruction of the solar activity

Analysis of Ground-Level Enhancements:strong events are hard

Abstract Ground Level Enhancements (GLEs) recorded by neutron monitor detectors are characterized by a variety of energy spectra of solar energetic particles (SEP), which vary between soft (as in August 1972) and hard (February 1956) ones. The aim of this work is to investigate the statistical relation between the hardness of the energy spectra and the event-integrated intensity. We calculated the event-integrated omnidirectional fluence of protons above 30 MeV (F₃₀) and above 200 MeV (F₂₀₀) using energy spectra reconstructed from both ground-based and space-borne data. The ratio of the F₃₀-to-F₂₀₀ fluences is considered as an index of the hardness of the events spectra. The main results of this study is that all strong events (with the event-integrated intensity greater than 100%*hr) are characterized by a hard or very hard spectrum, while weak and moderate events do not show any clear pattern between the hardness and the intensity of the event

Solar energetic-particle ground-level enhancements and the solar cycle

Abstract Severe geomagnetic storms appear to be ordered by the solar cycle in a number of ways. They occur more frequently close to solar maximum and the declining phase, are more common in larger solar cycles, and show different patterns of occurrence in odd- and even-numbered solar cycles. Our knowledge of the most extreme space-weather events, however, comes from spikes in cosmogenic-isotope (14C, 10Be, and 36Cl) records that are attributed to significantly larger solar energetic-particle (SEP) events than have been observed during the space age. Despite both storms and SEPs being driven by solar-eruptive phenomena, the event-by-event correspondence between extreme storms and extreme SEPs is low. Thus, it should not be assumed a priori that the solar-cycle patterns found for storms also hold for SEPs and the cosmogenic-isotope events. In this study, we investigate the solar-cycle trends in the timing and magnitude of the 67 SEP ground-level enhancements (GLEs) recorded by neutron monitors since the mid-1950s. Using a number of models of GLE-occurrence probability, we show that GLEs are around a factor of four more likely around solar maximum than around solar minimum, and that they preferentially occur earlier in even-numbered solar cycles than in odd-numbered cycles. There are insufficient data to conclusively determine whether larger solar cycles produce more GLEs. Implications for putative space-weather events in the cosmogenic-isotope records are discussed. We find that GLEs tend to cluster within a few tens of days, likely due to particularly productive individual active regions, and with approximately 11-year separations, owing to the solar-cycle ordering. However, these timescales would not explain any cosmogenic-isotope spikes requiring multiple extreme SEP events over consecutive years

Assessment of different sunspot number series using the cosmogenic isotope ⁴⁴Ti in meteorites

Abstract Many sunspot number series exist suggesting different levels of solar activity during the past centuries. Their reliability can be assessed only by comparing them with alternative indirect proxies. We test different sunspot number series against the updated record of cosmogenic radionuclide ⁴⁴Ti measured in meteorites. Two bounding scenarios of solar activity changes have been considered: the HH-scenario (based on the series by Svalgaard and Schatten), in particular, predicting moderate activity during the Maunder minimum, and the LL-scenario (based on the RG series by Lockwood et al.) predicting moderate activity for the 18th–19th centuries and the very low activity level for the Maunder minimum. For each scenario, the magnetic open solar flux, the heliospheric modulation potential and the expected production of ⁴⁴Ti were computed. The calculated production rates were compared with the corresponding measurements of ⁴⁴Ti activity in stony meteorites fallen since 1766. The analysis reveals that the LL-scenario is fully consistent with the measured ⁴⁴Ti data, in particular, recovering the observed secular trend between the 17th century and the Modern grand maximum. On the contrary, the HH-scenario appears significantly inconsistent with the data, mostly due to the moderate level of activity during the Maunder minimum. It is concluded that the HHscenario sunspot number reconstruction significantly overestimates solar activity prior to the mid-18th century, especially during the Maunder minimum. The exact level of solar activity after 1750 cannot be distinguished with this method, since both H- and L- scenarios appear statistically consistent with the data

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 (less than or similar to 1AU) heliosphere. Relativistic electrons as well as protons with energies >50MeV 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 degrees in longitude close to 1AU. 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 di ffusive propagation processes are likely involved.Peer reviewe