Understanding Solar Energetic Proton Effects in Space and Ground-level from GPS-based Measurements
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Heliospheric and Magnetospheric Physics↗
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Predicting cutoff L-shells of solar protons using the GPPSn particle dataset
Solar energetic protons (SEPs) arriving at the Earth trigger severe radiation storms in the near-Earth space, directly impacting space missions operating at various altitudes. Therefore, monitoring SEP events and predicting the penetration depths of solar protons are critical for aerospace sectors. Building on previous efforts, here we demonstrate the feasibility of using proton measurements from the Global Prompt Proton Sensor network (GPPSn), enabled by Los Alamos National Laboratory developed combined X-ray dosimeters aboard GPS satellites, to characterize and predict the penetration of solar protons into the geomagnetic field. The inclined medium-Earth-orbits (MEOs) of the global GPS constellation offer a unique advantage of allowing simultaneous measurements of penetrating solar protons inside both open- and closed-field line regions. Therefore, the L-profiles of ∼10s–100 MeV solar protons and their associated cutoff L-shells can be determined from the GPPSn dataset, using predefined threshold proton flux values rather than traditional flux ratios. After examining a list of SEP event intervals across solar cycles 23, 24 and 25—including the 2024 Mother’s Day superstorm, we showcase how the latest GPPSn proton dataset (release v1.10), reprocessed and calibrated, can not only be used to monitor solar proton distributions inside the dynamic geomagnetic field for individual events, but also to derive a new empirical model linking cutoff L-shells with several key space weather parameters. This newly developed SEPCL-MEO model demonstrates high predictive performance; for example, predictions for > 30 MeV solar protons yield a correlation coefficient of 0.85 and performance efficiency of 0.67 when validated against GPPSn observations. Results from this pilot study underscores the scientific and operational value of the GPPSn dataset, and this dataset—when paired with machine-learning techniques—can play a critical role in observing and predicting the effects of future incoming SEP events, including extreme ones.
58 GEOSCIENCES↗
Parker Solar Probe Observations of Solar Wind Energetic Proton Beams Produced by Magnetic Reconnection in the Near‐Sun Heliospheric Current Sheet
We report observations of reconnection exhausts in the Heliospheric Current Sheet (HCS) during Parker Solar Probe Encounters 08 and 07, at 16 Rs and 20 Rs, respectively. Heliospheric current sheet (HCS) reconnection accelerated protons to almost twice the solar wind speed and increased the proton core energy by a factor of ∼3, due to the Alfvén speed being comparable to the solar wind flow speed at these near-Sun distances. Furthermore, protons were energized to super-thermal energies. During E08, energized protons were found to have leaked out of the exhaust along separatrix field lines, appearing as field-aligned energetic proton beams in a broad region outside the HCS. Concurrent dropouts of strahl electrons, indicating disconnection from the Sun, provide further evidence for the HCS being the source of the beams. Around the HCS in E07, there were also proton beams but without electron strahl dropouts, indicating that their origin was not the local HCS reconnection exhaust.
T D Phan↗
Energetic protons from the solar flare of March 24, 1966.
Energetic protons from March 24, 1966 solar flare observed with OGO 1 satellite scintillation counter
PROTON ENERGY↗
Injection and diffusive transport of suprathermal through energetic solar flare protons (35 keV to 20 MeV)
Consideration is given to the injection and interplanetary propagation of low-energy protons caused by the solar particle event of July 20, 1981, in which flare protons in the range from 35 keV to 20 MeV were observed by instruments on ISEE 3. The observed time-intensity and time-anisotropy profiles were fitted over the entire energy range using a model based on the spherically symmetric Fokker-Plank equation, including convection, diffusion, and adiabatic deceleration. The results are used to discuss the behavior of the radial interplanetary diffusion coefficient and the scattering mean free path for protons. Also, evidence is found for diffusive coronal shock acceleration of protons during the event.
Beeck, J.↗
Predicting Well-Connected SEP Events from Observations of Solar EUVs and Energetic Protons
This study shows a quantitative assessment of the use of Extreme Ultraviolet (EUV) observations in the prediction of Solar Energetic Proton (SEP) events. The UMASEP scheme (Space Weather, 9, S07003, 2011; 13, 2015, 807-819) forecasts the occurrence and the intensity of the first hours of SEP events. in order to predict well-connected events, this scheme correlates Solar Soft X-rays (SXR) with differential proton fluxes of the GOES satellites. In this study, we explore the use of the EUV time history from GOES-EUVS and SDO-AIA instruments in the UMASEP scheme. This study presents the results of the prediction of the occurrence of well-connected >10 MeV SEP events, for the period from May 2010 to December 2017, in terms of Probability of Detection (POD), False Alarm Ratio (FAR), Crticial Success Index (CSI), and the average and median of the warning times. The UMASEP/EUV-based models were calibrated using GOES and SDO data from May 2010 to October 2014, and validated using out-of-sample SDO data from November 2014 to December 2017. The best results were obtained by those models that used EUV data in the range 50-340 angstroms. We conclude that the UMASEP/EUV-based models yield similar or better POD results, and similar or worse FAR results, than those of the current real-time UMSEP/SXR-based model. The reason for the higher POD of the UMASEP/EUV-based models in the range of 50-340 angstroms was due to the high percentage of successful predictions of well-connected SEP events associated with 10 MeV SEP events, improves the overall performance, obtaining a POD of 92.9% (39/42) compared with 81% (34/42) of the current tool, and a slightly worse FAR of 31.6% (18/57) compared with 29.2% (14/58) of the current tool.
Nunez, Marlon↗
Revealing the Formation of the <20 MeV Inner Proton Radiation Belt at L ∼ 2 During the 10–11 May 2024 Superstorm
A new proton radiation belt was identified during the geomagnetic superstorm of 10–11 May 2024. To investigate its origin, we use an MHD-test particle simulation to model solar energetic proton (SEP) trapping and the evolution of the initial trapped proton population during the storm. The simulation weights the injected SEP population with interplanetary proton measurements and the initial trapped proton radial profile with energy-resolved Weather System Follow-on-Microwave (WSF-M) proton data, enabling quantitative comparison with observations. Results show that SEP contributions are minimal; the new ∼2–18 MeV belt at L ∼ 2 forms mainly through redistribution and energization of the initial trapped population within hours of the CME shock, driven by subsequent electric field impulses, rather than the initial shock alone. These results provide quantitative evidence based on realistic, plasma-dependent field dynamics and significantly advance understanding of inner radiation belt formation.
79 ASTRONOMY AND ASTROPHYSICS↗
Deep Dielectric Charging of Spacecraft Polymers by Energetic Protons
The majority of research in the field of spacecraft charging concentrates on electron charging effects with little discussion of charging by protons. For spacecraft orbiting in the traditional LEO and GEO environments this emphasis on electrons is appropriate since energetic electrons are the dominant species in those orbits. But for spacecraft in orbits within the inner radiation belts or for interplanetary and lunar space probes, proton charging (center dot) effects may also be of concern. To examine bulk spacecraft charging effects in these environments several typical highly insulating spacecraft polymers were exposed to energetic protons (center dot) with energies from 1 Me V to lO Me V to simulate protons from the solar wind and from solar energetic proton events. Results indicate that effects in proton charged dielectrics are distinctly different than those observed due to electron charging. In most cases, the positive surface potential continued to increase for periods on the order of minutes to a day, followed by long time scale decay at rates similar to those observed for electron charging. All samples charged to positive potentials with substantially lower magnitudes than for equivalent electron doses. Possible explanations for the different behavior of the measured surface potentials from proton irradiation are discussed; these are related to the evolving internal charge distribution from energy dependent electron and proton transport, electron emission, charge migration due to dark current and radiation induced conductivity, and electron capture by embedded protons.
radiation induced conductivity↗
SCR neon and argon in Kapoeta feldspar: Evidence for an active ancient Sun
From etched feldspar size-fractions of Kapoeta, we determine a significant excess of cosmogenic Ne-21 and Ar-38 over that produced by galactic cosmic rays. This excess component is attributed to early production by energetic solar protons and suggest that the energetic proton flux from the ancient Sun was several hundred times more intense than that of the contemporary Sun.
Rao, M. N.↗
Solar flare nuclear gamma-rays and interplanetary proton events
Gamma-ray line (GRL) and solar energetic proton (SEP) events observed from February 1980 through January 1985 are compared in order to substantiate and better characterize the lack of correlation between GRL fluences and SEP event peak fluxes. The scatter plot of SEP event peak flux vs. GRL fluence is presented, and the ratio of 'solar' to 'interplanetary', about 10 MeV protons, is presented. It is shown that, while even large SEP events can originate in flares lacking detectable GRL emission, the converse case of flares with a significant GRL line fluence by lacking protons in space is rare. The ratio R of the number of about 10 MeV protons that produce GRL emission at the flare site to the number of about 10 MeV protons detected in space can vary from event to event by four orders of magnitude. There is a clear tendency for impulsive flares to have larger values of R than long-duration flares, where the flare time scale is given by the e-folding decay time of the associated soft X-ray emission.
Cliver, E. W.↗
The Mechanism Responsible for High Concentrations of Be-7 in the Near Space
In 1990 an unexpectedly high concentration of Be-7 was discovered on the LDEF satellite surface, facing in the RAM direction. The search for an explanation of this high concentration of Be-7 which is in thermal equilibrium in the upper atmosphere, led the researchers to the hypothesis of Be-7 transport by vertical turbulent fluxes from deeper layers in the Earth's atmosphere, where Be-7 is produced as a result of nuclear reactions between solar energetic protons (which penetrated there after a solar flare) and terrestrial atmosphere elements. The experiments carried out during 1995-1999 on 'Resource F1' and 'Cosmos' satellites not only confirmed the existence of high Be-7 concentrations at altitudes of about 200 km, but also permitted to establish correlation between the concentration of Be-7 in the upper atmosphere and flare activity on the Sun. More detailed analysis of the whole set of experimental data on Be-7 measurements at satellite altitudes showed, that the appearance of high Be-7 concentrations in the upper atmosphere of the Earth is a more complicated phenomenon. Two more mechanisms , explaining the observed effect can be indicated. Firstly, the observed concentrations could be associated with direct penetration of energetic Be-7 nuclei, originating in flares, into the terrestrial atmosphere. Calculations show, that in solar cosmic rays the flux of Be-7 nuclei should be maximum in comparison to the fluxes of other Beryllium isotopes. Secondly, the high concentration of Be-7 in the upper atmosphere of the Earth could be explained by solar wind penetration through the polar zones. Theoretical analysis of active processes including flares, occurring in the solar atmosphere, leads to the conclusion, that radioactive Beryllium is constantly present in the solar atmosphere, and, possibly, is the main isotope of solar Beryllium.
Panasyuk, M. I.↗
Correlation of Upper-Atmospheric 7-Be with Solar Energetic Particle Events
A surprisingly large concentration of radioactive 7-Be was observed in the upper atmosphere at altitudes above 320 km on the LDEF satellite that was recovered in January 1990. We report on follow-up experiments on Russian spacecraft at altitudes of 167 to 370 km during the period of 1996 to 1999, specifically designed to measure 7-Be concentrations in low earth orbit. Our data show a significant correlation between the 7-Be concentration and the solar energetic proton fluence at Earth, but not with the overall solar activity. During periods of low solar proton fluence, the concentration is correlated with the galactic cosmic ray fluence. This indicates that spallation of atmospheric N by both solar energetic particles and cosmic rays is the primary source of 7-Be in the ionosphere.
Phillips, G. W.↗
Solar flare nuclear gamma rays and interplanetary proton events
We compared flare gamma ray line (GRL) events and solar energetic proton (SEP) events for the period from Feb. 1980 - Jan. 1985 and substantiated earlier results showing a lack of correlation between gamma-ray-producing ions and interplanetary protons. This poor correlation results primarily from several large SEP events that originated in flares without detectable gamma ray emission. The converse case of GRL events unassociated with SEP events is rare. We present evidence which suggests that the ratio of trapped to escaping protons in GRL/SEP flares depends on the spatial scale size of the flare. We affirm the result of Bai and Dennis (1985) that GRL flares are generally accompanied (75 percent) by metric Type 2 bursts.
Cliver, E. W.↗
Prediction of Solar Energetic Particle Event Peak Proton Intensity Using a Simple Algorithm Based on CME Speed and Direction and Observations of Associated Solar Phenomena
We assess whether a formula obtained by Richardson et al. (2014,https://doi.org/10.1007/s11207-014-0524-8) relating the peak intensity of 14- to 24-MeV protons in a solar energetic particle (SEP) event at 1 AU to the solar event location and the speed of the associated coronal mass ejection (CME) may be used in a scheme to predict the intensity of an SEP event at any location at this heliocentric distance. Starting with all 334 CMEs in the CCMC/SWRC DONKI database in October 2011 to July 2012, we use the CME speed and direction to predict the proton intensity at Earth and the two Solar Terrestrial Relations Observatory spacecraft using this formula. Since most (85%)of these CMEs were not in fact associated with SEP events, many SEP events are predicted that are not actually observed. Such cases may be reduced by considering whether type II or type III radio emissions accompany the CMEs, or by selecting faster, wider CMEs. This method is also applied to predict the SEP intensities associated with 1,100 CMEs observed by the Solar and Heliospheric Observatory Large Angle and Spectrometric Coronagraph during 1997-2006 in solar cycle 23. Various skill scores are calculated, which assess different aspects of the skill of the SEP predictions. We conclude that the Richardson et al. (2014) formula has potential as a simple empirical SEP intensity prediction tool.
coronal mass ejections↗
Solar Particle Event Modeling Compared To Satellite Data
Solar protons are the primary source of ionizing radiation for certain missions. Several models of these solar energetic proton events exist, giving different results. We compare three models with satellite data to assess these differences.
Alexander Henderson↗
On the Onset Delays of Solar Energetic Electrons and Protons: Evidence for a Common Accelerator
The processes responsible for the acceleration of solar energetic particles (SEPs) are still not well understood, including whether SEP electrons and protons are accelerated by common or separate processes. Using a numerical particle transport model that includes both pitch-angle and perpendicular spatial diffusion, we simulate, among other quantities, the onset delay for MeV electrons and protons and compare the results to observations of SEPs from widely separated spacecraft. Such observations have previously been interpreted, in a simple scenario assuming no perpendicular diffusion, as evidence for different electron and proton sources. We show that, by assuming a common particle source together with perpendicular diffusion, we are able to simultaneously reproduce the onset delays for both electrons and protons. We argue that this points toward a common accelerator for these particles. Moreover, a relatively broad particle source is required in the model to correctly describe the observations. This is suggestive of diffusive shock acceleration occurring at large shock structures playing a significant role in the acceleration of these SEPs.
R D Strauss↗
Correlation of Upper-Atmospheric Be-7 With Solar Energetic Particle Events
Surprisingly large concentrations of radioactive Be-7 have been found in the upper atmosphere at levels of one to three orders of magnitude greater than observed in the stratosphere. This phenomenon was originally observed on the LDEF satellite which was recovered in January 1990 following a period of extremely high solar activity in the fall of 1989. We report on follow-up measurements on the Russian COSMOS and RESURS F1 spacecraft during the period of 1996 to 1999 which was a period of minimal to moderate solar activity. The Be-7 concentrations observed on these flights were down substantially from the LDEF observations but were still one to two orders of magnitude higher than stratospheric levels. A significant correlation is observed between the Be-7 activity and the combined fluence of solar energetic protons (SEP) and galactic cosmic-ray (GCR) protons. The Be-7 activity is not correlated with overall solar activity as represented by the solar x-ray flux. We discuss possible mechanisms for the solar proton correlation. However, it is likely that the Be-7 is ionized and it is unknown how this will affect the calculations. There were several large solar flares in the fall of 1989 that produced extraordinarily intense solar particle events at the Earth and record geophysical disturbances. These may have acted to increase production of Be-7 from spallation in the stratosphere and also to enhance transport to higher altitudes from the effects of heating and expansion of the upper atmosphere. Be-7 in the upper atmosphere may also have been produced directly at the Sun. Be-7 and Li-7 are produced in solar flares when accelerated alpha-particles fuse with He-4 in the solar atmosphere. Under optimistic assumptions for Sun to Earth transport and subsequent insertion into low Earth orbit, a Be-7 density of about 10(exp -7) atom/cubic cm at 310 km is estimated.
Phillips, G. W.↗
Space radiation incident on SATS missions
A special orbital radiation study was conducted in order to evaluate mission encountered energetic particle fluxes. This information is to be supplied to the project subsystem engineers for their guidance in designing flight hardware to withstand the expected radiation levels. Flux calculations were performed for a set of 20 nominal trajectories placed at several altitudes and inclinations. Temporal variations in the ambient electron environment were considered and partially accounted for. Magnetic field calculations were performed with a current field model, extrapolated to the tentative SATS launch epoch with linear time terms. Orbital flux integrations ware performed with the latest proton and electron environment models, using new computational methods. The results are presented in graphical and tabular form. Estimates of energetic solar proton fluxes are given for a one year mission at selected integral energies ranging from 10 to 100 Mev, calculated for a year of maximum solar activity during the next solar cycle.
Stassinopoulos, E. G.↗