Solar Proton Fluence Research Articles

Comparison of JPL and ESP Solar Proton Fluence Models Using the Background‐Subtracted RDSv2.0 Data Set

AbstractHigh energy protons from solar energetic particle (SEP) events are a hazard to spacecraft systems and instruments. For interplanetary and geosynchronous‐Earth‐orbiting spacecraft, a mission's cumulative SEP fluence is an important consideration for hardware design. The total solar proton fluence for a mission can be dominated by a small number of very high‐fluence events. Because of the sporadic and unpredictable nature of these large events, data sets collected over multiple solar cycles are needed to construct a statistical model that can predict a mission's risk of seeing a given fluence exposure during its mission. Several statistical models have been developed, including the JPL model and the Emission of Solar Protons (ESP) model. The models produce somewhat different results, which could be due in part to the different data sets from which they were derived. To understand the sensitivity of predicted mission fluence to the choice of data set and to the statistical distribution to which that data set is fit, we present a comparison of the JPL and ESP cumulative fluence models as reformulated from the same SEP data set, a background‐subtracted version of the Reference Data Set Version 2.0 (RDSv2.0) based on data from IMP‐8 and GOES, covering 41 years of SEP events from 1974 to 2015 with proton energies between 5 and 289 MeV. The comparisons show that different modeling approaches can produce a factor of 2 or greater difference in the mission fluences even when the same data set is used for model development.

Two solar proton fluence models based on ground level enhancement observations

Solar energetic particles (SEPs) constitute an important component of the radiation environment in interplanetary space. Accurate modeling of SEP events is crucial for the mitigation of radiation hazards in spacecraft design. In this study we present two new statistical models of high energy solar proton fluences based on ground level enhancement (GLE) observations during solar cycles 19–24. As the basis of our modeling, we utilize a four parameter double power law function (known as the Band function) fits to integral GLE fluence spectra in rigidity. In the first model, the integral and differential fluences for protons with energies between 10 MeV and 1 GeV are calculated using the fits, and the distributions of the fluences at certain energies are modeled with an exponentially cut-off power law function. In the second model, we use a more advanced methodology: by investigating the distributions and relationships of the spectral fit parameters we find that they can be modeled as two independent and two dependent variables. Therefore, instead of modeling the fluences separately at different energies, we can model the shape of the fluence spectrum. We present examples of modeling results and show that the two methodologies agree well except for a short mission duration (1 year) at low confidence level. We also show that there is a reasonable agreement between our models and three well-known solar proton models (JPL, ESP and SEPEM), despite the differences in both the modeling methodologies and the data used to construct the models.

Database of episode-integrated solar energetic proton fluences

A new database of proton episode-integrated fluences is described. This database contains data from two different instruments on multiple satellites. The data are from instruments on the Interplanetary Monitoring Platform-8 (IMP8) and the Geostationary Operational Environmental Satellites (GOES) series. A method to normalize one set of data to one another is presented to create a seamless database spanning 1973 to 2016. A discussion of some of the characteristics that episodes exhibit is presented, including episode duration and number of peaks. As an example of what can be understood about episodes, the July 4, 2012 episode is examined in detail. The coronal mass ejections and solar flares that caused many of the fluctuations of the proton flux seen at Earth are associated with peaks in the proton flux during this episode. The reasoning for each choice is laid out to provide a reference for how CME and solar flares associations are made.

Associations of morbidity and mortality from coronary heart disease with heliogeophysical factors.

The aim of this study was to evaluate the associations among morbidity of acute myocardial infarction (AMI) and mortality from ischemic heart disease (IHD) with heliogeophysical factors among the Kaunas population. The study population was stratified into three age categories: 25-54, 55-64, and ≥65years. In this study, solar flares (SF), solar proton fluences (SPF), and geomagnetic activity (GMA) were employed as heliogeophysical factors and used Poisson regression and two methods of time series modeling (lag and lead). Influence of GMA in different age and sex category is uneven. The mean number of AMI events per day was greatest (23%) among men aged 25-54years on the third day and the same sex aged 55-64years-increased 10% 2days before when the GMA intensity was A+S. Both for men and women aged ≥65years, the highest increase in the mean number of deaths from IHD events per day was observed on the second day when the GMA intensity was A+S-51 and 34%, respectively. Evaluating the impact of SF of 10(-5)≤SF<10(-4)W/m(2) (M+X) intensity, the mean number of AMI events per day was greatest for 55-64-year-old women and men on the same and second days. Such SF were associated with a 13 and 20% increase, respectively. Evaluating the impact of large fluence SPF, it was determined that the increase in the mean number of AMI events per day among 25-54-year-old men was greatest (30%) 1day, and death from IHD (54%) was observed among women aged ≥65years 2days before the energy of the SPF has increased.

Atmospheric impact of the Carrington event solar protons

The Carrington event of August/September 1859 was the most significant solar proton event (SPE) of the last 450 years, about four times larger than the solar proton fluence of the largest event from the “spacecraft era” (August 1972). Recently, much attention has focused upon increasing our understanding of the Carrington event, in order to better quantify the impact of extreme space weather events. In this study the Sodankylä Ion and Neutral Chemistry (SIC) model is used to estimate the impact of the Carrington event to the neutral atmosphere and the ionosphere, and the disruption to HF communication. We adopt a reported intensity‐time profile for the solar proton flux and examine the relative atmospheric response to different SPE‐energy spectra, and in particular, the comparatively soft energy spectrum of the August 1972 or March 1991 SPE which is believed to provide the best representation of the Carrington event. Our calculations indicate that large changes in electron density and atmospheric constituents occur during the period of SPE forcing, depending upon the nature of the spectrum and also on the hemisphere considered. However, the most important SPE‐driven atmospheric response is an unusually strong and long‐lived Ox decrease in the upper stratosphere (Ox levels drop by ∼40%) primarily caused by the very large fluxes of &gt;30 MeV protons. This depletion is an indication of the extreme changes possible for the largest SPE. We find that there are comparatively small long‐term differences in the atmospheric and ionospheric response between the 3 suggested SPE spectra.

Interplanetary proton cumulated fluence model update

Solar particle events leading to important increase of particle fluxes at energies of order of magnitude ranging from MeV to GeV constitute an important hazard for space missions. They may lead to effects seen in microelectronics or damage to solar cells and constitute a potential hazard for manned missions. Cumulative damage is commonly expressed as a function of fluence which is defined as the integral of the flux over time. A priori deterministic estimates of the expected fluence cannot be made because over the time scale of a space mission, the fluence can be dominated by the contribution of a few rare and unpredictable high intensity events. Therefore, statistical approaches are required in order to estimate fluences likely to be encountered by a space mission in advance. This paper extends work done by Rosenqvist et al. [Rosenqvist, L., Hilgers, A., Evans, H., Daly, E., Hapgood, M., Stamper, R., Zwickl, R., Bourdarie, S., Boscher, D. Toolkit for updating interplanetary proton-cumulated fluence models. J. Spacecraft Rockets, 42(6), 1077–1090, 2005] to describe an updated predictive engineering model for the proton interplanetary fluence with energies >30 MeV. This model is derived from a complete list of solar proton fluences based on data from a number of calibrated sources covering almost three solar cycles.

A theoretical model of the inner proton radiation belt

A theoretical calculation provides inner radiation belt proton intensities as a function of time and of the three adiabatic invariants, M, K, and L, in the kinetic energy range from ∼10 MeV to ∼4 GeV and the L range from 1.1 to 2.4. Long residence times for trapped protons of up to several thousand years require similarly long input time series for the geomagnetic field, solar activity, and solar proton fluences. Additional inputs include galactic cosmic ray spectra, nuclear scattering cross sections, and the neutral and plasma densities in the atmosphere, ionosphere, and plasmasphere. Trapped proton sources are cosmic ray albedo neutron decay (CRAND), calculated from a Monte Carlo particle transport simulation, and solar proton injection using a derived empirical injection efficiency that is ∼10−4 at 10 MeV. Radial diffusion provides inward transport of injected solar protons. Calculated intensities at energies ≲100 MeV and for L ≳ 1.3 are dominated by solar protons, CRAND being the dominant source otherwise. Losses are by ionization of the neutral atmosphere, energy transfer to plasma electrons, and inelastic nuclear scattering. Numerical trajectory tracing determines trapping limits and drift shell averages of the albedo neutron intensity and of neutral and plasma densities for loss rate calculations. Geomagnetic secular variations cause adiabatic energy and drift shell changes. Intensities are greater than they would be in a constant geomagnetic field by factors up to ∼10, a result of long proton residence times and the presently decreasing geomagnetic dipole moment.

The Carrington event: Possible solar proton intensity–time profile

A possible >30 MeV solar proton intensity–time profile associated with the Carrington solar flare event of 1 September 1859 is constructed. The derived profile is consistent with a >30 MeV proton omni-directional fluence of 1.9 × 10 10 cm −2 found by the analysis of solar proton generated NOy radicals that are deposited in polar ice. The intensity–time profile of the solar particle flux is constructed by assuming that the Carrington solar event is part of the class of interplanetary shock-dominated events where the maximum particle flux is observed as the shock passes the Earth. This assumption is based on the knowledge that the very large solar proton fluence events (those with >30 MeV omni-directional fluence exceeding 1.0 × 10 9 cm −2) associated with central meridian solar activity during the last 50 years belong to this class of event. The absence of a statistically significant increase in the observed concentration of the cosmogenic nuclide 10Be for 1859 indicates that the solar cosmic radiation produced in the Carrington event had a soft spectrum, similar to other interplanetary shock-dominated events.

Two groups of extremely large >30 MeV solar proton fluence events

The very large solar proton events, those having an omni-directional solar proton fluence greater than 10 9 cm −2 at energies >30 MeV, are the events that impose operational constraints on manned space missions and equipment. A systematic survey of these very large omni-directional fluence solar proton events shows an association with two solar source group locations. One group is the classical situation, where the spacecraft is well connected to the solar active region by the interplanetary magnetic field. The other and most often-occurring group is the interplanetary shock dominated event resulting from a fast coronal mass ejection (CME) shock near the location of the spacecraft-Sun line. This result is consistent with observations of solar particle data from Earth-orbiting spacecraft for the last 4 solar cycles and also with Earth-based observations of very large solar particle events for the last 7 solar cycles. We now have an ∼450-year record of these very large solar proton events from the analysis of the impulsive nitrate deposition events found in polar ice. The frequency distribution of these large events is consistent with the frequency distribution derived from the analysis of radionuclides found in moon rocks. These frequency distributions show that solar proton events with > 30 MeV omni-directional fluence exceeding 6 × 10 9 cm −2 are very rare.

Solar proton events for 450 years: The Carrington event in perspective

Using high resolution measurements of the impulsive nitrate events in polar ice as identifiers of solar proton events in the past, we have identified 19 events over the period 1561–1950 that equal or exceed the >30 MeV fluence measured during the August 1972 episode of solar proton events. The largest nitrate impulsive deposition event (and largest solar proton fluence above 30 MeV) occurred in late 1859 in time association with the Carrington flare of September 1859. The Carrington flare occurred near the central meridian of the sun; the interplanetary disturbance associated with the solar activity rapidly traveled toward the earth resulting in an extremely large geomagnetic storm commencing within 17.1 h of the visual observation of the solar flare. While this event was remarkable by itself, historical records indicate that the Carrington event was part of a sequence of solar activity as an active region traversed the solar disk. We compare the derived omni-directional solar proton fluence for the Carrington event of 1.9 × 10 10 cm −2 above 30 MeV with the solar proton fluence from the past and from more recent episodes of solar activity. The Carrington event is the largest solar proton event identified in our ∼450 year period, having almost twice the >30 MeV solar proton fluence than the second largest event in 1895, and approximately four times the solar proton fluence of the August 1972 events.

The 1859 Solar–Terrestrial Disturbance And the Current Limits of Extreme Space Weather Activity

It is generally appreciated that the September 1859 solar–terrestrial disturbance, the first recognized space weather event, was exceptionally large. How large and how exceptional? To answer these questions, we compiled rank order lists of the various measures of solar-induced disturbance for events from 1859 to the present. The parameters considered included: magnetic crochet amplitude, solar energetic proton fluence (McCracken et al., 2001a), Sun–Earth disturbance transit time, geomagnetic storm intensity, and low-latitude auroral extent. While the 1859 event has close rivals or superiors in each of the above categories of space weather activity, it is the only documented event of the last ∼150 years that appears at or near the top of all of the lists. Taken together, the top-ranking events in each of the disturbance categories comprise a set of benchmarks for extreme space weather activity.

The Use of Geophysical Data in Studies of the Historical Solar-Terrestrial Environment

Recent studies of the solar-terrestrial environment for the past 500 years have necessitated the use of a variety of historical databases: nitrates in ice cores, knowledge of large volcanic eruptions, sunspot numbers, mid-latitude aurora and geomagnetic records. The nitrate data are being used to identify large solar proton fluence events. The volcanic record helps to provide time markers for the ice core. The records of major geomagnetic storms and mid-latitude aurora have been used for additional identification. We also know that the Earth’s magnetic field is evolving with a present rapid decrease in magnitude. In addition the wandering magnetic pole must be considered in ascertaining what was “mid latitude” in historic times versus “mid latitude” in 2000. We illustrate how these databases are being used in recent studies of historic solar proton events.

Sensitivity of a statistical solar proton fluence model to the size of the event data set

Statistical models of high‐energy (typically above 10 MeV) solar proton fluences are needed to assess a broad range of cumulative effects observed in the solar system. Most models rely on a description of event fluences and occurrence based on a compound Poisson process for which the parameters are derived from observations. In this paper the effect of the size of the observation data set on the prediction of cumulated fluence by such models is assessed. The study shows that with the current size of the event data set of Solar Proton Events (about a couple of hundred events) the estimated parameters used as input to the model may lead to significant errors on the prediction of the quantiles of the fluence probability distribution function. Furthermore, it is shown that no significant accuracy improvement is expected unless the data set contains a much larger number of events (typically one thousand), which requires a long‐term data acquisition infrastructure.

Solar cosmic ray events for the period 1561–1994: 1. Identification in polar ice, 1561–1950

The geophysical significance of the thin nitrate‐rich layers that have been found in both Arctic and Antarctic firn and ice cores, dating from the period 1561–1991, is examined in detail. It is shown that variations of meteorological origin dominate the record until the snow has consolidated to high‐density firn some 30 years after deposition. The thin nitrate layers have a characteristic short timescale (&lt;6 weeks) and are highly correlated with periods of major solar‐terrestrial disturbance, the probability of chance correlation being less than 10−9. A one‐to‐one correlation is demonstrated between the seven largest solar proton fluence events that have been observed since continuous recording of the cosmic radiation started in 1936, and the corresponding thin nitrate layers for the event date. The probability of this occurring by chance is &lt;10−6. This high degree of statistical correlation, together with the modeling studies of Jackman, Vitt, and coworkers, is interpreted as establishing that the impulsive nitrate events are causally related to the generation of energetic particles by solar activity. The timescale of the nitrate events is too short to be understood in terms of transport mechanisms in the gaseous phase and indicates that the nitrate must be precipitated to the polar caps by the gravitational sedimentation of stratospheric solid particles. A conversion factor is established between the impulsive transient nitrate concentrations and the &gt;30 MeV solar proton fluence. The proton fluences (omnidirectional fluence cm−2) derived from the 70 largest impulsive nitrate events between 1561 and 1950 are tabulated. The proton fluence probability distribution derived from these large impulsive nitrate events are in good agreement with earlier studies of the cumulative probabilities of solar proton events and with the observation of cosmogenic isotopes in moon rocks. The cumulative probability curve derived from the impulsive nitrate events indicates a rapidly decreasing probability of occurrence of &gt;30 MeV solar proton events having an omnidirectional fluence exceeding 6 × 109 cm−2. It is concluded that the impulsive nitrate events are reliable indicators of the occurrence of large fluence solar proton events and that they provide a quantitative measure of these events. It is further concluded that the impulsive nitrate events will permit the study of solar activity for many thousands of years into the past.

Correlation of upper‐atmospheric 7Be with solar energetic particle events

A surprisingly large concentration of radioactive 7Be 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 7Be concentrations in low earth orbit. Our data show a significant correlation between the 7Be 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 7Be in the ionosphere.

Identification of major proton fluence events from nitrates in polar ice cores

Large transient concentrations of nitrates in polar ice cores have been identified as the signature of some major solar proton fluence events between 1940 and 1991. We review this solar proton proxy identification technique using nitrate concentration measurements in ice cores from the Arctic and Antarctic. Using this identification technique we go back in time in an attempt to identify major solar proton events during the past several centuries. There is a very large nitrate increase corresponding to the Carrington flare of 1859 evident in the Arctic ice core. Other significant nitrate increases may indicate that major solar proton events occurred toward the end of the last century. The problems associated with this new technique of using nitrates as proxies to identify solar proton events are discussed.

Long-term, solar flare fluence forecasting

The problem of forecasting solar flare proton fluences is discussed and some projection techniques are proposed for long-duration space missions. The proton energy ranges considered are > 10 and > 30 MeV. Results of modeling the proton fluences are compared with available observational data.

A model of radiation conditions during spacecraft flights in the interplanetary space and in the Earth's magnetosphere.

Based on the available measurement data, simulations of radiation conditions during spacecraft flights in the interplanetary space and in the Earth's and Jupiter's radiation belts has been carried out. The > or = 10 MeV and > or = 30 MeV solar flare proton fluence forecast has been proposed for Cycle 22. Radiation conditions due to both magnetospheric electrons and protons and to solar flare protons, magnetic rigidity cutoff being taken into account, have been evaluated on spacecraft trajectories in the Earth's and Jupiter's magnetospheres.