Energetic Particle Data Research Articles

Short-term Classification of Strong Solar Energetic Particle Events Using Multivariate Time-series Classifiers

Solar energetic particle (SEP) events are one of the most crucial aspects of space weather that require continuous monitoring and forecasting. Their prediction depends on various factors, including source eruptions. In the present work, we use the Geostationary Solar Energetic Particle data set covering solar cycles 22, 23, and 24. We develop a framework using time-series-based machine-learning (ML) models with the aim of developing robust short-term forecasts by classifying SEP events. For this purpose, we introduce an ensemble learning approach that merges the results from univariate time series of three proton channels (E ≥10, 50, and 100 MeV) and the long-band X-ray flux (1–8 Å) channel from the Geostationary Operational Environmental Satellite missions and analyze their performance. We consider three models, namely, time series forest, supervised time series forest (STSF), and Bag-of-Symbolic Fourier Approximation Symbols. Our study also focuses on understanding and developing confidence in the predictive capabilities of our models. Therefore, we utilize multiple evaluation techniques and metrics. Based on that, we find STSF to perform well in all scenarios. The summary of metrics for the STSF model is as follows: the area under the ROC curve = 0.981, F 1-score = 0.960, true skill statistics = 0.919, Heidke skill score = 0.920, Gilbert skill score = 0.852, and Matthew’s correlation coefficient = 0.920. The Brier score loss of the STSF model is 0.077. This work lays the foundation for building near-real-time short-term SEP event predictions using robust ML methods.

The 18–19 March 2022 series of 3He-rich events observed by Solar Orbiter at 0.36 au compared with EUV, X-ray, and radio observations

Context. During the first close perihelion pass of Solar Orbiter, a series of impulsive 3He-rich solar particle events was observed on 18–19 March 2022 from a distance of 0.36 au. In addition to the energetic particle, radio, and X-ray data from Solar Orbiter, the events were observed in radio and/or extreme ultraviolet by STEREO-A, SDO, Wind, and Parker Solar Probe. Aims. Observations of the event series along with remote sensing of flaring and radio emission with only small timing delays due to the close distance allow the association with energetic particles to be determined with much higher accuracy than previously possible from 1 au. Methods. By comparing the onsets of type-III bursts with the arrival of electrons of tens of keV at Solar Orbiter only a few minutes later, it can be seen that, overall, each of the more intense type-III bursts was associated with an electron and ion injection. Extreme ultraviolet data show that the times of the type-III bursts coincide with emission from a small (approximately Earth-sized) loop to the west of a nearby active region. Results. The energetic particle spectra and abundances show typical properties of impulsive 3He-rich flares and, when combined with the remote sensing observations, establish that the particle-accelerating mechanism in this series of events operates near the solar surface in association with magnetic loops, and in the absence of other phenomena such as jets and small coronal mass ejections.

Near‐Magnetic‐Field‐Aligned Energetic Electrons Above Saturn's Dark Polar Regions

AbstractSaturn's main auroral emissions define two oval‐shaped regions, one encircling each magnetic pole. The regions at higher latitudes are generally “dark” (i.e., devoid of auroras), and are magnetically connected to the distant planetary magnetosphere where there is a much‐debated interaction with the solar wind. Electric currents flow into the atmosphere along the magnetic field within these polar regions. Establishing whether polar magnetic flux is “open” or “closed” is key for diagnosing how the solar wind interaction works. Because energetic electrons moving almost parallel or anti‐parallel to the magnetic field shed light on the field topology, we survey Cassini energetic particle data for rare instances when the spacecraft was able to measure these parts of the distribution in the polar field environment close to the planet. Over the entire mission we find 16 intervals when measurements at ∼0 and ∼180 pitch angles were made simultaneously without sunlight contamination. Across all the events, above‐background field‐aligned fluxes were measured intermittently by the >15 keV electron channels, extending up to ∼300 keV when present. Uni‐directional anti‐planetward fluxes were observed during 10 of the events, and bi‐directional fluxes were observed during 6 of the events. We suggest the uni‐directional anti‐planetward fluxes indicate the presence of field‐aligned beams, and that the bi‐directional fluxes indicate regions of locally closed magnetic field. These results either mean the solar wind interaction is predominantly via global magnetic reconnection but is more complex than initially proposed, or that the interaction is instead predominantly “viscous‐like” at Saturn.

The Electric Field outward of Saturn's Main Rings

Cassini data are consistent with a global electric field in Saturn's magnetosphere that points approximately antisunward. The inner radial extent of this field was initially established using Saturn orbit insertion data but measurements of ultrarelativistic electrons from that pass cast some doubt on whether the electric field reaches all the way to the A ring. It was not until the so-called ring-grazing and proximal orbits near the end of the mission in 2017 that relevant data were again obtained on magnetic field lines that connect to the region just outward of the main rings. Here we report on the energetic charged particle data during those orbits, showing that electron observations at a wide range of energies are consistent with an electric field that influences charged particle drift paths near the outer edge of the A ring. We include a very detailed analysis of Cassini's ultrarelativistic electron measurements (channel E7 in the text) and argue they provide no information about the electric field. This result further strengthens the case of several studies that have used the presence of the electric field to explain signatures of acceleration in the data.

Cutoff Latitudes of Solar Proton Events Measured by GPS Satellites

AbstractSolar energetic particles (SEPs), one of the main causes of particle radiation in interplanetary space, can disrupt radio communication, induce spacecraft failures and change the heating and cooling rates in the atmosphere among others. To investigate the impact of SEPs and more specifically solar proton events (SPEs), we established a cutoff latitude database based on energetic particle data from Combined X‐ray Dosimeters (CXDs) on board the Global Positioning System (GPS) spacecraft. Introducing a novel normalization method involving proton fluxes from the Geostationary Operational Environmental Satellites enabled us to include the CXD data from its introduction (2001) onwards. The database contains 5714 cutoff latitudes divided over six energies between 18 and 115 MeV which occur during 58 SPEs from 2001 to 2015. Based on the database, a cutoff latitude parameterization as a function of solar wind dynamic pressure and geomagnetic indices Kp and Dst is created for each energy. Moreover, comparisons to previous studies on energetic particle data from the Polar Orbiting Environmental Satellites have been performed to put the GPS data into perspective. A 1–2° poleward offset is found for the GPS based cutoff latitude models, for which several causes are discussed. Furthermore, the limitation of GPS data to geomagnetic latitudes above 60° should be considered. All in all, the usage of the long time span of GPS data in this study combined with its recent release (2016) opens up a new range of studies involving GPS energetic particle data such as investigating long‐term trends with respect to our solar cycle or magnetospheric trends.

Influence of Solar Disturbances on Galactic Cosmic Rays in the Solar Wind, Heliosheath, and Local Interstellar Medium: Advanced Composition Explorer, New Horizons, and Voyager Observations

Abstract We augment the heliospheric network of galactic cosmic ray (GCR) monitors using 2012–2017 penetrating radiation measurements from the New Horizons (NH) Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI), obtaining intensities of ≳75 MeV particles. The new, predominantly GCR observations provide critical links between the Sun and Voyager 2 and Voyager 1 (V2 and V1), in the heliosheath and local interstellar medium (LISM), respectively. We provide NH, Advanced Composition Explorer (ACE), V2, and V1 GCR observations, using them to track solar cycle variations and short-term Forbush decreases from the Sun to the LISM, and to examine the interaction that results in the surprising, previously reported V1 LISM anisotropy episodes. To investigate these episodes and the hitherto unexplained lagging of associated in situ shock features at V1, propagating disturbances seen at ACE, NH, and V2 were compared to V1. We conclude that the region where LISM magnetic field lines drape around the heliopause is likely critical for communicating solar disturbance signals upstream of the heliosheath to V1. We propose that the anisotropy-causing physical process that suppresses intensities at ∼90° pitch angles relies on GCRs escaping from a single compression in the draping region, not on GCRs trapped between two compressions. We also show that NH suprathermal and energetic particle data from PEPSSI are consistent with the interpretation that traveling shocks and corotating interaction region (CIR) remnants can be distinguished by the existence or lack of Forbush decreases, respectively, because turbulent magnetic fields at local shocks inhibit GCR transport while older CIR structures reaching the outer heliosphere do not.

Saturn's Nightside Dynamics During Cassini's F Ring and Proximal Orbits: Response to Solar Wind and Planetary Period Oscillation Modulations

AbstractWe examine the final 44 orbits of the Cassini spacecraft traversing the midnight sector of Saturn's magnetosphere to distances of ~21 Saturn radii, to investigate responses to heliospheric conditions inferred from model solar wind and Cassini galactic cosmic ray flux data. Clear storm responses to anticipated magnetospheric compressions are observed in magnetic field and energetic particle data, together with Saturn kilometric radiation (SKR), auroral hiss, and ultraviolet auroral emissions. Most compression events are associated with corotating interaction regions, producing ~2–3.5 day intervals of magnetospheric activity that are recurrent with the ~26 day solar rotation period (one or two such events per rotation), though one on the final pass is related to a nonrecurrent interplanetary shock possibly associated with an earlier X‐class solar flare. The response to compressions is modulated by the concurrent relative phasing of the northern and southern planetary period oscillation (PPO) systems, with long (>1 planetary rotation) SKR low‐frequency extension (LFE) intervals associated with strong field‐aligned coupling currents being favored when the two PPO systems act together to thin and thicken the tail plasma sheet during each PPO cycle. LFE onsets/intensifications are then favored at thin plasma sheet phases most unstable to reconnection, producing energetic nightside particle injections and poleward contractions of dawn‐brightened auroras. Correspondingly, solar rotation recurrent intervals of magnetospheric quiet conditions also occur with weak energetic particle fluxes and auroral emissions, associated with extended solar wind rarefactions. Overall, the results emphasize how strongly activity in Saturn's magnetosphere is modulated by concurrent heliospheric conditions.

A possible explanation for the enhancement of energetic particles downstream of the heliospheric termination shock

Voyager 2 observations of the energetic particle “time-intensity” profiles from ~1.8 to ~40 MeV show that the flux peaks downstream of the heliospheric termination shock (HTS), which is inconsistent with the predictions of classical diffusive shock acceleration (DSA). Previous studies suggest that shocks are effective in generating downstream magnetic flux ropes, islands or plasmoids. These dynamically interacting small-scale structures can accelerate charged particles statistically through reconnection-related processes. We present a preliminary study of the magnetic field and plasma properties together with the energetic particle data during the V2 crossing of the HTS. We apply a local stochastic acceleration model associated with solar wind magnetic island dynamics to explain the unusual behavior of energetic particles observed in the vicinity of the HTS. An analytic solution for the particle velocity distribution function derived from the Zank et al. statistical transport theory is used to fit the observed particle flux amplification downstream of the HTS. The results show that stochastic acceleration by interacting magnetic islands can successfully predict the observed (i) peaking of particle intensities behind the HTS, instead of at the shock front; (ii) increasing of the particle flux amplification factor with increasing particle energy; and (iii) increase in distance between the particle intensity peak and the HTS with increasing particle energy; This study illustrates the possibility of local acceleration in the inner heliosheath due to the dynamical interaction of magnetic islands.

The Source, Significance, and Magnetospheric Impact of Periodic Density Structures Within Stream Interaction Regions

AbstractWe present several examples of magnetospheric ultralow frequency pulsations associated with stream interaction regions and demonstrate that the observed magnetospheric pulsations were also present in the solar wind number density. The distance of the solar wind monitor ranged from just upstream of Earth's bow shock to 261 RE, with a propagation time delay of up to 90 min. The number density oscillations far upstream of Earth are offset from similar oscillations observed within the magnetosphere by the advection timescale, suggesting that the periodic dynamic pressure enhancements were time stationary structures, passively advecting with the ambient solar wind. The density structures are larger than Earth's magnetosphere and slowly altered the dynamic pressure enveloping Earth, leading to a quasi‐static and globally coherent “forced‐breathing” of Earth's dayside magnetospheric cavity. The impact of these periodic solar wind density structures was observed in both magnetospheric magnetic field and energetic particle data. We further show that the structures were initially smaller‐amplitude, spatially larger, structures in the upstream slow solar wind and that the higher‐speed wind compressed and amplified these preexisting structures leading to a series of quasiperiodic density structures with periods typically near 20 min. Similar periodic density structures have been observed previously at L1 and in remote images, but never in the context of solar wind shocks and discontinuities. The existence of periodic density structures within stream interaction regions may play an important role in magnetospheric particle acceleration, loss, and transport, particularly for outer zone electrons that are highly responsive to ultralow frequency wave activity.

The September 2017 SEP Event in Context With the Current Solar Cycle: Mars Express ASPERA‐3/IMA and MAVEN/SEP Observations

AbstractWe use Mars Atmosphere and Volatile Evolution/Solar Energetic Particle (MAVEN/SEP) data to estimate the ranges of particle energies that generate background noise in the Analyzer of Space Plasmas and Energetic Atoms‐3/Ion Mass Analyzer (IMA) instrument on Mars Express. The particles that generate IMA background counts are estimated to be electrons with energies >1 MeV and protons >20 MeV. The September 2017 event at Mars resulted in the strongest flux of energetic particles measured by MAVEN/SEP. We correspondingly use the IMA background data to compare this event with the rest of the last solar cycle and back to 2004, finding the event to be the fourth strongest solar energetic particle event detected by Mars Express.

Strong non-radial propagation of energetic electrons in solar corona

Analyzing the sequence of solar energetic electron events measured at both STEREO-A (STA) and STEREO-B (STB) spacecraft during 17–21 July 2014, when their orbital separation was 34°, we found evidence of a strong non-radial electron propagation in the solar corona below the solar wind source surface. The impulsive electron events were associated with recurrent flare and jet (hereafter flare/jet) activity at the border of an isolated coronal hole situated close to the solar equator. We have focused our study on the solar energetic particle (SEP) event on 17 July 2014, during which both spacecraft detected a similar impulsive and anisotropic energetic electron event suggesting optimal connection of both spacecraft to the parent particle source, despite the large angular separation between the parent flare and the nominal magnetic footpoints on the source surface of STA and STB of 68° and 90°, respectively. Combining the remote-sensing extreme ultraviolet (EUV) observations, in-situ plasma, magnetic field, and energetic particle data we investigated and discuss here the origin and the propagation trajectory of energetic electrons in the solar corona. We find that the energetic electrons in the energy range of 55–195 keV together with the associated EUV jet were injected from the flare site toward the spacecraft’s magnetic footpoints and propagate along a strongly non-radial and inclined magnetic field below the source surface. From stereoscopic (EUV) observations we estimated the inclination angle of the jet trajectory and the respective magnetic field of 63° ± 11° relative to the radial direction. We show how the flare accelerated electrons reach very distant longitudes in the heliosphere, when the spacecraft are nominally not connected to the particle source. This example illustrates how ballistic backmapping can occasionally fail to characterize the magnetic connectivity during SEP events. This finding also provides an additional mechanism (one among others), which may explain the origin of widespread SEP events.

Mapping the South Atlantic Anomaly continuously over 27 years

The South Atlantic Anomaly (SAA) is a region of reduced magnetic intensity where the inner radiation belt makes its closest approach to the Earth's surface. Satellites in low-Earth orbit pass though the SAA periodically, exposing them to several minutes of strong radiation each time, creating problems for scientific instruments, human safety, and single event upsets (SEU). For the first time, we are able track the SAA movement continuously over 27 years, using overlapping satellites in similar orbits with similar instruments. The Defense Meteorological Satellite Program (DMSP) spacecraft have been carrying the Special Sensor J (SSJ) precipitating energetic particle spectrometers since 1982. The instruments are susceptible to MeV electrons and protons that pass through the spacecraft skin and instrument case and get counted. This “backgroundˮ is easily identified and we use it to map the movement of the SAA. Comparison with energetic particle data from the Energetic Particle Telescope (EPT) instrument on the Proba-V spacecraft indicates that the best match with the SSJ data occurs in the energy range above about 2.6 MeV for electrons and above about 29 MeV for protons. The peak flux and extent of the SAA from both the SSJ and EPT instruments are nearly identical in longitude while in latitude, the peak EPT flux is 5° south of the peak SSJ flux. However, the shapes of the SAA in latitude and the locations of the outer radiation belts are nearly identical. We find that the SAA moves 0.06° N/yr and 0.28° W/yr. We also find a difference with the movement and location of the SAA from the contamination by high energy particles on the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instrument on DMSP F16 (Shaefer et al., 2016). However, the SSUSI instrument is located on the opposite side/bottom of the spacecraft and Shaefer et al. (2016) estimated that most of the particle noise pulses in the SSUSI instrument are produced by protons greater than about 45 MeV. Thus the contamination in the SSUSI instrument is produced by a different population of particles that the contamination in the SSJ/5 instrument which would lead to differences in movement and location of the SAA. While this study focuses on the SAA movement on a yearly basis, further analysis will allow us to investigate the movement on shorter time scales, the variation of the flux intensity, the spatial extent of the SAA, and the dynamics of the outer radiation belt.

Energetic particle signatures of magnetic field‐aligned potentials over Jupiter's polar regions

AbstractRecent results of the first ever orbit through Jupiter's auroral region by NASA's Juno spacecraft did not show evidence of coherent acceleration in the auroral or polar region. However, in this letter, we show energetic particle data from Juno's Jupiter Energetic‐particle Detector Instrument instrument during the third auroral pass that exhibits conclusive evidence of downward parallel electric fields in portions of Jupiter's polar region. The energetic particle distributions show inverted‐V ion and electron structures in a downward electric current region with accelerated peaked distributions in hundreds of keV to ~1 MeV range. The origin of these large electric potential structures is investigated and discussed within the current theoretical framework of current‐voltage relationships at both Earth and Jupiter. Parallel electric fields responsible for accelerating particles to maintain the aurora/magnetospheric circuit appear to be a common phenomenon among strongly magnetized planets with conducting ionospheres; however, their origin and generation mechanisms are subjects of ongoing research.

Global Positioning System Sparks New Data Revolution

Energetic particle data from the Global Positioning System constellation opens avenues for new research.

Ultralow frequency wave characteristics extracted from particle data: Application of IGSO observations

Interaction between ultralow frequency (ULF) waves and charged particles plays an important role in the acceleration of particles in the Van Allen radiation belts. The strong wave-particle interaction predicts an energy-dependent observational signature of particle flux variations during different stages of the ULF wave evolution. In this paper, we find that the energetic particle data newly available from an IGSO spacecraft are quite consistent with theoretical predictions, which enables the application of a best-fit procedure to quantitatively extract key parameters of the ULF waves from the particle data. The general agreement between observations and the best-fit results validates the scenario of wave-particle drift resonance within the entire ULF life span, and provides a new technique to understand the ULF wave characteristics in the absence of electromagnetic field data. We also examine the minor differences between observations and the best-fit results, and propose that the differences may result from a longitudinal dependence of the ULF wave power to be considered in a future study.

Global Positioning System Energetic Particle Data: The Next Space Weather Data Revolution

The Global Positioning System (GPS) has revolutionized the process of getting from point A to point Band so much more. A large fraction of the worlds population relies on GPS (and its counterparts from other nations) for precision timing, location, and navigation. Most GPS users are unaware that the spacecraft providing the signals they rely on are operating in a very harsh space environment the radiation belts where energetic particles trapped in Earths magnetic field dash about at nearly the speed of light. These subatomic particles relentlessly pummel GPS satellites. So by design, every GPS satellite and its sensors are radiation hardened. Each spacecraft carries particle detectors that provide health and status data to system operators. Although these data reveal much about the state of the space radiation environment, heretofore they have been available only to system operators and supporting scientists. Research scientists have long sought a policy shift to allow more general access. With the release of the National Space Weather Strategy and Action Plan organized by the White House Office of Science Technology Policy (OSTP) a sample of these data have been made available to space weather researchers. Los Alamos National Laboratory (LANL) and the National Center for Environmental Information released a months worth of GPS energetic particle data from an interval of heightened space weather activity in early 2014 with the hope of stimulating integration of these data sets into the research arena. Even before the public data release GPS support scientists from LANL showed the extraordinary promise of these data.

The proton and electron radiation belts at geosynchronous orbit: Statistics and behavior during high‐speed stream‐driven storms

AbstractThe outer proton radiation belt (OPRB) and outer electron radiation belt (OERB) at geosynchronous orbit are investigated using a reanalysis of the LANL CPA (Charged Particle Analyzer) 8‐satellite 2‐solar cycle energetic particle data set from 1976 to 1995. Statistics of the OPRB and the OERB are calculated, including local time and solar cycle trends. The number density of the OPRB is about 10 times higher than the OERB, but the 1 MeV proton flux is about 1000 times less than the 1 MeV electron flux because the proton energy spectrum is softer than the electron spectrum. Using a collection of 94 high‐speed stream‐driven storms in 1976–1995, the storm time evolutions of the OPRB and OERB are studied via superposed epoch analysis. The evolution of the OERB shows the familiar sequence (1) prestorm decay of density and flux, (2) early‐storm dropout of density and flux, (3) sudden recovery of density, and (4) steady storm time heating to high fluxes. The evolution of the OPRB shows a sudden enhancement of density and flux early in the storm. The absence of a proton dropout when there is an electron dropout is noted. The sudden recovery of the density of the OERB and the sudden density enhancement of the OPRB are both associated with the occurrence of a substorm during the early stage of the storm when the superdense plasma sheet produces a “strong stretching phase” of the storm. These storm time substorms are seen to inject electrons to 1 MeV and protons to beyond 1 MeV into geosynchronous orbit, directly producing a suddenly enhanced radiation belt population.

Decrease in SYM-H during a storm main phase without evidence of a ring current injection

Changes in the Dst index, or the similarly constructed high-resolution SYM-H index, are thought to indicate changes in the total energy content of the ring current. However, this is not always the case. In this paper we examine an intense (SYM-H ∼ −435nT) magnetic storm that occurred on March 31, 2001. The arrival at Earth of strongly southward IMF produced an immediate negative response in the SYM-H index. While energetic particle and magnetometer data from geosynchronous orbit and inner magnetosphere energetic neutral atom imaging indicate that two substorm injections took place during the main phase, there was about one hour when the SYM-H decreased more than 200nT with no evidence in the data for ring current enhancement. Instead the near-Earth magnetotail exhibited a growth phase indicative of a strong, growing cross-tail current, with the large substorm expansion phase and the associated injection of energetic particles coming significantly later. Data from the DMSP spacecraft demonstrate that the polar cap flux grew rapidly in response to the strongly southward IMF. We present observations showing that the decrease in SYM-H occurred when polar cap flux was increasing and there was no evidence of injection into the ring current. Our findings strongly support the relationship between Dst and the polar cap flux proposed by theoretical studies that determined that the tail current system could be a significant contributor to Dst.

Issue Information

Cover. In Zanetti et al. [DOI: 10.1002/2014SW001108]: The example of Van Allen Probes space weather display shown here was especially configured to include the trajectory of NASA's JUNO spacecraft as it performed a gravity assist maneuver on 9 October 2013. Shown on the right are the Van Allen Probes spacecraft orbits, viewing Van Allen Probes/RBSP‐A and ‐B orbits from north zenith in GSE coordinates, the sun is toward the right. On the left are the ECT/REPT energetic particle data from RBSP‐A received and displayed in near real‐time, with L‐shell intensity vs. time. Approximately one month of data are shown. Also shown is the geomagnetic parameter DsT indicating geomagnetic activity. The middle electron intensity channel shown to the left is also used to paint the spacecraft orbit with that channel intensity. The real‐time Van Allen Probes data access – Science Gateway – can be found at http://rbspgway.jhuapl.edu. See pp. 577–581.

Structure and statistical properties of plasmoids in Jupiter's magnetotail

AbstractPlasmoids and other reconnection‐related signatures have been observed in Jupiter's magnetotail through analysis of magnetic field and energetic particle data. Previous studies have established the spatial distribution and recurrence period of tail reconnection events, and identified the location of a statistical X‐line separating inward and outward flow. Here we present new analysis focusing specifically on 43 plasmoid signatures observed in magnetometer data in order to establish the average properties and internal structure of Jovian plasmoids. We present statistics on the observed plasmoid length scale, duration, radial position, and local time distribution. On average, the observed plasmoids have a ~3 RJ radial extent and ~7 min duration and result in the closure of ~4–8 GWb of open flux from reconnection of open field lines in the postplasmoid plasma sheet. We also determine the amount of mass released and the magnetic flux closed in order to understand the role of tail reconnection in the transport of mass and flux in Jupiter's magnetosphere. The observed plasmoid properties are consistent with a mass loss rate of ~0.7–120 kg/s and a flux closure rate of ~7–70 GWb/d. We conclude that tail reconnection and plasmoid release is an important method of flux transport at Jupiter but likely cannot account for the mass input from Io, suggesting that additional mass loss mechanisms may be significant. Finally, we examine the plasmoid interior structure through minimum variance analysis and find that most plasmoids lack a core field and are better described by magnetic loops rather than flux ropes.