Nathan A. Schwadron

University of New Hampshire | UNH · Department of Physics

The Integrated Science Investigation of the Sun (IS$\bigodot$IS) energetic particle instrument suite on Parker Solar Probe is dedicated to measuring energetic ions and electrons in the near-Sun environment. It includes a half-sky-viewing time-of-flight mass spectrometer (EPI-Lo) and five high-energy silicon solid-state detector-telescopes (EPI-Hi)....

In this study, we employ the combined charged particle measurements from Integrated Science Investigation of the Sun on board the Parker Solar Probe (PSP) and Energetic Particle Detector on board the Solar Orbiter (SolO) to study the composition variation of the solar energetic particle (SEP) event occurring on 2023 May 16. During the event, SolO a...

In this study, we employ the combined charged particle measurements from Integrated Science Investigation of the Sun (\ISOIS) onboard the Parker Solar Probe (PSP) and Energetic Particle Detector (EPD) onboard the Solar Orbiter (SolO) to study the composition variation of the solar energetic particle (SEP) event occurring on May 16, 2023. During the...

We report observations of direct evidence of energetic protons being accelerated above ~400 keV within the reconnection exhaust of a heliospheric current sheet (HCS) crossing by NASA's Parker Solar Probe (PSP) at a distance of ~16.25 solar radii (Rs) from the Sun. Inside the extended exhaust, both the reconnection-generated plasma jets and the acce...

The IBEX-Lo instrument on the Interstellar Boundary Explorer (IBEX) mission observes primary and secondary interstellar helium in its 4 lowest energy steps. Observations of these helium populations have been systematically analyzed and compared to simulations using the analytic full integration of neutrals model (aFINM). A systematic difference is...

We present an event observed by Parker Solar Probe (PSP) at ∼0.2 au on 2022 March 2 in which imaging and in situ measurements coincide. During this event, PSP passed through structures on the flank of a streamer blowout coronal mass ejection (CME) including an isolated flux tube in front of the CME, a turbulent sheath, and the CME itself. Imaging o...

We present an event observed by Parker Solar Probe at $\sim$0.2 au on March 2, 2022 in which imaging and \emph{in situ} measurements coincide. During this event, PSP passed through structures on the flank of a streamer blowout CME including an isolated flux tube in front of the CME, a turbulent sheath, and the CME itself. Imaging observations and \...

On 2022 September 5, Parker Solar Probe (Parker) observed a large solar energetic particle (SEP) event at the unprecedented distance of only 15 R S from the Sun. The observations from the Integrated Science Investigation of the Sun (IS⊙IS) obtained over the course of this event are remarkably rich, and an overview is presented here. IS⊙IS is capabl...

Parker Solar Probe (PSP) observations of a small dispersive event on 2022 February 27 and 28 indicate scatter-free propagation as the dominant transport mechanism between the low corona and greater than 35 solar radii. The event occurred during unique orbital conditions that prevailed along specific flux tubes that PSP encountered repeatedly betwee...

Direct-sampling observations of interstellar neutral gas, including hydrogen and deuterium, have been performed for more than one cycle of solar activity by IBEX. The IBEX viewing is restricted to directions perpendicular to the spacecraft–Sun line, which limits the observations to several months each year. This restriction is removed in the forthc...

Solar energetic particle (SEP) events have been observed by the Parker Solar Probe (PSP) spacecraft since its launch in 2018. These events include sources from solar flares and coronal mass ejections (CMEs). The IS⊙IS instrument suite on board PSP is measuring ions over energies from ∼ 20 keV nucleon ⁻¹ to 200 MeV nucleon ⁻¹ and electrons from ∼ 20...

On 2022 February 15–16, multiple spacecraft measured one of the most intense solar energetic particle (SEP) events observed so far in Solar Cycle 25. This study provides an overview of interesting observations made by multiple spacecraft during this event. Parker Solar Probe (PSP) and BepiColombo were close to each other at 0.34–0.37 au (a radial s...

The Interstellar Boundary Explorer (IBEX) has been observing the outer heliosphere and its interactions with the very local interstellar medium (VLISM) via measurements of energetic neutral atoms (ENAs) for over 14 yr. We discovered the IBEX Ribbon—a structure completely unanticipated by any prior theory or model—that almost certainly resides beyon...

Angular scattering (AS) in charge exchange and elastic collisions between interstellar ions and neutral (ISN) atoms has been assumed to be negligible in previous studies. Here, we investigate the momentum transfer associated with the AS of H atoms using Monte Carlo calculations to simulate their transport through the outer heliosheath. We consider...

We present analyses of 0.05–2 MeV ions from the 2022 February 16 energetic storm particle event observed by Parker Solar Probe's (PSP) IS⊙IS/EPI-Lo instrument at 0.35 au from the Sun. This event was characterized by an enhancement in ion fluxes from a quiet background, increasing gradually with time with a nearly flat spectrum, rising sharply near...

Direct-sampling observations of interstellar neutral (ISN) species and their secondary populations give information about the physical state of the local interstellar medium and processes occurring in the outer heliosheath. Such observations are performed from Earth’s orbit by the IBEX-Lo experiment on board the Interstellar Boundary Explorer (IBEX...

Plain Language Summary Scientists use a combination of in situ measurements and remote sensing of energetic neutral atoms to determine the density of hydrogen in the geocorona, which a very tenuous neutral atmosphere surrounding the Earth. This method relies on global models of the magnetosphere to determine the geocoronal density accurately. To va...

We analyzed observations of energetic neutral atoms (ENAs) of hydrogen collected from the subsolar magnetosheath by the Interstellar Boundary Explorer (IBEX) in Solar Cycle 24. We looked for long‐term solar activity‐related variation and correlation between the H ENA flux and the solar wind parameters. The H ENA flux in the energy range from 0.5 to...

In situ observations of interstellar neutral (ISN) helium atoms by the IBEX-Lo instrument on board the Interstellar Boundary Explorer (IBEX) mission are used to determine the velocity and temperature of the pristine very local interstellar medium (VLISM). Most ISN helium atoms penetrating the heliosphere, known as the primary population, originate...

In situ observations of interstellar neutral (ISN) helium atoms by the IBEX-Lo instrument onboard the Interstellar Boundary Explorer (IBEX) mission are used to determine the velocity and temperature of the pristine very local interstellar medium (VLISM). Most ISN helium atoms penetrating the heliosphere, known as the primary population, originate i...

The IBEX-Lo instrument on the Interstellar Boundary Explorer (IBEX) mission measures interstellar neutral (ISN) helium atoms. The detection of helium atoms is made through negative hydrogen (H$^-$) ions sputtered by the helium atoms from the IBEX-Lo conversion surface. The energy spectrum of ions sputtered by ISN helium atoms is broad and overlaps...

A good understanding of the ionization rates of neutral species in the heliosphere is important for studies of the heliosphere and planetary atmospheres. So far, the intensities of the ionization reactions have been studied based on observations of the contributing phenomena, such as the solar spectral flux in the EUV band and the flux of the solar...

A detailed overview of the knowledge gaps in our understanding of the heliospheric interaction with the largely unexplored Very Local Interstellar Medium (VLISM) are provided along with predictions of with the scientific discoveries that await. The new measurements required to make progress in this expanding frontier of space physics are discussed...

We use Parker Solar Probe (PSP) observations to report the first direct measurements of the particle and field environments while crossing the leg of a coronal mass ejection (CME) very close to the Sun (∼14 Rs). An analysis that combines imaging from 1 au and PSP with a CME model, predicts an encounter time and duration that correspond to an unusua...

A good understanding of the ionization rates of neutral species in the heliosphere is important for studies of the heliosphere and planetary atmospheres. So far, the intensities of the ionization reactions have been studied based on observations of the contributing phenomena, such as the solar spectral flux in the EUV band and the flux of the solar...

Energetic charged particles are pervasive throughout the heliosphere with contributions from solar energetic particle events, stream and corotating interaction regions, galactic cosmic rays, anomalous cosmic rays, and suprathermal ions. The Integrated Science Investigation of the Sun (IS⊙IS) on board the Parker Solar Probe is a suite of energetic p...

As the solar wind (SW) crosses Earth's bow shock, it is heated and decelerated, resulting in a hot and dense magnetosheath ion population. This increases the probability of charge exchange between a magnetosheath proton and a geocoronal Hydrogen atom, which produces energetic neutral atoms (ENAs). These ENAs propagate away from the magnetosheath ca...

We analyze the reasons for the correlation between the temperature, direction, and speed of the interstellar neutral gas inflow into the heliosphere, obtained in analyses of observations performed by an onboard Interstellar Boundary Explorer (IBEX) instrument, IBEX-Lo. We point out that this correlation is the combined result of the inability to me...

We derive annual sky maps of the proton temperature in the inner heliosheath (IHS), and track their temporal evolution over the years 2009–2016 of Interstellar Boundary Explorer observations. Other associated thermodynamic parameters also determined are the density, kappa (the parameter that characterizes kappa distributions), temperature rate, pol...

We derive annual skymaps of the proton temperature in the inner heliosheath (IHS), and track their temporal evolution over the years from 2009 to 2016 of Interstellar Boundary Explorer observations. Other associated thermodynamic parameters also determined are the density, kappa, that is, the parameter that characterizes kappa distributions, temper...

We analyze the reasons for the correlation between the temperature, direction, and speed of the interstellar neutral gas inflow into the heliosphere, obtained in analyzes of observations performed by the IBEX-Lo instrument onboard Interstellar Boundary Explorer (IBEX). We point out that this correlation is the combined result of the inability to me...

Radiation transport codes have been an increasingly important tool for studying the space radiation environment, which includes high‐energy and high‐nuclear‐charge particles. The unique advantage of transport models lies in covering a wider range of particles, energies, and angles than would be attainable in a laboratory or measurable by an instrum...

The Interstellar Boundary Explorer (IBEX) is a NASA satellite in Earth orbit, dedicated to observing both interstellar neutral atoms entering the heliosphere and energetic neutral atoms (ENAs) from the interstellar boundaries from roughly 10 eV to 6 keV. This work presents the averaged maps, energy spectra, and temporal variability of heliospheric...

Energetic electrons of Jovian origin have been observed for decades throughout the heliosphere, as far as 11 au, and as close as 0.5 au, from the Sun. The treatment of Jupiter as a continuously emitting point source of energetic electrons has made Jovian electrons a valuable tool in the study of energetic electron transport within the heliosphere....

Measurements of starlight polarized by aligned interstellar dust grains are used to probe the relation between the orientation of the ambient interstellar magnetic field (ISMF) and the ISMF traced by the ribbons of energetic neutral atoms discovered by the Interstellar Boundary Explorer spacecraft. We utilize polarization data, many acquired specif...

The IBEX-Lo instrument on board the Interstellar Boundary Explorer (IBEX) mission samples interstellar neutral (ISN) helium atoms penetrating the heliosphere from the very local interstellar medium (VLISM). In this study, we analyze the IBEX-Lo ISN helium observations covering a complete solar cycle, from 2009 through 2020 using a comprehensive unc...

The Interstellar Boundary Explorer (IBEX) mission provides a unique opportunity to study Earth's magnetosphere on a global scale via energetic neutral atom imaging. Due to the orbital configuration, IBEX is in a side‐viewing vantage point relative to the magnetosphere for a few months every year. This allows the Earth's magnetosphere to be imaged i...

We present observations of ≳10–100 keV nucleon ⁻¹ suprathermal (ST) H, He, O, and Fe ions associated with crossings of the heliospheric current sheet (HCS) at radial distances of <0.1 au from the Sun. Our key findings are as follows: (1) very few heavy ions are detected during the first full crossing, the heavy-ion intensities are reduced during th...

In this paper we examine a low-energy solar energetic particle (SEP) event observed by IS⊙IS’s Energetic Particle Instrument-Low (EPI-Lo) inside 0.18 au on 2020 September 30. This small SEP event has a very interesting time profile and ion composition. Our results show that the maximum energy and peak in intensity are observed mainly along the open...

Since the beginning of the space age, the Sun has been in a multi‐cycle period of elevated activity (secular maximum). This secular maximum is the longest in the last 9300 years. Since the end of solar cycle 21 (SC21), however, the Sun has shown a decline in overall activity, which has remarkably increased the fluxes of galactic cosmic rays (GCRs)....

The Integrated Science Investigation of the Sun instrument suite onboard NASA’s Parker Solar Probe mission continues to measure solar energetic particles and cosmic rays closer to the Sun than ever before. Here, we present the first observations of cosmic rays into 0.1 au (21.5 solar radii), focusing specifically on oxygen from ∼2018.7 to ∼2021.2....

The IBEX-Lo instrument on board the Interstellar Boundary Explorer (IBEX) mission samples interstellar neutral (ISN) helium atoms penetrating the heliosphere from the very local interstellar medium (VLISM). In this study, we analyze the IBEX-Lo ISN helium observations covering a complete solar cycle, from 2009 through 2020 using a comprehensive unc...

Remote imaging of plasmas in the heliosphere and very local interstellar medium is possible with energetic neutral atoms (ENAs), created through the charge exchange of protons with interstellar neutral atoms. ENA observations collected by the Interstellar Boundary Explorer (IBEX) revealed two distinctive sources. One source is the globally distribu...

The Sun's motion through the interstellar medium leads to an interstellar neutral (ISN) wind through the heliosphere. Several ISN species, including He, moderately depleted by ionization are observed with pickup ions and directly imaged. Since 2009, analyzed Interstellar Boundary Explorer (IBEX) observations returned a precise 4D parameter tube ass...

In this paper we examine a low-energy SEP event observed by IS⊙IS's Energetic Particle Instrument-Low (EPI-Lo) inside 0.18 AU on September 30, 2020. This small SEP event has a very interesting time profile and ion composition. Our results show that the maximum energy and peak in intensity is observed mainly along the open radial magnetic field. The...

Aims. On 29 November 2020, at 12:34 UT, active region 12790 erupted with an M4.4 class flare and a 1700 km s⁻¹ coronal mass ejection. Parker Solar Probe (PSP) was completing its seventh orbit around the Sun and was located at 0.8 au when the Integrated Science Investigation of the Sun (IS⊙IS) measured the ensuing mid-sized solar energetic particle...

Context. Following a multi-year minimum of solar activity, a solar energetic particle event on 2020 Nov. 29 was observed by multiple spacecraft covering a wide range of solar longitudes including ACE, the Solar Terrestrial Relations Observatory-A, and the recently launched Parker Solar Probe and Solar Orbiter. Aims. Multi-point observations of a so...

We present observations of >10-100 keV/nucleon suprathermal (ST) H, He, O, and Fe ions associated with crossings of the heliospheric current sheet (HCS) at radial distances <0.1 au from the Sun. Our key findings are: 1) very few heavy ions are detected during the 1st full crossing, the heavy ion intensities are reduced during the 2nd partial crossi...

On 2020 November 30, Parker Solar Probe (PSP) was crossed by a coronal mass ejection (CME)-driven shock, which we suggest was also crossing a convected, isolated magnetic structure (MS) at about the same time. By analyzing PSP/FIELDS magnetic field measurements, we find that the leading edge of the MS coincided with the crossing of the shock, while...

The Integrated Science Investigation of the Sun instrument suite onboard NASA's Parker Solar Probe mission continues to measure solar energetic particles and cosmic rays closer to the Sun than ever before. Here, we present the first observations of cosmic rays into 0.1 au (21.5 solar radii), focusing specifically on oxygen from ~2018.7 to ~2021.2....

The zodiacal cloud is one of the largest structures in the solar system and strongly governed by meteoroid collisions near the Sun. Collisional erosion occurs throughout the zodiacal cloud, yet it is historically difficult to directly measure and has never been observed for discrete meteoroid streams. After six orbits with Parker Solar Probe (PSP),...

At the end of 2020 November, two coronal mass ejections (CMEs) erupted from the Sun and propagated through the interplanetary medium in the direction of Parker Solar Probe while the spacecraft was located at ∼0.81 au. The passage of these interplanetary CMEs (ICMEs) starting on November 29 (DOY 334) produced the largest enhancement of energetic ion...

Energetic particle transport in the interplanetary medium is known to be affected by magnetic structures. It has been demonstrated for solar energetic particles in near-Earth orbit studies, and also for the more energetic cosmic rays. In this paper, we show observational evidence that intensity variations of solar energetic particles can be correla...

Energetic particle transport in the interplanetary medium is known to be affected by magnetic structures. It has been demonstrated for solar energetic particles in near-Earth orbit studies, and also for the more energetic cosmic rays. In this paper, we show observational evidence that intensity variations of solar energetic particles can be correla...

Voyager 2 observations throughout the heliosheath from the termination shock to the heliopause are used to normalize and constrain model pickup ion (PUI) fluxes. Integrating normalized PUI fluxes along the Voyager 2 trajectory through the heliosheath, and combining these integral fluxes with the energy-dependent charge-exchange cross section and th...

We provide analysis of a coronal mass ejection (CME) that passed over Parker Solar Probe (PSP) on January 20, 2020 when the spacecraft was at just 0.32 AU. The Integrated Science Investigation of the Sun instrument suite measures energetic particle populations associated with the CME before, during, and after its passage over the spacecraft. We obs...

Understanding the elemental composition of the lunar regolith is important for expanding our knowledge of the history and geology of the Moon. Several methods have already been used to achieve this purpose, including direct analysis of lunar samples and satellite spectroscopy. Since computer modeling is important for processing the collected data,...

We analyze an energetic proton event associated with a stream interaction region (SIR) that was observed at Parker Solar Probe on day 320 of 2018 when the spacecraft was just 0.34 AU from the Sun. Using the Integrated Science Investigation of the Sun instrument suite, we perform a spectral analysis of the event and show how the observed spectra evo...

Early observations from the first orbit of Parker Solar Probe (PSP) show recurrent stream interaction regions that form close to the Sun. Energetic particle enhancements were observed on the 320th–326th day of the year 2018, which corresponds to ~1–7 days after the passage of the stream interface between faster and slower solar wind. Energetic part...

Aims. The Parker Solar Probe (PSP) orbit provides an opportunity to study the inner heliosphere at distances closer to the Sun than previously possible. Due to the solar minimum conditions, the initial orbits of PSP yielded only a few solar energetic particle (SEP) events for study. Recently during the fifth orbit, at distances from 0.45 to 0.3 au,...

Context. In 2020 May-June, six solar energetic ion events were observed by the Parker Solar Probe/IS⊙IS instrument suite at ≈0.35 AU from the Sun. From standard velocity-dispersion analysis, the apparent ion path length is ≈0.625 AU at the onset of each event. Aims. We develop a formalism for estimating the path length of random-walking magnetic fi...

Context. Silicon solid-state detectors are commonly used for measuring the specific ionization, dE∕dx, in instruments designed for identifying energetic nuclei using the dE∕dx versus total energy technique in space and in the laboratory. The energy threshold and species resolution of the technique strongly depend on the thickness and thickness unif...