George Chowah Ho

• PhD
• Senior Program Manager at Southwest Research Institute

It was the best of times, it was the worst of times, . . . - for the thermal/suprathermal particle populations in the vicinity of two traveling interplanetary shocks observed by Solar Orbiter on 2023-11-29 07:51:17 UTC and 2023-11-30 10:47:26 UTC at $\sim 0.83$ astronomical units from the Sun. We investigate these two very dissimilar shocks and elu...

With the launch of Solar Orbiter, the intensity and composition of suprathermal particles have been sampled within the inner heliosphere at distances between ∼0.3 and 1 au. This includes a multitude of observations of suprathermal ions associated with stream interaction regions (SIRs) measured by the Solar Orbiter Energetic Particle Detector, with...

Context. Solar energetic particle (SEP) events provide crucial insights into particle acceleration and transport mechanisms in the heliosphere. Inverse velocity dispersion (IVD) events, characterized by higher-energy particles that arrive later than lower-energy particles, challenge the classical understanding of SEP events and are increasingly obs...

We examine ³ He-rich solar energetic particles (SEPs) detected on 2023 October 24–25 by Solar Orbiter at 0.47 au. Measurements reveal that heavy-ion enhancements increase irregularly with mass, peaking at S. C, and especially N, Si, and S, stand out in the enhancement pattern with large abundances. Except for ³ He, heavy-ion spectra can only be mea...

On 2022 March 10 a coronal mass ejection erupted from the Sun, resulting in Solar Orbiter observations at 0.45 au of both dispersive solar energetic particles arriving prior to the interplanetary coronal mass ejection (ICME) and locally accelerated particles near the ICME-associated shock structure as it passed the spacecraft on 2022 March 11. This...

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...

A series of solar energetic electron (SEE) events was observed from 2022 November 9 to November 15 by Solar Orbiter, STEREO-A, and near-Earth spacecraft. At least 32 SEE intensity enhancements at energies >10 keV were clearly distinguishable in Solar Orbiter particle data, with 13 of them occurring on November 11. Several of these events were accom...

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 analyze the spectral properties of ³ He and ⁴ He as well as the heavy ions (oxygen, neon, magnesium, silicon, and iron) in 80 ³ He-rich solar energetic particle (SEP) events observed by the Ultra-Low-Energy Ion Spectrometer on board the Advanced Composition Explorer spacecraft since its launch in 1997 until 2024. We split the spectral analysis i...

We have surveyed ³ He-rich events on the Solar Orbiter mission from 2020 April to 2024 April, selecting isolated injections whose rollover ³ He spectral shape is presumed to represent the initial acceleration state, unprocessed by subsequent activity such as coronal mass ejections or jets. A main goal has been to find relationships between the spec...

Context. On 2022 January 20, the Energetic Particle Detector (EPD) on board Solar Orbiter measured a solar energetic particle (SEP) event showing unusual first arriving particles from the anti-Sun direction. Near-Earth spacecraft separated 17{\deg} in longitude to the west from Solar Orbiter measured classic antisunward-directed fluxes. STEREO-A an...

Context. By coupling the EUropean Heliospheric FORcasting Information Asset (EUHFORIA) and the improved Particle Acceleration and Transport in the Heliosphere (iPATH) model, two energetic storm particle (ESP) events, originating from the same active region (AR 13088) and observed by Solar Orbiter (SolO) on August 31 2022 and September 05 2022, are...

In the next decade, there is an opportunity for very high return on investment of relatively small budgets by elevating the priority of smallsat funding in heliophysics. We've learned in the past decade that these missions perform exceptionally well by traditional metrics, e.g., papers/year/\$M (Spence et al. 2022). It is also well established that...

In the next decade, there is an opportunity for very high return on investment of relatively small budgets by elevating the priority of smallsat funding in heliophysics. We've learned in the past decade that these missions perform exceptionally well by traditional metrics, e.g., papers/year/\$M (Spence et al. 2022 -- arXiv:2206.02968). It is also w...

In this study we present the observation of Mercury’s inner southern magnetosphere and surrounding regions, never previously explored, as detected by the two ion sensors of the instrument package: ‘Search for Exospheric Refilling and Emitted Natural Abundances’ (SERENA), named ‘Planetary Ion CAMera’ (PICAM) and ‘Miniaturized Ion Precipitation Analy...

Using ion measurements from Ultra-Low-Energy Isotope Spectrometer (ULEIS) observations onboard Advanced Composition Explorer (ACE) and Solar Isotope Spectrometer (SIS) observations onboard the Solar Terrestrial Observatory (STEREO)-A and STEREO-B spacecraft, we have identified 854 3He-rich time periods between 1997 September and 2021 March. We incl...

The ESA-JAXA BepiColombo mission will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric dynamics at Mercury as well as their interactions with the solar wind, radiation, and interplanetary dust. Many scientific instruments onboard the two spacecraft will be comp...

The velocity of alpha particles relative to protons can vary depending on the solar wind type and distance from the Sun (Marsch 2012). Measurements from the previous spacecraft provided the alpha-proton's differential velocities down to 0.3 au. Parker Solar Probe (PSP) now enables insights into differential flows of newly accelerated solar wind clo...

The velocity of alpha particles relative to protons can vary depending on the solar wind type and distance from the Sun. Measurements from the previous spacecraft provided the alpha–proton differential velocities down to 0.3 au. The Parker Solar Probe (PSP) now enables insights into differential flows of the newly accelerated solar wind closer to t...

We propose a model for interpreting highly variable ion composition ratios in solar energetic particle (SEP) events recently observed by the Parker Solar Probe (PSP) at 0.3–0.45 au. We use numerical simulations to calculate SEP propagation in a turbulent interplanetary magnetic field with a Kolmogorov power spectrum from large scales down to the gy...

Sheaths ahead of coronal mass ejections (CMEs) are large heliospheric structures that form with CME expansion and propagation. Turbulent and compressed sheaths contribute to the acceleration of particles in the corona and in interplanetary space, but the relation of their internal structures to particle energization is still relatively little studi...

Context. On 2020 November 29, the first widespread solar energetic particle (SEP) event of solar cycle 25 was observed at four widely separated locations in the inner (≲1 AU) heliosphere. Relativistic electrons as well as protons with energies > 50 MeV were observed by Solar Orbiter (SolO), Parker Solar Probe, the Solar Terrestrial Relations Observ...

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...

Context. Solar Orbiter strives to unveil how the Sun controls and shapes the heliosphere and fills it with energetic particle radiation. To this end, its Energetic Particle Detector (EPD) has now been in operation, providing excellent data, for just over a year. Aims. EPD measures suprathermal and energetic particles in the energy range from a few...

The Solar Orbiter flyby of Venus on 27 December 2020 allowed for an opportunity to measure the suprathermal to energetic ions in the Venusian system over a large range of radial distances to better understand the acceleration processes within the system and provide a characterization of galactic cosmic rays near the planet. Bursty suprathermal ion...

Solar Orbiter aims to unveil how the Sun controls and shapes the heliosphere and fills it with energetic particle radiation. To this end, its Energetic Particle Detector (EPD) has now been in operation and providing excellent data for just over a year. EPD consists on four different sensors measuring suprathermal and energetic particles in the ener...

We propose a model for interpreting highly variable ion composition ratios in solar energetic particles (SEP) events recently observed by Parker Solar Probe (PSP) at $0.3 - 0.45$ astronomical unit. We use numerical simulations to calculate SEP propagation in a turbulent interplanetary magnetic field with a Kolmogorov power spectrum from large scale...

This work presents an overview of the in-flight engineering data of the Energetic Particle Detector (EPD) instrument suite during its first year of operation. EPD is part of the in-situ scientific payload of the ESA/NASA Solar Orbiter mission which was launched in February 2020. After completion of its commissioning phase, Solar Orbiter started its...

A Correction to this paper has been published: https://doi.org/10.1007/s11214-021-00809-8

Aims. We present observations of the first coronal mass ejection (CME) observed at the Solar Orbiter spacecraft on April 19, 2020, and the associated Forbush decrease (FD) measured by its High Energy Telescope (HET). This CME is a multispacecraft event also seen near Earth the next day. Methods. We highlight the capabilities of HET for observing sm...

The ESA-JAXA BepiColombo mission to Mercury will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric particle dynamics at Mercury as well as their interactions with solar wind, solar radiation, and interplanetary dust. The particle instrument suite SERENA (Search...

Context. Solar Orbiter is expected to have flown close to the tail of comet C/2019 Y4 (ATLAS) during the spacecraft’s first perihelion in June 2020. Models predict a possible crossing of the comet tails by the spacecraft at a distance from the Sun of approximately 0.5 AU. Aims. This study is aimed at identifying possible signatures of the interact...

Solar Orbiter’s in situ coordination working group met frequently during the development of the mission with the goal of ensuring that its in situ payload has the necessary level of coordination to maximise science return. Here we present the results of that work, namely how the design of each of the in situ instruments (EPD, MAG, RPW, SWA) was gui...

The Parker Solar Probe was launched on 2018 August 12 and completed its second orbit on 2019 June 19 with perihelion of 35.7 solar radii. During this time, the Energetic particle Instrument-Hi (EPI-Hi, one of the two energetic particle instruments comprising the Integrated Science Investigation of the Sun, ISOIS) measured seven proton intensity inc...

The prediction of a supersonic solar wind¹ was first confirmed by spacecraft near Earth2,3 and later by spacecraft at heliocentric distances as small as 62 solar radii⁴. These missions showed that plasma accelerates as it emerges from the corona, aided by unidentified processes that transport energy outwards from the Sun before depositing it in the...

Suprathermal ion composition associated with corotating interaction regions (CIRs) exhibited a solar cycle variation during solar cycle 23 and the beginning of solar cycle 24. However, it is unclear if this variation would remain when considering all of solar cycle 24, or whether the variations in the CIR-associated suprathermal ion composition wou...

After decades of observations of solar energetic particles from space-based observatories, relevant questions on particle injection, transport, and acceleration remain open. To address these scientific topics, accurate measurements of the particle properties in the inner heliosphere are needed. In this paper we describe the Energetic Particle Detec...

Correction to: Solar Phys (2019) 294:3310.1007/s11207-019-1420-z The original article has been corrected due to typesetting mistakes made in the last paragraph of section 2. Observations.

We investigated ³He-rich solar energetic particle (SEP) events in the current solar cycle starting in 2009 through 2017. Both “impulsive” (flare-related) ³He-rich and CME-related “gradual” events are included. In the former solar cycle, we found the number of observed ³He-rich events correlated with solar activity. The same correlation is seen agai...

Solar Orbiter is a joint ESA-NASA mission planed for launch in October 2018. The science payload includes remote-sensing and in-situ instrumentation designed with the primary goal of understanding how the Sun creates and controls the heliosphere. The spacecraft will follow an elliptical orbit around the Sun, with perihelion as close as 0.28 AU. Dur...

The Solar Wind Electrons Alphas and Protons (SWEAP) Investigation on Solar Probe Plus is a four sensor instrument suite that provides complete measurements of the electrons and ionized helium and hydrogen that constitute the bulk of solar wind and coronal plasma. SWEAP consists of the Solar Probe Cup (SPC) and the Solar Probe Analyzers (SPAN). SPC...

The time-intensity profile of large solar energetic particle (SEP) event is well organized by solar longitude as observed at Earth orbit. This is mostly due to different magnetic connection to the shock that is associated with large SEP event propagates from the Sun to the heliosphere. Earlier studies have shown event averaged heavy ion abundance r...

The MESSENGER mission to Mercury has provided a wealth of new data about energetic particle phenomena. With observations from MESSENGER's Energetic Particle Spectrometer (EPS), as well as data arising from energetic electrons recorded by the X-Ray Spectrometer (XRS) and Gamma-Ray and Neutron Spectrometer (GRNS) instruments, recent work greatly exte...

The X-Ray Spectrometer (XRS) that flew on the MESSENGER spacecraft measured X-rays from the surface of Mercury in the energy range ~1–10 keV. Detection of characteristic Kα-line emissions from Mg, Al, Si, S, Ca, Ti, and Fe yielded the surface abundances of these geologically important elements. Spatial resolution as fine as ~40 km (across track) wa...

During solar energetic particle (SEP) events, the inner heliosphere is bathed in MeV electrons. Through magnetic reconnection, these relativistic electrons can enter the magnetosphere of Mercury, nearly instantaneously filling the regions of open field lines with precipitating particles. With energies sufficient to penetrate solid aluminum shieldin...

Coronal mass ejections (CMEs) and other transient solar phenomena play important roles in magnetospheric and exospheric dynamics. Although a planet may interact only occasionally with the interplanetary consequences of these events, such transient phenomena can result in departures from the background solar wind that often involve more than an orde...

Data from the MESSENGER Gamma-Ray and Neutron Spectrometer have been used to detect and characterize energetic electron (EE) events in Mercury's magnetosphere. This instrument detects EE events indirectly via bremsstrahlung photons that are emitted when instrument and spacecraft materials stop electrons having energies of tens to hundreds of keV. F...

Mercury's regolith, derived from the crustal bedrock, has been altered by a set of space weathering processes. Before we can interpret crustal composition, it is necessary to understand the nature of these surface alterations. The processes that space weather the surface are the same as those that form Mercury's exosphere (micrometeoroid flux and s...

We discuss measurements of the Jovian and Europan plasma environments necessary for magnetic sounding of Europa's subsurface oceans. We introduce a suite of Faraday cup instrumentation that can provide these high quality plasma measurements.

The Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) on the two Van Allen Probes spacecraft is the magnetosphere ring current instrument that will provide data for answering the three over-arching questions for the Van Allen Probes Program: RBSPICE will determine “how space weather creates the storm-time ring current around Earth, h...

Particle Environment Package (PEP) is a suite of particle sensors proposed for the ESA JUICE mission. PEP includes sensors for the comprehensive measurements of electrons, ions, energetic neutrals, and neutral gas. PEP covers over nine decades of energy <0.001 eV to >1 MeV with full angular coverage. Combining remote global imaging via energetic ne...

Radiation tolerant charged particle detectors to be flown to Jupiter. Instrumentation to focus on the in situ detection of energetic charged particles in a magnetospheric environment.

Understanding the physical processes operating in Solar Energetic Particle (SEP) events is a major goal of the Solar Orbiter mission because of the importance of acceleration processes in solar system and astrophysical sites, and because of the potential impact of these events on space hardware. The association of the largest SEP events with shocks...

MESSENGER's 14 January and 6 October 2008 and 29 September 2009 encounters with Mer-cury have provided new measurements of dynamic variations in the planet's coupled atmo-sphere-magnetosphere system. The three flybys took place under very different interplanetary magnetic field (IMF) conditions. Consistent with predictions of magnetospheric models...

Mercury does not have a dense atmosphere whose altitude dependence is described by a single scale height. The Ultraviolet Spectrometer (UVS) instrument on Mariner 10 discovered a tenuous exosphere with gaseous species H, He, and O. Since the Mariner 10 flybys, ground-based telescopes have been used to observe the exosphere of Mercury in the Na and...

‘Search for Exospheric Refilling and Emitted Natural Abundances’ (SERENA) is an instrument package that will fly on board the BepiColombo/Mercury Planetary Orbiter (MPO). It will investigate Mercury's complex particle environment that is composed of thermal and directional neutral atoms (exosphere) caused by surface release and charge-exchange proc...

Multiple processes in the solar atmosphere or near the Sun are capable of energizing electrons and ions which are remotely observed as Solar Energetic Particle (SEP) events. SEP events are of great interest not only because they can cause large radiation increases in the interplanetary space and over the Earth's polar regions, but also because they...

Collisionless shocks accelerate charged particles throughout heliosphere, from low in the solar corona to the outer edge of the supersonic solar wind. Particles can gain energy while interacting with shocks in different ways, depending on conditions at the shock and on particle species and energy. Different acceleration processes generally produce...

SERENA (`Search for Exospheric Refilling and Emitted Natural Abundances') is an instrument package that will fly on board the BepiColombo Mercury Planetary Orbiter (MPO) it will investigate the Mercury's complex particle environment that surrounds the planet. Such an environment is composed by thermal and directional neutral atoms (exosphere) origi...

NASA's MESSENGER mission to the planet Mercury includes a comprehensive set of advanced instruments. Launched in August 2004, MESSENGER thus far has successfully completed four planetary flybys (one of Earth, two of Venus, and one of Mercury) and is well on its way to complete two more Mercury flybys before insertion into orbit about Mercury in 201...

Our knowledge of Mercury's magnetosphere had been derived from two Mariner 10 flybys in 1974-1975 that established the presence of an intrinsic magnetic field and of some energetic and plasma electrons. Launched on August 3, 2004, MESSENGER executed the first of three flybys of Mercury on January 14, 2008. The Magnetometer provided high-resolution...

Ionic charge states measurements of suprathermal and energetic ions are a powerful diagnostic tool. It is important in determining the sources, injection and acceleration processes involved in the generation of these populations in interplanetary space. To distinguish between singly and multiply charged ions is crucial to the question of how much i...

A prototype multi-foil sensor has been developed to study the secondary electron distributions generated by ions penetrating multiple thin foils The sensor includes a mechanical support for one to four foils electrostatic deflection microchannel plate MCP for the secondary electron detection and amplification adjustable high voltage HV biasing for...

ESA's BepiColombo mission to the planetary Mercury includes a comprehensive set of advanced instruments. Strofio, one of the instruments on the SERENA neutral and ionizing particle suite on the Mercury Planet Orbit (MPO), is a high mass resolution, time-of-flight system for low energy neutral particles. Key questions addressed by Strofio are: * Wha...

We are developing a system to predict the arrival of interplanetary (IP) shocks at the Earth. These events are routinely detected by the Electron, Proton, and Alpha Monitor (EPAM) instrument aboard NASA’s ACE spacecraft, which is positioned at Lagrange Point 1 (L1). In this work, we use historical EPAM data to train an IP shock forecasting algorith...

At very strong shock passages, protons (and other ions) may be accelerated at or near a spacecraft resulting in substantial particle intensities increases. Such events may be a significant space weather hazard, yet we are still unable to accurately forecast their arrival time or the magnitude of the particle increase. Here, we classify the >10 MeV...

The characterization of energetic electrons in space plasmas is fundamental to the scientific understanding of those plasmas, their magnetic topology, and the electric fields and waves which may be modifying the plasma. High time resolution is often very important as is high-energy resolution, clean separation of ions and electrons, and comprehensi...

Recent theoretical work has posited that proton‐generated Alfvén waves scatterions according to their rigidity during propagation from the acceleration region to the observed position. In particular, predictions have been made for the initial behavior of the high energy (> 2 MeV/nucleon) He/H and Fe/O ratios during large solar energetic particle (S...

In the course of this decade, two NASA deep space mission to the inner and outer heliosphere, MESSENGER to the planet Mercury and New Horizons to the planet Pluto, will carry onboard energetic particle spectrometers. The combination of measurements near the Sun (0.3 AU), and from the outer heliosphere (up to almost 40 AU), will ideally complement t...

Using data from the Active Magnetospheric Particle Tracer Explorers/Charge Composition Explorer spacecraft, we make a detailed comparison between the observed polarization properties of electromagnetic ion cyclotron (EMIC) waves and those predicted by theory. The polarization can be described by three parameters: the ellipticity ε, the ratio of par...

We present a study of the proton cyclotron instability in the Earth's outer magneto- sphere, L > 7, using Active Magnetosphere Particle Tracer Explorers/Charge Composition Explorer (AMPTE/CCE) magnetic field, ion, and plasma wave data. The analysis addresses the energy of protons that generate the waves, the ability of linear theory to predict both...

We compare the substructures of the 1997 February 07 coronal mass ejection (CME) observed near the Sun with a corresponding event in the interplanetary medium to determine the origin of magnetic clouds (MCs). We find that the eruptive prominence core of the CME observed near the Sun may not directly become a magnetic cloud as suggested by some auth...

Impulsive solar energetic particle (SEP) events are associated with impulsive X-ray flares. They are often (but not always) accompanied by non-relativistic electrons (10100 keV), metric solar type III radio bursts, and also occasional large enhancements of the 3 He/4 He ratio compared to the value typical of the solar wind (10-4 ). Using the ULEIS...

The time-intensity profile of large solar energetic particle (SEP) event is well organized by solar longitude as observed at Earth orbit. This is mostly due to different magnetic connection to the shock that is associated with large SEP event propagates out from the Sun to the heliosphere. Recent studies have shown event averaged heavy ion abundanc...