Robert Colby Allen

Robert Colby Allen
Johns Hopkins University | JHU · Applied Physics Laboratory

Ph.D. Physics

About

109
Publications
10,062
Reads
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1,271
Citations
Introduction
My research interests lie in space plasma phenomena. This includes particle acceleration in the solar wind, interactions between the solar wind and planetary magnetospheres and surfaces, sources and evolution of magnetospheric plasma, wave-particle interactions, and space flight instrumentation. Experience includes comprehensive studies of solar wind-originating plasma injection and subsequent evolution in the magnetospheres of Earth and Saturn, investigations on EMIC wave generation and propagation in the Earth’s outer magnetosphere, particle acceleration in stream interaction regions, as well as space flight instrumentation and calibration.
Additional affiliations
June 2019 - present
Johns Hopkins University
Position
  • Professor (Full)
September 2017 - June 2019
Johns Hopkins University
Position
  • PostDoc Position
June 2017 - September 2017
NASA Goddard Planetary Heliophysics Institute - University of Maryland Baltimore County
Position
  • General Associate
Education
January 2014 - May 2017
August 2007 - May 2011

Publications

Publications (109)
Article
Full-text available
is well accepted that the propagation of electromagnetic ion cyclotron (EMIC) waves are bidirectional near their source regions and unidirectional when away from these regions. The generally believed source region for EMIC waves is around the magnetic equatorial plane. Here we describe a series of EMIC waves in the Pc1 (0.2-5 Hz) frequency band abo...
Article
Full-text available
Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, and local p...
Article
Full-text available
Geomagnetically trapped oxygen ions of solar and ionospheric origin have previously been observed in the Earth's magnetosphere. Early observations from AMPTE/CCE have studied this distribution within a limited spatial range of L-shells over all magnetic local times (MLT). This study expands on these early results using observations from the Polar s...
Preprint
Full-text available
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...
Article
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...
Chapter
Energetic neutral atom (ENA) imaging of the terrestrial magnetosphere is reviewed. The history from the first measurements of ENAs to the realization that their detection can be used as a remote imaging diagnostic is presented and the basic production mechanism of ENAs are described. The measurement principle is laid out and categorized for high (≥...
Article
Full-text available
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...
Article
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...
Article
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...
Article
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...
Poster
Full-text available
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...
Preprint
Full-text available
We report observations of a relatively long period of 3He-rich solar energetic particles (SEPs) measured by Solar Orbiter. The period consists of several well-resolved ion injections. The high-resolution STEREO-A imaging observations reveal that the injections coincide with EUV jets/brightenings near the east limb, not far from the nominal magnetic...
Preprint
Full-text available
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. EPD measures suprathermal and energetic particles in the energy range from a few keV up to (near...
Article
Full-text available
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...
Article
Context. On December 27, 2020, Solar Orbiter completed its first gravity assist manoeuvre of Venus (VGAM1). While this flyby was performed to provide the spacecraft with sufficient velocity to get closer to the Sun and observe its poles from progressively higher inclinations, the Radio and Plasma Wave (RPW) consortium, along with other operational...
Article
Full-text available
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...
Article
Full-text available
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...
Article
Context. The induced magnetosphere of Venus is caused by the interaction of the solar wind and embedded interplanetary magnetic field with the exosphere and ionosphere of Venus. Solar Orbiter entered Venus’s magnetotail far downstream, > 70 Venus radii, of the planet and exited the magnetosphere over the north pole. This offered a unique view of th...
Preprint
Context. The induced magnetosphere of Venus is caused by the interaction of the solar wind and embedded interplanetary magnetic field with the exosphere and ionosphere of Venus. Solar Orbiter entered Venus’s magnetotail far downstream, > 70 Venus radii, of the planet and exited the magnetosphere over the north pole. This offered a unique view of th...
Article
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...
Preprint
Full-text available
The spatial distribution of energetic protons contributes towards the understanding of magnetospheric dynamics. Based upon 17 years of the Cluster/RAPID observations, we have derived machine learning-based models to predict the proton intensities at energies from 28 to 1,885 keV in the 3D terrestrial magnetosphere at radial distances between 6 and...
Article
Full-text available
Plain Language Summary The Earth's magnetosphere is a very dilute cloud of charged particles that are trapped in the Earth's magnetic field. This cloud is surrounded by the solar wind, another very dilute gas that flows supersonically throughout the solar system. These two plasmas can couple to each other via magnetic reconnection, a fundamental pl...
Article
Full-text available
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...
Article
Full-text available
Electromagnetic ion cyclotron (EMIC) waves play important roles in particle loss processes in the magnetosphere. Determining the evolution of EMIC waves as they propagate and how this evolution affects wave-particle interactions requires accurate knowledge of the wave vector, k. We present a technique using the curl of the wave magnetic field to de...
Article
Full-text available
We discuss scientific mysteries in the planetary systems of Uranus and Neptune and argue that magnetosphere-related measurements are key to resolve them. Uranus and Neptune represent a distinct class of planets that remains the least-investigated in the solar system and marks the frontier for a wide range of scientific areas. Several reviews have p...
Preprint
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...
Article
Full-text available
The addition of Parker Solar Probe (PSP) to the Heliophysics System Observatory has allowed for the unprecedented ability to study Corotating Interaction Regions (CIRs) at multiple radial distances without significant temporal/longitudinal variations. On September 19, 2019, PSP observed a CIR at ∼0.5 au when it was nearly radially aligned with the...
Article
Energetic particles (>∼25 keV) have been observed routinely in the terrestrial magnetosheath, but have not been well studied at the magnetosheaths of the outer planets. Here we analyze energetic electrons and ions (mostly protons) in the vicinity (±1 RS) of Saturn's magnetopause, using particle data acquired with the low‐energy magnetosphere measur...
Article
Full-text available
Energetic particles (>∼25 keV) have been observed routinely in the terrestrial magnetosheath, but have not been well studied at the magnetosheaths of the outer planets. Here we analyze energetic electrons and ions (mostly protons) in the vicinity (±1 RS) of Saturn's magnetopause, using particle data acquired with the low‐energy magnetosphere measur...
Presentation
Full-text available
Solar Orbiter was launched on Febrauary 10, 2020 and its Energetic Particle Detector (EPD) suite started returning data on February 29, 2020. The four EPD sensors STEP, EPT, SIS, and HET measure suprathermal and energetic particles between a few keV and ~ 1 GeV/nuc. The Sun is currently exiting its deep and prolonged activity minimum, and first par...
Article
Full-text available
An extended interval of perturbed magnetospheric conditions in November 2016 supported increased convection and sunward transport of plasmaspheric material. During this period of time the Magnetospheric Multiscale satellites, with their apogees along Earth's dusk‐side outer magnetosphere, encountered several cold plasma density structures at the sa...
Article
Full-text available
Stream interaction regions (SIRs) and corotating interaction regions (CIRs) are important phenomena in heliospheric physics. These large-scale structures vary temporally and spatially, both in latitude and with radial distance. The additions of Parker Solar Probe (PSP) and Solar Orbiter have allowed for investigations into the radial evolution of t...
Article
Full-text available
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 V...
Article
One of the major and unfortunately unforeseen sources of background for the current generation of X-ray telescopes are few tens to hundreds of keV (soft) protons concentrated by the mirrors. One such telescope is the European Space Agency's (ESA) X-ray Multi-Mirror Mission (XMM-Newton). Its observing time lost due to background contamination is abo...
Preprint
Full-text available
One of the major and unfortunately unforeseen sources of background for the current generation of X-ray telescopes are few tens to hundreds of keV (soft) protons concentrated by the mirrors. One such telescope is the European Space Agency's (ESA) X-ray Multi-Mirror Mission (XMM-Newton). Its observing time lost due to background contamination is abo...
Article
Full-text available
In this paper, we exploit the charge-dependent nature of auroral phenomena in Jupiter's polar cap region to infer the charge states of energetic oxygen and sulfur. To date, there are very limited and sparse measurements of the >50 keV oxygen and sulfur charge states, yet many studies have demonstrated their importance in understanding the details o...
Article
Full-text available
Uranus and Neptune are the least-explored planets in our Solar System. This paper summarizes mysteries about these incredibly intriguing planets and their environments spurred by our limited observations from Voyager 2 and Earth-based systems. Several of these observations are either inconsistent with our current understanding built from exploring...
Article
Full-text available
Advanced warning of a stream interaction region (SIR) or co-rotating interaction region (CIR)impinging upon the magnetosphere of Earth is important for space weather forecasting, due to the ability ofSIRs/CIRs to trigger geomagnetic storms and affect ionospheric composition and winds. However, a focused investigation of the likelihood that either a...
Article
Full-text available
The Energetic Particle Instrument–Low Energy (EPI-Lo) experiment has detected several weak, low-energy (~30–300 keV nucleon⁻¹) solar energetic particle (SEP) events during its first two closest approaches to the Sun, providing a unique opportunity to explore the sources of low-energy particle acceleration. As part of the Parker Solar Probe (PSP) In...
Article
Full-text available
Several fast solar wind streams and stream interaction regions (SIRs) were observed by the Parker Solar Probe (PSP) during its first orbit (2018 September–2019 January). During this time, several recurring SIRs were also seen at 1 au at both L1 (Advanced Composition Explorer (ACE) and Wind) and the location of the Solar Terrestrial Relations Observ...
Article
Full-text available
The Integrated Science Investigation of the Sun (IS⊙IS) suite on board NASA's Parker Solar Probe (PSP) observed six distinct enhancements in the intensities of suprathermal-through-energetic (~0.03–3 MeV nucleon⁻¹) He ions associated with corotating or stream interaction regions (CIR or SIR) during its first two orbits. Our results from a survey of...
Article
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, IS⊙IS) measured seven proton intensity inc...
Article
Full-text available
We present an analysis of Parker Solar Probe (PSP) IS⊙IS observations of ~30–300 keV n⁻¹ ions on 2018 November 11 when PSP was about 0.25 au from the Sun. Five hours before the onset of a solar energetic particle (SEP) event, a coronal mass ejection (CME) was observed by STEREO-A/COR2, which crossed PSP about a day later. No shock was observed loca...
Article
Full-text available
A solar energetic particle event was detected by the Integrated Science Investigation of the Sun (IS⊙IS) instrument suite on Parker Solar Probe (PSP) on 2019 April 4 when the spacecraft was inside of 0.17 au and less than 1 day before its second perihelion, providing an opportunity to study solar particle acceleration and transport unprecedentedly...