Harlan Spence

Harlan Spence
University of New Hampshire | UNH · Institute for the Study of Earth, Oceans, and Space

Doctor of Philosophy

About

640
Publications
47,125
Reads
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17,630
Citations
Introduction
Harlan E. Spence earned his BA in Astronomy and Physics at Boston Univ. and his MS/PhD in Geophysics and Space Physics at UCLA, then worked at The Aerospace Corporation. He returned to BU as a faculty member in the Astronomy Dept.. In 2010, Spence joined UNH as Director of EOS and Professor of Physics. His research Interests include: theoretical and experimental space plasma physics; cosmic rays and radiation belt processes; heliospheric, planetary magnetospheric, lunar, and auroral physics.
Additional affiliations
January 2010 - present
University of New Hampshire
Position
  • Managing Director
January 2010 - present
University of New Hampshire
Position
  • Professor
April 1994 - December 2009
Boston University
Position
  • Professor of Astronomy

Publications

Publications (640)
Article
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This paper presents the highlights of joint observations of the inner magnetosphere by the Arase spacecraft, the Van Allen Probes spacecraft, and ground-based experiments integrated into spacecraft programs. The concurrent operation of the two missions in 2017–2019 facilitated the separation of the spatial and temporal structures of dynamic phenome...
Preprint
When the first CubeSats were launched nearly two decades ago, few people believed that the miniature satellites would likely prove to be a useful scientific tool. Skeptics abounded. However, the last decade has seen the highly successful implementation of space missions that make creative and innovative use of fast-advancing CubeSat and small satel...
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We present an observation of rapid flux depressions in relativistic electrons, which is referred to as “EMIC‐induced drifting electron holes (EDEHs).” The Arase, Van Allen Probes, and THEMIS detected simultaneously electron flux fluctuations. The time variation of flux shows depressions of 1‐min scale with energy dispersion, which appear only in th...
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We present a statistical study on the properties of equatorial electron pitch angle distributions (PADs) in the Earth's outer radiation belt, for the first time based on particle measurements from the entire Van Allen Probes mission. A detailed selection criteria is used to identify intervals when flux measurements at energies from 0.2 to 3.4 MeV a...
Article
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Flux enhancements of field‐aligned low‐energy O⁺ ion (FALEO) are simultaneously observed by Arase, Van Allen Probes A and B in the nightside inner magnetosphere during 05–07 UT on September 22, 2018. FALEOs appear after a magnetic dipolarization signature with approximately 6–20 min delay. It has the energy‐dispersion signature from a few keV to ∼1...
Article
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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)....
Article
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Previous spacecraft studies showed that stormtime poloidal ultralow‐frequency (ULF) waves in the ring current region have an antisymmetric (second harmonic) mode structure about the magnetic equator. This paper reports Van Allen Probes observations of symmetric ULF waves in the postnoon sector during a moderate geomagnetic storm. The mode structure...
Article
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Plain Language Summary Electromagnetic ion cyclotron (EMIC) waves are an important plasma waves that control energetic ion and relativistic electron precipitations in the terrestrial inner magnetosphere. We investigated the growth and propagation of fine‐structured EMIC waves observed simultaneously by two spacecraft (Japanese Arase and U.S. Van Al...
Article
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Measurements from NASA's Van Allen Probes have transformed our understanding of the dynamics of Earth's geomagnetically-trapped, charged particle radiation. The Van Allen Probes were equipped with the Magnetic Electron Ion Spectrometers (MagEIS) that measured energetic and relativistic electrons, along with energetic ions, in the radiation belts. A...
Article
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We present a machine‐learning‐based model of relativistic electron fluxes >1.8 MeV using a neural network approach in the Earth's outer radiation belt. The Outer RadIation belt Electron Neural net model for Relativistic electrons (ORIENT‐R) uses only solar wind conditions and geomagnetic indices as input. For the first time, we show that the state...
Article
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To examine the species dependence of the sustained energy spectrum gaps, in this letter, we analyzed the magnetic local time distribution of sustained proton and oxygen gaps and find that there is a clear difference between proton and oxygen ions: proton sustained gaps are predominantly distributed near the prenoon sector, while oxygen sustained ga...
Article
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Properly characterizing fast relativistic electron losses in the terrestrial Van Allen belts remains a significant challenge for accurately simulating their dynamics. In particular, magnetopause shadowing losses can deplete the radiation belt within hours or even minutes, but can have long‐lasting impacts on the subsequent belt dynamics. By statist...
Article
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This study investigates the energy spectrum of electron microbursts observed by the Focused Investigations of Relativistic Electron Burst Intensity, Range, and Dynamics II (FIREBIRD‐II, henceforth FIREBIRD) CubeSats. FIREBIRD is a pair of CubeSats, launched in January 2015 into a low Earth orbit, which focuses on studying electron microbursts. High...
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Plain Language Summary Very high energy electrons in near‐Earth space constitute a space radiation threat to spacecraft. All of this space radiation is traveling close to the speed of light. However, as we show here, nature remarkably imposes a limit to the number of these space radiation particles which can be generated once the acceleration is st...
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Plain Language Summary A pulsating aurora is known as the aurora that blinks in seconds to tens of seconds and a microburst is the periodic and short durational precipitation of ∼MeV energy electrons. These two phenomena have similar spatiotemporal features such as their hierarchy structure in time and occurrence time from midnight to morning. Othe...
Preprint
Full-text available
We present a machine-learning-based model of relativistic electron fluxes >1.8 MeV using a neural network approach in the Earth's outer radiation belt. The Outer RadIation belt Electron Neural net model for Relativistic electrons (ORIENT-R) uses only solar wind conditions and geomagnetic indices as input. For the first time, we show that the state...
Article
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The Relativistic Electron-Proton Telescope (REPT) instruments were designed to measure ∼2 to >18 MeV electrons and ∼18 to > 115 MeV protons as part of the science payloads onboard the dual Radiation Belt Storm Probes (RBSP) spacecraft. The REPT instruments were turned on and configured in their science acquisition modes about 2 days after the RBSP...
Article
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Plain Language Summary Hiss is a plasma wave with a broad frequency range spanning from tens to several thousand Hz, commonly observed in the dayside plasmasphere and plumes of the Earth's magnetosphere, and plays an important role in the loss of energetic electrons. Subject to the interaction with hiss waves, the radiation belt electrons precipita...
Article
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,...
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A dipolarization of the background magnetic field was observed during a conjunction of the Magnetospheric Multiscale (MMS) spacecraft and Van Allen Probe B on September 22, 2018. The spacecraft were located in the inner magnetosphere at L ∼ 6–7 just before midnight magnetic local time (MLT). The radial separation between MMS and Probe B was ∼1RE. G...
Article
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Isolated proton auroras (IPAs) appearing at subauroral latitudes are generated by energetic protons precipitating from the magnetosphere through interaction with electromagnetic ion cyclotron (EMIC) waves. An IPA thus indicates the spatial scale and temporal variation of wave‐particle interactions in the magnetosphere. In this study, a unique event...
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This study considers the impact of electron precipitation from Earth's radiation belts on atmospheric composition using observations from the NASA Van Allen Probes and NSF Focused Investigations of Relativistic Electron Burst Intensity, Range, and Dynamics (FIREBIRD II) CubeSats. Ratios of electron flux between the Van Allen Probes (in near-equator...
Article
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Stable auroral red (SAR) arcs are optical events with dominant 630.0‐nm emission caused by low‐energy electron heat flux into the topside ionosphere from the inner magnetosphere. SAR arcs are observed at subauroral latitudes and often occur during the recovery phase of magnetic storms and substorms. Past studies concluded that these low‐energy elec...
Article
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Van Allen Probes observations of ion spectra often show a sustained gap within a very narrow energy range throughout the full orbit. To understand their formation mechanism, we statistically investigate the characteristics of the narrow gaps for oxygen ions and find that they are most frequently observed near the noon sector with a peak occurrence...
Article
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Plain Language Summary ElectroMagnetic Ion Cyclotron (EMIC) waves occur in the Earth's magnetosphere and are excited during injections of hot ions from the magnetotail toward Earth. EMIC waves are known to cause precipitation of ∼MeV electrons into the upper atmosphere, which can lead to enhancements of ionization and chemical reactions, but some s...
Article
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We describe a new data product combining pitch angle resolved electron flux measurements from the Radiation Belt Storm Probes (RBSP) Energetic Particle Composition and Thermal Plasma (ECT) suite on the National Aeronautics and Space Administration’s Van Allen Probes. We describe the methodology used to combine each of the data sets and produce a co...
Article
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Plain Language Summary Electromagnetic waves caused by plasma particles in the Earth's magnetic fields are known to interact with high energy particles in the Earth's radiation belts, leading to loss of the particles into the Earth's atmosphere. We report on observations of the wave phenomena and their interaction with radiation belt particles usin...
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The two Van Allen Probes simultaneously recorded a coherently modulated quasiperiodic (QP) emission that persisted for 3 h. The magnetic field pulsation at the locations of the two satellites showed a substantial difference, and their frequencies were close to but did not exactly match the repetition frequency of QP emissions for most of the time,...
Article
We investigate the formation of He⁺ and O⁺ multiple-nose structures observed by the Helium, Oxygen, Proton, and Electron instrument onboard Van Allen Probes A on December 2, 2012. Previous studies have suggested that multiple-nose structures can be formed by changes in the convection electric field. However, the specifics of how these changes can p...
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We use Van Allen Probes (Radiation Belt Storm Probes A and B, henceforth RBSP-A and RBSP-B) and GOES-13 and GOES-15 (henceforth G-13 and G-15) multipoint magnetic field, electric field, plasma, and energetic particle observations to study the spatial, temporal, and spectral characteristics of compressional Pc5 pulsations observed during the recover...
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In this study, ion data from the HOPE spectrometers onboard 9 Van Allen Probes reveal the existence of wedge-like structures of O + , He + 10 and H + ions deep in the inner magnetosphere. The behaviors of the wedge-11 like structures in terms of temporal evolution, spatial distribution, upper en-12 ergy limit, as well as dependence on solar wind an...
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The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) has been orbiting the Moon since 2009 aboard the Lunar Reconnaissance Orbiter (LRO). From this vantage point, it samples the interplanetary energetic particle population outside the shielding of the Earth's magnetosphere. We report the sensor's observations of galactic cosmic rays (GCRs...
Article
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Recent solar conditions indicate a persistent decline in solar activity—possibly similar to the past solar grand minima. During such periods of low solar activity, the fluxes of galactic cosmic rays (GCRs) increase remarkably, presenting a hazard for long‐term crewed space missions. We used data from the Cosmic Ray Telescope for the Effects of Radi...
Article
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In this study we focus on the radiation belt dynamics driven by the geomagnetic storms during September 2017. Besides the long-lasting three-belt structures of ultrarelativistic electrons (>2 MeV, existing for tens of days), which has been studied intensively during the Van Allen Probe era, it is found that magnetospheric electrons of hundreds of k...
Article
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Plain Language Summary Whistler mode chorus is an electromagnetic emission present in the low‐density region of Earth's magnetosphere. Chorus waves can change the electron distribution in the plasma sheet to cause electron precipitation into Earth's upper atmosphere, leading to the diffuse aurora. We use satellite measurements of waves and electron...
Article
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Plain Language Summary The background electron density decreases away from the Earth with a sharp boundary in the density profile, which is defined as the plasmapause. Density irregularities are frequently observed near the plasmapause, and these density structures are believed to play an important role in the generation and propagation of plasma w...
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We investigate the longitudinal structure of the oxygen torus in the inner magnetosphere for a specific event found on 12 September 2017, using simultaneous observations from the Van Allen Probe B and Arase satellites. It is found that Probe B observed a clear enhancement in the average plasma mass (M) up to 3–4 amu at L = 3.3–3.6 and magnetic loca...
Preprint
Full-text available
We use Van Allen Probes and GOES-13 and -15 multipoint magnetic field, electric field, plasma, and energetic particle observations to study the spatial, temporal, and spectral characteristics of compressional Pc5 pulsations observed during the recovery phase of a strong geomagnetic storm on January 1, 2016. From ~ 19:00 UT to 23:02 UT, successive m...
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The radiation environment in free space and the related radiation exposure is seen as one of the main health detriments for future long-duration human exploration missions beyond Low Earth Orbit (LEO). The steady flux of energetic particles in the galactic cosmic radiation (GCR) produces a low dose-rate radiation exposure, which is heavily influenc...
Article
When high energy galactic cosmic ray (GCR) particles collide with the lunar regolith, they eject “albedo” particles from the surface. The albedo particles could be either scattered incident ions, or secondary ions and neutrons produced by the collisions of incident ions with the lunar regolith. In an effort to understand the nature of these albedo...
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Forecasting relativistic electron fluxes at geostationary Earth orbit (GEO) has been a long term goal of the scientific community, and significant advances have been made in the past, but the relation to the interior of the radiation belts, that is, to lower L‐shells is still not clear. In this work we have identified 60 relativistic electron enhan...
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Prolonged exposure to the galactic cosmic ray (GCR) environment is a potentially limiting factor for manned missions in deep space. Evaluating the risk associated with the expected GCR environment is an essential step in planning a deep space mission. This requires an understanding of how the local interstellar spectrum is modulated by the heliosph...
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Plain Language Summary We present a statistical study of the location of particles, particularly electrons, in currents around the Earth whose intensity is increased, or enhanced, rapidly (within 1 day). We use over 5 years of particle intensity and plasma density data from the Van Allen Probes satellites. We find that these quick enhancement event...
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This paper presents the first combined use of data from Magnetospheric Multiscale (MMS), Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS), and Van Allen Probes (RBSP) to study the 10 August 2016 magnetic dipolarization. We report the first correlation of MMS tail observations with TWINS energetic neutral atom (ENA) images of the ring curre...
Article
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The plasmasphere is a critical region of the magnetosphere. It is important for the evolution of Earth's radiation belts. Waves in the plasmasphere interior (hiss) and vicinity (electromagnetic ion cyclotron, chorus) help control the acceleration and loss of radiation belt particles. Thus, understanding the extent, structure, content, and dynamics...
Article
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Lightning discharges are known to inject whistler waves into the inner magnetosphere over a wide region around their source. When a discharge occurs, it radiates electromagnetic energy into the Earth‐ionosphere waveguide, some of which couples into the whistler mode and propagates through the ionospheric plasma away from the Earth. Previous studies...