Dennis K. Haggerty

Proton, helium, and electron spectra during the large solar particle events of October-November 2003

The extraordinary period from late October through early November 2003 was marked by more than 40 coronal mass ejections (CME), eight X-class flares, and five large solar energetic particle (SEP) events. Using data from instruments on the ACE, SAMPEX, and GOES-11 spacecraft, the fluences of H, He, O, and electrons have been measured in these five events over the energy interval from ∼0.1 to >100 MeV/nucleon for the ions and ∼0.04 to 8 MeV for electrons. The H, He, and O spectra are found to resemble double power laws, with a break in the spectral index between ∼5 and ∼50 MeV/nucleon which appears to depend on the charge-to-mass ratio of the species. Possible interpretations of the relative location of the H and He breaks are discussed. The electron spectra can also be characterized by double power laws, but incomplete energy coverage prevents an exact determination of where and how the spectra steepen. The proton and electron fluences in the 28 October 2003 SEP event are comparable to the largest observed during the previous solar maximum, and within a factor of 2 or 3 of the largest SEP events observed during the last 50 years. The 2-week period covered by these observations accounted for ∼20% of the high-energy solar-particle fluence over the years from 1997 to 2003. By integrating over the energy spectra, the total energy content of energetic protons, He, and electrons in the interplanetary medium can be estimated. After correcting for the location of the events, it is found that the kinetic energy in energetic particles amounts to a significant fraction of the estimated CME kinetic energy, implying that shock acceleration must be relatively efficient in these events.

Impulsive Near-relativistic Solar Electron Events: Delayed Injection with Respect to Solar Electromagnetic Emission

The time histories of near-relativistic scatter-free impulsive beamlike electron events (38-315 keV, 0.4 < v/c < 0.8) measured at 1 AU provide unique information on their solar acceleration and release. We have identified 79 such impulsive events from 1997 August through 2000 September. Detailed statistical analysis of the timing between the near-relativistic electron injection and the soft X-ray, microwave, chromospheric H?, and metric and decametric type III radio emission shows that the near-relativistic electrons measured by the Advanced Composition Explorer/Electron, Proton, and Alpha Monitor in orbit around the Earths first Lagrangian point are associated with western hemisphere events and are injected with a median delay of ~10 minutes after the start of the electromagnetic emissions (including metric and decametric type III events). The delayed injection, as well as there being only a weak statistical correlation between the intensities of the near-relativistic electrons and the characteristics of the electromagnetic emissions, indicates that the escaping near-relativistic electron populations are not directly related to those that generate the prompt flare-related emissions. The observations are consistent with acceleration of the escaping near-relativistic electrons by an outgoing coronal shock (V ~ 1000 km s-1) launched near the time of the prompt electromagnetic emissions.

Observations of Jovian upstream events by Ulysses

The heliosphere instrument for spectra composition and anisotropy at low energy (HISCALE) experiment on board the Ulysses spacecraft, during the Jovian flyby. measured 192 distinct 61-77 keV upstream ion events of probable Jovian origin. Event-averaged characteristics such as intensities, anisotropies, power law spectral exponents, averaged event duration, and magnetic field configurations were obtained. Within 1000 R J . all ion observations >2.92 particles/(cm 2 sr s keV) were found to be of probable Jovian origin. Evidence for velocity dispersion and convecting spatial structures was discovered through detailed analysis of individual events. Jupiter was found to be a significant source of interplanetary ions and electrons.

Composition of energetic particles in the Jovian magnetotail

[1] The New Horizons spacecraft offered a unique opportunity to explore the distant Jovian magnetotail to over 2565 Jovian Radii. Previous observations of ion abundances were available only out to ∼150 Jovian Radii. During the 100+-day exploration of the magnetotail, New Horizons observed a number of energetic particle bursts, similar to particle bursts observed by Galileo much closer to Jupiter. We examine the composition of these dynamic structures and compare the ion abundances with those found in more quiescent regions. We show that the composition of these energetic bursts is Iogenic and suggest it is within these bursts that Jupiter releases the bulk of its energetic material. We report on the ion composition ratios as a function distance down the Jovian magnetotail, finding an increasing intrusion of interplanetary He into the tail with distance from the planet. These observations show that the radial gradients in particle flux observed by Galileo in the magnetotail close to Jupiter extend deep into the magnetotail. We observed large electron intensities at the noon magnetopause crossing and continuous strong 10-h modulations in electron intensity to nearly 500 Jovian Radii toward the tail. Our current hypothesis is that Jupiter enforces azimuthal rotation on some fields to distances of over a few hundred Jovian Radii. At distances greater than 500 Jovian Radii we observed long-duration periods of strong electron anisotropy beaming down the magnetotail. Intermittent observations of 10-h electron modulations continue into distant regions of the magnetotail and we suggest these are a signature of occasional field line connection to the magnetosphere.

Escaping near-relativistic electron beams from the solar corona

Abstract Processes in the solar corona are prodigious accelerators of energetic ions, and electrons. The angular distribution, composition, and spectra of energetic particles observed near Earth gives information on the acceleration mechanisms. A class of energetic particle observations particularly useful in understanding the solar acceleration is the near-relativistic impulsive beam-like electron events. During five years of operation the Advanced Composition Explorer (ACE) has measured well over 400 electron events. Approximately 25% of these electron events are impulsive beam-like events that are released onto interplanetary field lines predominantly from western solar longitudes. We extend our initial ∼3 year study during the rise to solar maximum ( Haggerty and Roelof , 2002; Simnett et al., 2002 ) to a five year statistical analysis of these beam-like energetic electron events in relationship to optical flares, microwave emission, soft X-ray emission, metric and decametric type-III radio bursts, and coronal mass ejections.

Electron scattering in solid state detectors: Geant 4 simulations

Abstract All plasmas in the magnetosphere and interplanetary space contain non-thermal populations. Critical information on their acceleration mechanisms is provided by the slope of their energy spectra. The measurement of how energetic (non-thermal) electron spectra evolve in time provides fundamental information on how their acceleration processes develop. In an effort to characterize the response of current energetic particle instruments to energetic electrons we have taken advantage of the Geometry and Tracking toolkit (GEANT4) to provide the framework for an instrument model and a simulation environment. The results of these simulations match very well with data collected during various instrument calibration tests and give us confidence that GEANT4 handles electron interactions with matter in a reasonable fashion. The results of a specific Monte Carlo simulation (the response of the ACE/EPAM instrument to near-relativistic solar electron events) will be discussed. Given the usefulness of these simulations the GEANT4 toolkit has become an integral part of current and future energetic particle instrument development efforts.

Discrete and broadband electron acceleration in Jupiter's powerful aurora

The most intense auroral emissions from Earth’s polar regions, called discrete for their sharply defined spatial configurations, are generated by a process involving coherent acceleration of electrons by slowly evolving, powerful electric fields directed along the magnetic field lines that connect Earth’s space environment to its polar regions. In contrast, Earth’s less intense auroras are generally caused by wave scattering of magnetically trapped populations of hot electrons (in the case of diffuse aurora) or by the turbulent or stochastic downward acceleration of electrons along magnetic field lines by waves during transitory periods (in the case of broadband or Alfvénic aurora). Jupiter’s relatively steady main aurora has a power density that is so much larger than Earth’s that it has been taken for granted that it must be generated primarily by the discrete auroral process. However, preliminary in situ measurements of Jupiter’s auroral regions yielded no evidence of such a process. Here we report observations of distinct, high-energy, downward, discrete electron acceleration in Jupiter’s auroral polar regions. We also infer upward magnetic-field-aligned electric potentials of up to 400 kiloelectronvolts, an order of magnitude larger than the largest potentials observed at Earth. Despite the magnitude of these upward electric potentials and the expectations from observations at Earth, the downward energy flux from discrete acceleration is less at Jupiter than that caused by broadband or stochastic processes, with broadband and stochastic characteristics that are substantially different from those at Earth.

Observation and interpretation of energetic ion conics in Jupiter's polar magnetosphere

NASAs Juno spacecraft successfully completed its first science polar pass over Jupiters northern and southern aurora, with all the instruments powered, on 27 August 2016. Observations of conical energetic proton distributions at low altitudes (<6 RJ) over the northern polar region are interpreted as resulting from transversely (to the local magnetic field lines) accelerated H+ at a position planetward of the point of observation. The proton conics were observed within a broad region of upward beaming electrons and were accompanied by broadband low-frequency wave emissions as well as low-altitude trapped magnetospheric protons and heavy ions. The characteristic energies associated with these accelerated ion conics are ~100 times more energetic than similar distributions observed in the Earths auroral region and similar in energy to those found at Saturn. In addition, the ion conics also exhibited pitch angle dispersion with time that is interpreted as a consequence of the structure of the source location. Mapping these distributions along magnetic field lines connected from the spacecraft to the ionosphere suggests that the source region exists at altitudes between ~3 and 5 RJ. These new and exciting observations of accelerated ions over the polar region of Jupiter open up new areas for comparative planetary auroral physics.

Observations of a 3He-rich SEP event over a broad range of heliographic longitudes: results from STEREO and ACE

Observations of energetic ions and electrons from STEREO and ACE have been used to investigate the longitudinal extent of particle emissions from 3He ‐rich solar energetic particle (SEP) events. In the event of 3–4 Nov 2008, ions and electrons were detected 20° ahead and behind the nominal connection from the source region to 1 AU, and electrons were also detected 60° ahead. The results are consistent with those of earlier studies that correlated data from near‐Earth spacecraft with Helios data or with observations of source regions on the Sun.

Jovian bow shock and magnetopause encounters by the Juno spacecraft

The Juno spacecraft has crossed Jupiters bow shock (BS) and magnetopause (MP) multiple times in the dawn sector (near 0600 local time), both during the approach to Jupiter and during the first three apojove periods. A survey of all of these crossings using the Juno field and particle instruments has been performed, with 51 bow shock and 97 magnetopause crossings being detected. The BS crossings ranged from 92 to 128 RJ with 1 encounter during the approach, 36 during the first apojove period, 0 on the second, and 14 during the third. The MP crossings ranged from 73 to 114 RJ, with 8 MP encounters during the approach, 40 encounters during the first apojove period, 24 encounters on the second, and 46 during the third. During the approach, Juno initially encountered an expanding magnetosphere resulting in a single BS and MP crossing, followed a few days later by a contracting magnetosphere, resulting in 7 more MP crossings and a BS crossing on the first outbound orbit at 92 RJ. The lack of BS crossings and the limited number of MP crossings during the second apojove period suggests a long period of an expanded magnetosphere, likely caused by a prolonged period of low solar wind dynamic pressure associated with a rarefaction region. The detection of BS crossings on the third apojove period suggests another period of a highly compressed magnetosphere.