The disappearance and reappearance of outer zone energetic electrons during the November 3{endash}4, 1993, magnetic storm is examined utilizing data from the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX), the Global Positioning System (GPS) series, and the Los Alamos National Laboratory (LANL) sensors onboard geosynchronous satellites. The relativistic electron flux drops during the main phase of the magnetic storm in association with the large negative interplanetary B{sub z} and rapid solar wind pressure increase late on November 3. Outer zone electrons with E{gt}3MeV measured by SAMPEX disappear for over 12 hours at the beginning of November 4. This represents a 3 orders of magnitude decrease down to the cosmic ray background of the detector. GPS and LANL sensors show similar effects, confirming that the flux drop of the energetic electrons occurs near the magnetic equator and at all pitch angles. Enhanced electron precipitation was measured by SAMPEX at L{ge}3.5. The outer zone electron fluxes then recover and exceed prestorm levels within one day of the storm onset and the inner boundary of the outer zone moves inward to smaller L ({lt}3). These measurements provide a data set which is examined in detail and used to determine the mechanisms contributing tomore » the loss and recovery of the outer zone electron flux. The loss of the inner part of the outer zone electrons is partly due to the adiabatic effects associated with the decrease of Dst, while the loss of most of the outer part (those electrons initially at L{ge}4.0) is due to either precipitation into the atmosphere or drift to the magnetopause because of the strong compression of the magnetosphere by the solar wind. The recovery of the energetic electron flux is due to the adiabatic effects associated with the increase in Dst, and at lower energies ({lt}0.5MeV) due to rapid radial diffusion driven by the strong magnetic activity during the recovery phase of the storm. (Abstract Truncated)« less

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97JA01101

Multisatellite observations of the outer zone electron variation during the November 3–4, 1993, magnetic storm

[1] We examine signatures of two types of waves that may be involved in the acceleration of energetic electrons in Earth's outer radiation belts. We have compiled a database of ULF wave power from SAMNET and IMAGE ground magnetometer stations for 1987–2001. Long-duration, comprehensive, in situ VLF/ELF chorus wave observations are not available, so we infer chorus wave activity from low-altitude SAMPEX observations of MeV electron microbursts for 1996–2001 since microbursts are thought to be caused by interactions between chorus and trapped electrons. We compare the ULF and microburst observations to in situ trapped electrons observed by high-altitude satellites from 1989–2001. We find that electron acceleration at low L shells is closely associated with both ULF activity and MeV microbursts and thereby probably also with chorus activity. Electron flux enhancements across the outer radiation belt are, in general, related to both ULF and VLF/ELF activity. However, we suggest that electron flux peaks observed at L ∼ 4.5 are likely caused by VLF/ELF wave acceleration, while ULF activity probably produces the dominant electron acceleration at geosynchronous orbit and beyond.

/pdf/energization-of-relativistic-electrons-in-the-presence-of-3fu6q3yvy7.pdf

Energization of relativistic electrons in the presence of ULF power and mev microbursts: Evidence for dual ULF and VLF acceleration

The scientific objectives of the NASA small-class explorer mission SAMPEX are summarized. A brief history of the Small Explorer Program is provided along with a description of the SAMPEX project development and structure. The spacecraft and scientific instrument configuration is presented. The orbit of SAMPEX has an altitude of 520 by 670 km and an 82 degrees inclination. Maximum possible power is provided by articulated solar arrays that point continuously toward the sun. Highly sensitive scientific instruments point generally toward the local zenith, especially over the terrestrial poles, in order to measure optimally the galactic and solar cosmic ray flux. Energetic magnetospheric particle precipitation is monitored at lower geomagnetic latitudes. The spacecraft uses several innovative approaches including an optical fiber bus, powerful onboard computers, and large solid state memories (instead of tape recorders). Spacecraft communication and data acquisition are discussed and the space- and ground-segment data flows are summarized. >

An overview of the Solar Anomalous, and Magnetospheric Particle Explorer (SAMPEX) mission

The Solar, Anomalous and Magnetospheric Particle Explorer (SAMPEX) satellite frequently observes relativistic (> 1 MeV) electron precipitation in the radiation belts at L shells of 4–6 with bursty temporal structure lasting < 1 s. This phenomenon can occur at all local times but is most often seen between 0200 and 1000 magnetic local time. VLF chorus is also observed to occur preferentially at these same local times. Using electron observations from the SAMPEX satellite Heavy Ion Large Telescope and data from the Polar satellite plasma wave instrument, we show correlation between observations of relativistic electron microbursts and VLF chorus with frequencies <2 kHz. In addition, the duration of the individual rising frequency chorus elements is comparable to the duration of the relativistic electron microbursts. It has been speculated that relativistic electron microbursts are caused by wave-particle interactions, which strongly scatter electrons into the loss cone for a short period. Lower-energy electron microbursts in the range from tens to hundreds of keV have long been associated with chorus waves, since these lower-energy electrons can resonate at the equator with whistler-mode waves at chorus frequencies. Electrons of MeV energies do not satisfy the first-order cyclotron resonance condition with chorus wave frequencies at the equator. However, MeV electrons may interact with chorus through higher-order resonances or off-equatorial interactions.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000JA003018

Observations of relativistic electron microbursts in association with VLF chorus

High-energy electrons have been measured systematically in a low-altitude (520 × 675 km), nearly polar (inclination = 82°) orbit by sensitive instruments onboard the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX). Count rate channels with electron energy thresholds ranging from 0.4 MeV to 3.5 MeV in three different instruments have been used to examine relativistic electron variations as a function of L-shell parameter and time. A long run of essentially continuous data (July 1992–July 1993) shows substantial acceleration of energetic electrons throughout much of the magnetosphere on rapid time scales. This acceleration appears to be due to solar wind velocity enhancements and is surprisingly large in that the radiation belt “slot” region often is filled temporarily and electron fluxes are strongly enhanced even at very low L-values (L ∼ 2). A superposed epoch analysis shows that electron fluxes rise rapidly for 2.5 ≲ L ≲ 5. These increases occur on a time scale of order 1–2 days and are most abrupt for L-values near 3. The temporal decay rate of the fluxes is dependent on energy and L-value and may be described by J = Ke-t/to with to ≈ 5–10 days. Thus, these results suggest that the Earth's magnetosphere is a cosmic electron accelerator of substantial strength and efficiency.

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Relativistic Electron Acceleration and Decay Time Scales in the Inner and Outer Radiation Belts: SAMPEX

The HILT sensor has been designed to measure heavy ion elemental abundances, energy spectra, and direction of incidence in the mass range from helium to iron and in the energy range 4-250 MeV/nucleon. With its large geometric factor of 60 cm/sup 2/ sr the sensor is optimized to provide compositional and spectral measurements for low-intensity cosmic rays, i.e., for small solar energetic particle events and for the anomalous component of cosmic rays. The instrument combines a large-area ion-drift-chamber-proportional-counter system with two arrays of 16 Li-drifted solid state detectors and 16 CsI crystals. The multi-dE/dx-E technique provides a low-background mass and energy determination. The sensor also measures particle direction. By combining these measurements with the information on the spacecraft position and attitude in the low-altitude polar orbit, it will be possible to infer the ionic charge of the ions from the local cutoff of the Earth's magnetic field. The ionic charge in this energy range is of particular interest because it provides unique clues to the origin of these particles and has not been investigated systematically so far. >

HILT: a heavy ion large area proportional counter telescope for solar and anomalous cosmic rays

Although the primary function of the CEPPAD/IPS instrument on Polar is the measurement of energetic ions in-situ, it has also proven to be a very capable Energetic Neutral Atom (ENA) imager. Raw ENA images are currently being constructed on a routine basis with a temporal resolution of minutes during both active and quiet times. However, while analyses of these images by themselves provide much information on the spatial distribution and dynamics of the energetic ion population in the ring current, detailed modeling is required to extract the actual ion distributions. In this paper, we present the initial results of forward modeling an IPS ENA image obtained during a small geo-magnetic storm on June 9, 1997. The equatorial ion distribution inferred with this technique reproduces the expected large noon/midnight and dawn/dusk asymmetries. The limitations of the model are discussed and a number of modifications to the basic forward modeling technique are proposed which should significantly improve its performance in future studies.

/pdf/energetic-neutral-atom-imaging-with-the-polar-ceppad-ips-3b20vcw9hn.pdf

Energetic neutral atom imaging with the Polar CEPPAD/IPS instrument: Initial forward modeling results

Although the primary function of the CEP-PAD/IPS instrument on Polar is the measurement of energetic ions in-situ, it has also proven to be a very capable Energetic neutral Atom (ENA) imager. Raw ENA images are currently being constructed on a routine basis with a temporal resolution of minutes during both active and quiet times. However, while analyses of these images by themselves provide much information on the spatial distribution and dynamics of the energetic ion population in the ring current, detailed modeling is required to extract the actual ion distributions. In this paper, the authors present the initial results of forward modeling an IPS ENA image obtained during a small geo-magnetic storm on June 9, 1997. The equatorial ion distribution inferred with this technique reproduces the expected large noon/midnight and dawn/dusk asymmetries. The limitations of the model are discussed and a number of modifications to the basic forward modeling technique are proposed which should significantly improve its performance in future studies.

https://digital.library.unt.edu/ark:/67531/metadc674446/m2/1/high_res_d/296779.pdf

An improved radiation dosimeter device in an improved radiation dosimeter system provides a DC analog output voltage that is proportional to the total ionizing dose accumulated as a function of time at the location of the dosimeter in a host spacecraft, so as to operate in a system bus voltage range common to spacecraft systems with the output being compatible with conventional spacecraft analog inputs, while the total dose is measured precisely by continually monitoring the energy deposited in a silicon test mass accumulating charge including charge contribution prior to radiation threshold detection for improved measurement of the total accumulated charge with the dosimeters being daisy-chained and distributed about the spacecraft for providing a spacecraft dose profile about the spacecraft using the improved radiation dosimeter system.

J. B. Blake

Papers

HILT: a heavy ion large area proportional counter telescope for solar and anomalous cosmic rays

Energetic neutral atom imaging with the Polar CEPPAD/IPS instrument: Initial forward modeling results

Energetic neutral atom imaging with the Polar CEPPAD/IPS instrument: Initial forward modeling results

Radiation dosimeter device

Experiment for Charge Determination of Cosmic Rays of Interplanetary and Solar Origin on the Space Shuttle