S. G. Kanekal

Acceleration mechanism responsible for the formation of the new radiation belt during the 2003 Halloween solar storm

Observations of the relativistic electron flux increases during the first days of November, 2003 are compared to model simulations of two leading mechanisms for electron acceleration. It is demonstrated that radial diffusion driven by ULF waves cannot explain the formation of the new radiation belt in the slot region and instead predicts a decay of fluxes during the recovery phase of the October 31st storm. Compression of the plasmasphere during the main phases of the storm created preferential conditions for local acceleration during interactions with VLF chorus. Local acceleration of electrons at L = 3 is modelled with a 2-D pitch-angle, energy diffusion code. We show that the energy diffusion driven by whistler mode waves can explain the gradual build up of fluxes to energies exceeding 3 MeV in a new radiation belt which is formed in the slot region normally devoid of high energy electrons.

Recurrent geomagnetic storms and relativistic electron enhancements in the outer magnetosphere: ISTP coordinated measurements

New, coordinated measurements from the International Solar-Terrestrial Physics (ISTP) constellation of spacecraft are presented to show the causes and effects of recurrent geomagnetic activity during recent solar minimum conditions. It is found using WIND and POLAR data that even for modest geomagnetic storms, relativistic electron fluxes are strongly and rapidly enhanced within the outer radiation zone of the Earths magnetosphere. Solar wind data are utilized to identify the drivers of magnetospheric acceleration processes. Yohkoh solar soft X-ray data are also used to identify the solar coronal holes that produce the high-speed solar wind streams which, in turn, cause the recurrent geomagnetic activity. It is concluded that even during extremely quiet solar conditions (sunspot minimum) there are discernible coronal holes and resultant solar wind streams which can produce intense magnetospheric particle acceleration. As a practical consequence of this Sun-Earth connection, it is noted that a long-lasting E>1MeV electron event in late March 1996 appears to have contributed significantly to a major spacecraft (Anik E1) operational failure.

Radiation belt electron acceleration by chorus waves during the 17 March 2013 storm

Local acceleration driven by whistler-mode chorus waves is fundamentally important for accelerating seed electron populations to highly relativistic energies in the outer radiation belt. In this study, we quantitatively evaluate chorus-driven electron acceleration during the 17 March 2013 storm, when the Van Allen Probes observed very rapid electron acceleration up to several MeV within ~12 hours. A clear radial peak in electron phase space density (PSD) observed near L* ~4 indicates that an internal local acceleration process was operating. We construct the global distribution of chorus wave intensity from the low-altitude electron measurements made by multiple Polar Orbiting Environmental Satellites (POES) satellites over a broad region, which is ultimately used to simulate the radiation belt electron dynamics driven by chorus waves. Our simulation results show remarkable agreement in magnitude, timing, energy dependence, and pitch angle distribution with the observed electron PSD near its peak location. However, radial diffusion and other loss processes may be required to explain the differences between the observation and simulation at other locations away from the PSD peak. Our simulation results, together with previous studies, suggest that local acceleration by chorus waves is a robust and ubiquitous process and plays a critical role in accelerating injected seed electrons with convective energies (~100 keV) to highly relativistic energies (several MeV).

Are energetic electrons in the solar wind the source of the outer radiation belt

Using data from WIND, SAMPEX (Solar Anomalous, and Magnetospheric Particle Explorer), and the Los Alamos National Laboratory (LANL) sensors onboard geostationary satellites, we investigate the correlation of energetic electrons in the 20–200 keV range in the solar wind and of high speed solar wind streams with relativistic electrons in the magnetosphere to determine whether energetic electrons in the solar wind are the source of the outer relativistic electron radiation belt. Though there is some correlation between energetic electron enhancements in the solar wind and enhancements in the outer radiation belt, the phase space density of 20–200 keV electrons in the solar wind is not adequate to supply the outer radiation belt electrons. Although lower energy electrons in the solar wind could be a seed population of the outer radiation belt, such lower energy electrons cannot achieve relativistic energies through the normal process of radial transport which conserves the first adiabatic invariant. Thus additional internal acceleration processes are required within the magnetosphere to produce the outer radiation belt. High speed solar wind streams are well correlated with increased magnetic activity and with increased fluxes in the outer radiation belt. The maximum correlation between the high speed streams and the radiation belt flux occurs with an increasing time delay for higher energies and and lower L values. We conclude that acceleration processes within the magnetosphere which are well correlated with high speed solar wind streams are responsible for the outer radiation belt electrons.

A strong CME‐related magnetic cloud interaction with the Earth's Magnetosphere: ISTP observations of rapid relativistic electron acceleration on May 15, 1997

A geoeffective magnetic cloud impacted the Earth early on 15 May 1997. The cloud exhibited strong initial southward interplanetary magnetic field (BZ∼−25 nT), which caused intense substorm activity and an intense geomagnetic storm (Dst ∼−170 nT). SAMPEX data showed that relativistic electrons (E ≳ 1.0 MeV) appeared suddenly deep in the magnetosphere at L=3 to 4. These electrons were not directly “injected” from higher altitudes (i.e., from the magnetotail), nor did they come from an interplanetary source. The electron increase was preceded (for ∼2 hrs) by remarkably strong low-frequency wave activity as seen by CANOPUS ground stations and by the GOES-8 spacecraft at geostationary orbit. POLAR/CEPPAD measurements support the result that high-energy electrons suddenly appeared deep in the magnetosphere. Thus, these new multi-point data suggest that strong magnetospheric waves can quickly and efficiently accelerate electrons to multi-MeV energies deep in the radiation belts on timescales of tens of minutes.

DISTURBED SPACE ENVIRONMENT MAY HAVE BEEN RELATED TO PAGER SATELLITE FAILURE

A very intense flux of electrons, evident in the magnetosphere earlier this year, may have caused a satellite failure (or at least exacerbated the situation) leading to the loss of pager service to 45 million customers, research has shown. The electrons, known as highly relativistic electrons (HREs), were especially numerous in the weeks preceding the failure. Researchers say HREs have triggered spacecraft anomalies in the past through a process of deep dielectric charging when fluxes are elevated. They therefore believe this energetic electron environment could have been behind the failure in the attitude control system of the Galaxy 4 spacecraft at 2200 UT on May 19,1998. A backup system also failed, either at the same time or earlier, so operators were unable to maintain a stable Earth link [Silverstein, 1998].

Gradual diffusion and punctuated phase space density enhancements of highly relativistic electrons: Van Allen Probes observations

The dual-spacecraft Van Allen Probes mission has provided a new window into mega electron volt (MeV) particle dynamics in the Earths radiation belts. Observations (up to E ~10 MeV) show clearly the behavior of the outer electron radiation belt at different timescales: months-long periods of gradual inward radial diffusive transport and weak loss being punctuated by dramatic flux changes driven by strong solar wind transient events. We present analysis of multi-MeV electron flux and phase space density (PSD) changes during March 2013 in the context of the first year of Van Allen Probes operation. This March period demonstrates the classic signatures both of inward radial diffusive energization and abrupt localized acceleration deep within the outer Van Allen zone (L ~4.0 ± 0.5). This reveals graphically that both “competing” mechanisms of multi-MeV electron energization are at play in the radiation belts, often acting almost concurrently or at least in rapid succession.

Strong electron acceleration in the Earth's magnetosphere

Abstract Electron data are examined over long periods in the outer zone of electron trapping (L ≳ 3). Energetic particle detectors at geostationary orbit and onboard the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) satellite show evidence of strong electron acceleration in Earths outer radiation belts. Data are studied according to L-value and are compared with concurrent solar wind and geomagnetic conditions. Evidence is presented of a strong correlation between high-speed solar wind speeds and the occurrence of high energy electrons in the Earths outer radiation belts. Thus, high-speed solar wind streams apparently drive the acceleration of electrons throughout the outer zone on time scales of days. The processes by which electrons are accelerated to high energies (E>1 MeV) are found to consist of two temporally distinct steps. The first involves prompt, relatively modest, acceleration of many electrons during magnetospheric substorms. The second step involves higher energy acceleration of a portion of the substorm electrons throughouth the outer trapping region on a time scale of days.

Multisatellite measurements of relativistic electrons: Global coherence

In this paper we report on multisatellite measurements of relativistic electrons (energies of ≥2 MeV) in the outer zone using detectors on board SAMPEX, HEO, GOES, and Polar satellites. These satellites are in distinct orbits around the Earth, ranging from polar low-Earth to geosynchronous orbits. The data thus comprise a broad sampling of the relativistic electron populations of various pitch angles, local times, and energy range and of time resolutions ranging from tens of minutes to a day. By a quantitative intercomparison of these multisatellite electron measurements collected over a period of 2 years (from 1998 to 1999), we find that the relativistic electron populations exhibit a remarkable degree of coherence throughout the outer zone. The correlation coefficients between fluxes measured by different satellites as a function of lag time and at different L shells, are highest at or very near zero lag. The strong correlation between electron fluxes measured at different altitudes is seen over a range of L shells. This suggests that the magnetospheric processes responsible for electron acceleration and decay in the outer zone may be of a global nature. The highest correlation being at nearly zero lag suggests that either the underlying acceleration mechanisms are largely pitch angle independent or that the isotropization timescales for these electrons are quite short (of the order of half a day at most). Our observations thus provide a valuable constraint on the various theoretical models that have been proposed for the acceleration and decay of the relativistic electron population in the outer zone.

Satellite anomalies linked to electron increase in the magnetosphere

On January 20, 1994, at 1443 UT, the momentum wheel control circuitry of the Intelsat K spacecraft at geostationary orbit suffered an operational anomaly causing a loss of attitude control. The system was switched to the backup circuitry, and control was reestablished. The same day, at 1735 UT, the Anik E-l spacecraft, also at geostationary orbit, suffered the same kind of operational anomaly in the momentum wheel control circuitry [Rostoker, 1994]. According to newspaper accounts the next day, Telesat Canada operators struggled for 8 hours to regain control of the Anik E-1 satellite. They were able to finally switch to the backup momentum wheel controller and resume reasonably normal operations.