SM23C-01 INVITED
Solar Energetic Particle Trapping During Geomagnetic Storms
The prompt trapping of Solar Energetic Particles (SEPs) in the inner magnetosphere inside of L = 4 has been reported, including protons and heavier ions, in association with high speed interplanetary shocks and Storm Sudden Commencements (SSCs). These observations include the Bastille Day 2000 CME-driven storm as well as two in November 2001, which produced a long-lived new proton belt, as well as trapping of heavy ions up to Fe in all three cases. A survey of such events around the most recent solar maximum, including high altitude measurements from Polar, HEO and ICO satellites along with low altitude measurements from SAMPEX, indicates similarities to the well-studied March 24, 1991 SSC event. In this event, electrons and protons in drift resonance with a magnetosonic impulse were transported radially inward, requiring a source population which is multi-MeV at geosynchronous. A requirement for such shock-induced acceleration is a high-speed CME- shock at 1 AU, which launches a perturbation with comparable velocity inside the magnetosphere. Secondly, there must be a source population which is drift-resonant with the impulse. The CME-shock itself is a source of solar energetic particles, both protons and heavy ions, with higher fluxes and harder spectra associated with faster moving CMEs. A 3D Lorentz integration of SEP trajectories in electric and magnetic fields taken from the Lyon-Fedder-Mobarry (LFM) global MHD model, using solar wind input parameters from spacecraft measurements upstream from the bow shock, has been carried out for two November, 2001 SEP trapping events, and a CME-shock associated with the Halloween 2003 storm period, 29 October, which transported outer zone electrons and trapped solar energetic electrons into around L = 2.5, with little effect on SEPs. These results indicate that an enhancement in solar wind dynamic pressure for these events plays a role in the observed injection of ions (and electrons) to low L-values, as does the extent of the plasmasphere, included in the total density calculation constraining MHD fields. The plasmasphere affects the magnitude and penetration of the induction electric field transporting electrons and ions to low L values. The dawn-dusk asymmetry of the plasmasphere may create an asymmetry in the effectiveness of the inductive electric field impulse on electrons and ions, and from event to event, depending on the state of plasmapause erosion.
SM23C-02 INVITED
Trapped Solar Energetic Particles in the Inner Magnetosphere in Solar Cycle 23
A wide range of instrumentation on spacecraft such as SAMPEX, Polar, and HEO vehicles has been sampling the diverse trapped and transient particle populations in the Earth's magnetosphere during solar cycle 23. We will review the observational facts of the intriguing phenomenon of the creation of new radiation belts near L-shells of 2-3 during intense SEP events and CME-related shocks. New radiation belts in this region of the magnetosphere had been glimpsed with shorter-lived missions as long as 40 years ago. In the talk we will use magnetospheric particle sensors with wide energy coverage and mass composition, combined with upstream solar wind and SEP monitors, to survey the conditions that might be necessary to form these new belts. These necessary ingredients appear to include a source population of solar particles, access to low L-shells due to supressed particle cutoffs, and trapping due to non-adiabatic effects. The presence of ~1 MeV/n ions up to iron in some events provides a new diagnostic of the entire trapping process. We will review the published instances of the new belts, and examine the maximum observed energies of the trapped heavy ions.
SM23C-03 INVITED
Multi-satellite SEP observations by the GPS energetic particle detector constellation
Los Alamos National Laboratory has been flying energetic particle detectors on the GPS spacecraft for the last two solar cycles. The latest generation of instruments - CXD (Combined X-ray Dosimeters) are currently deployed on 7 GPS spacecraft providing unprecedented temporal and spatial coverage in the outer radiation belts above L=4 (invariant latitude ~60 degrees), for proton energies from 6 to >75 MeV. Access of SEP to the inner magnetosphere is a function of both energy, altitude and geomagnetic activity. Typical vertical cutoff rigidity at L=4 is around 1 GV (momentum per unit charge) or ~ 400MeV for protons. However, Thus the GPS constellation is well suited to observing the geomagnetic cutoff process "in action" for energies from ~ 6 to ~ 100 MeV and to investigate the detailed MLT, L and activity dependence of the SEP spectra. We will present here details of the SEP data available from the CXD instruments together with the spectral inversion techniques used to recover detailed spectra from the wide energy response dosimeter channels. We will then use this data to present detailed multi-spacecraft observations of the solar energetic proton events starting December 7 and 13, 2006 and their entry into the magnetosphere to L=4.
SM23C-04
Solar Energetic Particle Contribution to the Particle Population at Geosynchronous Orbit
To understand the formation of radiation belts it is important to assess the contributions of different upstream particle populations. Different sources can contribute to the energetic trapped particle population at geosyncronous orbit: Solar energetic particle (SEP) ions with energies above typical ring current energies (100 keV), lower energy SEPs below 100 keV that are accelerated to higher energies, and strongly accelerated solar wind particles. To study the entry and acceleration processes of SEPs we performed particle tracing calculations in the electric and magnetic fields from global magnetohydrodynamic (MHD) simulations of selected intervals. The weight of these particles in contributing to the observed particle flux is determined by using the flux observed by spacecraft in the solar wind. These calculations will be supplemented by trajectory calculations of lower energy particles to determine the dominant sources and acceleration models of energetic particles observed by geosynchronous spacecraft.
SM23C-05
Comparisons Between Numerically Determined and Observed Geomagnetic Cutoff Variations During Geomagnetic Storms
Geomagnetic cutoff variations during several storms are numerically determined using trajectory computations in fields from (1) the Tsyganenko 2005 geomagnetic field model and (2) the Lyon-Fedder-Mobarry MHD magnetospheric simulation code. The modeled cutoffs are compared with observed cutoffs obtained from SAMPEX energetic ion data.
SM23C-06
An investigation of the role of magnetic field line curvature in the detrapping of the August 1990 transient proton belt
Magnetic field line curvature (FLC) induced pitch angle scattering may be an important storm-time detrapping mechanism for energetic ions near the boundaries of the ion radiation belts. During magnetic storms the intensified ring current distorts the magnetic field causing increased curvature of the magnetic field lines. In regions where the curvature becomes strong enough the magnetic moments of the particle gyro-orbits are no longer conserved and the particles diffuse in pitch angle until they are captured by the Earth's atmosphere. To study the importance of FLC detrapping we simulate the decay of a temporarily trapped population seen in the CRRES PROTEL data. Because FLC pitch angle scattering is sensitive to the field line radius of curvature we completed multiple simulations of the decay using different Tsyganenko magnetic field models.
SM23C-07
Magnetic Shielding of Energetic Ions
Shielding spacecraft and occupants from energetic ions is one of the many challenges that must be overcome before long duration manned space missions become a reality. Of the many different methods proposed, active magnetic shields appear to show promise and share some similarities with the geophysical counterpart in planetary magnetospheres. In both situations Störmer theory has been used to describe forbidden regions from which energetic particles of a given rigidity are excluded. While Störmer theory is strictly only valid for a pure dipole magnetic field it has been extended to include the field of a finite radius current-carrying coil. It is therefore possible to numerically determine forbidden regions for non-dipole geometries. We utilize this technique to determine the forbidden regions of a novel spacecraft shield constructed of circular coils of wire arranged roughly in the shape of a torus. With this geometry it is shown that the magnetic field inside the torus can be made to be exactly zero everywhere and still provide total shielding of energetic ions below a given rigidity.