AEROSPACE REPORT NO. ATR-2009(5236)-1

Current Understanding of Radiation Belt Acceleration, Transport, and Loss 30 January 2009 Paul O’Brien and Joe Mazur Space Science Applications Laboratory Physical Sciences Laboratories Prepared for NASA/Goddard Space Flight Center Greenbelt, MD 20771

Contract No. NNG05GM22G Authorized by: Engineering and Technology Group

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PUBLIC RELEASE IS AUTHORIZED

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AEROSPACE REPORT NO. ATR-2009(5236)-1

Current Understanding of Radiation Belt Acceleration, Transport, and Loss 30 January 2009 Paul O’Brien and Joe Mazur Space Science Applications Laboratory Physical Sciences Laboratories Prepared for NASA/Goddard Space Flight Center Greenbelt, MD 20771

Contract No. NNG05GM22G

Authorized by: Engineering and Technology Group

PUBLIC RELEASE IS AUTHORIZED

ii

Current Understanding of Radiation Belt Acceleration, Transport and Loss

Paul O’Brien and Joe Mazur Space Science Department [email protected]

AGU Fall Meeting, 2008, San Francisco, CA U21B-03 This project was supported in part by NASA’s ATR 2009(5236)-1 © The Aerospace Corporation 2008

LWS TR&T Program through a grant to The Aerospace Corporation

Outline • •

Radiation Belt Topology The Proton Belt – Sources – Losses – Transient Proton Belts

• •

Trapped Heavy Ions and Antimatter The Electron Belts – – – – –

• 2

Radial Transport Local Acceleration Precipitation Mechanisms Slot Filling The Mystery of the Inner Electron Belt

Conclusions

Radiation Belt Topology

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• •

Inner Belt Slot Outer Belt

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• •

A static view divides the radiation belts into inner and outer belts, with a slot in between. The inner belt is associated with energetic protons (up to GeV) The outer belt is associated with energetic electrons (up to ~10 MeV) The inner belt also includes electrons up to a few MeV The slot is an energy and time-dependent local minimum in electron flux

The Proton Belt: Sources The “quiet time” source of the inner belt is Cosmic Ray Albedo Neutron Decay, CRAND, which supplies protons up to GeV energies

With Solar Proton Source Without Solar Proton Source

Solar energetic particles can also be trapped during passage of interplanetary shocks and intense magnetic storms Figure from Selesnick et al., 2007, JGR, doi:10.1029/2006SW000275 4

The Proton Belt: Losses • • •

Over solar-cycle atmosphere inflates and deflates, this leads to periodic losses at inner L shells and higher K’s. Magnetic reconfigurations & kinked field lines cause losses at outer L shells. Radial transport carries particles into these two sinks.

•Magnetic storms chop off outer edge of inner belt. •Loss depends on energy via loss of adiabaticity on “kinked” field lines •Upward slope evidence of outward radial transport

Figure from Selesnick et al., 2007, JGR, doi:10.1029/2006SW000275

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Figure courtesy J.B. Blake

Day of 2003

The Proton Belt: Transient Proton Belts •

• • •

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Large storms, especially those with associated solar particle events and sudden commencements can create transient proton belts. These belts occur at L>2 and can last for days to months. Transient belts are more frequent at higher L and lower energy. Figures from Lorentzen et al., JGR, 2002, doi:10.1029/2001JA000276.

Trapped Heavy Ions and Antimatter •

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Trapped heavy ions from solar particle events and Anomalous Cosmic Rays can be modified in much the same way as solar protons (shocks and large storms). The Blake-Friesen effect (exospheric stripping) supplies trapped ACRs during quiet times.

• • Figure from Boezio et al., “First Results from the PAMELA Space Mission”, 24th International Conference on High Energy Physics, Philadelphia, 2008, 7 http://arxiv.org/PS_cache/arxiv/pdf/0810/0810.3508v1.pdf

•

Yes, Virginia, there really is an antimatter belt. It originates from CRAND antineutrons. It contains antiprotons and positrons

Trapped Anomalous Cosmic Rays • • • •

The HiLET instrument (launched 2008 with TWINS2), in a HEO/molniya orbit, measures heavy ions up to ~30 MeV/amu down to L<2. Low-ionization state ACRs reach low altitude and lose one or more electrons to the exosphere, becoming trapped. This process is most efficient near the geomagnetic cutoff, leading to a trapped ACR belt near L~2-2.5 For more, see Poster U13A-0040, Mazur et al., New Measurements of Trapped Anomalous Cosmic Rays and Other Heavy Ions in the Inner Magnetosphere.

Illustration courtesy of NASA

ACR GCR

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Spectrum from Simpson, 1995, ASR, doi:10.1016/02731177(95)00326-A

The Electron Belts: Radial Transport M = 500 MeV/G, K=0

Radial transport via drift resonance with ULF (mHz) waves is thought to determine the quiet time topology of the outer belt. Electric (L6) and Magnetic (L10) diffusion coefficients vary strongly with L and magnetic activity.

DLLE ~ L6

DLLM ~ L10

Figure from Brautigam and Albert, 2000, JGR, doi:10.1029/1999JA900344

Acts as source

Acts as loss

Figure from Selesnick and Blake, 2000, JGR, doi:10.1029/1999JA900445 9

Radial transport is a source and loss mechanism, depending on the conditions in the plasma sheet

The Electron Belts: Local Acceleration Chorus

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•

•

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Figure from Horne et al., 2003, GRL, doi:10.1029/2003GL016963

Chorus (kHz) and magnetosonic waves (10s Hz) can produce energy and pitch-angle diffusion on timescales of ~1 day or faster Chorus, unlike magnetosonic waves can scatter particles all the way into the loss cone The mechanism are Landau resonance (both) and Dopplershifted cyclotron resonance (chorus).

Magnetosonic

Figure from Horne et al., 2007, GRL, doi:10.1029/2007GL030267

The Electron Belts: Precipitation Mechanisms >1 MeV Electron Flux (#/cm2/s/sr)

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From Abel and Thorne, 1998, JGR, doi:10.1029/97JA02919

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15:20 UT 19-Oct-1998 MLT = 09, 240O E Southern Hemisphere

103 Microburst Flux

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101

20 msec Flux

Baseline 6 sec Flux

Area of Precipitation = 9.1x1015 cm2 Total Electons Lost = 8.3x1023

100 From Albert, 2003, JGR, doi:10.1029/2002JA009792

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3

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IGRF L

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A variety of plasma waves, some man-made, can precipitate outer zone electrons into the atmosphere: whistler-mode chorus & hiss, EMIC waves, and VLF transmitters. These weave determine the topology of the inner electron belt and slot. Storm-time microbursts, associated with chorus, may be able to deplete the entire outer zone in a day. EMIC waves may catalyze chorus and hissrelated losses. Loss of adiabaticity at the outer trapping boundary can also lead to precipitation at high L.

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The Electron Belts: Slot Filling • •

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During some storms, the slot region fills with energetic electrons. This phenomenon has been associated with penetration of the plasmapause and plasmasheet to low L. Chorus waves (among others) can then have access to slot drift shells and lead to essentially the same acceleration processes that occur in the outer zone during more modest activity. Figure from Thorne et al., 2007, JGR, doi:10.1029/2006JA012176

The Mystery of the Inner Electron Belt SAMPEX ELO 2-6 MeV Electrons 2.5 L

2 1.5

Dst, nT

0 -200 -400 1995

• • • • • •

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1997

2000

2002

What causes the dynamics at L<2? Radial diffusion likely very weak (L6 or stronger dependence) Hiss, which is common in the inner belt, isn’t traditionally thought of as an acceleration mechanism. Chorus and EMIC only likely near and beyond the plasmapause. Magnetosonic waves are unknown in the inner belt (generated from ion ring distribution, i.e., ring current). O’Brien and Moldwin [JGR, 2003, doi:10.1029/2002GL016007] model of plasmapause location indicates Dst < -550 nT required to penetrate L<2. That only happens ~once per solar cycle.

Conclusions •

Most of our observations and our knowledge concern the outer belt electrons Acceleration, transport and loss processes couple particles from eV to MeV, and waves from mHz to kHz

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The inner belt and slot are poorly sampled, but potentially fascinating This domain is home to some exotic trapped particles. Interplanetary shocks and very large storms appear to be important for modifications of these domains.

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Upcoming science missions will remedy some, but not all, of the shortfall The remaining challenge is threefold: getting a mission in an orbit with access to the inner belts and slot, building instruments capable of making clean measurements amid intense penetrating background, and sustaining the mission long enough to observe multiple events.

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