local acceleration and loss of relativistic electrons in the earth’s outer radiation belt
DESCRIPTION
Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt. Nigel P. Meredith British Antarctic Survey. GEM Workshop Zermatt Resort, Utah 22 nd – 27 th June, 2008. Outline. Introduction Local Acceleration Mechanisms Chorus Magnetosonic waves - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/1.jpg)
Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt
GEM WorkshopZermatt Resort, Utah 22nd – 27th June, 2008
Nigel P. Meredith
British Antarctic Survey
![Page 2: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/2.jpg)
• Introduction
• Local Acceleration Mechanisms– Chorus– Magnetosonic waves
• Local Loss Mechanisms– Plasmaspheric hiss– EMIC waves– Chorus
• Conclusions
NASA
Outline
![Page 3: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/3.jpg)
• Energetic electrons (E > 100 keV) in the Earth’s radiation belts are generally confined to two distinct regions.
• Inner radiation belt – 1.2 < L < 2 – exhibits long term stability
• Outer radiation belt– 3 < L < 7 – highly dynamic
Earth’s Radiation Belts
2 4 5 6 73
104
103
102
101
100
1
L shell
flux
E = 876 keV
Outer beltInner belt
NASA
![Page 4: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/4.jpg)
Variability of Outer Radiation Belt Electrons
Baker et al., AG, 2008
• Fluxes change dramatically on a variety of different time scales.• Covers a range of over 4 orders of magnitude.
![Page 5: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/5.jpg)
Variability of Outer Radiation Belt Electrons
• Most intense fluxes are seen during the declining phase of the solar cycle.
Baker et al., AG, 2008
![Page 6: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/6.jpg)
• Enhanced fluxes of relativistic electrons:
– damage satellites, e.g.,• 1994: Intelsat K, Anik E1, & E2• 1997: Telstar 401• 1998: Galaxy IV
– risk to humans in space.
Importance
Baker et al., AG, 2008
![Page 7: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/7.jpg)
stratosphere
mesosphere
thermosphere
• Energetic electrons can penetrate to low altitudes where they drive changes in atmospheric chemistry primarily in the mesosphere.
Relevance to the Middle Atmosphere
![Page 8: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/8.jpg)
stratosphere
mesosphere
thermosphere
• Energetic electrons can penetrate to low altitudes where they drive changes in atmospheric chemistry primarily in the mesosphere.
Relevance to the Middle Atmosphere
![Page 9: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/9.jpg)
stratosphere
mesosphere
• Energetic electrons can penetrate to low altitudes where they drive changes in atmospheric chemistry primarily in the mesosphere.
Relevance to the Middle Atmosphere
![Page 10: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/10.jpg)
stratosphere
mesosphere
• Energetic electrons can penetrate to low altitudes where they drive changes in atmospheric chemistry primarily in the mesosphere.
Relevance to the Middle Atmosphere
![Page 11: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/11.jpg)
stratosphere
mesosphere
• Energetic electrons can penetrate to low altitudes where they drive changes in atmospheric chemistry primarily in the mesosphere.
• Electron precipitation from the Earth’s radiation belts could thus be very important for communicating solar variability to the Earth’s middle atmosphere [e.g., Kozyra et al., AGU, 2006].
Relevance to the Middle Atmosphere
![Page 12: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/12.jpg)
• Characterise, understand, and ultimately predict the variability of outer radiation belt electrons.
• Complex problem involving a variety of source, transport and loss processes.
L = 3
L = 7
L = 3
L = 7
L = 7
L = 3
Challenge
![Page 13: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/13.jpg)
• Relativistic electron variability driven by activity on the Sun.
• Two types of solar driver:
Solar Drivers
![Page 14: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/14.jpg)
• Relativistic electron variability driven by activity on the Sun.
• Two types of solar driver:
– Episodic storms caused by solar wind disturbances driven by coronal mass ejections.
Solar Drivers
Image courtesy of the LASCO team
![Page 15: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/15.jpg)
• Relativistic electron variability driven by activity on the Sun.
• Two types of solar driver:
– Episodic storms caused by solar wind disturbances driven by coronal mass ejections.
– Recurrent storms caused by high speed solar wind streams from coronal holes.
Reeves, GRL, 1998
Solar Drivers
Image courtesy of the LASCO team
![Page 16: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/16.jpg)
Relativistic Electron Variability
Reeves et al., GRL, 2003
• The fluxes of relativistic electrons (E>1 MeV) in the outer zone are enhanced by a factor of 2 or more in ~50% of all moderate and intense storms.
![Page 17: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/17.jpg)
Relativistic Electron Variability
• The fluxes of relativistic electrons (E>1 MeV) in the outer zone are enhanced by a factor of 2 or more in ~50% of all moderate and intense storms.
• However, in sharp contrast, ~20% of these storms decrease the fluxes by a factor of 2 or more.
• This emphasizes the need to study loss processes as well as acceleration processes.
Reeves et al., GRL, 2003
![Page 18: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/18.jpg)
bouncemotion
driftmotion
• Energetic particles in the Earth’s radiation belts undergo three types of periodic motion:
Periodic Motions
![Page 19: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/19.jpg)
gyromotion
bouncemotion
driftmotion
• Energetic particles in the Earth’s radiation belts undergo three types of periodic motion:
– They gyrate around the magnetic field
Periodic Motions
![Page 20: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/20.jpg)
gyromotion
bouncemotion
driftmotion
• Energetic particles in the Earth’s radiation belts undergo three types of periodic motion:
– They gyrate around the magnetic field
10 kHz
0.1 ms
f
T
1 MeV electron ( = 45o) at L = 4.5
Periodic Motions
![Page 21: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/21.jpg)
gyromotion
driftmotion
• Energetic particles in the Earth’s radiation belts undergo three types of periodic motion:
– They gyrate around the magnetic field
– They bounce between the mirror points
bouncemotion
10 kHz
0.1 ms
3 Hz
0.36 s
f
T
1 MeV electron ( = 45o) at L = 4.5
Periodic Motions
![Page 22: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/22.jpg)
• Energetic particles in the Earth’s radiation belts undergo three types of periodic motion:
– They gyrate around the magnetic field
– They bounce between the mirror points
– They drift around the Earth
gyromotion
bouncemotion
driftmotion
10 kHz 3 Hz 1 mHz
0.1 ms 0.36 s 15 min
1 MeV electron ( = 45o) at L = 4.5
f
T
Periodic Motions
![Page 23: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/23.jpg)
• Each periodic motion is associated with a conserved quantity called an adiabatic invariant.
Adiabatic Invariants
![Page 24: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/24.jpg)
• Each periodic motion is associated with a conserved quantity called an adiabatic invariant.
Bm
p
2
2
- First adiabatic invariant is associated with the gyromotion:
Adiabatic Invariants
![Page 25: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/25.jpg)
• Each periodic motion is associated with a conserved quantity called an adiabatic invariant.
bounce
dspJ ||
Bm
p
2
2
- First adiabatic invariant is associated with the gyromotion:
- Second adiabatic invariant is associated with the bounce motion:
Adiabatic Invariants
![Page 26: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/26.jpg)
• Each periodic motion is associated with a conserved quantity called an adiabatic invariant.
bounce
dspJ ||
Bm
p
2
2
drift
BdS
- First adiabatic invariant is associated with the gyromotion:
- Second adiabatic invariant is associated with the bounce motion:
- Third adiabatic invariant is associated with the drift motion:
Adiabatic Invariants
![Page 27: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/27.jpg)
• Each periodic motion is associated with a conserved quantity called an adiabatic invariant.
bounce
dspJ ||
Bm
p
2
2
drift
BdS
- First adiabatic invariant is associated with the gyromotion:
- Second adiabatic invariant is associated with the bounce motion:
- Third adiabatic invariant is associated with the drift motion:
• A given adiabatic invariant is conserved when forces controlling the motion take place on a timescale that is large compared to the associated period of motion.
Adiabatic Invariants
![Page 28: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/28.jpg)
Radial diffusion is an important transport process in the Earth’s radiation
belts:
– driven by fluctuations in the Earth’s electric and magnetic fields on timescales of the drift period
– enhanced by ULF waves [e.g., Hudson et al., 1999; Elkington et al., 1999]
– conserves the first two adiabatic invariants BUT breaks the third adiabatic invariant
Radial Diffusion
![Page 29: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/29.jpg)
Radial Diffusion
• Conservation of first invariant implies:
p2
= 2meB
• Inward radial diffusion leads to significant energisation.
courtesy of M. Lam
L shell
Ene
rgy
(keV
)
![Page 30: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/30.jpg)
Radial Diffusion
• Conservation of first invariant implies:
p2
= 2meB
• Inward radial diffusion leads to significant energisation.
• Outward radial diffusion combined with magnetopause losses can be a significant loss process [Shprits et al., JGR, 2006].
courtesy of M. Lam
L shell
Ene
rgy
(keV
)
![Page 31: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/31.jpg)
• Recent new results show that gyroresonant wave-particle interactions play a key role in the Earth’s radiation belts.
• These interactions can occur when the wave frequency, , is Doppler-shifted to a multiple of the relativistic electron gyrofrequency, e.
- k║v║ = ne/
Gyroresonant Wave-Particle Interactions
– k║ is the wave number parallel to the magnetic field
– v║ is the electron velocity parallel to the magnetic field
is the relativistic factor
![Page 32: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/32.jpg)
Gyroresonant Wave-Particle Interactions
• These interactions break the first and second adiabatic invariants.
• Such interactions [e.g., Kennel and Petschek, JGR, 1966] lead to:
– pitch angle scattering and potential loss to the atmosphere
– energy diffusion
![Page 33: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/33.jpg)
• Processes associated with the temporal variability of the radiation belts can usually be treated using diffusion theory [e.g., Schulz and Lanzerotti, 1974].
• Timescales associated with acceleration and loss can be determined from the resulting diffusion coefficients.
Diffusion Theory
![Page 34: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/34.jpg)
PADIE(Pitch Angle and energy Diffusion of Ions and Electrons)
• The PADIE code [Glauert and Horne, JGR, 2005] has been developed to model the effects of electromagnetic waves on charged particles trapped in a magnetic field.
• The code calculates the bounce-averaged, relativistic, diffusion coefficients
![Page 35: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/35.jpg)
EMIC waves
plasmaspherichiss
magnetopause
plasmaspause
Sun
chorus
• Plasma waves that can lead to efficient gyroresonant wave particle interactions with relativistic electrons include:
- Chorus waves
- Magnetosonic waves
- Plasmaspheric hiss
- EMIC waves.
magnetosonicwaves
Important Wave Modes
![Page 36: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/36.jpg)
Whistler Mode Chorus
• Whistler mode chorus is an intense electromagnetic emission observed outside of the plasmapause in the frequency range 0.1fce < f < 0.8fce.
• The waves are generated by plasma sheet electrons injected during substorms and/or enhanced convection.
![Page 37: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/37.jpg)
Wave Data
chorus waves
plasmapause
plasmapausefuhr
fce
flhr
Meredith et al., JGR, 2004
![Page 38: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/38.jpg)
• Enhanced storm-time convection electric fields provide a seed population of outer zone electrons with energies up to a few hundred keV [e.g., Baker et al., ASR, 1998; Obara et al., EPS, 2000].
• Gyroresonant wave-particle interactions with whistler-mode chorus then provide a mechanism for accelerating these seed electrons to relativistic energies [e.g., Horne and Thorne, GRL, 1998].
Gyroresonant Wave Particle Interactions
![Page 39: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/39.jpg)
Iles et al., JGR, 2006
October 9th 1990 Storm
Recovery phase associated with:
Meredith et al., JGR, 2002
![Page 40: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/40.jpg)
October 9th 1990 Storm
Recovery phase associated with:
– enhanced AE activity
Meredith et al., JGR, 2002
![Page 41: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/41.jpg)
October 9th 1990 Storm
Recovery phase associated with:
– enhanced AE activity
– enhanced levels of whistler mode chorus
Meredith et al., JGR, 2002
![Page 42: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/42.jpg)
October 9th 1990 Storm
Recovery phase associated with:
– enhanced AE activity
– enhanced levels of whistler mode chorus
– gradual acceleration of electrons to relativistic energies
Meredith et al., JGR, 2002
![Page 43: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/43.jpg)
• Important information on the nature of the acceleration process can be found through phase space density analysis.
Phase Space Density Analysis
![Page 44: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/44.jpg)
• Important information on the nature of the acceleration process can be found through phase space density analysis.
• Acceleration by inward radial diffusion driven by positive gradients in the phase space density.
L*
Radial Diffusion
phas
e sp
ace
dens
ity
NASA
Phase Space Density Analysis
![Page 45: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/45.jpg)
• Important information on the nature of the acceleration process can be found through phase space density analysis.
• Acceleration by inward radial diffusion driven by positive gradients in the phase space density.
• Local acceleration produces peaks in phase space density.
L*
L*
Radial Diffusion
Local Acceleration
phas
e sp
ace
dens
ity
phas
e sp
ace
dens
ity
NASA
NASA
Phase Space Density Analysis
![Page 46: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/46.jpg)
Phase Space Density Analysis
Iles et al., JGR, 2006
3.0 3.5 4.54.0 5.0 6.56.05.5
L*
10-7
10-8
10-9
f(,
K,L
*) (
cm M
eV/c
)-3
= 550 MeV/G; K = 0.11 G1/2RE
10 11 12 139UT date (September 1990)
![Page 47: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/47.jpg)
Phase Space Density Analysis
Iles et al., JGR, 2006
• Evidence for a developing peak in the electron phase space density at ~ MeV energies.
• Local acceleration plays a key role during the recovery phase of this storm.
3.0 3.5 4.54.0 5.0 6.56.05.5
L*
10-7
10-8
10-9
f(,
K,L
*) (
cm M
eV/c
)-3
= 550 MeV/G; K = 0.11 G1/2RE
10 11 12 139UT date (September 1990)
![Page 48: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/48.jpg)
• Developing peaks in the electron PSD have also been observed by Polar.
• Data from multiple satellites show frequent and persistent peaks in the equatorial PSD.
• Local acceleration is an important mechanism for radiation belt dynamics.
Chen et al., Nature Physics, 2007
Green and Kivelson, JGR, 2004
Phase Space Density Analysis
![Page 49: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/49.jpg)
tAE>100 (days) tAE>300 (days)
Seed flux Chorus power (pT2day)
Rel
ativ
isti
c el
ectr
on f
lux
chan
geR
ela
tivis
tic e
lect
ron
flu
x ch
an
ge
Seed Electrons Chorus Waves
All Substorms Large SubstormsL = 5
Survey of 26 Geomagnetic Storms
Meredith et al., JGR, 2003
![Page 50: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/50.jpg)
tAE>100 (days) tAE>300 (days)
Seed flux Chorus power (pT2day)
Rel
ativ
isti
c el
ectr
on f
lux
chan
geR
ela
tivis
tic e
lect
ron
flu
x ch
an
ge
Seed Electrons Chorus Waves
All Substorms Large SubstormsL = 5
• Trend for larger relativistic electron flux enhancements to be associated with:
– longer durations of prolonged AE activity
Meredith et al., JGR, 2003
Survey of 26 Geomagnetic Storms
![Page 51: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/51.jpg)
tAE>100 (days) tAE>300 (days)
Seed flux Chorus power (pT2day)
Rel
ativ
isti
c el
ectr
on f
lux
chan
geR
ela
tivis
tic e
lect
ron
flu
x ch
an
ge
Seed Electrons Chorus Waves
All Substorms Large SubstormsL = 5
• Trend for larger relativistic electron flux enhancements to be associated with:
– longer durations of prolonged AE activity
– larger fluxes of seed electrons
Meredith et al., JGR, 2003
Survey of 26 Geomagnetic Storms
![Page 52: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/52.jpg)
• Trend for larger relativistic electron flux enhancements to be associated with:
– longer durations of prolonged AE activity
– larger fluxes of seed electrons
– larger integrated lower-band chorus power
tAE>100 (days) tAE>300 (days)
Seed flux Chorus power (pT2day)
Rel
ativ
isti
c el
ectr
on f
lux
chan
geR
ela
tivis
tic e
lect
ron
flu
x ch
an
ge
Seed Electrons Chorus Waves
All Substorms Large SubstormsL = 5
Meredith et al., JGR, 2003
Survey of 26 Geomagnetic Storms
![Page 53: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/53.jpg)
Energy Diffusion
• Pitch angle and energy diffusion rates for scattering by whistler mode waves depend on:– the wave magnetic field intensity– the frequency distribution of the waves– the ratio fpe/fce
• Relativistic electrons interact most readily with lower-band chorus (Horne and Thorne, GRL, 1998).
• Energy diffusion is most effective in regions of low fpe/fce (Summers et al., JGR, 1998).
![Page 54: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/54.jpg)
Equatorial Region (-15o < λm < 15o)
Moderate
ModerateQuiet
Quiet Active
Active
Meredith et al., GRL, 2003
![Page 55: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/55.jpg)
Equatorial Region (-15o < λm < 15o)
Moderate
ModerateQuiet
Quiet Active
Active
active conditions 4 < L < 6 23 – 13 MLT
Meredith et al., GRL, 2003
![Page 56: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/56.jpg)
Mid-Latitude Region (15o < |λm| < 30o)
Moderate Active
Quiet Moderate Active
Quiet
Meredith et al., GRL, 2003
![Page 57: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/57.jpg)
Mid-Latitude Region (15o < |λm| < 30o)
active conditions4 < L < 606 – 14 MLT
Moderate Active
Quiet Moderate Active
Quiet
Meredith et al., GRL, 2003
![Page 58: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/58.jpg)
Timescale for Acceleration
• Use 1D Fokker-Planck equation to calculate evolution of particle flux.
• Loss and acceleration by chorus are included using the PADIE code with CRRES wave model.
– timescale to increase the flux at 1 MeV by an order of magnitude is ~ 1 day.
– consistent with satellite observations during the recovery phase of storms.
Horne et al., JGR, 2005
L = 4.5
![Page 59: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/59.jpg)
Global Modelling
• Varotsou et al. (GRL, 2005) incorporated radial diffusion and resonant interactions with whistler mode chorus waves in the Salammbô code.
• Salammbô (Beutier and Boscher, JGR, 1995) calculates the change in phase space density from a Fokker-Planck equation.
![Page 60: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/60.jpg)
Fokker-Planck Equation
• Fokker-Planck Equation includes:
– Radial diffusion
![Page 61: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/61.jpg)
Fokker-Planck Equation
• Fokker-Planck Equation includes:
– Radial diffusion
– Pitch angle diffusion
![Page 62: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/62.jpg)
Fokker-Planck Equation
• Fokker-Planck Equation includes:
– Radial diffusion
– Pitch angle diffusion
– Energy diffusion
![Page 63: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/63.jpg)
Fokker-Planck Equation
• Fokker-Planck Equation includes:
– Radial diffusion
– Pitch angle diffusion
– Energy diffusion
– Energy loss due to Coulomb collisions
![Page 64: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/64.jpg)
Results with Radial Diffusion
• Model was set up to find the steady-state solution for Kp = 1.8 that includes chorus and radial diffusion.
• A radiation belt is formed with a peak in the flux near L = 4.5.
• A magnetically active period was simulated by setting Kp = 4 for 4 days.
• With radial diffusion alone peak flux increases and moves to lower L.
Horne et al., AGU, 2006
![Page 65: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/65.jpg)
Results with Radial Diffusion and Chorus
• When chorus was included with radial diffusion:
– 1 MeV flux increases for 3.5 < L < 5.5.
– slight increase in flux at 400 keV
– major decrease in flux of 100 keV electrons inside L = 6.6.
Horne et al., AGU, 2006
![Page 66: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/66.jpg)
Phase Space Density Analysis
• Initial steady state is flat at large L and is in equilibrium with the conditions imposed by the outer boundary condition where radial diffusion is most effective.
• The phase space density falls at low L due to the decrease in efficiency of radial diffusion and the increasing importance of losses.
Horne et al., AGU, 2006
![Page 67: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/67.jpg)
Phase Space Density Analysis
• At low (100 MeV/G)
– Simulation for chorus alone shows a reduction in psd near L = 5.5.
– When radial diffusion is included the radial profile is smoothed resulting in a positive radial gradient from low L out to about L = 6.5.
Horne et al., AGU, 2006
![Page 68: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/68.jpg)
Phase Space Density Analysis
• At high (3000 MeV/G)
– Simulation for chorus alone shows the development of a large peak near L = 5.5.
– When radial diffusion is included the peak is reduced and smoothed by both inward and outward diffusion.
Horne et al., AGU, 2006
![Page 69: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/69.jpg)
Local Acceleration by Whistler Mode Chorus
• Local acceleration by whistler mode chorus plays a major role in the dynamics of the outer radiation belt during extended periods of enhanced magnetic activity .
![Page 70: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/70.jpg)
Magnetosonic Waves
• intense electromagnetic emissions, fcp < f < flhr
• compressional waves, propagate across B0
• generated by proton ring distributions [Boardsen et al., JGR, 1992]
Cluster 3 - 25 November 2002magnetosonic waves
![Page 71: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/71.jpg)
Global Distribution of Magnetosonic Waves
• Note: Low frequency limit of CRRES PWE restricts frequency and L shell coverage.
Meredith et al., JGR, 2008
![Page 72: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/72.jpg)
Global Distribution of Magnetosonic Waves
Strongest waves:• active conditions• most local times
• Note: Low frequency limit of CRRES PWE restricts frequency and L shell coverage.
Meredith et al., JGR, 2008
![Page 73: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/73.jpg)
Global Distribution of Magnetosonic Waves
Strongest waves:• active conditions• dusk side
Strongest waves:• active conditions• most local times
• Note: Low frequency limit of CRRES PWE restricts frequency and L shell coverage.
Meredith et al., JGR, 2008
![Page 74: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/74.jpg)
Global Distribution of Magnetosonic Waves
• Wave power increases with increasing magnetic activity suggesting they are related to periods of enhanced convection and/or substorm activity.
Strongest waves:• active conditions• dusk side
Strongest waves:• active conditions• most local times
![Page 75: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/75.jpg)
Energy Diffusion Rates at L = 4.5
• Energy diffusion rates have been estimated using Cluster wave observations and the PADIE code.
• Timescale of the order of a day
– 0.3 < E < 1 MeV outside the plasmapause
– 0.03 < E < 0.3 MeV inside the plasmapause
Outside plasmapause
Inside plasmapause
day
day
Horne et al., GRL, 2007
Magnetosonic waves may provide a
significant energy transfer process
between the ring current and the outer
radiation belt.
![Page 76: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/76.jpg)
Local Acceleration by Magnetosonic Waves
Local acceleration by magnetosonic waves may also play an important
role in radiation belt dynamics.
![Page 77: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/77.jpg)
Loss Mechanisms
• Several wave modes contribute to pitch angle scattering and subsequent loss to the atmosphere.
• Three potentially important loss processes – the scattering due to gyro-resonant interactions with:
– Plasmaspheric hiss
– EMIC waves
– Chorus waves
![Page 78: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/78.jpg)
Plasmaspheric Hiss
• Plasmaspheric hiss is a broadband, structureless, ELF emission that occurs in the frequency range from 100 Hz to several kHz.
• This whistler mode emission is confined to the higher density
regions associated with the plasmasphere or plasmaspheric plumes.
![Page 79: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/79.jpg)
Wave Data
hiss hiss
plasmapause
plasmapausefuhr
fce
flhr
Meredith et al., JGR, 2004
![Page 80: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/80.jpg)
moderatequiet active
quiet moderate active
Global Distribution of Plasmaspheric Hiss
Meredith et al., JGR, 2004
![Page 81: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/81.jpg)
moderatequiet active
quiet moderate active
active2 < L < 406 – 21 MLT
Global Distribution of Plasmaspheric Hiss
Meredith et al., JGR, 2004
![Page 82: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/82.jpg)
moderatequiet active
quiet moderate active
active2 < L < 406 – 21 MLT
active2 < L < 409 – 18 MLT
Global Distribution of Plasmaspheric Hiss
Meredith et al., JGR, 2004
![Page 83: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/83.jpg)
Origin of Plasmaspheric Hiss
Bortnik et al., Nature, 2008
• Ray tracing studies show that chorus waves can propagate into the plasmasphere and evolve into plasmaspheric hiss.
• Results account for the
essential features of hiss.
![Page 84: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/84.jpg)
Slot Region Loss Timescales
• Slot region can become filled during exceptionally large storms such as the Halloween Storms of 2003.
• Slot region subsequently reforms.
• Loss timescales for 2-6 MeV electrons at L = 2.5 estimated to be of the order of 2.9 – 4.6 days.
• The dominant loss process must be able to explain this decay.
Baker et al., Nature, 2004
SAMPEX 2-6 MeV Electrons
slot
![Page 85: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/85.jpg)
f < 2 kHz
f > 2 kHz
f > 2 kHz
• Broadband plasmaspheric emissions can be split into two categories [Meredith et al., 2006]:
– Plamaspheric hiss• 100 Hz < f < 2 kHz• generated by whistler mode
chorus
– MR whistlers• 2 kHz < f < 5 kHz • produced by thunderstorms
on Earth
Broadband Plasmaspheric Emissions
![Page 86: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/86.jpg)
Calculation of Losses Due To Hiss
• Use global models of the wave spectral intensity based on CRRES observations.
• Calculate bounce-averaged pitch angle rates using the PADIE code.
• Loss timescale calculated using the 1D pitch angle diffusion equation following Lyons et al., [1972].
Meredith et al., JGR, 2007
![Page 87: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/87.jpg)
Slot Region Loss Timescales
Active Conditions (AE* > 500 nT)Quiet Conditions (AE* < 100 nT)
MR Whistlers
• Loss timescales due to MR whistlers are prohibitively long.
Meredith et al., JGR, 2007
L = 2.5
![Page 88: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/88.jpg)
Slot Region Loss Timescales
Quiet Conditions (AE* < 100 nT)
Hiss (m = 80o )
Quiet Conditions (AE* < 100 nT)Active Conditions (AE* > 500 nT)
• Loss timescales due to hiss propagating at large wave normal angles are also prohibitively long.
Meredith et al., JGR, 2007
L = 2.5
![Page 89: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/89.jpg)
Slot Region Loss Timescales
Quiet Conditions (AE* < 100 nT)Quiet Conditions (AE* < 100 nT)Active Conditions (AE* > 500 nT)
Hiss (m = 52o)
• Hiss propagating at medium wave normal angles can lead to loss timescales of the order of 10 days during active conditions.
Meredith et al., JGR, 2007
L = 2.5
![Page 90: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/90.jpg)
Slot Region Loss Timescales
Quiet Conditions (AE* < 100 nT)Quiet Conditions (AE* < 100 nT)Active Conditions (AE* > 500 nT)
Hiss (m = 0o)• Hiss propagating at small wave
normal angles can lead to loss timescales of the order of 1 – 10 days depending on magnetic activity.
• Hiss propagating at small wave normal angles is largely responsible for the formation of the slot region.
Meredith et al., JGR, 2007
L = 2.5
![Page 91: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/91.jpg)
Quiet-time Decay
Experimental loss timescale is 5.70.6 days
Meredith et al., JGR, 2006
![Page 92: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/92.jpg)
Quiet-time Decay
Meredith et al., JGR, 2006
Experimental loss timescale is 2.00.1 days
![Page 93: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/93.jpg)
Quiet Time Loss Timescales
• Quiet time loss timescales in the outer radiation belt increase with increasing energy.
• Loss timescales range from
– 1.5 – 3.5 days for 214 keV electrons
– 5.5 – 6.5 days for 1.09 MeV electrons
Meredith et al., JGR, 2006
L shell
Loss
tim
esca
le (
days
)
Loss Timescale versus L shell
![Page 94: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/94.jpg)
Quiet Time Loss Timescales
• Quiet-time decay associated with:
– Large values of fpe/fce (> 7)
– <Kp> < 3-
Meredith et al., JGR, 2006
L shell
L shell
Kp index versus L shell
fpe/fce versus L shell
Kp
in
de
xfp
e/f
ce
![Page 95: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/95.jpg)
Calculation of Quiet Time Losses Due To Hiss
• Use the PADIE code and the 1D pitch angle diffusion equation.
• Use a wave model based on CRRES observations for Kp < 3-.
Meredith et al., JGR, 2006
![Page 96: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/96.jpg)
Comparison with QL Diffusion due to Hiss
• Plasmaspheric hiss propagating at small and/or medium wave normal angles can explain much of the observed quiet time decay.
• Plasmaspheric hiss propagating at large wave normal angles does not contribute to the loss rates
Meredith et al., JGR, 2006
![Page 97: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/97.jpg)
Comparison with QL Diffusion due to Hiss
• MeV loss timescales overestimated by a factor of 5 in region 4.5 < L < 5.0.
• EMIC waves may play a role in this region.
Meredith et al., JGR, 2006
![Page 98: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/98.jpg)
Loss Timescales During Active Conditions
• During active conditions loss timescales can be of the order of a day or less in the region 3.0 < L < 4.0
• Plasmaspheric hiss could thus play an important role in the loss of energetic electrons in the inner region of the outer radiation belt during enhanced magnetic activity.
Summers et al., JGR, 2007
![Page 99: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/99.jpg)
Hiss in Plasmaspheric Plumes
• Plasmaspheric hiss is also observed in plasmaspheric plumes
Summers et al., JGR, 2008
![Page 100: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/100.jpg)
Loss Timescales in Plasmaspheric Plumes
• Loss timescales estimated to be:
– days to tens of days at 1 MeV
– hours to a day at 100 keV
• Hiss in plumes can efficiently scatter energetic electrons.
Summers et al., JGR, 2008
![Page 101: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/101.jpg)
• During active conditions losses due to plasmaspheric hiss may occur on a timescale of 1 day or less and may play an important role during the main phase of magnetic storms.
Role of Plasmaspheric Hiss
• During quiet conditions losses due to plasmaspheric hiss occur on a timescale of several days or more and can explain the quiet time decay of radiation belt fluxes.
![Page 102: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/102.jpg)
EMIC Waves
• EMIC waves are low frequency waves (0.1-5 Hz) which are excited in bands below the proton gyrofrequency.
• They are generated by medium energy (1-100 keV) ring current ions injected during storms and substorms.
• They are able to resonate with MeV electrons causing pitch angle scattering and loss to the atmosphere.
He+
O+
Figure courtesy of Brian Fraser
![Page 103: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/103.jpg)
• EMIC waves are primarily observed between 13:00 and 19:00 MLT over a range of L shells > 3.
Location of Events
Meredith et al., JGR, 2003
![Page 104: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/104.jpg)
Spatial Distribution
• The L-mode minimum resonant energies fall below 2 MeV during ~12.5 % of the observations.
• These lower energy events occur outside L=4.5.
• The R-mode minimum resonant energies tend to be greater than 2 MeV.
Meredith et al., JGR, 2003
![Page 105: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/105.jpg)
Dependence on fpe/fce
• The L-mode minimum resonant energies fall below 2 MeV in high density regions where fpe/fce > 10.
• Such conditions are found in regions of high plasma density and low magnetic field such as the dusk-side plasmasphere or plasmaspheric plumes.
Meredith et al., JGR, 2003
![Page 106: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/106.jpg)
Dependence on Frequency
• The L-mode minimum resonant energies are sensitive to the normalised frequency.
• The lower energy events occur over a range of frequencies below the helium ion gyrofrequency.
Meredith et al., JGR, 2003
![Page 107: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/107.jpg)
Dependence on Frequency
• For lower concentrations of heavy ions the lower energy events can also occur over a range of frequencies below the hydrogen ion gyrofrequency.
Meredith et al., JGR, 2003
![Page 108: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/108.jpg)
Dependence on Dst Index
Meredith et al., JGR, 2003
• The L-mode electron minimum resonant energies may fall below 2 MeV for almost any value of the Dst index.
![Page 109: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/109.jpg)
Dependence on Dst Index
Meredith et al., JGR, 2003
• The L-mode electron minimum resonant energies may fall below 2 MeV for almost any value of the Dst index.
• The majority (84%) of the lower energy events occur during storms.
• The L-mode minimum electron resonant energies can fall below 2 MeV during the initial phase of a storm when the Dst index is positive.
![Page 110: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/110.jpg)
Proton Minimum Resonant Energies
• Electron minimum energies below 2 MeV are associated with proton minimum resonant energies below 2 keV.
• This interesting new result suggests that EMIC waves which resonate with ~MeV electrons are produced by ~keV protons.
Meredith et al., JGR, 2003
![Page 111: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/111.jpg)
• Loss timescale near equatorial loss cone:
– ~1 hour for 2 MeV electrons.
– several hours for 1 MeV electrons.
Pitch Angle, (o)D
(
s -1)
Bw = 1 nT1% drift averaging
Summers et al., JGR, 2007
Scattering Rates in the Helium Band
![Page 112: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/112.jpg)
• Analysis of an EMIC wave event on CRRES at the start of the main phase of a storm show:
– Emin falls in the 1-2 MeV range
– D is comparable to SD limit
– suggesting enhanced MeV precipitation.
Loto’aniu et al., JGR, 2006
20 40 60 80
Pitch angle, (o)
DSD
DSD
Case Study – EMIC Wave Event
![Page 113: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/113.jpg)
• Relativistic electrons observed to drop by an order of magnitude during the event.
• Results consistent with the suggestion that EMIC waves may lead to substantial loss of relativistic electrons during the main phase of geomagnetic storms.
Loto’aniu et al., JGR, 2006
Case Study – EMIC Wave Event
![Page 114: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/114.jpg)
• Nine REP events were observed by the GeD instrument on board the MAXIS balloon.
• The events lasted from minutes-to-hours and covered a range of L shells from L = 3.8 to L = 7.0.
• The events were restricted to the afternoon/dusk sectors consistent with EMIC scattering.
Dusk
Dawn
Millan et al., GRL, 2002
Evidence for Relativistic Electron Precipitation
![Page 115: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/115.jpg)
Role of EMIC Waves
• Losses due to EMIC waves may occur on a timescale of several hours to a day and are likely to play an important role during the main phase of magnetic storms.
![Page 116: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/116.jpg)
Losses due to Chorus
• Relativistic electrons near the loss cone can also resonate with chorus at high geomagnetic latitudes.
• Bursty nature of chorus leads to < 1 second intensifications of precipitation known as microbursts.
Lorentzen et al., JGR, 2001
![Page 117: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/117.jpg)
• Microburst precipitation observed by SAMPEX– outside the plasmapause– on the dawnside– near L = 5.
• Peak rates in the dawn to noon sector.
• Similar to the distribution of high latitude chorus waves.
O’Brien et al., JGR, 2003
Microburst Precipitation
![Page 118: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/118.jpg)
• Comparison between precipitating flux observed by SAMPEX and the trapped flux measured by Polar.
• Effective lifetimes are of the order of 1 day.
Thorne et al., JGR, 2005
1 day
Microburst Loss Rates – Case Study
![Page 119: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/119.jpg)
Losses due to Chorus
• Bounce-averaged diffusion rates for 100 pT chorus waves at L = 4 show:
– loss timescales near the loss cone due to chorus can approach 1 day.
– requires chorus at latitudes greater than 300.
Thorne et al., JGR, 2005
mb = 1 day
![Page 120: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/120.jpg)
Microburst Precipitation
• Losses are sensitive to changes in trough plasma density.
• Losses expected to be of the order of a day or less outside the plasmapause during the main phase of a storm.
• Lifetimes subsequently increase during the storm recovery phase as densities increase.
mb = 1 day
Thorne et al., JGR, 2005
![Page 121: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/121.jpg)
Dual Role of Whistler-Mode Chorus
• Local acceleration by whistler mode chorus plays a major role in the dynamics of the outer radiation belt during extended periods of enhanced magnetic activity.
• Losses due to whistler mode chorus may occur on a timescale of 1 day or less and may play an important role during the main phase of magnetic storms.
![Page 122: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/122.jpg)
Importance of Plasmasphere
• Electron acceleration and loss by VLF chorus takes place in the low density region outside the plasmapause.
• Losses due to hiss and EMIC waves take place in the high density plasmasphere and plasmaspheric plumes.
Summers et al., JGR, 1998
![Page 123: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/123.jpg)
Importance of Plasmasphere
Summers et al., JGR, 1998
• The generation and global distribution of energetic electrons are thus greatly influenced by the cold plasma.
![Page 124: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/124.jpg)
magnetopause
plasmaspause
Sun
Conclusions
Chorus
• Chorus waves are an important acceleration and loss mechanism for electrons with energies from 0.1 to a few MeV.
![Page 125: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/125.jpg)
magnetopause
plasmaspause
Sun
Conclusions
Chorusmagnetosonicwaves
• Chorus waves are an important acceleration and loss mechanism for electrons with energies from 0.1 to a few MeV.
• Magnetosonic waves may be an important acceleration mechanism.
![Page 126: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/126.jpg)
plasmaspherichiss
magnetopause
plasmaspause
Sun
Conclusions
Chorusmagnetosonicwaves
• Chorus waves are an important acceleration and loss mechanism for electrons with energies from 0.1 to a few MeV.
• Magnetosonic waves may be an important acceleration mechanism.
• Plasmaspheric hiss is a major loss process for electron energies from 0.1 to a few MeV
![Page 127: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/127.jpg)
EMIC waves
plasmaspherichiss
magnetopause
plasmaspause
Sun
Conclusions
Chorus
• Chorus waves are an important acceleration and loss mechanism for electrons with energies from 0.1 to a few MeV.
• Magnetosonic waves may be an important acceleration mechanism.
• Plasmaspheric hiss is a major loss process for electron energies from 0.1 to a few MeV
• EMIC waves are an important loss mechanism for MeV electrons.
magnetosonicwaves
![Page 128: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/128.jpg)
Outstanding Science Questions
1. What are the relative roles of the following processes in the acceleration of outer radiation belt electrons ?
– Inward radial diffusion
– Local acceleration by:
• whistler mode chorus
• magnetosonic waves
• Z mode waves
![Page 129: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/129.jpg)
Outstanding Science Questions
2. What are the relative roles of the following processes affecting the loss of outer radiation belt electrons ?
– Outward radial diffusion and loss to the magnetopause
– Losses due to gyroresonant wave particle interactions with:
• EMIC waves
• plasmaspheric hiss
• whistler mode chorus
![Page 130: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/130.jpg)
Future Satellite Missions
• These key questions will be addressed by ongoing studies and two new satellite missions:
– NASA Radiation Belt Storm Probes Mission (proposed launch: April 2012)
– Canadian ORBITALS Mission (proposed launch: 2011-2013)
![Page 131: Local Acceleration and Loss of Relativistic Electrons in the Earth’s Outer Radiation Belt](https://reader038.vdocuments.mx/reader038/viewer/2022102819/56814b08550346895db8216a/html5/thumbnails/131.jpg)
Acknowledgment
• I would like to thank the National Science Foundation for providing support for this visit.