Energetic particles in the Heliosphere and
the Magnetosphere
Shri Kanekal
LASP
Section 1 Overview of particle populations in the Heliosphere
Section 2 Characteristics of charged particles
Section 3 Charged particle detection and measurement
Section 4 Electrons and Protons in the Magnetosphere
i.
ii.
iii.
iv.
Outer zone radiation belt electrons
Inner zone protons
Solar energetic particles (mainly protons)
Jovian electrons
A tour of our space environment
from the perspective of
energetic particle populations
Section 1
The Milky way, our local galaxy
The Sun, our local star
The Earth, our planet
Particle populations are diverse
Galactic cosmic rays
(GCR)
> Energy range from ~ 100s of MeV to 10s of GeV
> Consist of nuclei of atoms, ranging from the lightest
to the heaviest elements in the periodic table
> Originate from supernova explosions
Solar energetic particles (SEP)
> Energy range from ~ 10s of MeV to 100s of MeV
> Provide compositional information of the Sun
 Anomalous cosmic rays
> Interstellar neutrals ionized by solar wind &
accelerated at the “heliopause”
> comprise of only those elements that are difficult
to ionize, including He, N, O, Ne, and Ar
Particle populations are diverse
 Magnetospheric particles
> stably trapped and transient
> Energy range from ~ 10s of MeV to 100s of MeV
> electrons, protons, ionospheric solar ions, trapped
cosmic rays
> Earth, Jupiter, … other planets with magnetic fields
 Magnetospheric bulk plasma
> bulk plasma eV & low energy keV particles
> can influence behaviour of high energy particles !
We will focus mostly on magnetospheric “high energy”
electrons and briefly discuss solar energetic protons
Galactic comic ray map : from EGRET instrument
By measuring photon intensity which is proportional to GCR
intensity via their interaction with the interstellar gas
Solar energetic particle observations
hour of january 20 2005
Lasco coronograph picture of
the Sun onboard SoHo
spacecraft showing “snow” from
SEPs
Protons and X-ray intensities
From GOES spacecraft
Anomalous cosmic rays
interstellar neutrals become charged by photo-ionization or
charge exchange with the solar wind.The Sun's magnetic carries
them outward to the solar wind termination shock.
“high energy” electrons in the Earth’s magnetosphere
27-oct-2003
28-oct-2003
29-oct-2003
These “relativistic electrons” are highly variable and dynamic.
Note the large increase in particle flux in just two days !
Plasmasphere images taken by the EUV instrument
onboard IMAGE spacecraft
Plasmasphere comprises of cold plasma ~ few eV
Let us define some terms
regarding energetic particles
Section 2
what do we measure in space ?
omnidirectional flux
differential flux
pitch angle distribution
time evolution of
particle fluxes,
& pitch angle distributions
Integral,Differential, Omnidirectional … flux
Integral directional flux
particle counts = N /second
(particles with E > E’)
detector area = A cm2
field of view =  sr (solid
angle)
flux = N / [ A* ]
units = cm-2 -Sr-sec
differential directional flux
flux = N / [ A**E]
units = cm-2 -Sr-sec-MeV
detector counts particles with E1 < E < E2 = E
Omnidirectional flux => over full 4 sr
Observations of electron fluxes in the Earth’s magnetosphere
From Baker and Kanekal, GRL (to be submitted)
B
Pitch angle : angle between the
local magnetic field vector and
particle momentum

commonly observed distributions
particles  to B

Particles to B
“Pancake”
and
“Cigar” shaped distributions
Observations of pitch angle distributions
Cigar shape
Counter streaming electrons observed in
the interplanetary space
(Steinberg et al. JGR 2005)
Measured Pitch angle distributions
of electron in the magnetosphere
(Selesnick and Blake, JGR 2002)
How do we detect and identify charged particles ? Section 3
principle methods of particle detection
examples of particle detectors
Interaction of charged particles with matter
When charged particles pass through matter (M > me )
a) they lose energy
 inelastic collisions mainly with atomic electrons
causes ionization or excitation of the atom
many many many collisions !!
statistical average
energy loss/unit length “dE/dx”
b) they change direction
 elastic scattering from atomic nuclei
electrons are different !
 braking radiation or “bremsstrahlung”
( we will ignore interaction of photons with matter )
Ionization loss of charged particles in matter
Principle of operation : simple solid state detector
Q  E
Charged particle passing through Silicon creates electron-hole
Pairs. The total charge collected is proportional to the energy
Lost by the charged particle
Principle of operation : simple scinitillation detector
Photons are emitted by
excited atoms returning to
their ground state after
being ionized by charged
particles which are detected
by a photo multiplier Tube
(PMT).
Two instruments currently operating on spacecraft
PET : Proton Electron Telescope
Onboard SAMPEX spacecraft
HIST : High Sensitivity Telescope
Onboard Polar spacecraft
An electron spectrometer type instrument
Electrons bend in a magnetic
field and reach the detection
plane at different distances
proportonal to their energies
and are detected by dE/dx
loss in individual solid state
detectors.
An instrument that is being developed here at LASP
REPT :Relativistic Electron Proton Telescope
Instruments are calibrated in beam tests and simulations
50mm
Al 10mm
(5mm) W+(5mm )x2 Al
10 mm
Kapton cover 0.025 mm
W 7mm
R9
R1
Monte Carlo simulation of electrons entering the instrument
Minimum ionizing
Stopping particles
Identification of particle species in a dE/dx instrument
Particle species are
identified by the energy
deposition pattern in a
stack of solid state detectors
Energetic particles in the Earth’s Magnetosphere Section 4
Radiation belt electrons, and protons
 trapped anomalous cosmic rays
 trapped and transient solar energetic particles
 jovian electrons, … etc etc
The Terrestrial Magnetosphere
Outer Belt
SAMPEX
Geostationary Transfer Orbit
Inner Belt
Slot Region
Relatively stable inner belt
mostly Protons
Sources : CRAND protons
SEP events
Dynamic Outer belt
mostly electrons
Sources : Magnetotail electrons
The dynamic outer zone electrons
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
22 October 2003 (295)
29 October 2003 (302)
3 November 2003 (307)
Key Regions of Particle Acceleration in the Magnetosphere
Auroral Region
Acceleration
Bow
Shock
Cusp
Shock
Acceleration
Tail Reconnection
Acceleration
Inner Magnetosphere
Acceleration
Solar Wind
Magnetopause
Acceleration
The Solar wind plays a crucial role in the acceleration processes
Particle motions in a magnetic dipole : recap
L = equatorial
distance of a
field line in a
dipole field
Observations of conservation of the first adiabatic invariant.
Particle fluxes of different
local pitch angles measured
along the same field line
transformed into equatorial
pitch angles.
From Liouville’s theorem
J(1,B1,L1) = J(2,B2,L2)
sin21/ B1 = sin22/ B2
1 and 2 are pitch angles at
two different locations on the
same field line
Electron energization - overview
 High solar wind speeds
and southward Bz
(reconnection, waves, radial
diffusion …)
 Substorm generated
seed population
 hundreds of keV
relativistic energies
 usually associated with
geomagnetic storms
 physical processes
 radial transport
 in-situ acceleration
 combination
Relativistic Electrons : Radial Diffusion
• Initial electron ring
– r = r0
• Sudden asymmetric
compression 
– Electrons on different
constant B paths
• Resultant smeared
out electron band
• Long timescales
– ≈ Days to weeks
In-situ acceleration Example:
Resonant Interactions with VLF Waves
Summers et al. (JGR 103,
20487, 1998) proposed that
resonant interaction with
VLF waves could heat
particles:
• Whistler-mode chorus at
dawn combined with EMIC
interactions heat and
isotropize particles
• Leads to transport in M, K,
and L
See also Horne et al., (Nature, 2005)
Acceleration Models: Expected pitch angle distribution
Radial diffusion
Pancake distribution
Stochastic acceleration
(VLF waves)
Isotropization on drift time
scales
Magnetic pumping
Continual isotropization
Many wave-particle interaction models include pitch
angle scattering
Pure radial diffusion does not - separate process
Relativistic Electrons & Geomagnetic Storms
• Recovery phase
– Increased fluxes
– Energization
[See Kanekal et al., 2004; Reeves et al., 2003]
•
Main phase
– Flux dropout
– Adiabatic field
change & particle
loss
•
Flux changes
– Decrease or no
change in about
50% of storms GEO data
Spacecraft and Data
 SAMPEX
POLAR
LEO orbit ≈ 650 km
820 inclination
≈ 90 min period
2.-6. MeV electrons
SAMPEX
geo
 POLAR
elliptical orbit 2x9 Re
≈ 18 hrs period
> 2 MeV electrons
 complete coverage
of the outer zone
L ≈ 2.5 to 6.5
Relativistic electrons : energization and loss
Energization => increasing flux
loss => decreasing flux
Relativistic electrons : energization and loss
flux increase and decay
times set lower bounds on
energization and loss time
scales of proposed
physical models.
Flux increase or decrease
is a balance between
Energization
&
Loss
Energization
dominates
Loss dominates
Relativistic electrons : global coherence
 flux increase
over a large
L range
 high-altitude
and
low-altitude
fluxes track
each other
(fluxes are 30-day
running averages)
Note that Polar being at a higher altitude samples a larger part of the equatorial
pitch angle distribution than SAMPEX.
Tracking of high-altitude
and low-altitude fluxes
=>
Pitch angle distribution
(i.e flux) isotropization
Compare SAMPEX and
polar (largest eq. Pitch angle)
At L=4
Global coherence : High- & Low- altitude Flux Ratio
Flux ratio increases during a flux enhancement event  Enhanced
isotropization
Global coherence : High- & Low- altitude Flux Ratio
isotropization weakens at L shells further away from flux maximum.
Global coherence : High- & Low- altitude Flux Correlation
 correlation vs. lag time at
select L values
 correlation vs. lag time at
geo L = 6.6
 day-average fluxes for 1998
 orbit-average fluxes for 1999
Lag times are less than 1 day  rapid and/or simultaneous isotropization
Relativistic electrons : location of flux maximum
Lmax ~ 1.3 Lpp
Lpp - function of
minimum Dst
O’Brien and Moldwin (2003)
Very low energy
plasma in the
Plasmasphere
controls high
energy electrons
Most intense energization correlated with plasmapause location
Relativistic electrons : location of flux maximum
indicative of coupling between
electron energization and
the plasmapause and the ring
current.
Perhaps via the growth of
Whistler and EMIC waves which
are driven by anisotropy of ring
current protons and electrons
Halloween storms (oct-nov 2003) are not included
First observed by Tverskaya 1986
Whistler waves predominate
outside plasmapause
EMIC waves predominate
the dusk side region along
the plasmapause.
EMIC waves lead to particle
loss within the plasmapause
Strong Semi-Annual Variation in Outer Zone
Seasonal Average Fluxes : 1992 - 1999
2.0
SAMPEX Electrons
2.5 < L < 6.5
Normailized Electron Flux
2 - 6 MeV
1.5
Fall
Spring
Possible causes
tilt of the Earth’s
dipole axis relative
to the solar ecliptic
(Russell-McPherron)
1.0
Winter
Summer
0.5
0.0
February April
Baker et al. (GRL,1999)
May July
August October
November January
exposure to high
speed solar wind
(axial effect)
varying solar wind
coupling efficiency
(equinoctial effect)
Relativistic Electrons : Solar Cycle Effects
CME
HSS
Declining phase - many recurrent high speed streams
Ascending phase - sporadic coronal mass ejections
Electron Energization Summary
 energization occurs over a large radial region (L shell)
(measurements of 1-day time resolution) [Global]
 energization appears to be intimately related to pitch angle
scattering leading to rapid pitch angle isotropization.
Some in-situ mechanisms include near-simultaneous
energization and pitch angle scattering. ‘simple’ radial
diffusion needs to be augmented with pitch angle scattering
mechanisms. [Coherent]
 Clues to discriminating between various mechanisms include
association of Lmax with plasmapause location and |Dst|
 Relativistic electrons in the magnetosphere show seasonal
and solar cycle dependence.
Inner Zone Protons
Sources : CRAND & SEP
Cosmic Ray Albedo Neutron Decay
Inner Zone Protons
Some Presently Used Platforms
A solar proton event observed by SAMPEX
 Interplanetary particles have access vis the open
field lines over the Earth’s polar regions
 Proton rates summed over invariant latitude > 70 deg
 Orbital time resolution of ~ 90 minutes
SEP entry into the magnetosphere: Charged particle cutoffs
 The cutoff latitude
is a well defined
latitude below which
a charged particle of
a given rigidity
(momentum per unit
charge) arriving from
a given direction
cannot penetrate.
Quiet time cutoffs
Ogliore et al., ICRC, 2001
Rc = 15.062cos4() -0.363 GV
= invariant latitude
cos2  = 1 / L
Charged particle cutoffs during disturbed times
During geomagnetic
storms SEP cutoffs are
lowered and are a
potential radiation
hazard
c = 0.053Dst + 65.8 (0.6)
Birch et al., JGR,2005
Location of > 16 MeV Oxygen during October-November 1992 SEP events.
Solid lines are ISS ground tracks (green area is the nominal polar cap)
Leske et al, JGR, 2001
Measuring cutoff latitude: Data (SAMPEX)
Proton counts
• 6 seconds time resolution
• invariant latitude bins 0.40
wide smoothed over 2.00
The polar region
between 700 and 750 ( blue
line)
The cutoff latitude is
determined as the latitude
at which the count rate is
half the polar average.
Note contamination from
radiation belt electrons at
about 600 inv. lat.
Proton count rate as a function of invariant latitude for
the descending part of an orbit over the south pole.
Measured cutoff latitudes: November 1997
Proton cutoff as a function of time during the november 1997
geomagnetic storm. The black trace shows the Dst index. The cutoff
location follows the Dst index closely.
Calculating cutoff latitude: Particle tracing
Proton trajectory simulations :
Energy: 25 MeV
launch: 2700 longitude. and 47.750 latitude.
SAMPEX location at L = 5
scan : 20 degrees below and 15 degrees
above in 0.5 degree steps
trajectory type:
i) trapped: particle drifts at least 2
times around the Earth
ii) quasi-trapped: drifts once then exits
the magnetosphere
iii) penetrating: exits the magnetosphere
Trajectories of a 25 MeV proton in the noonmidnight and equatorial planes for Dst of -200
nT.
The cutoff latitude is defined as that latitude
at which only directly penetrating
populations remain as we trace particles
starting from low latitudes and move to
higher latitudes.
Cutoff location model and observations: November 1997
c = 0.053Dst + 66.1
c = 0.063Dst + 65.8
Proton cutoff as a function of the Dst index for the november 1997
geomagnetic storm. The black trace is a straight line fit to the data
and the red trace for the protons traced in the T96 field.
Trapped SEP ions: 24 Nov 2001
Mazur et al., AGU
Monograph 165, 2006
Clear trapping of solar particles: 13 of 26
SEP penetration events inside L=4, 98-03
Protons:
Protons:19-26
19-28 MeV
MeV(SAMPEX/PET)
(SAMPEX/PET)
 Pitch angle
SEP Protons
New belt of trapped Protons
Trapped and Solar Energetic Particle Summary
 sources of inner belt protons include the CRAND and solar
protons.
 Interplanetary charged particles have access to the Earth’s
magnetosphere over the polar regions and reach latitudes
depending upon their rigidity. They are some times trapped and
form stable long lived “new belts”. Trapping could be the
result of pitch angle scattering.
 Global magnetic field models reproduce general behavior of
the variation of cutoff location during disturbed times but
consistently over estimate value of the cutoff location.
Jovian electrons : 13 month synodic period at 1 AU
The interplanetary magnetic field modulates charged particles
in the heliosphere
Jovian electrons : Evidence for source modulation
Kanekal et al, GRL 2003
Transport/Modulation effects ruled out by comparisons to IMP8 data
Jovian electrons Summary
 Jovian magnetosphere is a source of ~MeV which are
transported along the Parker spiral and reach the Earth.
 The optimal magnetic connection occurs once every 13 months,
the jovian synodic period at the Earth. These electrons are
useful in the study of influence of the interplanetary magnetic
field on the propagation of charged particles.
 Using SAMPEX and IMP8 sensors a puzzling lack of the Jovian
electrons was observed during 1995-1997 ( 2 jovian cycles)
which can be attributed to possible changes of the Jovian
source itself rather than changes in transport/modulation .
Home work assignment
1. What are chief measurements that are made regarding
charged particles in space ?
2. Describe some of the techniques used to measure
charged particles.
3. How does the solar wind influence particle populations
in the magnetosphere ?
4. What are the two main classes of electron energization
in the magnetosphere ? How do we distinguish between
them ?
5. What is the cause for the slot region ? Briefly describe
the energy/species dependence of the slot region.
6. Can you think of a way SEP to get trapped in the
magnetosphere ?
7. Research the discovery of Jovian electrons.
Solar wind : plasma outflow from the Sun