Energetic particles in the Heliosphere and the Magnetosphere

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Energetic particles in the Heliosphere and the
Magnetosphere Shri Kanekal LASP
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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. Outer zone radiation belt electrons
ii. Inner zone protons iii.
Solar energetic particles (mainly protons)
iv. Jovian electrons
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A tour of our space environment
Section 1 from the perspective of
energetic particle populations
The Milky way,
our local galaxy
The Sun, our local star
The Earth, our
planet
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Particle populations are diverse

• Galactic cosmic rays (GCR)
• gt Energy range from 100s of MeV to 10s of
  GeV
• gt Consist of nuclei of atoms, ranging from
  the lightest
• to the heaviest elements in the periodic
  table
• gt Originate from supernova explosions
• Solar energetic particles (SEP)
• gt Energy range from 10s of MeV to 100s of
  MeV
• gt Provide compositional information of the
  Sun
• Anomalous cosmic rays
• gt Interstellar neutrals ionized by solar wind
  
• accelerated at the heliopause
• gt comprise of only those elements that are
  difficult
• to ionize, including He, N, O, Ne, and Ar

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Particle populations are diverse

• Magnetospheric particles
• gt stably trapped and transient
• gt Energy range from 10s of MeV to 100s of
  MeV
• gt electrons, protons, ionospheric solar ions,
  trapped
• cosmic rays
• gt Earth, Jupiter, other planets with
  magnetic fields
• Magnetospheric bulk plasma
• gt bulk plasma eV low energy keV particles
• gt can influence behaviour of high energy
  particles !

We will focus mostly on magnetospheric high
energy electrons and briefly discuss solar
energetic protons
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Galactic comic ray map from EGRET instrument
By measuring photon intensity which is
proportional to GCR intensity via their
interaction with the interstellar gas
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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
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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.
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high energy electrons in the Earths
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 !
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Plasmasphere images taken by the EUV instrument
onboard IMAGE spacecraft
Plasmasphere comprises of cold plasma few eV
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Let us define some terms
Section 2 regarding energetic
particles what do we measure in space
? omnidirectional flux
differential flux
pitch angle distribution
time evolution of
particle fluxes,
pitch angle
distributions
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Integral,Differential, Omnidirectional flux
Integral directional flux particle counts N
/second (particles with E gt 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 lt E lt E2
?E Omnidirectional flux gt over full 4? sr
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Observations of electron fluxes in the Earths
magnetosphere
From Baker and Kanekal, GRL (to be submitted)
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Pitch angle angle between the local magnetic
field vector and particle momentum
B
?
commonly observed distributions
particles ? to B
?
Particles to B
Pancake and
Cigar shaped distributions
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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)
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How do we detect and identify charged particles ?
Section 3
principle methods of particle detection
examples of particle detectors
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Interaction of charged particles with matter
When charged particles pass through matter (M gt
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
)
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Ionization loss of charged particles in matter
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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
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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).
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Two instruments currently operating on spacecraft
HIST High Sensitivity Telescope Onboard Polar
spacecraft
PET Proton Electron Telescope Onboard SAMPEX
spacecraft
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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.
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An instrument that is being developed here at
LASP
REPT Relativistic Electron Proton Telescope
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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
R1
R9
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Monte Carlo simulation of electrons entering the
instrument
Stopping particles
Minimum ionizing
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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
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Energetic particles in the Earths Magnetosphere
Section 4 ?Radiation belt
electrons, and protons ? trapped anomalous
cosmic rays ? trapped and transient
solar energetic particles ?
jovian electrons, etc etc
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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
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The dynamic outer zone electrons
22 October 2003 (295)
29 October 2003 (302)
3 November 2003 (307)
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Key Regions of Particle Acceleration in the
Magnetosphere
The Solar wind plays a crucial role in the
acceleration processes
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Particle motions in a magnetic dipole recap
L equatorial distance of a field line in a
dipole field
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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 Liouvilles
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
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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

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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

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In-situ acceleration ExampleResonant
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)
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Acceleration Models Expected pitch angle
distribution
Many wave-particle interaction models include
pitch angle scattering Pure radial diffusion
does not - separate process
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Relativistic Electrons Geomagnetic Storms

• Recovery phase
• Increased fluxes
• Energization
• Main phase
• Flux dropout
• Adiabatic field change particle loss
• Flux changes
• Decrease or no change in about 50 of storms -
  GEO data

See Kanekal et al., 2004 Reeves et al., 2003
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Spacecraft and Data

• SAMPEX
• LEO orbit 650 km
• 820 inclination
• 90 min period
• 2.-6. MeV electrons
• POLAR
• elliptical orbit 2x9 Re
• 18 hrs period
• gt 2 MeV electrons
• complete coverage
• of the outer zone
• L 2.5 to 6.5

POLAR
SAMPEX
geo
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Relativistic electrons energization and loss
loss gt decreasing flux
Energization gt increasing flux
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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
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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.
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Tracking of high-altitude and low-altitude
fluxes gt Pitch angle
distribution (i.e flux) isotropization
Compare SAMPEX and polar (largest eq. Pitch
angle) At L4
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Global coherence High- Low- altitude Flux
Ratio
Flux ratio increases during a flux enhancement
event ? Enhanced isotropization
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Global coherence High- Low- altitude Flux
Ratio
isotropization weakens at L shells further away
from flux maximum.
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Global coherence High- Low- altitude Flux
Correlation

• correlation vs. lag time at
• select L values
• day-average fluxes for 1998

• correlation vs. lag time at
• geo L 6.6
• orbit-average fluxes for 1999

Lag times are less than 1 day ? rapid and/or
simultaneous isotropization
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Relativistic electrons location of flux
maximum
Lmax 1.3 Lpp
Lpp - function of minimum Dst OBrien and
Moldwin (2003)
Very low energy plasma in the Plasmasphere contro
ls high energy electrons
Most intense energization correlated with
plasmapause location
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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 Whistler
waves predominate outside plasmapause EMIC waves
predominate the dusk side region along the
plasmapause. EMIC waves lead to particle loss
within the plasmapause
Halloween storms (oct-nov 2003) are not included
First observed by Tverskaya 1986
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Strong Semi-Annual Variation in Outer Zone
Possible causes tilt of the Earths dipole
axis relative to the solar ecliptic
(Russell-McPherron) exposure to high speed
solar wind (axial effect) varying solar wind
coupling efficiency (equinoctial effect)
Baker et al. (GRL,1999)
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Relativistic Electrons Solar Cycle Effects
CME
HSS
Declining phase - many recurrent high speed
streams Ascending phase - sporadic coronal mass
ejections
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• 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.

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Inner Zone Protons
Sources CRAND SEP Cosmic Ray Albedo Neutron
Decay
Inner Zone Protons
Some Presently Used Platforms
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A solar proton event observed by SAMPEX

• Interplanetary particles have access vis the
  open
• field lines over the Earths polar regions
• Proton rates summed over invariant latitude gt 70
  deg
• Orbital time resolution of 90 minutes

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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

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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
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Location of gt 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
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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.
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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.
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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 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.
Trajectories of a 25 MeV proton in the
noon-midnight and equatorial planes for Dst of
-200 nT.
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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.
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Trapped SEP ions 24 Nov 2001
Clear trapping of solar particles 13 of 26 SEP
penetration events inside L4, 98-03
Mazur et al., AGU Monograph 165, 2006
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Protons 19-28 MeV (SAMPEX/PET)
Protons 19-26 MeV (SAMPEX/PET)
SEP Protons
? Pitch angle
New belt of trapped Protons
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• Trapped and Solar Energetic Particle Summary
• sources of inner belt protons include the CRAND
  and solar
• protons.
• Interplanetary charged particles have access to
  the Earths
• 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.

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Jovian electrons 13 month synodic period at 1 AU
The interplanetary magnetic field modulates
charged particles in the heliosphere
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Jovian electrons Evidence for source modulation
Kanekal et al, GRL 2003
Transport/Modulation effects ruled out by
comparisons to IMP8 data
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• 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 .

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Home work assignment

• 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.

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Solar wind plasma outflow from the Sun