The recent observation of plasma waves and particles Qianli Ma

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Transcript The recent observation of plasma waves and particles Qianli Ma

The recent observation of plasma waves and particles
in the inner magnetosphere
Qianli Ma
University of California, Los Angeles
2014 GEM
Outline
• A sketch of waves and particles in the inner
magnetosphere.
• Recent satellites in the inner magnetosphere.
• Wave and particle data measurements and their
relations.
• Other interesting findings by Van Allen probes.
• Summary.
What we see in the inner magnetosphere –
plasma waves and particle populations
 In the inner magnetosphere, the
particles perform energy and
charge dependent drift motion.
 The anisotropy and positive
gradients in the particle
distribution can provide the free
energy for wave excitation.
 The waves can cause the lose or
acceleration of the particles.
 The diffusion processes become
important in the inner
magnetosphere, and the wave and
particle measurement is an
important focus in the recent
spacecraft missions.
[Thorne GRL 2010]
Time series of frequency spectrum
Satellite orbits in the inner magnetosphere
 Van Allen Probes:
Highly elliptical equatorial orbits
1.1 RE to 5.8 RE
9 hours period
 THEMIS inner satellite (A, D, E):
Highly elliptical equatorial orbits
1.1 RE to 10 or 12 RE
22 hours period
 Cluster:
Elliptical polar orbits
3 RE to 19 RE
57 hours period
 GOES:
Geosynchronous orbit
6.6 RE
24 hours period
Satellite instruments and data
THEMIS
Van Allen Probes
• EFI: electric field variations.
• ECT: particle measurements.
HOPE: low energy particle flux up
to 45 keV.
MagEIS: 30 keV to 4 MeV electrons
and 20 keV to 1 MeV ions.
REPT: energetic electrons (up to 10
MeV) and protons ( up to 75 MeV).
• EMFISIS: wave measurements.
WFR: 10 Hz to 12 kHz electric and
magnetic fluctuation matrix.
HFR: 10 kHz to 400 kHz electric
fluctuation.
• EFI: DC to 12 Hz electric field.
• FGM: background B0 and low
frequency (< 64 Hz) magnetic
field fluctuations.
• SCM: magnetic fluctuations up to
4 kHz.
• DFB: spectral processing.
• ESA: particle flux from a few eV
to 25 keV (ion) or 30 keV
(electron).
• SST: particle flux from 25 keV to 6
MeV.
E-flux Ellipticity Normal WFR WFR
E
B
Angle
(90°)
HFR
Observation of waves and particles –
whistler-mode Chorus
[Li et al. GRL 2013]
• Intense chorus waves
outside the plasmapause are
observed between 0.1 fce
and 0.8 fce.
• Ellipticity ~ 1: right-hand
nearly circularly polarized.
• Increase in electron energy
flux indicates stronger
convection or injection.
• Chorus waves excitation may
be associated with the
electron convection.
E-flux Ellipticity Normal WFR WFR
E
B
Angle
(90°)
HFR
Observation of waves and particles –
Plasmaspheric Hiss
• Broadband structureless
hiss emissions are observed
inside the plasmapause.
• Wave normal angle is low > nearly field-aligned
propagation.
• Wave ellipticity is ~1.
• Increase in electron energy
flux is observed inside the
plasmapause.
Ne
P-flux
PA
P-flux
Ek
Normal
Angle
B
Observation of waves and particles –
EMIC waves
[Zhang et al. GRL 2014]
• EMIC waves are observed in
H+ band only (#1), and in
both H+ and He+ band (#2).
• The “nose-like” structure in
proton distribution is also
observed.
• The an-isotropic in the
proton pitch angle
distribution may be the
source of the waves.
Ellipticity Normal WFR WFR
E
B
Angle
P-flux
(90°)
HFR
AE
Observation of waves and particles –
magnetosonic waves
• Magnetosonic waves
are observed between
fcp and fLHR.
• Wave normal angle is
close to 90° => nearly
perpendicular
propagation.
• Wave ellipticity is ~0
=> nearly linear
polarization.
• Proton ring
distribution is also
observed.
• ∂f/∂vper > 0 in proton
ring distribution may
provide the source of
wave excitation.
Statistical study of waves example –
Global distribution of whistler-mode Chorus
• 2 years survey of chorus
waves using THEMIS wave
magnetic field data.
• Chorus waves are strongest
near prenoon sectors, near
magnetic equator, at
disturbed conditions.
• RMS averaged wave
amplitude peaks at ~60 pT.
[Li et al. GRL 2009]
Several messages from Van Allen Probes –
The local acceleration of energetic electrons
• Electron phase space
density increased by nearly
3 orders in less than 12
hours.
• Electron phase space
density peaks around L* =
4.2 during the acceleration.
• The local acceleration
around L* = 4.2 is robust.
[Reeves et al. Science 2013]
Several messages from Van Allen Probes –
The relativistic storage ring
• In the first 4 days, the storage ring at L ~ 3.2 resulted from the loss of
more distant electrons in the outer zone L > 4.
• The outer zone electrons recovered and were variable.
• The storage ring was stable until the abrupt demise by the storm.
[Baker et al. Nature 2013]
EMFISIS
B wave
MagEIS
E-flux
Several messages from Van Allen Probes –
Direct observation of wave particle interactions
• One to one correlation between electron bursts and chorus wave
intensification was observed.
• The pitch angle distribution of electrons (with maxima at 75-80°)
indicates wave-particle interactions.
[Fennell et al. GRL 2014]
Summary
• The recent spacecraft provide high resolution data
about the space environment, plasma waves and
particle populations in the inner magnetosphere.
-- A great opportunity to better understand the space.
• More interesting phenomena are right behind the
spacecraft data.
-- Check the data out!