UNCLASSIFIED
Direct measurements of chorus wave
effects on electrons in the 5-40 KeV
range from the Van Allen Probes Mission
R. Friedel1,
Z. Hong2, B. Larsen1,
G. Reeves1, R. Skoug1,
C. Kletzing3, M.
Henderson1 and Y. Chen1
LANL1, LASP2,University of Iowa3
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AGU Chapman Conference, Jeju, South Korea, August 31 – September 5, 2104
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Contents
•
•
Motivation
Pitch angle Statistics from HOPE and MagEIS
–
–
•
Pitch angle model
First results
Two Spacecraft Event Selection
– Matching Drift Paths
– Filtering ephemeris information
•
•
•
•
Event with waves at spacecraft at later MLT
Event with NO waves
Events summary
Summary/Conclusion
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AGU Chapman Conference, Jeju, South Korea, August 31 – September 5, 2104
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Motivation
•
The Van Allen Probe Mission with 2
spacecraft and exquisite particle and
wave instrumentation is designed to explore
the effects of Magnetospheric waves on the
in-situ particle populations.
•
We focus on the region of most active chorus wave activity, just outside the
plasmapause, and on the energy range of particles most strongly affected by
chorus waves (10's of keV, the top energy range of HOPE), and seek out changes
in the pitch angle distribution (PAD) of the electrons that drift from one probe to the
other– in either the presence or absence of chorus waves.
•
Hypothesis:
–
We expect NO change in the PAD or flux levels for NO waves.
–
We expect a lowering of the flux levels and a flattening of the PAD
(isotropization) in the presence of waves.
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Pitch angle distribution (PAD)
characterization / fitting (Chen et al., 2014)
• Use Legendre polynomials
– where α is the pitch angle, j is the flux, Pn is the Legendre polynomial,
Cn is the corresponding coefficient.
– P0, P2, P4, P6 …: symmetric; P1, P3, P5, ….: asymmetric
• Normalization
– Directionally averaged flux
• Only keep c2, c4 and c6
for statistics
• PAD Selection
–
–
–
–
Equatorial PAD
counts >50
assume 90O symmetry
keep good fits only
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AGU Chapman Conference, Jeju, South Korea, August 31 – September 5, 2104
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Pitch angle distribution (PAD)
characterization / fitting (Chen et al., 2014)
Normal PAD
Butterfly PAD
Flattop PAD
Butterfly PAD:
negative c4
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AGU Chapman Conference, Jeju, South Korea, August 31 – September 5, 2104
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PAD comparison under different Kp
(MagEIS E=35 keV)
Kp ≤ 1+
1+ < Kp ≤ 3+
Work done by Z. Hong, 2014
LANL SW Summer School
Kp > 3+
c2
c4
c6
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PAD comparison under different Kp
(MagEIS E=35 keV) – Sample PADs
L=4.0
Inside Plasmasphere
Peaked @ 90O
L=4.8
->
->
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Work done by Z. Hong, 2014
LANL SW Summer School
L=5.5
Outside Plasmasphere
“Head and Shoulders”
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AGU Chapman Conference, Jeju, South Korea, August 31 – September 5, 2104
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PAD comparison under different Kp
(HOPE E=5 keV)
Kp ≤ 1+
1+ < Kp ≤ 3+
Work done by Z. Hong, 2014
LANL SW Summer School
Kp > 3+
c2
c4
c6
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AGU Chapman Conference, Jeju, South Korea, August 31 – September 5, 2104
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PAD comparison under different Kp
(HOPE E=5 keV) – Sample PADs
Kp ≤ 1+
L=5.0
L=4.0
Inside Plasmasphere
Peaked @ 90O
->
->
LANL SW Summer School
L=5.8
Outside Plasmasphere
Very weak “Head and Shoulders”
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Work done by Z. Hong, 2014
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AGU Chapman Conference, Jeju, South Korea, August 31 – September 5, 2104
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PAD comparison under different Kp
(HOPE E=5 keV) – Sample PADs
1+ < Kp ≤ 3+ L=4.0
Inside Plasmasphere
Peaked @ 90O
L=5.0
->
->
LANL SW Summer School
L=5.8
Outside Plasmasphere
Weak “Head and Shoulders”
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Work done by Z. Hong, 2014
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AGU Chapman Conference, Jeju, South Korea, August 31 – September 5, 2104
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PAD comparison under different Kp
(HOPE E=5 keV) – Sample PADs
Kp > 3+
L=5.0
L=4.0
Work done by Z. Hong, 2014
LANL SW Summer School
L=5.8
Not enough statistics!
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Two Spacecraft Event Selection –
Criteria
Statistical Chorus Occurrence
Starts before midnight towards
dawn, outside Plasmasphere.
Mededith, Ae = 300
Compare RBSP Spacecraft at
0-2 MLT and 3.5-5.5 MLT, when
both are near L=4.5-5.0
Drift paths for electrons 5-40 KeV
approximate circular in this sector.
Drift times for 4hrs MLT:
35 keV ~ 1 hour
5 keV ~ 10 hours
5 KeV
40
KeV
(max radial deviation 0.25 Re)
UBK, Dipole / Volland-Stern, KP=3
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Two Spacecraft Event Selection –
Very few events
Used first year of HOPE pitch angle data – launch to
09/23/2013 (there is a reason…)
A at later MLT wrt to B:
2013-02-21 08:42 to 2013-02-21 10:14 1
2013-02-22 11:40 to 2013-02-22 13:11 2
2013-02-23 05:44 to 2013-02-23 07:21 3
2013-02-24 08:42 to 2013-02-24 10:25 4
SUN
B at later MLT wrt to B:
2013-02-14 10:05 to 2013-02-14 11:38 1
2013-02-16 07:02 to 2013-02-16 08:49 2
2013-02-17 09:58 to 2013-02-17 11:49 3
2013-02-18 04:10 to 2013-02-18 05:45 4
2013-02-19 07:11 to 2013-02-19 08:45 5
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Chorus at A, no chorus at B
10
10
RBSP-A HOPE PITCH_ANGLE=90.0
3
2
1
150.
RBSP-A HOPE Energy=5.2keV
9
10
1 08
7
10
6
10
5
10
4
10
10
100.
-1
50.
10
10
2000.
10
10
10
10
4
RBSP-B HOPE PITCH_ANGLE=90.0
3
2
-9
9
10
1 08
7
10
6
10
5
10
4
10
10
7
-2
100.
-1
50.
10
10
2000.
10
10
-6
-7
-8
-9
PSD (nT^2/Hz)
RBSP-B EMFISIS Total Power B
6
-1
10
0.
10000.
8000.
6000.
4000.
RBSP A
5.2keV
-1
RBSP-B HOPE Energy=5.2keV
-8
(s c m ster keV )
150.
-7
e- flux
Electron Energy
(eV)
10
-6
PSD (nT^2/Hz)
RBSP-A EMFISIS Total Power B
6
-1
10
0.
10000.
8000.
6000.
4000.
pitch angle
7
-2
pitch angle
10
4
-1
Frequency (Hz)
10
5
(s c m ster keV )
Frequency (Hz)
10
e- flux
Electron Energy
(eV)
2013-02-22 12:10 to 12:41
UNCLASSIFIED
11:40
12:00
12:20
12:40
2 0 1 3 - 0 2 -by
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Operated
13:00
Pitch angle distribution peaked at 90 at B at 9E6 reduced to 3.7E6 at A ~ 41 % loss
RBSP B
5.2keV
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AGU Chapman Conference, Jeju, South Korea, August 31 – September 5, 2104
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LEO particle precipitation proxy for high altitude
wave distribution and intensity (Y. Chen, LANL)
Comparing CRRES
wave statistics with
NOAA 30 KeV
precipitation statistics
– deriving model
relationship
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Proxy for waves for 6hr period centered around
2013-02-22 12:30UT v. “best guess”
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No chorus at A, no chorus at B
2013-02-23 06:14 to 06:51
RBSP A
5.2keV
RBSP B
5.2keV
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Pitch angle distribution peaked at 90 at B at 9E6 reduced to 3.7E6 at A ~ 59% loss
Slide 17
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Proxy for waves for 6hr period centered around
2013-02-23 6:30UT
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Two Spacecraft Event Summary
A or B at 0-2 MLT, L=4.5-5, 5 keV electrons
A at later MLT wrt to B:
2013-02-21 08:42 to 10:14 – B in Plasmasphere / structured hiss; A in Plasmasheet boundary
2013-02-22 11:40 to 13:11 – Both outside Plasmasphere, No chorus at B, chorus at A, 59% reduction
2013-02-23 05:44 to 07:21 – Both outside Plasmasphere, No chorus at both, same flux
2013-02-24 08:42 to 10:25 – Both in Plasmasphere, close to plasmapause
B at later MLT wrt to B:
2013-02-14 10:05 to 11:38 – Both outside Plasmasphere, No chorus at A, chorus at B, 75% reduction
No LEO NOAA data
2013-02-16 07:02 to 08:49 – Both in Plasmasphere, B sees broadband Hiss, A observes no hiss
2013-02-17 09:58 to 11:49 – A in Plasmasheet, with chorus; B in Plasmasphere, hiss
2013-02-18 04:10 to 05:45 – A in Plasmasphere / structured hiss; B in Plasmasheet, no chorus
2013-02-19 07:11 to 08:45 – A in Plasmasphere / curious hiss?; B in Plasmasheet, no chorus
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100.
50.
1 07
6
10
5
10
1 04
-6
10
-7
10
2000.
-8
10
3
10
1 02
2000.
-8
10
-9
10
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07:15
2013-02-19
07:30
07:45
08:00
08:15
08:30
-6
10
1 0- 7
08:45
PSD (nT^2/Hz)
RBSP-B EMFISIS Total Power B
-1
0.
10000.
8000.
6000.
4000.
-1
1 05
4
10
3
10
50.
-2
100.
7
10
1 06
-1
RBSP-B HOPE Energy=5.2keV
150.
9
10
1 08
7
10
6
10
1 05
4
10
(s c m ster keV )
pitch angle
RBSP-B HOPE PITCH_ANGLE=90.0
4
10
e- flux
Electron Energy
(eV)
-9
10
PSD (nT^2/Hz)
RBSP-A EMFISIS Total Power B
-1
3
10
0.
10000.
8000.
6000.
4000.
-1
pitch angle
RBSP-A HOPE Energy=5.2keV
150.
Hiss rising tone
2 -4 KHz
~4 min repetition
-2
Frequency (Hz)
2
10
-1
Frequency (Hz)
1 03
9
10
8
10
7
10
6
10
5
10
4
10
(s c m ster keV )
RBSP-A HOPE PITCH_ANGLE=90.0
1 04
e- flux
Electron Energy
(eV)
Study Bonus –
Curious Hiss observation
Slide 20
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Summary / Conclusion
Statistical Study:
35 keV: Statistically little variation with Kp. Outside
plasmasphere persistent “head and shoulder” distributions –
evidence for enhanced PA diffusion at more field-aligned
pitch angles. Little variation with MLT
5 keV: Statistically very little variation with Kp. Little
variation with MLT, mainly 90o peaked distributions –
surprising given the long drift times and local time
distribution of waves.
HOPE data still incomplete for coverage at all MLT (noon
time sector not covered).
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Summary / Conclusion
Drift – matching case studies:
Show measureable depletion of 5 keV electrons in the
presence of waves.
Very little change in pitch angle distribution shape – what is
maintaining anisotropy? No evidence of development of
“head and shoulders” distribution as seen in statistics.
Study offers opportunity to quantitatively test predictions of
wave-particle interaction theory.
Future extension of work to use more sophisticated drift
matching calculations and extend work to larger energy
range.
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Slide 22