Locations of Boundaries
of the Outer and Inner Radiation Belts
during the Recent Solar Minimum,
as Observed by Cluster and Double Star
Natalia Ganushkina (1,2) , Iannis Dandouras (3),
Yuri Shprits (4) , Jinbin Cao (5,6)
(1)
(2)
(3)
(4)
(5)
(6)
Finnish Meteorological Institute, Helsinki, Finland
University of Michigan, Ann Arbor, USA
IRAP (ex-CESR), CNRS / University of Toulouse, Toulouse, France
IGPP, University of California, Los Angeles, USA
Beijing University of Aeronautics and Astronautics, Beijing, China
State Key Laboratory of Space Weather, CSSAR, CAS, Beijing, China
ILWS - 11 Science Workshop, Beijing, China, Aug-Sep 2011
Outline
 Introduction: The Terrestrial Radiation Belts
 Methodology: Analysing the Terrestrial Radiation Belts
with low-energy particle instruments :
CIS onboard Cluster and HIA onboard Double Star
 Radiation Belts boundaries locations: Results
 Conclusion
Omnidirectional integrated
electron fluxes (cm-2 s-1 )
trapped in the radiation belt.
From NASA AE8 max model.
Energy > 1 MeV
Omnidirectional integrated
proton fluxes (cm-2 s-1 )
trapped in the radiation belt.
From NASA AP8 min model.
Energy > 10 MeV
Omnidirectional differential
flux spectra for trapped
electrons (AE8 max) and
trapped protons (AP8 min)
Cluster and Double Star TC-1 orbits
DS TC-1:
2003 - 2007
1.09 x 13.4 RE
Cluster:
Orbit evolution
since 2007
Cluster:
the “early years”
(2000 – 2006)
4 x 19.6 RE
The CIS Experiment
Onboard Cluster
Onboard Cluster & TC-1
CODIF (CIS-1)
HIA (CIS-2)
Ion Composition and Distribution
Function Analyser
Hot Ion Analyser
3D ion distributions with mass-per-charge
composition determination
3D ion distributions with high angular
resolution
5 eV/q - 32 keV/q Energy Range
~0 - 40 keV/q Energy Range
Rème et al., 2001, 2005
Ion 3-D distributions:
i
E, f, q, t
5 eV/q - 32 keV/q
Cluster & TC-1: CIS / HIA:
Hot Ion Analyser
E
q
 k  V
How can we analyse
high-Energy (> MeV) particles
with a low-Energy (< 100 keV) instrument ?
Radiation Belt
penetrating
particle
i+
Accumulated wall thickness, for HIA onboard Cluster:
Typically 4 mm Al (2 mm minimum)
For HIA onboard Double Star: additional 4 mm Al
Energy of penetrating particles
for HIA and CODIF
CLUSTER: Proton threshold: ~30 MeV
Electron threshold: ~2 MeV
Cluster: CIS / CODIF:
Ion Composition and Distribution Function Analyser
i+
Main entrance
E
q
TOF system
L
m
q

e-
i+
 E 

2  
 q 
 L 


TOF


2
Ion 3-D distributions
and mass analysis:
E, m, f, q, t
0 eV/q - 40 keV/q
Boundaries of outer and inner radiation belts
as observed by Cluster CIS:
Turning instrument background into science data
Background counts (penetrating high-energy particles)
B2
B3
B4
B5 B6
CODIF
HIA
B1
Outer RB
Inner RB
Outer RB
Reduced background due to TOF double coincidence
Ring current
ion drift bands
To determine a boundary location:
1. At a first instance, the spacecraft entry into a radiation belt appears as a
substantial, homogeneous increase of count rate over all energy channels.
2. To more accurately define the boundary position, we then determine the first
time moment when the Δc/s / Δt are the largest and same for all energy
channels (sharpest gradient) and place a boundary there.
CLUSTER orbit at perigee on June 30, 2008
ORB
IRB
ORB
Boundaries of outer and inner radiation belts
as observed by Cluster CIS at different orbits
B1
B2
Outer RB
ORB
ORB
B5 B6
Outer RB
B3
B4
Inner RB
IRB
Example of boundaries’ locations at Double Star
B2
Outer RB
B3 B0
B4 B5
Inner Inner
Outer RB
Locations of Rad-Belt boundaries for all events, MLT distribution
(Cluster-CIS data): April 2007 - June 2009
B1 and B6:
outer boundary of
outer RB
B2 and B5:
inner boundary of
outer RB
B3 and B4:
outer boundary of
inner RB
Ganushkina, Dandouras, et al.,
JGR, in press, 2011
Locations of boundaries for all events with activity indices
B1 and B6:
outer boundary of
outer RB
B2 and B5:
inner boundary of
outer RB
B3 and B4:
outer boundary of
inner RB
Dst: moderate, no change
Kp and AE: decrease
Locations of boundaries
for all events with
SW parameters
B1 and B6:
outer boundary of
outer RB
B2 and B5:
inner boundary of
outer RB
Running Average
Zoom
B3 and B4:
outer boundary of
inner RB
Psw: no ave. change
Vsw: decrease
Dips of outer RB to lower L shells
Zoom on Outer RB
boundary dip
Outer boundary of outer RB:
- comes closer to Earth L=4
- then moves tailward L=6
Time scale: 50 days
Before boundary dip:
- Vsw from 430 to 540 km/sec
- Kp to 5
- Dst drop to -28 nT
- AE to 700 nT
- 2 peaks in Psw, 8 and 5 nPa
After boundary dip:
- Vsw to 650 km/s
- Kp to 5
- Dst drop to -50 nT
- AE to 800 nT
- Psw at 3 nPa
Locations and width of slot region
slot widening:
during:
* low Vsw
* low AE
B2 and B5:
inner boundary of
outer RB
B3 and B4:
outer boundary of
inner RB
B0:
Inner boundary
of inner RB
Locations of boundaries
Observed at Double Star
Summary
 During the period between April 2007 and June 2009 Cluster was deep in the
radiation belts, coming to Earth at its perigee as close as L = 2.
 During that period: Psw, Dst no change, Vsw decrease, Kp and AE decrease.
 Dips of outer boundary of outer RB: comes closer to Earth at L=4,
then moves tailward at L=6. Before dip: peaks in Psw.
After boundary dip: Vsw, Kp, AE increase, Dst drop, Psw no change.
Always peaks in Psw right before the flux drop out.
 Slot region widening (from 1.5 to 3 RE) during low activity,
when Vsw and AE decrease:
consistent with weaker inward radial diffusion,
and also consistent with weaker local acceleration.
 Boundaries determined from background measurements provide
additional information on Radiation Belts, useful for
Radiation Belts model development and validation.
Thank you !