Ring Current Formation

Report
Dynamics of
the Radiation Belts &
the Ring Current
Ioannis A. Daglis
Institute for Space Applications
Athens
Dynamics of the near-space
particle radiation environment
Main issue: mechanism(s)
that can efficiently
accelerate and/or transport
charged particles, leading
to
- build-up of storm-time
ring current
- enhanced fluxes of MeV
radiation belt electrons.
Dynamics of the near-space
particle radiation environment
In both cases, the most
obvious driver
the magnetospheric
substorm
appears to be insufficient
Dynamics of Radiation Belts
Substorms produce
electrons with energies
of 10s to 100s of keV,
but only few of MeV
energies.
Dynamics of Ring Current
(Individual) Substorms
inject plenty of hot
ions to the inner
magnetosphere,
but not enough to
create/sustain
the ring current.
Dynamics of the near-space
particle radiation environment
Presumably,
the ring current build-up and
the radiation belt
enhancement,
being processes of a
higher level of complexity,
display properties not evident
at the lower levels
Dynamics of Radiation Belts
Close association
of storm-time enhancements
of relativistic electron fluxes
with spacecraft failure.
Spacecraft operational
anomalies, SAMPEX data
[Baker & Daglis, 2006]
Dynamics of Radiation Belts
Each new mission in the inner MS brings new
insights (SAMPEX, CRRES)
Close correlation with storms / Large dynamic range: 10 to 10^4
(Li et al. 2001).
Dynamics of Radiation Belts
Location of the
peak electron flux
as a function of
minimum Dst
moves to lower L
O’Brien et al., JGR2003
Dynamics of Radiation Belts
Association of MeV
electrons with ULF
waves / radial
diffusion [Baker and
Daglis, 2006]
Green and Kivelson, 2004 – Polar/HIST data 1997-1999
Dynamics of Radiation Belts – Internal/external
MeV Electron Flux evolution after a Storm
Dst
Kp
300-500 keV 1.1-1.5 MeV
300-500 keV 1.1-1.5 MeV
GEO
GEO max
GEO max
GPS
GPS max
T=0

Equatorial fluxes reach max in:
- 2.5 days at GEO orbit
- 16 hours at GPS orbit
1.22 MeV
equatorial flux
(L=4.2)
GPS max
T=0
 Equatorial fluxes reach max in:
- 2 days at GEO orbit
- 6 days at GPS orbit
Dynamics of Radiation Belts
September 5, 1995 (Solar Min)
[Vassiliadis et al., JGR 2002]
Region P1:
• Slow (2-3-day) response to
hi-speed streams
• Characteristic of GEO orbit
• Prob. involves ULF waves
• Representative study:
Paulikas and Blake, 1979.
May 4, 1998 (Solar Max)
Region P0:
• Rapid (<1-day) response to
magnetic clouds/ICMEs.
• Characterizes L<4.
• Representative events:
January 1997, May 1998:
- Baker et al., GRL 1998;
- Reeves et al., GRL 1998
Dynamics of Radiation Belts
O’Brien et al., JGR2003
SAMPEX, HEO-3 data
/ SAMNET, IMAGE
Dynamics of Radiation Belts
Both ULF waves and microbursts are
strongest during the main phase of
storms, both progress to lower L
during stronger magnetic activity,
both continue to be active during the
recovery phase of events, and both
appear to be more active during
intervals of high solar wind velocity.
Dynamics of Radiation Belts
Close to GEO, ULF-wave enhanced
radial diffusion is more important,
pushing electrons inward and
accelerating them.
Around L~5, VLF chorus waves
accelerate electrons (microbursts)
without displacing them in L.
Dynamics of Radiation Belts - Salammbô model
8
8
1025
2100 MeV/G, equator, Kp =1.8
7
2100 MeV/G, equator, Kp =1.8
7
1024
1023
L
plasmapause
5
1023
plasmapause
5
4
4
3 MeV
2
1025
1022
1022
3
(MeV-3s-3)
1024
1 MeV
6
6
1021
3
1020
2
1021
1020
Iteration number
Iteration number
1.E+26
Distribution Functions
(MeV-3s-3)
L
2. Plus chorus waves:
(MeV-3s-3)
1. Radial diffusion only:
DLL and Chorus
1.E+25
L=5.5:
Values 100 times
higher!
1.E+24
1.E+23
DLL
1.E+22
1.E+21
Lpp
1.E+20
3
4
5
6
L
7
8
Varotsou et al.
Dynamics of Radiation Belts
Not simply a superposition, but
a synergy of various lower-level
processes
(combined effect > sum of
individual effects)
- feature of the emergent order
of higher levels of complexity
Dynamics of Radiation Belts - Future
Fully understand and specify
radiation belt variability
(CRRES, Bernie Blake)
Dynamics of Radiation Belts - Future



Explain rapid acceleration of electrons to
relativistic energies
Identify loss mechanisms
Develop accurate energetic electron model
The classical ring concept
Image courtesy Hannu Koskinen, FMI
Ring Current Dynamics
- RC sources (composition) /
RC [a]symmetry
- RC formation: IMF driver
- RC formation: role of substorms
Ring Current Sources / Composition
Daglis, Magnetic Storms Monograph [1997]
Ring current asymmetry
Fig. 6 of Daglis et al. JGR2003
Ring Current Asymmetry
& Ion Composition
A very asymmetric ring
current distribution during
the main and early
recovery phases of an
intense storm
Near Dst minimum O+
becomes the dominant ion
in agreement with previous
observations of intense
storms
Jordanova et al. [2003]
Ring Current Dynamics
- RC sources (composition) / RC
[a]symmetry
- RC formation: IMF driver
- RC formation: role of substorms
Ring Current Formation – IMF Driver
Empirical certainty:
Prolonged southward IMF drives
strong convection (westward Ey)
and therefore storms.
Large IMF Bs => intense storms.
Ring Current Formation – IMF Driver
Modeling (RAM Code: Kozyra, Liemohn, et al.)
Comparative study of
a solar-max and a solar-min intense storms:
 IMF comparable.
 “Resulting” Dst different.
Ring Current Formation – IMF Driver
Storm intensity defined by
IMF Bs size and duration?
Not exclusively!
Ring Current Dynamics
- RC sources (composition) / RC
[a]symmetry
- RC formation: IMF driver
- RC formation: role of
substorms
Ring Current Formation – Substorms
Role of substorms
 1960s Chapman and Akasofu: storms =
cumulative result of substorms
 1990s McPherron, Iyemori, et al.: purely
solar driven, no substorm influence
 2000s Daglis, Metallinou, Fok,
Ganushkina, et al.: substorms act as
catalysts
Daglis [1997, 1999]
Ganushkina et al.
showed that the
observed H+
acceleration at high
energies can be
reproduced in
modeling studies only
through substorm-style
induced E pulses.
Fig. 5 of Ganushkina et al., AnnGeo2005
Fig. 10 of Ganushkina et al., AnnGeo2005
Ring Current Formation – Substorms
Substorm-induced
transient electric fields
clearly contribute to
particle acceleration
Ring Current Formation – Substorms
Ring Current Formation – Substorms
Effect of recurrent
(periodic) substorms on
particle acceleration
Ring Current Formation – Substorms
Ring Current Formation – Substorms
Dynamics of Ring Current
Not simply a superposition, but
a synergy of convection,
substorm-induced electric fiels
and wave-particle interactions
(combined effect > sum of
individual effects) - a feature of the emergent
order of higher levels of
complexity
Summary RC
 The ring current is a very dynamic
population, strongly coupling the
inner magnetosphere with the
ionosphere, which is an “increasingly
important” source and modulator
 IMF not the sole ruler: Plasma sheet
density, ionospheric outflow,
substorm occurrence, all have their
role in storm development.
Summary RC
 Substorms act catalytically: they
accelerate ions to high(er) energies/
they preferentially accelerate O+
ions, which dominate during
intense storms.
 Storms, being phenomena of a
higher level of complexity display
properties not evident at the lower
levels (substorms / convection)
Dynamics of
the Radiation Belts &
the Ring Current
End
Dynamics of Radiation Belts - Future
RB models need better satellite measurements:
 Particle measurements with full pitch-angle
information
 Comprehensive magnetic field
measurements
Wave measurements
Particle measurements in inner zone
Radiation belt modeling Problems
Known problems:
 AE8 models overestimate electron doses:
shown by measurements in HEO, MEO
orbits and by CRRES (Gussenhoven et al.,
1992). Also by POLE model for GEO.
Radiation belt modeling - Problems
Known problems:
 AE8 models do not specify lower energy
environment. Low energy electron (< 100
keV) flux intensity much higher than
extrapolation of AE spectra.
Radiation belt modeling Problems
Known problems:
 Magnetic field models are not accurate for
disturbed times
 Radial diffusion models: What is the source
population? / Can r.d. transport particles
efficiently enough to low L?
Ring Current Formation – IMF Driver
May 4, 1998, medium energies (20-80 keV)
(a)
(c)
(b)
(d)
May 4, 1998, high energies (80-200 keV)
(a)
(b)
(c)
(d)

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