Dynamics of the Radiation Belts & the Ring Current

Dynamics ofthe Radiation Belts &

the Ring Current

Ioannis A. DaglisInstitute 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.


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.


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


Close association

of storm-time enhancements of relativistic electron fluxes

with spacecraft failure.

Spacecraft operational anomalies, SAMPEX data[Baker & Daglis, 2006]


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).

Location of the peak electron flux as a function of minimum Dst moves to lower L

O’Brien et al., JGR2003


Association of MeV electrons with ULF waves / radial diffusion [Baker and Daglis, 2006]


Gre

en a

nd K

ivel

son,

200

4 –

Pol

ar/H

IST

dat

a 19

97-1

999

Dynamics of Radiation Belts – Internal/external

300-500 keV 1.1-1.5 MeV300-500 keV 1.1-1.5 MeV

Dst

Kp

GEO

GPS

1.22 MeVequatorial flux

(L=4.2)

MeV Electron Flux evolution after a Storm

Equatorial fluxes reach max in:- 2.5 days at GEO orbit- 16 hours at GPS orbit

Equatorial fluxes reach max in:- 2 days at GEO orbit- 6 days at GPS orbit

T=0 T=0

GPS max GPS max

GEO max GEO max


[Va

ssili

ad

is e

t a

l., J

GR

20

02

]

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.

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

September 5, 1995 (Solar Min)

May 4, 1998 (Solar Max)

O’Brien et al., JGR2003 SAMPEX, HEO-3 data / SAMNET, IMAGE


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.


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.


1. Radial diffusion only:1. Radial diffusion only:

plasmapause

2100 MeV/G, equator, Kp =1.8

Iteration number

1025

1024

1023

1022

1021

1020

8

7

6

5

4

3

2

L

(MeV-3s-3) 2. Plus chorus waves:2. Plus chorus waves:1025

1024

1023

1022

1021

1020

Iteration number

plasmapause

8

7

6

5

4

3

2

L

2100 MeV/G, equator, Kp =1.8

(MeV-3s-3)

1 MeV

3 MeV

L

L=5.5:L=5.5:Values 100 times Values 100 times higher!higher!

1.E+20

1.E+21

1.E+22

1.E+23

1.E+24

1.E+25

1.E+26

3 4 5 6 7 8

Dis

trib

utio

n F

un

ctio

ns

(Me

V-3s-3

)

DLL and Chorus

DLL

Lpp

Varotsou et al.Varotsou et al.

Dynamics of Radiation Belts - Salammbô model


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

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 mechanismsDevelop 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]

Fig. 6 of Daglis et al. JGR2003

Ring current asymmetry

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 Asymmetry & Ion Composition



-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.

Modeling (RAM Code: Kozyra, Liemohn, et al.)

Comparative study of a solar-max and a solar-min intense

storms: IMF comparable. “Resulting” Dst different.


Storm intensity defined by IMF Bs size and duration? Not exclusively!




-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]

Fig. 5 of Ganushkina et al., AnnGeo2005

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. 10 of Ganushkina et al., AnnGeo2005

Substorm-induced transient electric

fields clearly contribute to particle

acceleration


Effect of recurrent (periodic) substorms

on particle acceleration


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

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)

Summary RC

Dynamics ofthe Radiation Belts &

the Ring Current

End

RB models need better satellite measurements: Particle measurements with full pitch-angle information Comprehensive magnetic field measurementsWave measurementsParticle measurements in inner zone


Radiation belt modeling - Radiation belt modeling - ProblemsProblems

Known problems:Known problems: AE8 models overestimate electron doses: AE8 models overestimate electron doses:

shown by measurements in HEO, MEO shown by measurements in HEO, MEO orbits and by CRRES (Gussenhoven et al., orbits and by CRRES (Gussenhoven et al., 1992). Also by POLE model for GEO.1992). Also by POLE model for GEO.

Radiation belt modeling - ProblemsKnown problems:Known problems: AE8 models do not specify lower AE8 models do not specify lower

energy environment. Low energy energy environment. Low energy electron (< 100 keV) flux intensity electron (< 100 keV) flux intensity much higher than extrapolation of AE much higher than extrapolation of AE spectra.spectra.

Radiation belt modeling - Radiation belt modeling - ProblemsProblems

Known problems:Known problems: Magnetic field models are not accurate for Magnetic field models are not accurate for

disturbed timesdisturbed times Radial diffusion models: What is the source Radial diffusion models: What is the source

population? / Can r.d. transport particles population? / Can r.d. transport particles efficiently enough to low L?efficiently enough to low L?

May 4, 1998, medium energies (20-80 keV)

(a) (b)

(c) (d)

May 4, 1998, high energies (80-200 keV)

(a) (b)

(c) (d)

Dynamics of the Radiation Belts & the Ring Current

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