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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) Finnish Meteorological Institute, Helsinki, Finland

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slide1

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)
      • 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
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
slide3

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)

slide4

Cluster and Double Star TC-1 orbits

Cluster:

the “early years” (2000 – 2006)

4 x 19.6 RE

DS TC-1: 2003 - 2007

1.09 x 13.4 RE

Cluster: Orbit evolution since 2007

slide5

The CIS Experiment

Onboard Cluster

Onboard Cluster & TC-1

CODIF (CIS-1)

Ion Composition and Distribution Function Analyser

3D ion distributions with mass-per-charge composition determination

~0 - 40 keV/q Energy Range

HIA (CIS-2)

Hot Ion Analyser

3D ion distributions with high angular resolution

5 eV/q - 32 keV/q Energy Range

Rème et al., 2001, 2005

slide6

i

Ion 3-D distributions:

E, f, q, t

5 eV/q - 32 keV/q

Cluster & TC-1: CIS / HIA: Hot Ion Analyser

slide7

How can we analyse

high-Energy (> MeV) particles

with a low-Energy (< 100 keV) instrument ?

slide8

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

slide9

Energy of penetrating particles

for HIA and CODIF

CLUSTER: Proton threshold: ~30 MeV Electron threshold: ~2 MeV

slide10

Cluster: CIS / CODIF: Ion Composition and Distribution Function Analyser

TOF system

L

i+

Main entrance

i +

e-

Ion 3-D distributionsand mass analysis:

E, m, f, q, t

0 eV/q - 40 keV/q

slide11

Boundaries of outer and inner radiation belts as observed by Cluster CIS:Turning instrument background into science data

Background counts (penetrating high-energy particles)

B1

B2

B3

B4

B5

B6

HIA

CODIF

Outer RB

Inner RB

Outer RB

Reduced background due to TOF double coincidence

Ring current ion drift bands

slide12

To determine a boundary location:

At a first instance, the spacecraft entry into a radiation belt appears as a substantial, homogeneous increase of count rate over all energy channels.

To more accurately define the boundary position, we then determine the first time momentwhen the Δc/s / Δt are the largest and same for all energy channels(sharpest gradient) and place a boundary there.

slide14

Boundaries of outer and inner radiation belts

as observed by Cluster CIS at different orbits

B1

B2

B5

B6

B3

B4

Outer RB

Outer RB

Inner RB

ORB

IRB

ORB

slide15

Example of boundaries’ locations at Double Star

B2

B3

B0

B4

B5

Outer RB

Outer RB

Inner

Inner

slide16

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

slide17

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

slide18

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

B3 and B4:

outer boundary of

inner RB

Running Average

Zoom

Psw: no ave. change

Vsw: decrease

Dips of outer RB to lower L shells

slide19

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
slide20

Locations and width of slot region

slot widening:

during: * low Vsw * low AE

slide21

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

slide22

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 tailwardat 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.
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