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) Finnish Meteorological Institute, Helsinki, Finland

(2) University of Michigan, Ann Arbor, USA

(3) IRAP (ex-CESR), CNRS / University of Toulouse, Toulouse, France

(4) IGPP, University of California, Los Angeles, USA

(5) Beijing University of Aeronautics and Astronautics, Beijing, China

(6) 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 proton fluxes (cm-2 s-1 ) trapped in the radiation belt.From NASA AP8 min model.

Energy > 10 MeV

Omnidirectional integrated electron fluxes (cm-2 s-1 ) trapped in the radiation belt.From NASA AE8 max model.

Energy > 1 MeV

Omnidirectional differential flux spectra for trapped electrons (AE8 max) and trapped protons (AP8 min)

Cluster and Double Star TC-1 orbits

Cluster: the “early years” (2000 – 2006)

4 x 19.6 RE

Cluster: Orbit evolution

since 2007

DS TC-1: 2003 - 2007

1.09 x 13.4 RE

The CIS Experiment

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

Onboard Cluster Onboard Cluster & TC-1

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

Vkq

E

Ion 3-D distributions:

E, , , t

5 eV/q - 32 keV/q

i

How can we analyse

high-Energy (> MeV) particles

with a low-Energy (< 100 keV)

instrument ?

i+

Radiation Belt penetrating

particle

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

TOF system

2

2

TOFL

qE

q

m

L

q

EMain entrance

i +e-

i+

Ion 3-D distributionsand mass analysis:

E, m, , , t

0 eV/q - 40 keV/q

Outer RB

B1 B2 B3 B4 B5 B6

Outer RBInner RB

Boundaries of outer and inner radiation belts as observed by Cluster CIS:

Turning instrument background into science data

HIA

CO

DIF

Ring current ion drift bands

Reduced background due to TOF double coincidence

Background counts (penetrating high-energy particles)

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

B3 B4

Inner RBOuter RB Outer RB

B1 B2 B5 B6

ORB

ORB IRB

Example of boundaries’ locations at Double Star

B2 B3 B0 B4 B5

Outer RB Inner Outer RBInner

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

Zoom

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

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

Locations of boundaries Observed at Double Star

B2 and B5:inner boundary of outer RB

B3 and B4:outer boundary of inner RB

B0:Inner boundary of inner RB

SummaryDuring 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 !