Locations of boundaries of outer and inner radiation belts as observed by

Cluster and Double Star

Natalia Ganushkina (1, 2), Iannis Dandouras (3), Yuri Shprits (4)and Jinbin Cao (5)

(1) Finnish Meteorological Institute, Helsinki, Finland(2) University of Michigan, Ann Arbor, USA

(3) CESR, Toulouse, France(4) UCLA, USA

(5) State Key Laboratory of Space Weather, CSSAR, CAS, Beijing, China

2011 Joint CEDAR-GEM Workshop,26 June - 01 July 2011, Santa Fe, NM, USA

CLUSTER CIS measurements between April 2007 and June 2009

The Cluster Ion Spectrometry (CIS) experiment on board Cluster:- provides the three-dimensional ion distributions with one spacecraft spin (4 sec) time resolution [Rème et al., 2001];- consists of two complementary spectrometers HIA and CODIF.

Time-of-flight ion COmposition and DIstribution Function (CODIF) sensor:- high-sensitivity mass-resolving spectrometer to measure complete 3D distribution functions;- for major ion species H+, He++, He+ and O+ within one spin period; - covers the energy range between 0.02 and 40 keV/charge.

Hot Ion Analyser (HIA) sensor:- Ions in the energy range ~ 5 eV/e – 32 keV/e;- does not provide mass discrimination;- but has a better angular resolution (~ 5.6°).

CLUSTER orbit at perigee on June 30, 2008During 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.

ORB

IRB

ORB

B1(a)

Outer RB

B2 B3 B4 B5 B6

Outer RBInner RB

(b)

Example of boundaries of outer and inner radiation belts as observed by Cluster CIS

B2 (a)

Outer RB Outer RB

B1 B5 B6

Inner RBInner RB

B3 B4 (b)

Boundaries of outer and inner radiation belts as observed by Cluster CIS at different orbits

ORB

ORBIRB

protons

electrons

4 8

32

Ener

gy

Thickness

4 Cluster8 Double Star

3040

Energy of penetrating electrons for HIA and CODIF at CLUSTER and Double Star

Locations of boundaries for all events, MLT distribution

B1 and B6:outer boundary of outer RB

B2 and B5:inner boundary of outer RB

B3 and B4:outer boundary of inner RB

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

Zoom 1

Zoom 2

Locations of boundaries for all events with SW parameters

Zoom 3B1 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 1Outer 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

Zoom 2Outer boundary of outer RB:- comes closer to Earth L=4.5- then moves tailward L=7

Time scale: 40 days

Before boundary dip:- Vsw decreased to 300 km/sec- Kp to 2- Dst at +5 nT- AE to 300 nT- peak in Psw to 5.5 nPa and to 8 nPa at dip

After boundary dip:- Vsw to 650 km/s- Kp to 4- Dst drop to -25 nT- AE to 700 nT- Psw at 1 nPa

Zoom 3

Outer boundary of outer RB:- comes closer to Earth L=5- then moves tailward L=7(7.5)

Time scale: 70 days

Picture is the same:

Before boundaries’ dip:peaks in Psw to 4 and 5.5 nPa

After boundaries’ dip:- Vsw jumps to 60 km/s- Kp to 4 and 3- Dst drops to -20 nT- AE to 600(500) nT

Locations and width of slot region

Zoom ofslot widening

Example of boundaries’ locations at Double Star

B2 B3 B0 B4 B5

Outer RB Inner RB Outer RBInner RB

Locations of boundaries observed at Double Star

Summary

- boundaries of radiation belts determined from background measurements on the instruments with energy ranges that do not cover the radiation belts’ energies provide valuable additional information that is useful for radiation belts’ model development and validation;

- solar wind pressure increases are important for the Earthward shift of the outer boundary of the outer belt;

- during intervals of low activity in the solar wind parameters, the slot region widens, which is consistent with weaker inward radial diffusion and weak local acceleration that can occur only at higher L-shells outside the plasmasphere.

Locations of boundaries for all events, MLT distribution