ILWS - 11 Science Workshop, Beijing, China, Aug-Sep 2011

1. 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

2. 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

3. 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)

4. 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

5. 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

6. i Ion 3-D distributions: E, f, q, t 5 eV/q - 32 keV/q Cluster & TC-1: CIS / HIA: Hot Ion Analyser

7. How can we analyse high-Energy (> MeV) particles with a low-Energy (< 100 keV) instrument ?

8. 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

9. Energy of penetrating particles for HIA and CODIF CLUSTER: Proton threshold: ~30 MeV Electron threshold: ~2 MeV

10. 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

11. 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

12. 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.

13. CLUSTER orbit at perigee on June 30, 2008 ORB IRB ORB

14. 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

15. Example of boundaries’ locations at Double Star B2 B3 B0 B4 B5 Outer RB Outer RB Inner Inner

16. 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

17. 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

18. 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

19. 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

20. Locations and width of slot region slot widening: during: * low Vsw * low AE

21. 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

22. 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.

23. Thank you !