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 R E Cluster: Orbit evolution since 2007 DS TC-1: x 13.4 R E

The CIS Experiment CODIF (CIS-1) Ion Composition and Distribution Function Analyser 3D ion distributions with mass-per-charge composition determination ~ 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 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+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 L Main entrance i + e-e- i+i+ Ion 3-D distributions and mass analysis: E, m, , , t  0 eV/q - 40 keV/q

Outer RB B1B2B3B4B5B6 Outer RBInner RB Boundaries of outer and inner radiation belts as observed by Cluster CIS: Turning instrument background into science data HIA CODIF 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 Δ c/s / Δ t 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 B3B4 Inner RBOuter RB B1B2B5B6 ORB IRB

Example of boundaries’ locations at Double Star B2B3B0B4B5 Outer RBInner Outer RB Inner

Locations of Rad-Belt boundaries for all events, MLT distribution (Cluster-CIS data): April 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

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 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 R E ) during low activity, when V sw 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 !

Cluster orbit since 2007 : deeper passages in the inner magnetosphere 30 June 2008 example: Cluster was deep in the radiation belts coming to Earth at its perigee as close as L = 2

HIA: Electrostatic Analyser Energy Sweep 256 micro-steps, ms each 62.5 ms (5.625° of sc rotation) E max = eV/q (4 184 V at the analyser) E min = 5.0 eV/q (0.65 V at the analyser) Analyser HV reset (8 micro-steps)

20 MeV H + ions 30 MeV H + ions Simulation of High-Energy Ion Penetration Through the Instrument Walls

2 MeV electrons Simulation of High-Energy Electron Penetration Through the Instrument Walls 4 MeV electrons

Bremsstrahlung- produced X-rays from 100 keV electrons Bremsstrahlung- produced X-rays from 10 keV electrons: all absorbed Bremsstrahlung- produced X-rays from 1 MeV electrons In addition to the background from the direct detection of penetrating protons (> 30 MeV) and electrons (> 2 MeV), some secondary background from bremsstrahlung-produced X-rays and γ–rays, from > 100 keV electrons produced absorbed

>100 keV electrons in the pl. sheet during a strong substorm (AE=800 nT): no background detected by CIS => instrument sensitivity to bremsstrahlung-produced X-rays from these electrons is negligible HIA CODIF RAPID-IES

SEPs arrival and penetration into HIA-Cluster, while in the solar wind at 15.5 R E, during the 17 Jan 2005 extreme solar event Considering SEPs Penetration SEPs

Zoom 2 Outer 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

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

CODIF Energy Range: 0.7 eV/q – 40 keV/q HIA Energy Range: 5 eV/q – 32 keV/q CIS Dynamic Range CIS : Cluster Ion Spectrometry

Zoom of slot widening

Inner belt Outer belt Plasmasphere detectable in the slot region

Energy Radiation belts Ring current carriers Plasmasphere - 1 MeV - 1 keV - 1 eV - 10 keV keV - 10 eV The Inner Magnetosphere Populations Various populations exist Electrons Ions Neutral atoms Plasma waves => Numerous interactions between these populations eV Sub-keV populations Region where most of the energy is dissipated during storms and substorms

ZAZA  ZAZA Detectors: Micro-Channel Plates

ABSTRACT Cluster-CIS ion spectrograms measured during the period of the recent solar minimum between April 2007 and June 2009, when Cluster was deep in the radiation belts with its perigee as close as L = 2, are analyzed. The analysis is complemented by Double Star TC-1 satellite data from HIA ion spectrograms on perigee passes during the period of May to September We demonstrate how the background counts produced by energetic particles of the radiation belts in the Cluster-CIS and Double Star-HIA instruments can be interpreted to obtain the locations of the boundaries of the outer and inner belts. The obtained L-MLT distribution of boundaries reflects the general structure of the radiation belts. Closer examination of the time-dependent L locations of the boundaries reveals several dips to lower L-shells (from L = 6 to L = 4) in the outer boundary location. The importance of the solar wind pressure increases for the Earthward shift of the outer boundary of the outer belt is discussed. The location and thickness of the slot region are studied using the determined inner boundaries of the outer belt and the outer boundaries of the inner belt. It was found that during intervals of low activity in the solar wind parameters the slot region widens, which is consistent with weaker inward radial diffusion, and also with weaker local acceleration that can occur only at higher L-shells outside the plasmasphere. We conclude that 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.

Zoom of slot widening