Sciencexpress Reports A Long-Lived Relativistic Electron Prior key measurements of Earth's radiation environment have been made (//-13),but some of the longest and Storage Ring Embedded in Earth's most comprehensive radiation belt ob- servations previously have come from Outer Van Allen Belt sensors on board the Solar,Anomalous. and Magnetospheric Particle Explorer (SAMPEX)mission (/4).This space- D.N.Baker,1*S.G.Kanekal,2 V.C.Hoxie,1 M.G.Henderson,3 X.Li,1 H.E. craft made low-Earth orbit (LEO)ob- Spence,4 S.R.Elkington,1 R.H.W.Friedel,3 J.Goldstein,5 M.K.Hudson,5 G.D. servations of inner and outer zone particles from its launch in July 1992 Reeves,3 R.M.Thorne,?C.A.Kletzing,8 S.G.Claudepierre until its recent atmospheric reentry and 'Laboratory for Atmospheric and Space Physics,University of Colorado,Boulder,CO,USA.2Goddard demise on 13 November 2012 (/5.16) Space Flight Center,Greenbelt,MD,USA.Los Alamos National Laboratory,Los Alamos,NM,USA. SAMPEX measured E>I MeV elec- Institute for the Study of Earth,Oceans,and Space,University of New Hampshire,Durham,NH,USA. trons at the near-Earth foot of magnetic Space Science and Engineering Division,Southwest Research Institute,San Antonio,TX,USA field lines but never was able to look Department of Physics and Astronomy,Dartmouth College,Hanover,NH,USA.'Department of into the "throat"of the radiation belt Atmospheric and Oceanic Sciences.University of California-Los Angeles,Los Angeles,CA,USA Department of Physics and Astronomy,University of lowa,lowa City,IA,USA.The Aerospace accelerator in the magnetospheric equa- Corporation,Los Angeles,CA,USA torial plane.This contrasts dramatically with the REPT-A and REPT-B instru- "To whom correspondence should be addressed.E-mail:daniel.baker@lasp.colorado.edu ent data collected by the Vanllen Probes from 1 September 2012 through Since their discovery over 50 years ago,the Earth's Van Allen radiation belts have early October 2012(Fig.1).These data5 been considered to consist of two distinct zones of trapped,highly energetic show that a powerful electron accelera- charged particles.The outer zone is comprised predominantly of mega-electron volt tion event was already in progress as 乏 (Mev)electrons that wax and wane in intensity on time scales ranging from hours to the instruments were first turned on. days depending primarily on external forcing by the solar wind.The spatially The entire outer radiation belt was en- g separated inner zone is comprised of commingled high-energy electrons and very hanced in electron flux from E ~2.0 energetic positive ions(mostly protons),the latter being stable in intensity levels MeV (Fig.1A)up to energies well over years to decades.In situ energy-specific and temporally resolved spacecraft above the 6.22 Mev) (Fig.1C).At this time,the radiation electrons that formed on 2 September 2012 and persisted largely unchanged in the belt populations clearly had the ex- geocentric radial range of 3.0 to ~3.5 Earth radii for over four weeks before being pected double-belt structure with an disrupted(and virtually annihilated)by a powerful interplanetary shock wave inner zone,an outer zone,anda“slot” passage region of greatly diminished intensity separating the two. E The magnetically confined radiation zones surrounding the Earth were What is most striking (and unex- the first major discovery of the Space Age in 1958(1-4).Long-term pected)is the clear emergence of a separate,previously unseen belt,or observations of these energetic particle populations subsequently have "storage ring,"of high-energy electrons that stands out clearly after 2 shown dramatic,highly dynamic changes of the outer Van Allen belt. September.This belt is evident in the E=4.0-5.0 MeV range(Fig.IB) Previous,rather sparse measurements of the radiation environment sug- and is the dominant flux feature in the E=5.0-6.2 MeV energy range gested that powerful acceleration events for relativistic electrons occur (Fig.IC).This distinctive ring of highly relativistic electrons persists, on time scales ranging from minutes (5,6)to many hours (7,8).Thus. changing only gradually,until its abrupt and almost complete disappear- there has been direct as well as circumstantial evidence that an immense- ance late on I October.While the inner zone,the slot region,and the ly powerful and efficient accelerator operates within the terrestrial mag- relativistic storage ring (3.04.0 beginning on about 7 September and intensifying greatly inclination orbits around the Earth.The RBSP satellites are fully instru- over a period of two weeks.Subsequently,the outermost parts of the mented with identical energetic particle,plasma,magnetic field,and outer Van Allen zone grew and diminished further with little effect on plasma wave sensors to measure and thoroughly characterize the radia- the storage ring feature until the abrupt demise of virtually the entire tion belt regions(9).The scientific payloads on board the RBSP space- outer zone electron population at the end of 1 October.Other electron craft(renamed the Van Allen Probes mission by NASA at a formal sensor systems on board the Van Allen Probes spacecraft,overlapping ceremony on 9 November 2012)have unprecedented detection sensitivi- partially in energy coverage with the REPT sensors,also detected the ty,energy resolution,and temporal sampling capability.In particular,the storage ring feature (/7). Relativistic Electron-Proton Telescope (REPT)experiment (/0) The distinct storage ring feature is more clearly evident in the merid- measures the key ~1 MeV to ~20 MeV electron population throughout ional plane projection of 4.0-5.0 MeV electrons from the combined the RBSP orbit which extends from geocentric distances of r 1.2 Re to REPT-A and REPT-B instrument records (Fig.2).In the earliest obser- r=5.8 RE (IRE,Earth radius-6372 km).The REPT sensors were vational phase (1-3 September)the expected two-belt structure of the among the first instruments turned on(1 September 2012)and have been Van Allen zones is clear(Fig.2A).In the next phase from 3 to 6 Sep- returning nearly continuous data since that time from both Van Allen tember,the relativistic storage ring was formed(Fig.2B)probably large- Probes spacecraft. ly by erosion and loss of the more distant parts of the outer zone.It then persisted in a remarkably stable fashion(Fig.2,C and D)throughout the Sciencexpress/http://www.sciencemag.org/content/early/recent/28 February 2013/Page 1/10.1126/science.1233518
Reports / http://www.sciencemag.org/content/early/recent / 28 February 2013 / Page 1 / 10.1126/science.1233518 The magnetically confined radiation zones surrounding the Earth were the first major discovery of the Space Age in 1958 (1–4). Long-term observations of these energetic particle populations subsequently have shown dramatic, highly dynamic changes of the outer Van Allen belt. Previous, rather sparse measurements of the radiation environment suggested that powerful acceleration events for relativistic electrons occur on time scales ranging from minutes (5, 6) to many hours (7, 8). Thus, there has been direct as well as circumstantial evidence that an immensely powerful and efficient accelerator operates within the terrestrial magnetosphere just a few thousand kilometers above the Earth’s surface. On 30 August 2012, twin NASA spacecraft, the Radiation Belt Storm Probes (RBSP), were launched into highly elliptical, lowinclination orbits around the Earth. The RBSP satellites are fully instrumented with identical energetic particle, plasma, magnetic field, and plasma wave sensors to measure and thoroughly characterize the radiation belt regions (9). The scientific payloads on board the RBSP spacecraft (renamed the Van Allen Probes mission by NASA at a formal ceremony on 9 November 2012) have unprecedented detection sensitivity, energy resolution, and temporal sampling capability. In particular, the Relativistic Electron-Proton Telescope (REPT) experiment (10) measures the key ~1 MeV to ~20 MeV electron population throughout the RBSP orbit which extends from geocentric distances of r = 1.2 RE to r = 5.8 RE (1RE, Earth radius – 6372 km). The REPT sensors were among the first instruments turned on (1 September 2012) and have been returning nearly continuous data since that time from both Van Allen Probes spacecraft. Prior key measurements of Earth’s radiation environment have been made (11–13), but some of the longest and most comprehensive radiation belt observations previously have come from sensors on board the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) mission (14). This spacecraft made low-Earth orbit (LEO) observations of inner and outer zone particles from its launch in July 1992 until its recent atmospheric reentry and demise on 13 November 2012 (15, 16). SAMPEX measured E > 1 MeV electrons at the near-Earth foot of magnetic field lines but never was able to look into the “throat” of the radiation belt accelerator in the magnetospheric equatorial plane. This contrasts dramatically with the REPT-A and REPT-B instrument data collected by the Van Allen Probes from 1 September 2012 through early October 2012 (Fig. 1). These data show that a powerful electron acceleration event was already in progress as the instruments were first turned on. The entire outer radiation belt was enhanced in electron flux from E ~2.0 MeV (Fig. 1A) up to energies well above the 6.2 4.0 beginning on about 7 September and intensifying greatly over a period of two weeks. Subsequently, the outermost parts of the outer Van Allen zone grew and diminished further with little effect on the storage ring feature until the abrupt demise of virtually the entire outer zone electron population at the end of 1 October. Other electron sensor systems on board the Van Allen Probes spacecraft, overlapping partially in energy coverage with the REPT sensors, also detected the storage ring feature (17). The distinct storage ring feature is more clearly evident in the meridional plane projection of 4.0-5.0 MeV electrons from the combined REPT-A and REPT-B instrument records (Fig. 2). In the earliest observational phase (1-3 September) the expected two-belt structure of the Van Allen zones is clear (Fig. 2A). In the next phase from 3 to 6 September, the relativistic storage ring was formed (Fig. 2B) probably largely by erosion and loss of the more distant parts of the outer zone. It then persisted in a remarkably stable fashion (Fig. 2, C and D) throughout the A Long-Lived Relativistic Electron Storage Ring Embedded in Earth’s Outer Van Allen Belt D. N. Baker,1 * S. G. Kanekal,2 V. C. Hoxie,1 M. G. Henderson,3 X. Li,1 H. E. Spence,4 S. R. Elkington,1 R. H. W. Friedel,3 J. Goldstein,5 M. K. Hudson,6 G. D. Reeves,3 R. M. Thorne,7 C. A. Kletzing,8 S. G. Claudepierre9 1 Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA. 2 Goddard Space Flight Center, Greenbelt, MD, USA. 3 Los Alamos National Laboratory, Los Alamos, NM, USA. 4 Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH, USA. 5 Space Science and Engineering Division, Southwest Research Institute, San Antonio, TX, USA. 6 Department of Physics and Astronomy, Dartmouth College, Hanover, NH, USA. 7 Department of Atmospheric and Oceanic Sciences, University of California – Los Angeles, Los Angeles, CA, USA. 8 Department of Physics and Astronomy, University of Iowa, Iowa City, IA, USA. 9 The Aerospace Corporation, Los Angeles, CA, USA. *To whom correspondence should be addressed. E-mail: daniel.baker@lasp.colorado.edu Since their discovery over 50 years ago, the Earth’s Van Allen radiation belts have been considered to consist of two distinct zones of trapped, highly energetic charged particles. The outer zone is comprised predominantly of mega-electron volt (MeV) electrons that wax and wane in intensity on time scales ranging from hours to days depending primarily on external forcing by the solar wind. The spatially separated inner zone is comprised of commingled high-energy electrons and very energetic positive ions (mostly protons), the latter being stable in intensity levels over years to decades. In situ energy-specific and temporally resolved spacecraft observations reveal an isolated third ring, or torus, of high-energy (E > 2 MeV) electrons that formed on 2 September 2012 and persisted largely unchanged in the geocentric radial range of 3.0 to ~3.5 Earth radii for over four weeks before being disrupted (and virtually annihilated) by a powerful interplanetary shock wave passage. on March 6, 2013 www.sciencemag.org Downloaded from
remainder of September until its almost complete annihilation early in 1991.Geophys.Res.Let.19,821(1992).doi:10.1029/92GL00624 October 2012 6.X.Li et al,Simulation of the prompt energization and transport of radiation We note that powerful "injection"of high-energy electrons and pro- belt particles during the March 24,1991 SSC.Geophys.Res.Lett.20,2423 tons deep into the inner part of the Earth's magnetosphere on 24 March (1993).doi:10.1029/93GL02701 1991 (5,18,/9)was observed by instruments on board the CRRES 7.D.N.Baker et al.,Relativistic electron acceleration and decay time scales in the inner and outer radiation belts:SAMPEX.Geophys.Res.Left.21,409 spacecraft (/3).It was a highly impulsive event caused by an exception- (1994).doi:10.1029/93GL03532 ally strong interplanetary shock wave (5,6).This March 1991 event was 8.R.B.Home et al.,Timescale for radiation belt electron acceleration by whistler a stark example of the sudden appearance of a newly energized popula- mode chorus waves.J.Geophys.Res.110,A03225 (2005). tion of both protons and electrons in a localized portion of the slot region doi:10.10292004JA010811 of the radiation belts that normally is nearly devoid of very energetic 9.B.H.Mauk et al.,Science objectives and rationale for the Radiation Belt Storm particles(19,20).This prior event contrasts with the storage ring feature Probes mission.Space Sci.Rev.10.1007/s1 1214-012-9908-y (2012). observed by the Van Allen Probes sensors:The storage ring clearly re- 10.D.N.Baker et al.,The Relativistic Electron-Proton Telescope (REPT) sulted largely from loss of the more distant portion of the outer zone instrument on board the Radiation Belt Storm Probes (RBSP)spacecraft: electron population rather than fresh,localized injection of the March Characterization of Earth's radiation belt high-energy particle populations. Space Sci.Rev.10.1007/s11214-012-9950-9(2012). 1991 type.The original acceleration of the electron population(prior to the turn-on of REPT on I September)that eventually formed the storage 11.Since the initial Van Allen belt discovery,there have been many missions that have measured key aspects of the radiation properties around the Earth.Some ring may have resulted either from local wave heating (2/,22)or from of these have been from "operational"satellite systems such as the National enhanced radial diffusion (23,24)or both. Oceanic and Atmospheric Administration (NOAA)weather satellites in Based on prior radiation belt research [e.g.,(7,15)],the outer Van geostationary Earth orbit (GEO)(www.oso.noaa.gov/goesstatus)or polar low- m Allen zone electron populations would be expected to respond rather Earth (LEO)(www.oso.noaa.gov/poesstatus)orbits.Other measurements have directly to changes in the solar wind,interplanetary magnetic field been made using sor on board perational GE spacecraft or theGloba (IMF),and geomagnetic activity.Indeed,the development of the storage Positioning Satellite(GPS)timing and navigation constellation of spacecraft ring feature itself (Fig.3)was closely associated with loss of outer belt as well as the Polar and Cluster scientific satellites (/2).These prior satellites electrons following passage of an interplanetary shock wave on 3 Sep- have provided key long-term monitoring of radiation belt changes,but have tember,seen as a sharp increase in solar wind speed(Fig.3B)and abrupt generally not made measurements directly in the heart of the radiation belt 乏 regions.Only the Combined Release and Radiation Effects Satellite (CRRES) change in the IMF(Fig.3C).Subsequently,a new population of highly relativistic electrons emerged at a region around L4.0 and grew in mission (/3)operated briefly (1990-91)in the heart of the radiation belts but lacked the background rejection and the temporal,energy,and spatial intensity and spatial extent(Fig.3A)following a high-speed solar wind resolution now provided by the dual Van Allen Probes. episode(Fig.3B)on 5 September.Another such period of high-energy 12.R.H.W.Friedel,G.D.Reeves,T.Obara,Relativistic electron dynamics in electron flux diminution,reappearance,and intensification was seen the inner magnetosphere -a review.J.Atmos.Sol.Terr.Phys.64,265 from ~21 September through to 1 October(Fig.3A),again this sequence (2002).doi:10.1016/S1364-68260100088-8 occurring in the wake of a powerful high-speed solar wind stream on 20- 13.M.H.Johnson,J.Kierein,Combined Release and Radiation Effects Satellite 21 September (Fig.3B).As noted above,one of the most abrupt and (CRRES):Spacecraft and mission.J.Spacecr.Rockets 29,556 (1992). doi:10.2514/3.55641 striking features of the entire data set was the nearly complete disappear- 14.D.N.Baker et al.,An overview of the Solar Anomalous,and Magnetospheric ance of the entire outer zone electron population late on 1 October asso- Particle Explorer(SAMPEX)mission.IEEE Trans.Geosci.Rem.Sens.31, ciated with another interplanetary shock wave (Fig.3,B and C)and 531(1993).doi:101109/36.225519 relatively strong geomagnetic storm (seen in Dst,which measures global 15.X.Li,M.Temerin,D.N.Baker,G.D.Reeves,Behavior of MeV electrons at magnetic field disturbance,Fig.3D) geosynchronous orbit during last two solar cycles.J.Geophys.Res.116, Figure 3A shows that for the period of 1-4 September,the average A11207(2011).doi:10.10292011JA016934 品 plasmapause boundary was relatively close to the Earth(L*~3)and a 16.D.N.Baker,J.E.Mazur,G.M.Mason,SAMPEX to reenter atmosphere: powerful outer zone electron acceleration event was occurring in the low Twenty-year mission will end.Space Weather 10,S05006 (2012). doi:10.10292012SW000804 plasma-density region outside the plasmasphere.However,from~4 Sep- tember until ~6 October,the plasmapause was much farther outward, 17.See data and methods in the accompanying supplementary materials on Science Online. ranging at L*>4.Thus,the storage ring feature as well as most of the 18.A.L.Vampola,A.Korth,electron drift echoes in the inner magnetosphere. outer Van Allen zone E>4.5 MeV electron population was inside the Geophys.Res.Let.19,625(1992).doi10.1029/92GL00121 high-density plasmasphere.However,in the traditional picture the outer 19.E.G.Mullen,M.S.Gussenhoven,K.Ray,M.Violet,A double-peaked inner zone electron belt would largely be outside the plasmasphere and the slot radiation belt:cause and effect as seen on CRRES.IEEE Trans.Nucl.Sci.38. region inside the plasmasphere outer boundary (2/-23,25). 1713(1991).doi10110923.124167 The radiation belt particle populations are determined by a complex 20.D.H.Brautigam,JASTP 64,1709 (2002). superposition of acceleration,transport,and loss processes modulated by 21.R.B.Horne et al.,Wave acceleration of electrons in the Van Allen radiation their interactions with plasma waves (24).We are now seeing unex- belts.Nature 437,227(2005).doi:10.1038/nature03939 Medline pected radiation belt structures (Fig.4),but have yet to fully understand 22.Y.Y.Shprits et al.,Acceleration mechanism responsible for the formation of them in the context of present radiation belt theory. the new radiation belt during the 2003 Halloween solar storm.Geoplrys.Res Lett.33,L05104(2006).doi:10.10292005GL024256 23.X.Li,D.N.Baker,T.P.O'Brien,L.Xie,Q.G.Zong,Correlation between References and Notes the inner edge of outer radiation belt electrons and the innermost plasmapause 1.J.A.Van Allen et al.,Jet Propuls.28,588(1958). location.Geophys.Res.Left.33,L14107 (2006).doi:10.1029/2006GL026294 2.J.A.Van Allen,The geomagnetically trapped corpuscular radiation.. 24.R.M.Thorne,Radiation belt dynamics:The importance of wave-particle Geophys..Res.64,1683(1959).doi:10.1029/JZ064i011p01683 interactions. Geophys. Res. Lett. 37, L22107 (2010). 3.J.A.Van Allen,L.A.Frank,Radiation around the Earth to a radial fistance of doi:10.1029/2010GL044990 107,400km.Nature183,430(1959).doiI0.1038/183430a0 25.L.R.Lyons,R.M.Thorne,Equilibrium structure of radiation belt electrons 4.S.C.Freden,R.S.White,Protons in the Earth's magnetic field.Phys.Rev J.Geophys.Res.78,2142(1973).doi10.10290A078i013p02142 Lett.3,9 (1959).doi:10.1103/PhvsRevLett.3.9 5.J.B.Blake,W.A.Kolasinski,R.W.Fillius,E.G.Mullen,Injection of 26.J.Goldstein,Plasmasphere response:Tutorial and review of recent imaging results.Space Sci.Rev.124,203 (2006). electrons and protons with energies of tens of MeV into L<3 on 24 March Sciencexpress/http://www.sciencemag.org/content/early/recent /28 February 2013/Page 2/10.1126/science.1233518
/ http://www.sciencemag.org/content/early/recent / 28 February 2013 / Page 2 / 10.1126/science.1233518 remainder of September until its almost complete annihilation early in October 2012. We note that powerful “injection” of high-energy electrons and protons deep into the inner part of the Earth’s magnetosphere on 24 March 1991 (5, 18, 19) was observed by instruments on board the CRRES spacecraft (13). It was a highly impulsive event caused by an exceptionally strong interplanetary shock wave (5, 6). This March 1991 event was a stark example of the sudden appearance of a newly energized population of both protons and electrons in a localized portion of the slot region of the radiation belts that normally is nearly devoid of very energetic particles (19, 20). This prior event contrasts with the storage ring feature observed by the Van Allen Probes sensors: The storage ring clearly resulted largely from loss of the more distant portion of the outer zone electron population rather than fresh, localized injection of the March 1991 type. The original acceleration of the electron population (prior to the turn-on of REPT on 1 September) that eventually formed the storage ring may have resulted either from local wave heating (21, 22) or from enhanced radial diffusion (23, 24) or both. Based on prior radiation belt research [e.g., (7, 15)], the outer Van Allen zone electron populations would be expected to respond rather directly to changes in the solar wind, interplanetary magnetic field (IMF), and geomagnetic activity. Indeed, the development of the storage ring feature itself (Fig. 3) was closely associated with loss of outer belt electrons following passage of an interplanetary shock wave on 3 September, seen as a sharp increase in solar wind speed (Fig. 3B) and abrupt change in the IMF (Fig. 3C). Subsequently, a new population of highly relativistic electrons emerged at a region around L* ~4.0 and grew in intensity and spatial extent (Fig. 3A) following a high-speed solar wind episode (Fig. 3B) on 5 September. Another such period of high-energy electron flux diminution, reappearance, and intensification was seen from ~21 September through to 1 October (Fig. 3A), again this sequence occurring in the wake of a powerful high-speed solar wind stream on 20- 21 September (Fig. 3B). As noted above, one of the most abrupt and striking features of the entire data set was the nearly complete disappearance of the entire outer zone electron population late on 1 October associated with another interplanetary shock wave (Fig. 3, B and C) and relatively strong geomagnetic storm (seen in Dst, which measures global magnetic field disturbance, Fig. 3D). Figure 3A shows that for the period of 1-4 September, the average plasmapause boundary was relatively close to the Earth (L* ~ 3) and a powerful outer zone electron acceleration event was occurring in the low plasma-density region outside the plasmasphere. However, from ~4 September until ~6 October, the plasmapause was much farther outward, ranging at L* > 4. Thus, the storage ring feature as well as most of the outer Van Allen zone E > 4.5 MeV electron population was inside the high-density plasmasphere. However, in the traditional picture the outer zone electron belt would largely be outside the plasmasphere and the slot region inside the plasmasphere outer boundary (21–23, 25). The radiation belt particle populations are determined by a complex superposition of acceleration, transport, and loss processes modulated by their interactions with plasma waves (24). We are now seeing unexpected radiation belt structures (Fig. 4), but have yet to fully understand them in the context of present radiation belt theory. References and Notes 1. J. A. Van Allen et al., Jet Propuls. 28, 588 (1958). 2. J. A. Van Allen, The geomagnetically trapped corpuscular radiation. J. Geophys. Res. 64, 1683 (1959). doi:10.1029/JZ064i011p01683 3. J. A. Van Allen, L. A. Frank, Radiation around the Earth to a radial fistance of 107,400 km. Nature 183, 430 (1959). doi:10.1038/183430a0 4. S. C. Freden, R. S. White, Protons in the Earth’s magnetic field. Phys. Rev. Lett. 3, 9 (1959). doi:10.1103/PhysRevLett.3.9 5. J. B. Blake, W. A. Kolasinski, R. W. Fillius, E. G. Mullen, Injection of electrons and protons with energies of tens of MeV into L < 3 on 24 March 1991. Geophys. Res. Lett. 19, 821 (1992). doi:10.1029/92GL00624 6. X. Li et al., Simulation of the prompt energization and transport of radiation belt particles during the March 24, 1991 SSC. Geophys. Res. Lett. 20, 2423 (1993). doi:10.1029/93GL02701 7. D. N. Baker et al., Relativistic electron acceleration and decay time scales in the inner and outer radiation belts: SAMPEX. Geophys. Res. Lett. 21, 409 (1994). doi:10.1029/93GL03532 8. R. B. Horne et al., Timescale for radiation belt electron acceleration by whistler mode chorus waves. J. Geophys. Res. 110, A03225 (2005). doi:10.1029/2004JA010811 9. B. H. Mauk et al., Science objectives and rationale for the Radiation Belt Storm Probes mission. Space Sci. Rev. 10.1007/s11214-012-9908-y (2012). 10. D. N. Baker et al., The Relativistic Electron-Proton Telescope (REPT) instrument on board the Radiation Belt Storm Probes (RBSP) spacecraft: Characterization of Earth’s radiation belt high-energy particle populations. Space Sci. Rev. 10.1007/s11214-012-9950-9 (2012). 11. Since the initial Van Allen belt discovery, there have been many missions that have measured key aspects of the radiation properties around the Earth. Some of these have been from “operational” satellite systems such as the National Oceanic and Atmospheric Administration (NOAA) weather satellites in geostationary Earth orbit (GEO) (www.oso.noaa.gov/goesstatus) or polar lowEarth (LEO) (www.oso.noaa.gov/poesstatus) orbits. Other measurements have been made using sensors on board operational GEO spacecraft or the Global Positioning Satellite (GPS) timing and navigation constellation of spacecraft as well as the Polar and Cluster scientific satellites (12). These prior satellites have provided key long-term monitoring of radiation belt changes, but have generally not made measurements directly in the heart of the radiation belt regions. Only the Combined Release and Radiation Effects Satellite (CRRES) mission (13) operated briefly (1990-91) in the heart of the radiation belts but lacked the background rejection and the temporal, energy, and spatial resolution now provided by the dual Van Allen Probes. 12. R. H. W. Friedel, G. D. Reeves, T. Obara, Relativistic electron dynamics in the inner magnetosphere — a review. J. Atmos. Sol. Terr. Phys. 64, 265 (2002). doi:10.1016/S1364-6826(01)00088-8 13. M. H. Johnson, J. Kierein, Combined Release and Radiation Effects Satellite (CRRES): Spacecraft and mission. J. Spacecr. Rockets 29, 556 (1992). doi:10.2514/3.55641 14. D. N. Baker et al., An overview of the Solar Anomalous, and Magnetospheric Particle Explorer (SAMPEX) mission. IEEE Trans. Geosci. Rem. Sens. 31, 531 (1993). doi:10.1109/36.225519 15. X. Li, M. Temerin, D. N. Baker, G. D. Reeves, Behavior of MeV electrons at geosynchronous orbit during last two solar cycles. J. Geophys. Res. 116, A11207 (2011). doi:10.1029/2011JA016934 16. D. N. Baker, J. E. Mazur, G. M. Mason, SAMPEX to reenter atmosphere: Twenty-year mission will end. Space Weather 10, S05006 (2012). doi:10.1029/2012SW000804 17. See data and methods in the accompanying supplementary materials on Science Online. 18. A. L. Vampola, A. Korth, electron drift echoes in the inner magnetosphere. Geophys. Res. Lett. 19, 625 (1992). doi:10.1029/92GL00121 19. E. G. Mullen, M. S. Gussenhoven, K. Ray, M. Violet, A double-peaked inner radiation belt: cause and effect as seen on CRRES. IEEE Trans. Nucl. Sci. 38, 1713 (1991). doi:10.1109/23.124167 20. D. H. Brautigam, JASTP 64, 1709 (2002). 21. R. B. Horne et al., Wave acceleration of electrons in the Van Allen radiation belts. Nature 437, 227 (2005). doi:10.1038/nature03939 Medline 22. Y. Y. Shprits et al., Acceleration mechanism responsible for the formation of the new radiation belt during the 2003 Halloween solar storm. Geophys. Res. Lett. 33, L05104 (2006). doi:10.1029/2005GL024256 23. X. Li, D. N. Baker, T. P. O’Brien, L. Xie, Q. G. Zong, Correlation between the inner edge of outer radiation belt electrons and the innermost plasmapause location. Geophys. Res. Lett. 33, L14107 (2006). doi:10.1029/2006GL026294 24. R. M. Thorne, Radiation belt dynamics: The importance of wave-particle interactions. Geophys. Res. Lett. 37, L22107 (2010). doi:10.1029/2010GL044990 25. L. R. Lyons, R. M. Thorne, Equilibrium structure of radiation belt electrons. J. Geophys. Res. 78, 2142 (1973). doi:10.1029/JA078i013p02142 26. J. Goldstein, Plasmasphere response: Tutorial and review of recent imaging results. Space Sci. Rev. 124, 203 (2006). on March 6, 2013 www.sciencemag.org Downloaded from
27.J.Goldstein,B.R.Sandel,W.T.Forrester,M.F.Thomsen,M.R.Hairston Global plasmasphere evolution 22-23 April 2001.J.Geop/nys.Res.110, A12218(2005).doi10.1029/2005JA011282 28.R.E.Denton et al.,Magnetospheric electron density long-term (>I day) refilling rates inferred from passive radio emissions measured by IMAGE RP during geomagnetically quiet times.J.Geophys.Res.117,A03221 (2012) doi:10.10292011JA017274 Acknowledgments:This work was supported by RBSP-ECT funding provided by JHU/APL contract no.967399 while EMFISIS work was supported on JHU/APL contract no.921649 both under NASA's Prime contract no.NAS5- 01072.All Van Allen Probes observations used in this study,along with display and analysis software,are publicly available at the Web site www.rbsp-ect.lanl.gov. Supplementary Materials www.sciencemag.org/cgi/content/full/science.1233518/DCI Supplementary Text Figs.S1 and S2 References 3 December 2012;accepted 5 February 2013 Published online 28 February 2013 10.1126/science..1233518 Sciencexpress/http://www.sciencemag.org/content/early/recent /28 February 2013/Page 3/10.1126/science.1233518
/ http://www.sciencemag.org/content/early/recent / 28 February 2013 / Page 3 / 10.1126/science.1233518 27. J. Goldstein, B. R. Sandel, W. T. Forrester, M. F. Thomsen, M. R. Hairston, Global plasmasphere evolution 22–23 April 2001. J. Geophys. Res. 110, A12218 (2005). doi:10.1029/2005JA011282 28. R. E. Denton et al., Magnetospheric electron density long-term (>1 day) refilling rates inferred from passive radio emissions measured by IMAGE RPI during geomagnetically quiet times. J. Geophys. Res. 117, A03221 (2012). doi:10.1029/2011JA017274 Acknowledgments: This work was supported by RBSP-ECT funding provided by JHU/APL contract no. 967399 while EMFISIS work was supported on JHU/APL contract no. 921649 both under NASA’s Prime contract no. NAS5- 01072. All Van Allen Probes observations used in this study, along with display and analysis software, are publicly available at the Web site www.rbsp-ect.lanl.gov. Supplementary Materials www.sciencemag.org/cgi/content/full/science.1233518/DC1 Supplementary Text Figs. S1 and S2 References 3 December 2012; accepted 5 February 2013 Published online 28 February 2013 10.1126/science.1233518 on March 6, 2013 www.sciencemag.org Downloaded from
6 3.6 Mev 703 TIE× 4.5 MeV 03 5 6 MeV 10 electrons/cm2-s-sr-Mev 100 2012-09-10 2012-09-20 2012-09-30 Fig.1.Energetic electron data from the Radiation Belt Storm Probes (RBSP)satellites in eccentric orbits around the Earth showing several discrete energy channels of the Relativistic Electron-Proton Telescope (REPT)instruments on board the spatially separated RBSP-A and RBSP-B spacecraft.Each panel's vertical axis is the L*parameter which is effectively the distance in Earth radi at which a magnetic field line crosses the magnetic equatorial plane.The horizontal axis is time from 1 September 2012 to 4 October 2012.Electron differential flux values (in units of electrons/cm--s-sr-MeV)are in a color- coded logarithmic scale as shown to the right of the figure.(A)Electrons in the energy range3.2≤E≤4.0MeV.(B)Electrons with4.0sEs5.0MeV.(c)Electrons with5.0≤E≤ 6.2 MeV. Sciencexpress/http://www.sciencemag.org/content/early/recent/28 February 2013/Page 4/10.1126/science.1233518
/ http://www.sciencemag.org/content/early/recent / 28 February 2013 / Page 4 / 10.1126/science.1233518 Fig. 1. Energetic electron data from the Radiation Belt Storm Probes (RBSP) satellites in eccentric orbits around the Earth showing several discrete energy channels of the Relativistic Electron-Proton Telescope (REPT) instruments on board the spatially separated RBSP-A and RBSP-B spacecraft. Each panel’s vertical axis is the L* parameter which is effectively the distance in Earth radii at which a magnetic field line crosses the magnetic equatorial plane. The horizontal axis is time from 1 September 2012 to 4 October 2012. Electron differential flux values (in units of electrons/cm2 -s-sr-MeV) are in a colorcoded logarithmic scale as shown to the right of the figure. (A) Electrons in the energy range 3.2 ≤ E ≤ 4.0 MeV. (B) Electrons with 4.0 ≤ E ≤ 5.0 MeV. (C) Electrons with 5.0 ≤ E ≤ 6.2 MeV. on March 6, 2013 www.sciencemag.org Downloaded from
6 30N -10 o Mag 9/12012-9/3/2012 L=4 L=2 10 30N ce Mag Fig.2.Meridional plane projections of the REPT-A and REPT-B electron flux (4.0-5.0 MeV)values as shown according to the logarithmic color scale to the right of the figure.Each panel shows a limited interval of time in a magnetic latitude -L*coordinate system.(A)For 1-3 9/3/2012-9/16/2012 September the expected two-belt Van Allen zone structure =4 10 with an inner zone electron population(L*3.0).(B)From 3 September through 6 September only an intense belt of electrons remains in the range 3.03.8.(D)The storage ring 需 9/122012-9/15/2012 feature remains while the outer zone at L*>3.8 decays 10 away.(E)The entire outer zone (L*>~3.0)has virtually disappeared at these energies. 30°N 0 Mag 9/18/2012-9/212012 30°N 4.5 MeV Electron Flux(cm's sr MeV) 0 Mag 10/12012-10/4/2012 Sciencexpress/http://www.sciencemag org/content/early/recent /28 February 2013/Page 5/10.1126/science.1233518
/ http://www.sciencemag.org/content/early/recent / 28 February 2013 / Page 5 / 10.1126/science.1233518 Fig. 2. Meridional plane projections of the REPT-A and REPT-B electron flux (4.0-5.0 MeV) values as shown according to the logarithmic color scale to the right of the figure. Each panel shows a limited interval of time in a magnetic latitude – L* coordinate system. (A) For 1-3 September the expected two-belt Van Allen zone structure with an inner zone electron population (L* 3.0). (B) From 3 September through 6 September only an intense belt of electrons remains in the range 3.0 3.8. (D) The storage ring feature remains while the outer zone at L* > 3.8 decays away. (E) The entire outer zone (L* > ~3.0) has virtually disappeared at these energies. on March 6, 2013 www.sciencemag.org Downloaded from
"Storage Ring"-Remnant New Slot-Like Outer Limit of of previous outer belt minimum Outer Belt the PlasmaSphere Re-energization a Typical 2-Belt New 3-Belt Outer Belt Structure Structure Dropout Rs8gbeBer6. Slot Region Inner Electron Radiation Belt 600. 400 20 0 -50 -100 2012-08-31 2012-09-10 2012-09-20 2012-09-30 2012-10-10 Fig.3.(A)Similar to panel(B)of Fig.1 but including the plasmapause,the outer boundary of the plasmasphere(26)for the period 1 September to 7 October 2012.The white curve over-plotted upon the color-coded electron particle flux data in Fig.3A shows the modeled,3-day averaged plasmapause radial location that is in agreement with concurrent plasma wave data (17,27,28).(B)The concurrently measured solar wind speed upstream of the Earth's magnetosphere.(C)The interplanetary magnetic field for the interval under study.(D)The geomagnetic activity index Dst for the period under study Sciencexpress/http://www.sciencemag org/content/early/recent /28 February 2013/Page 6/10.1126/science.1233518
/ http://www.sciencemag.org/content/early/recent / 28 February 2013 / Page 6 / 10.1126/science.1233518 Fig. 3. (A) Similar to panel (B) of Fig. 1 but including the plasmapause, the outer boundary of the plasmasphere (26) for the period 1 September to 7 October 2012. The white curve over-plotted upon the color-coded electron particle flux data in Fig. 3A shows the modeled, 3-day averaged plasmapause radial location that is in agreement with concurrent plasma wave data (17, 27, 28). (B) The concurrently measured solar wind speed upstream of the Earth’s magnetosphere. (C) The interplanetary magnetic field for the interval under study. (D) The geomagnetic activity index Dst for the period under study. on March 6, 2013 www.sciencemag.org Downloaded from
⊙ 6 Plasmasphere Plasmasphere Storage Ring Extent Extent New Slot Outer Belt Slot Inner Belt Typical 2-Belt Structure New 3-Belt Structure Fig.4.Diagrams providing a cross-sectional view of the Earth's radiation belt structure and relationship to the 詈 plasmasphere.(A)A schematic diagram showing the Earth,the outer and inner radiation belts and the normal plasmaspheric location.(B)Similar to(A)but showing a more highly distended plasmasphere and quite unexpected triple radiation belt properties during the September 2012 period.These diagrams show the highest electron fluxes as white and the lowest fluxes as blue.The radiation belts are really 'doughnut'or torus-shaped entities in three dimensions.The Earth is portrayed at the center.Also shown,as a translucent green overlay in each diagram,is the plasmasphere. Sciencexpress/http://www.sciencemag.org/content/early/recent /28 February 2013/Page 7/10.1126/science.1233518
/ http://www.sciencemag.org/content/early/recent / 28 February 2013 / Page 7 / 10.1126/science.1233518 Fig. 4. Diagrams providing a cross-sectional view of the Earth’s radiation belt structure and relationship to the plasmasphere. (A) A schematic diagram showing the Earth, the outer and inner radiation belts and the normal plasmaspheric location. (B) Similar to (A) but showing a more highly distended plasmasphere and quite unexpected triple radiation belt properties during the September 2012 period. These diagrams show the highest electron fluxes as white and the lowest fluxes as blue. The radiation belts are really ‘doughnut’ or torus-shaped entities in three dimensions. The Earth is portrayed at the center. Also shown, as a translucent green overlay in each diagram, is the plasmasphere. on March 6, 2013 www.sciencemag.org Downloaded from
