1. Energetic particles in the Heliosphere and the Magnetosphere Shri Kanekal LASP

2. Section 1 Overview of particle populations in the Heliosphere Section 2 Characteristics of charged particles Section 3 Charged particle detection and measurement Section 4 Electrons and Protons in the Magnetosphere i. Outer zone radiation belt electrons ii. Inner zone protons iii. Solar energetic particles (mainly protons) iv. Jovian electrons

3. A tour of our space environment Section 1 from the perspective of energetic particle populations The Milky way, our local galaxy The Sun, our local star The Earth, our planet

4. Particle populations are diverse  Galactic cosmic rays (GCR) > Energy range from ~ 100s of MeV to 10s of GeV > Consist of nuclei of atoms, ranging from the lightest to the heaviest elements in the periodic table > Originate from supernova explosions  Solar energetic particles (SEP) > Energy range from ~ 10s of MeV to 100s of MeV > Provide compositional information of the Sun  Anomalous cosmic rays > Interstellar neutrals ionized by solar wind & accelerated at the “heliopause” > comprise of only those elements that are difficult to ionize, including He, N, O, Ne, and Ar

5. Particle populations are diverse  Magnetospheric particles > stably trapped and transient > Energy range from ~ 10s of MeV to 100s of MeV > electrons, protons, ionospheric solar ions, trapped cosmic rays > Earth, Jupiter, … other planets with magnetic fields  Magnetospheric bulk plasma > bulk plasma eV & low energy keV particles > can influence behaviour of high energy particles ! We will focus mostly on magnetospheric “high energy” electrons and briefly discuss solar energetic protons

6. Galactic comic ray map : from EGRET instrument By measuring photon intensity which is proportional to GCR intensity via their interaction with the interstellar gas

7. Lasco coronograph picture of the Sun onboard SoHo spacecraft showing “snow” from SEPs Solar energetic particle observations Protons and X-ray intensities From GOES spacecraft hour of january 20 2005

8. Anomalous cosmic rays interstellar neutrals become charged by photo-ionization or charge exchange with the solar wind.The Sun's magnetic carries them outward to the solar wind termination shock.

9. “high energy” electrons in the Earth’s magnetosphere 27-oct-2003 28-oct-2003 29-oct-2003 These “relativistic electrons” are highly variable and dynamic. Note the large increase in particle flux in just two days !

10. Plasmasphere images taken by the EUV instrument onboard IMAGE spacecraft Plasmasphere comprises of cold plasma ~ few eV

11. Let us define some terms Section 2 regarding energetic particles what do we measure in space ? omnidirectional flux differential flux pitch angle distribution time evolution of particle fluxes, & pitch angle distributions

12. Integral directional flux particle counts = N /second (particles with E > E’) detector area = A cm 2 field of view =  sr (solid angle) flux = N / [ A*  ] units = cm -2 -Sr-sec Integral,Differential, Omnidirectional … flux differential directional flux flux = N / [ A*  *  E] units = cm -2 -Sr-sec-MeV detector counts particles with E1 < E < E2 =  E Omnidirectional flux => over full 4  sr

13. Observations of electron fluxes in the Earth’s magnetosphere From Baker and Kanekal, GRL (to be submitted)

14. B  Pitch angle : angle between the local magnetic field vector and particle momentum “Pancake” and “Cigar” shaped distributions commonly observed distributions particles  to B Particles to B 

15. Measured Pitch angle distributions of electron in the magnetosphere (Selesnick and Blake, JGR 2002) Observations of pitch angle distributions Counter streaming electrons observed in the interplanetary space (Steinberg et al. JGR 2005) Cigar shape

16. How do we detect and identify charged particles ? Section 3 principle methods of particle detection examples of particle detectors

17. Interaction of charged particles with matter When charged particles pass through matter (M > m e ) a) they lose energy  inelastic collisions mainly with atomic electrons causes ionization or excitation of the atom many many many collisions !! statistical average energy loss/unit length “dE/dx” b) they change direction  elastic scattering from atomic nuclei electrons are different !  braking radiation or “bremsstrahlung” ( we will ignore interaction of photons with matter )

18. Ionization loss of charged particles in matter

19. Principle of operation : simple solid state detector Charged particle passing through Silicon creates electron-hole Pairs. The total charge collected is proportional to the energy Lost by the charged particle Q   E

20. Principle of operation : simple scinitillation detector Photons are emitted by excited atoms returning to their ground state after being ionized by charged particles which are detected by a photo multiplier Tube (PMT).

21. Two instruments currently operating on spacecraft PET : Proton Electron Telescope Onboard SAMPEX spacecraft HIST : High Sensitivity Telescope Onboard Polar spacecraft

22. An electron spectrometer type instrument Electrons bend in a magnetic field and reach the detection plane at different distances proportonal to their energies and are detected by dE/dx loss in individual solid state detectors.

23. An instrument that is being developed here at LASP REPT :Relativistic Electron Proton Telescope

24. Instruments are calibrated in beam tests and simulations 50mm (5mm) W+(5mm )x2 Al Al 10mm W 7mm 10 mm R1R9 Kapton cover 0.025 mm

25. Monte Carlo simulation of electrons entering the instrument Stopping particlesMinimum ionizing

26. Identification of particle species in a dE/dx instrument Particle species are identified by the energy deposition pattern in a stack of solid state detectors

27. Energetic particles in the Earth’s Magnetosphere Section 4  Radiation belt electrons, and protons  trapped anomalous cosmic rays  trapped and transient solar energetic particles  jovian electrons, … etc etc

28. Geostationary Transfer Orbit SAMPEX Inner Belt Outer Belt Slot Region Dynamic Outer belt mostly electrons Sources : Magnetotail electrons The Terrestrial Magnetosphere Relatively stable inner belt mostly Protons Sources : CRAND protons SEP events

29. The dynamic outer zone electrons 3 November 2003 (307) 22 October 2003 (295) 29 October 2003 (302)

30. Key Regions of Particle Acceleration in the Magnetosphere Bow Shock Cusp Solar Wind Shock Acceleration Auroral Region Acceleration Magnetopause Acceleration Inner Magnetosphere Acceleration Tail Reconnection Acceleration The Solar wind plays a crucial role in the acceleration processes

31. Particle motions in a magnetic dipole : recap L = equatorial distance of a field line in a dipole field

32. Particle fluxes of different local pitch angles measured along the same field line transformed into equatorial pitch angles. From Liouville’s theorem J(  1,B 1,L 1 ) = J(  2,B 2,L 2 ) sin 2  1 / B 1 = sin 2  2 / B 2  1 and  2 are pitch angles at two different locations on the same field line Observations of conservation of the first adiabatic invariant.

33.  High solar wind speeds and southward B z (reconnection, waves, radial diffusion …)  Substorm generated seed population  hundreds of keV relativistic energies  usually associated with geomagnetic storms  physical processes  radial transport  in-situ acceleration  combination Electron energization - overview

34. Relativistic Electrons : Radial Diffusion Initial electron ring –r = r 0 Sudden asymmetric compression  –Electrons on different constant B paths Resultant smeared out electron band Long timescales –≈ Days to weeks

35. In-situ acceleration Example: Resonant Interactions with VLF Waves Whistler-mode chorus at dawn combined with EMIC interactions heat and isotropize particles Leads to transport in M, K, and L Summers et al. (JGR 103, 20487, 1998) proposed that resonant interaction with VLF waves could heat particles: See also Horne et al., (Nature, 2005)

36. Acceleration Models: Expected pitch angle distribution Radial diffusionPancake distribution Stochastic acceleration (VLF waves) Isotropization on drift time scales Magnetic pumpingContinual isotropization Many wave-particle interaction models include pitch angle scattering Pure radial diffusion does not - separate process

37. Relativistic Electrons & Geomagnetic Storms Recovery phase –Increased fluxes –Energization Main phase –Flux dropout –Adiabatic field change & particle loss Flux changes –Decrease or no change in about 50% of storms - GEO data [See Kanekal et al., 2004; Reeves et al., 2003]

38.  SAMPEX LEO orbit ≈ 650 km 82 0 inclination ≈ 90 min period 2.-6. MeV electrons  POLAR elliptical orbit 2x9 R e ≈ 18 hrs period > 2 MeV electrons  complete coverage of the outer zone L ≈ 2.5 to 6.5 POLAR SAMPEX geo Spacecraft and Data

39. Relativistic electrons : energization and loss Energization => increasing flux loss => decreasing flux

40. Relativistic electrons : energization and loss flux increase and decay times set lower bounds on energization and loss time scales of proposed physical models. Flux increase or decrease is a balance between Energization & Loss Loss dominates Energization dominates

41. Relativistic electrons : global coherence  flux increase over a large L range  high-altitude and low-altitude fluxes track each other ( fluxes are 30-day running averages) Note that Polar being at a higher altitude samples a larger part of the equatorial pitch angle distribution than SAMPEX.

42. Compare SAMPEX and polar (largest eq. Pitch angle) At L=4 Tracking of high-altitude and low-altitude fluxes => Pitch angle distribution (i.e flux) isotropization

43. Flux ratio increases during a flux enhancement event  Enhanced isotropization Global coherence : High- & Low- altitude Flux Ratio

44. isotropization weakens at L shells further away from flux maximum. Global coherence : High- & Low- altitude Flux Ratio

45. Global coherence : High- & Low- altitude Flux Correlation  correlation vs. lag time at select L values  day-average fluxes for 1998  correlation vs. lag time at geo L = 6.6  orbit-average fluxes for 1999 Lag times are less than 1 day  rapid and/or simultaneous isotropization

46. Relativistic electrons : location of flux maximum L max ~ 1.3 L pp Lpp - function of minimum Dst O’Brien and Moldwin (2003) Most intense energization correlated with plasmapause location Very low energy plasma in the Plasmasphere controls high energy electrons

47. Relativistic electrons : location of flux maximum Halloween storms (oct-nov 2003) are not included indicative of coupling between electron energization and the plasmapause and the ring current. Perhaps via the growth of Whistler and EMIC waves which are driven by anisotropy of ring current protons and electrons Whistler waves predominate outside plasmapause EMIC waves predominate the dusk side region along the plasmapause. EMIC waves lead to particle loss within the plasmapause First observed by Tverskaya 1986

48. Strong Semi-Annual Variation in Outer Zone Baker et al. (GRL,1999) Possible causes tilt of the Earth’s dipole axis relative to the solar ecliptic (Russell-McPherron) exposure to high speed solar wind (axial effect) varying solar wind coupling efficiency (equinoctial effect)

49. Relativistic Electrons : Solar Cycle Effects HSS CME Declining phase - many recurrent high speed streams Ascending phase - sporadic coronal mass ejections

50. Electron Energization Summary  energization occurs over a large radial region (L shell) (measurements of 1-day time resolution) [Global]  energization appears to be intimately related to pitch angle scattering leading to rapid pitch angle isotropization. Some in-situ mechanisms include near-simultaneous energization and pitch angle scattering. ‘simple’ radial diffusion needs to be augmented with pitch angle scattering mechanisms. [Coherent]  Clues to discriminating between various mechanisms include association of L max with plasmapause location and |D st |  Relativistic electrons in the magnetosphere show seasonal and solar cycle dependence.

51. Inner Zone Protons Some Presently Used Platforms Sources : CRAND & SEP Cosmic Ray Albedo Neutron Decay

52. A solar proton event observed by SAMPEX  Interplanetary particles have access vis the open field lines over the Earth’s polar regions  Proton rates summed over invariant latitude > 70 deg  Orbital time resolution of ~ 90 minutes

53.  The cutoff latitude is a well defined latitude below which a charged particle of a given rigidity (momentum per unit charge) arriving from a given direction cannot penetrate. SEP entry into the magnetosphere: Charged particle cutoffs Quiet time cutoffs Ogliore et al., ICRC, 2001 R c = 15.062cos 4 (  ) -0.363 GV  = invariant latitude cos 2  = 1 / L

54. During geomagnetic storms SEP cutoffs are lowered and are a potential radiation hazard Charged particle cutoffs during disturbed times Birch et al., JGR,2005 c = 0.053D st + 65.8 (  0.6)

55. Location of > 16 MeV Oxygen during October-November 1992 SEP events. Solid lines are ISS ground tracks (green area is the nominal polar cap) Leske et al, JGR, 2001

56. Measuring cutoff latitude: Data (SAMPEX) Proton counts 6 seconds time resolution invariant latitude bins 0.4 0 wide smoothed over 2.0 0 The polar region between 70 0 and 75 0 ( blue line) The cutoff latitude is determined as the latitude at which the count rate is half the polar average. Note contamination from radiation belt electrons at about 60 0 inv. lat. Proton count rate as a function of invariant latitude for the descending part of an orbit over the south pole.

57. Measured cutoff latitudes: November 1997 Proton cutoff as a function of time during the november 1997 geomagnetic storm. The black trace shows the D st index. The cutoff location follows the D st index closely.

58. Calculating cutoff latitude: Particle tracing Trajectories of a 25 MeV proton in the noon- midnight and equatorial planes for D st of -200 nT. Proton trajectory simulations : Energy: 25 MeV launch: 270 0 longitude. and 47.75 0 latitude. SAMPEX location at L = 5 scan : 20 degrees below and 15 degrees above in 0.5 degree steps trajectory type: i) trapped: particle drifts at least 2 times around the Earth ii) quasi-trapped: drifts once then exits the magnetosphere iii) penetrating: exits the magnetosphere The cutoff latitude is defined as that latitude at which only directly penetrating populations remain as we trace particles starting from low latitudes and move to higher latitudes.

59. Cutoff location model and observations: November 1997 Proton cutoff as a function of the D st index for the november 1997 geomagnetic storm. The black trace is a straight line fit to the data and the red trace for the protons traced in the T96 field. c = 0.063D st + 65.8 c = 0.053D st + 66.1

60. Trapped SEP ions: 24 Nov 2001 Clear trapping of solar particles: 13 of 26 SEP penetration events inside L=4, 98-03 Mazur et al., AGU Monograph 165, 2006

61. Protons: 19-28 MeV (SAMPEX/PET)Protons: 19-26 MeV (SAMPEX/PET) New belt of trapped Protons SEP Protons  Pitch angle

62. Trapped and Solar Energetic Particle Summary  sources of inner belt protons include the CRAND and solar protons.  Interplanetary charged particles have access to the Earth’s magnetosphere over the polar regions and reach latitudes depending upon their rigidity. They are some times trapped and form stable long lived “new belts”. Trapping could be the result of pitch angle scattering.  Global magnetic field models reproduce general behavior of the variation of cutoff location during disturbed times but consistently over estimate value of the cutoff location.

63. Jovian electrons : 13 month synodic period at 1 AU The interplanetary magnetic field modulates charged particles in the heliosphere

64. Jovian electrons : Evidence for source modulation Kanekal et al, GRL 2003 Transport/Modulation effects ruled out by comparisons to IMP8 data

65. Jovian electrons Summary  Jovian magnetosphere is a source of ~MeV which are transported along the Parker spiral and reach the Earth.  The optimal magnetic connection occurs once every 13 months, the jovian synodic period at the Earth. These electrons are useful in the study of influence of the interplanetary magnetic field on the propagation of charged particles.  Using SAMPEX and IMP8 sensors a puzzling lack of the Jovian electrons was observed during 1995-1997 ( 2 jovian cycles) which can be attributed to possible changes of the Jovian source itself rather than changes in transport/modulation.

66. Home work assignment 1. What are chief measurements that are made regarding charged particles in space ? 2. Describe some of the techniques used to measure charged particles. 3. How does the solar wind influence particle populations in the magnetosphere ? 4. What are the two main classes of electron energization in the magnetosphere ? How do we distinguish between them ? 5. What is the cause for the slot region ? Briefly describe the energy/species dependence of the slot region. 6. Can you think of a way SEP to get trapped in the magnetosphere ? 7. Research the discovery of Jovian electrons.

68. Solar wind : plasma outflow from the Sun