Energetic particles in the Heliosphere and the Magnetosphere

Shri Kanekal LASP

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

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

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

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

Galactic comic ray map : from EGRET instrument

By measuring photon intensity which is proportional to GCR intensity via their interaction with the interstellar gas

Lasco coronograph picture of the Sun onboard SoHo spacecraft showing “snow” from SEPs

Solar energetic particle observations

Protons and X-ray intensitiesFrom GOES spacecraft

hour of january 20 2005

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.

“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 !

Plasmasphere images taken by the EUV instrument onboard IMAGE spacecraft

Plasmasphere comprises of cold plasma ~ few eV

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

Integral directional flux particle counts = N /second (particles with E > E’) detector area = A cm2

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 = EOmnidirectional flux => over full 4 sr

Observations of electron fluxes in the Earth’s magnetosphere

From Baker and Kanekal, GRL (to be submitted)

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

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

How do we detect and identify charged particles ? Section 3

principle methods of particle detection examples of particle detectors

Interaction of charged particles with matter

When charged particles pass through matter (M > me ) 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 !electrons are different ! braking radiation or “bremsstrahlung”

( we will ignore interaction of photons with matter )

Ionization loss of charged particles in matter

Principle of operation : simple solid state detector

Charged particle passing through Silicon creates electron-holePairs. The total charge collected is proportional to the energyLost by the charged particle

Q E

Principle of operation : simple scinitillation detector

Photons are emitted byexcited atoms returning totheir ground state afterbeing ionized by chargedparticles which are detected by a photo multiplier Tube (PMT).

Two instruments currently operating on spacecraft

PET : Proton Electron Telescope Onboard SAMPEX spacecraft

HIST : High Sensitivity TelescopeOnboard Polar spacecraft

An electron spectrometer type instrument

Electrons bend in a magneticfield and reach the detectionplane at different distancesproportonal to their energiesand are detected by dE/dxloss in individual solid statedetectors.

An instrument that is being developed here at LASP

REPT :Relativistic Electron Proton Telescope

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

Monte Carlo simulation of electrons entering the instrument

Stopping particlesMinimum ionizing

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

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

Geostationary Transfer Orbit

SAMPEX

Inner Belt

Outer Belt

Slot Region

Dynamic Outer belt mostly electronsSources : Magnetotail electrons

The Terrestrial Magnetosphere

Relatively stable inner belt mostly ProtonsSources : CRAND protons SEP events

QuickTime™ and aCinepak decompressor

are needed to see this picture.

The dynamic outer zone electrons

3 November 2003 (307)

22 October 2003 (295)

29 October 2003 (302)

Key Regions of Particle Acceleration in the Magnetosphere

BowShock

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

Particle motions in a magnetic dipole : recap

L = equatorialdistance of a field line in a dipole field

Particle fluxes of different local pitch angles measured along the same field line transformed into equatorial pitch angles.

From Liouville’s theoremJ(1,B1,L1) = J(2,B2,L2)

sin21/ B1 = sin22/ B2

1 and 2 are pitch angles at two different locations on the same field line

Observations of conservation of the first adiabatic invariant.

High solar wind speeds and southward Bz

(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

Relativistic Electrons : Radial Diffusion

• Initial electron ring– r = r0

• Sudden asymmetric compression – Electrons on

different constant B paths

• Resultant smeared out electron band

• Long timescales– ≈ Days to weeks

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)

Acceleration Models: Expected pitch angle distribution

Radial diffusion Pancake distribution

Stochastic acceleration(VLF waves)

Isotropization on drift time scales

Magnetic pumping Continual isotropization

Many wave-particle interaction models include pitchangle scattering

Pure radial diffusion does not - separate process

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]

SAMPEX LEO orbit ≈ 650 km 820 inclination ≈ 90 min period 2.-6. MeV electrons

POLAR elliptical orbit 2x9 Re

≈ 18 hrs period > 2 MeV electrons

complete coverage of the outer zone L ≈ 2.5 to 6.5

POLAR

SAMPEX

geo

Spacecraft and Data

Relativistic electrons : energization and loss

Energization => increasing flux loss => decreasing flux

Relativistic electrons : energization and loss

flux increase and decay times set lower bounds on energization and loss time scales of proposedphysical models.

Flux increase or decrease is a balance between Energization & Loss

Loss dominatesEnergization dominates

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.

Compare SAMPEX and polar (largest eq. Pitch angle)At L=4

Tracking of high-altitudeand low-altitude fluxes =>Pitch angle distribution(i.e flux) isotropization

Flux ratio increases during a flux enhancement event Enhanced isotropization

Global coherence : High- & Low- altitude Flux Ratio

isotropization weakens at L shells further away from flux maximum.

Global coherence : High- & Low- altitude Flux Ratio

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

Relativistic electrons : location of flux maximum

Lmax ~ 1.3 Lpp

Lpp - function of minimum Dst O’Brien and Moldwin (2003)

Most intense energization correlated with plasmapause location

Very low energyplasma in the Plasmaspherecontrols highenergy electrons

Relativistic electrons : location of flux maximum

Halloween storms (oct-nov 2003) are not included

indicative of coupling between electron energization andthe plasmapause and the ring current. Perhaps via the growth of Whistler and EMIC waves whichare driven by anisotropy of ring current protons and electrons

Whistler waves predominateoutside plasmapause

EMIC waves predominate the dusk side region alongthe plasmapause.

EMIC waves lead to particleloss within the plasmapause

First observed by Tverskaya 1986

Strong Semi-Annual Variation in Outer Zone

0.0

0.5

1.0

1.5

2.0

Seasonal Average Fluxes : 1992 - 1999

February - April

May - July

August -October

November - January

SAMPEX Electrons 2.5 < L < 6.5 2 - 6 MeV

Spring

Summer

Fall

Winter

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)

Relativistic Electrons : Solar Cycle Effects

HSS

CME

Declining phase - many recurrent high speed streamsAscending phase - sporadic coronal mass ejections

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 Lmax with plasmapause location and |Dst|

Relativistic electrons in the magnetosphere show seasonal and solar cycle dependence.

Inner Zone Protons

Inner Zone Protons

Some Presently Used Platforms

Sources : CRAND & SEPCosmic Ray Albedo Neutron Decay

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

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, 2001Rc = 15.062cos4() -0.363 GV

= invariant latitudecos2 = 1 / L

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 = 0.053Dst + 65.8 (0.6)

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

Measuring cutoff latitude: Data (SAMPEX)Proton counts• 6 seconds time resolution

• invariant latitude bins 0.40 wide smoothed over 2.00

The polar region between 700 and 750 ( 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 600 inv. lat.

Proton count rate as a function of invariant latitude for the descending part of an orbit over the south pole.

Measured cutoff latitudes: November 1997

Proton cutoff as a function of time during the november 1997 geomagnetic storm. The black trace shows the Dst index. The cutoff location follows the Dst index closely.

Calculating cutoff latitude: Particle tracing

Trajectories of a 25 MeV proton in the noon-midnight and equatorial planes for Dst of -200 nT.

Proton trajectory simulations : Energy: 25 MeV launch: 2700 longitude. and 47.750 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.

Cutoff location model and observations: November 1997

Proton cutoff as a function of the Dst index for the november 1997 geomagnetic storm. The black trace is a straight line fit to the dataand the red trace for the protons traced in the T96 field.

c = 0.063Dst + 65.8

c = 0.053Dst + 66.1

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

Protons: 19-28 MeV (SAMPEX/PET)Protons: 19-26 MeV (SAMPEX/PET)

New belt of trapped Protons

SEP Protons Pitch angle

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.

Jovian electrons : 13 month synodic period at 1 AU

The interplanetary magnetic field modulates charged particles in the heliosphere

Jovian electrons : Evidence for source modulation

Kanekal et al, GRL 2003

Transport/Modulation effects ruled out by comparisons to IMP8 data

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 .

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.

Solar wind : plasma outflow from the Sun