energetic particles in the heliosphere and the magnetosphere shri kanekal lasp
TRANSCRIPT
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 )
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.
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
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.