Solar Energetic Particles: A Modern Primer on Understanding Sources, Acceleration and Propagation

136 Pages·2017·6.44 MB·English

by  Donald V. Reames (auth.)

Lecture Notes in Physics 932
Donald V. Reames
Solar
Energetic
Particles
A Modern Primer on Understanding
Sources, Acceleration and Propagation
Lecture Notes in Physics
Volume 932
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Donald V. Reames
Solar Energetic Particles
A Modern Primer on Understanding Sources,
Acceleration and Propagation
DonaldV.Reames
InstituteforPhysicalScienceandTechnology
UniversityofMaryland
CollegePark,MD
USA
ISSN0075-8450 ISSN1616-6361 (electronic)
LectureNotesinPhysics
ISBN978-3-319-50870-2 ISBN978-3-319-50871-9 (eBook)
DOI10.1007/978-3-319-50871-9
LibraryofCongressControlNumber:2017935369
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Preface
It is common for scientific texts to be organized in logical rather than historical
order.Unfortunately,perhaps,naturedoesnotalwaysproceedinthatfashion.Inan
activelyevolvingfield,newideasandobservationsbuildslowly,stepbystep,often
reversing course, and a student should be prepared for this. Therefore, I have
included much of the backing and filling and the individual observations which
haveledtoourpresentunderstanding.
Inreadingthisbook,itisimportanttokeepinmindthatarealisticunderstanding
mustincorporatedifferentkindsofobservations.Nosingleinquirywillsuffice.Like
reading a murder mystery, it is normal to speculate along the way, but we must
eventuallyconsideralltheevidence,whichisnotavailableearlyinthestory.There
aremanypiecesofevidence,ofmanydifferentkinds,inthismystery.Thereisnow
a wealth of evidence on abundances of chemical elements and isotopes and their
ionizationstatesandmuchonelectrons;thereisonsettiming,radioevidence,and
thestreaminglimit;thereareinjectionprofiles,intensitydropouts,energyspectral
shapes,spectralknees,andparticlereservoirs,inadditiontothesolarassociations.
All of these help us find the origin, acceleration, distribution, and transport of the
solarenergeticparticles(affectionatelySEPs).Thishasbecomearichfield.Unlike
the murder mystery, however, our hard-won understanding also raises new ques-
tionsforfuturescientiststoaddress.
The story of SEPs is actually covered in five chapters. Chapter 1 provides a
background and an introduction to SEP properties. Chapters 2 and 3 present the
history and much of the physical evidence for the separation of impulsive and
gradual SEP events. Chapters4 and 5 consider properties of each of these classes
individually. The later chapters provide supplementary information on high ener-
giesandradiationhazardsofSEPs(Chap.6)andonSEPmeasurements(Chap.7)
andaSummaryandConclusions(Chap.8).
IhopestudentsofSEPswillenjoyreadingthisbookasmuchasIhaveenjoyed
writingit.
CollegePark,MD DonaldV.Reames
v
Acknowledgments
First,Iwouldliketothankthosescientistswhohavecontributedtheireffortstothe
progress of this field and those who have contributed the figures I have used to
illustratetheirdiscoveries.
Special thanks go to Louis Barbier, Daniel Berdichevshy, Ed Cliver, Steve
Kahler, Mary Ann Linzmayer, Chee Ng, Ron Turner, and Gary Zank for reading
and commenting on this manuscript and for helpful discussions leading to its
preparation. I would especially like to thank Chee Ng for his assistance with the
theoryofparticletransport,wavegrowth,andshockacceleration.
vii
About the Author
Born and raised in Florida, Don Reames received
his education, leading in 1964 to a PhD in
Nuclear Physics, at the University of California
at Berkeley. He then joined a group at NASA’s
Goddard Space Flight Center in Maryland using
sounding rockets and balloons to study galactic
cosmic rays and energetic particles from the Sun.
He subsequently used data from experiments on
the Gemini, IMP, ISEE, Helios, Voyager, Wind,
and STEREO missions, as well as many related
solar missions, to study those particles and their
origins more extensively. He retired from NASA
in 2003 to assume an Emeritus position but also
soonjoinedtheInstituteforPhysicalScienceandTechnologyattheUniversityof
Maryland in College Park to become a Senior Research Scientist. His honors
include the2012GeorgeElleryHalePrizefromtheSolarPhysicsDivisionofthe
American Astronomical Society for his work on the composition and transport of
solar energetic particles.
ix
Contents
1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 TheStructureoftheSun. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 TheSolarMagneticField. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 CoronalMassEjections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 InterplanetarySpace. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.5 SolarEnergeticParticles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.5.1 TimeDuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.5.2 Abundances.. . . .. . . .. . . .. . . .. . . .. . . .. . . .. . . .. 7
1.5.3 TheSolarCycle. . . .. . . . . .. . . . . . .. . . . . .. . . . . .. . 10
1.5.4 RelativisticKinematics. . . . . . . . . . . . . . . . . . . . . . . . . 11
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2 History. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1 TheFirstSEPs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.2 SolarRadioBurstsandElectrons. . . . . . . . .. . . . . . . . . . . . .. . 16
2.3 TheSpatialDistribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.3.1 DiffusionandtheBirdcageModel. . . . . . . . . . . . . . . . . 17
2.3.2 LargeScaleShockAccelerationandCMEs. . . . . . . . . . . 17
2.3.3 TheLongitudeDistribution. . . . . . . . . . . . . . . . . . . . . . 18
2.3.4 Scatter-FreeEvents. . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.3.5 Field-LineRandomWalk. . . . . . . . . . . . . . . . . . . . . . . . 19
2.4 ElementAbundances. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.4.1 FirstIonizationPotential(FIP)andA/Q. . . . . . . . . . . . . 21
2.4.2 3He-RichEvents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.4.3 TheSeedPopulation. . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.5 IonizationStates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.6 ShockTheory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.7 Disappearing-FilamentEvents. . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.8 “TheSolarFlareMyth”. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
xi
xii Contents
2.9 WaveGenerationandtheStreamingLimit. . . . . . . . . . . . . . . . . 31
2.10 SEP–CMECorrelation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3 DistinguishingtheSources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.1 SEPOnsetTimes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.2 RealisticShock-SEPTimingandCorrelations. . . . . . . . . . . . . . 42
3.3 InjectionProfiles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.4 High-EnergySpectraandSpectralKnees. . . . . . . . . . . . . . . . . . 45
3.5 IntensityDropoutsandCompactSources. . . . . . . . . . . . . . . . . . 46
3.6 Abundances. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.7 Electrons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
3.8 SEPsasProbes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4 ImpulsiveSEPEvents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.1 SelectingImpulsiveEvents. . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.2 SampleImpulsiveEvents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4.3 EnergyDependence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.4 AbundancesforZ(cid:1)26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.5 Abundancesfor34(cid:1)Z(cid:1)82. . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.6 Power-LawEnhancementsinA/Q:Source-Plasma
Temperatures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.7 Associations:CMEs,Flares,andJets. . . . . . . . . . . . . . . . . . . . . 63
4.8 CanWeHaveItBothWays?. . . . . . . . . . . . . . . . . . . . . . . . . . 67
4.9 NuclearReactions:Gamma-RayLinesandNeutrons. . . . . . . . . 68
4.10 OpenQuestions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5 GradualSEPEvents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
5.1 ParallelTransport. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
5.1.1 DiffusiveTransport. . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
5.1.2 WaveGrowth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
5.1.3 ParticleTransport. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
5.1.4 InitialAbundanceRatios. . . . . . . . . . . . . . . . . . . . . . . . 77
5.1.5 TheStreamingLimit. . . . . . . . . . . . . . . . . . . . . . . . . . . 78
5.1.6 ElectronTransport. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
5.2 AngularDistributions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
5.3 ModelsandShockAcceleration. . . . . . . . . . . . . . . . . . . . . . . . 81
5.4 ShockAccelerationInSitu. . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
5.5 AbundancesandFIP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
5.6 Source-PlasmaTemperatures. . . . . . . . . . . . . . . . . . . . . . . . . . 87
5.7 SpatialDistributionsandtheReservoir. . . . . . . . . . . . . . . . . . . 92
5.8 Non-thermalVariations:ImpulsiveVs.GradualSEPs. . . . . . . .. 95
5.9 OpenQuestions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98