Table Of ContentThe Heliosphere through the Solar Activity Cycle
Andre´ Balogh, Louis J. Lanzerotti
and Steven T. Suess
The Heliosphere
through the Solar
Activity Cycle
Published inassociationwith
PPrraaxxiiss PPuubblliisshhiinngg
Chichester, UK
Professor Andre´ Balogh Professor Louis J. Lanzerotti
The Blackett Laboratory Center for Solar–Terrestrial Research
Imperial College New Jersey Institute of Technology
London Newark
UK New Jersey
USA
Dr Steven T. Suess
National Space Science & Technology Center
NASA Marshall Space Flight Center
Huntsville
Alabama
USA
SPRINGER–PRAXIS BOOKS IN ASTRONOMY AND SPACE SCIENCES
SUBJECTADVISORYEDITOR:JohnMasonB.Sc.,M.Sc.,Ph.D.
ISBN 978-3-540-74301-9 Springer Berlin Heidelberg New York
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Contents
Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv
List of figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii
List of abbreviations and acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . xxiii
1 The heliosphere: Its origin and exploration . . . . . . . . . . . . . . . . . . . 1
1.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 The pre–space age heliosphere . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.1 The expanding hot solar atmosphere. . . . . . . . . . . . . . 2
1.2.2 Energetic particles in the heliosphere. . . . . . . . . . . . . . 5
1.3 The heliosphere and its boundaries. . . . . . . . . . . . . . . . . . . . 7
1.3.1 The size of the heliosphere . . . . . . . . . . . . . . . . . . . . 8
1.3.2 The termination shock and beyond: Voyager 1 results . . 11
1.4 Heliospheric structure and dynamics over the solar cycle. . . . . . 12
1.4.1 The solar wind through the solar activity cycle. . . . . . . 12
1.4.2 Close to solar-minimum activity: corotating interaction
regions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.4.3 Around solar-maximum activity: coronal mass ejections . 14
1.4.4 Energetic solar particles . . . . . . . . . . . . . . . . . . . . . . 15
1.4.5 Large-scale structures and the modulation of cosmic rays 16
1.5 The exploration of the heliosphere . . . . . . . . . . . . . . . . . . . . 16
1.5.1 Inner heliosphere . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.5.2 Earth-orbiting missions . . . . . . . . . . . . . . . . . . . . . . 17
1.5.3 L1 spacecraft. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.5.4 Outer heliosphere . . . . . . . . . . . . . . . . . . . . . . . . . . 18
vi Contents
1.5.5 Future heliosphere missions . . . . . . . . . . . . . . . . . . . 18
1.5.6 Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2 Solar cycle 23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2 Solar activity cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.3 Cycle 23 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.4 The extension of cycle 23 into the interplanetary medium . . . . . 31
2.5 Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.6 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3 The solar wind throughout the solar cycle . . . . . . . . . . . . . . . . . . . . 41
3.1 Introduction: the pre-Ulysses picture. . . . . . . . . . . . . . . . . . . 41
3.2 Morphology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.3 Distribution functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.3.1 H and He distribution functions . . . . . . . . . . . . . . . . 49
3.3.2 Heavy ion distribution functions . . . . . . . . . . . . . . . . 51
3.4 Composition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.4.1 Charge-state composition . . . . . . . . . . . . . . . . . . . . . 54
3.4.2 Elemental composition. . . . . . . . . . . . . . . . . . . . . . . 58
3.4.3 Correlation between composition and kinetic parameters. 61
3.5 Transients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
3.5.1 Corotating interaction regions . . . . . . . . . . . . . . . . . . 62
3.5.2 Coronal mass ejections. . . . . . . . . . . . . . . . . . . . . . . 64
3.5.3 Other transients . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
3.6 The Ulysses picture: the solar wind in four dimensions. . . . . . . 70
3.7 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
3.8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
4 The global heliospheric magnetic field. . . . . . . . . . . . . . . . . . . . . . . 79
4.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
4.2 The heliospheric magnetic field: a global perspective. . . . . . . . . 80
4.2.1 The Parker field model. . . . . . . . . . . . . . . . . . . . . . . 80
4.2.2 B and open flux. . . . . . . . . . . . . . . . . . . . . . . . . . . 84
r
4.2.3 B and the Parker spiral angle . . . . . . . . . . . . . . . . . 87
T
4.2.4 The north–south component, B . . . . . . . . . . . . . . . . 93
N
4.3 The heliospheric magnetic field at solar minimum . . . . . . . . . . 95
4.3.1 Dipole tilt, sector structure, and heliospheric current sheet 95
4.3.2 Sector structure and source surface models . . . . . . . . . 97
4.3.3 Heliospheric current sheet and plasma sheet: properties . 98
Contents vii
4.3.4 The HMF and testing of source surface models . . . . . . 101
4.4 The HMF and heliospheric structure . . . . . . . . . . . . . . . . . . 103
4.4.1 Solar and solar wind structure . . . . . . . . . . . . . . . . . 103
4.4.2 Evolution and interaction of fast and slow wind . . . . . 105
4.4.3 CIRs, shocks, and dipole tilt . . . . . . . . . . . . . . . . . . 108
4.4.4 CIRs, energetic particles, and their access to high latitudes 111
4.4.5 Corotating rarefaction regions and the spiral angle . . . . 116
4.4.6 Magnetic field strength and flux deficit . . . . . . . . . . . . 118
4.5 North–south asymmetry of the solar dipole and its solar cycle
variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
4.6 Temporal variations—coronal mass ejections . . . . . . . . . . . . . 123
4.7 HMF at solar maximum and its solar cycle variation . . . . . . . 125
4.7.1 Introduction to solar maximum and the Hale cycle . . . 125
4.7.2 Solar magnetic field at solar maximum . . . . . . . . . . . 125
4.7.3 Magnetic dipole and polarity reversal . . . . . . . . . . . . 128
4.7.4 Inclination of the HCS and solar dipole . . . . . . . . . . . 129
4.7.5 The radial component at solar maximum . . . . . . . . . . 134
4.7.6 Solar cycle variation of open flux . . . . . . . . . . . . . . . 136
4.7.7 Solar cycle variations in field magnitude . . . . . . . . . . . 138
4.8 Summary—solar cycle variations . . . . . . . . . . . . . . . . . . . . . 139
4.9 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
4.10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
5 Heliospheric energetic particle variations. . . . . . . . . . . . . . . . . . . . . 151
5.1 Energetic particle populations in the inner heliosphere . . . . . . . 151
5.2 Solar minimum orbit (1992–1998) . . . . . . . . . . . . . . . . . . . . 152
5.2.1 Summary of the Ulysses solar-minimum observations . . 154
5.2.2 Energetic particle origin, transport, and acceleration pro-
cesses in the solar-minimum inner heliosphere . . . . . . . 156
5.3 Solar maximum orbit (1998–2004). . . . . . . . . . . . . . . . . . . . . 159
5.4 Composition analyses (1990–2005) . . . . . . . . . . . . . . . . . . . . 165
5.5 Multi-spacecraft observations of SEP events: Ulysses and near-
Earth observations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
5.5.1 The Bastille flare/CME event (2000 July 14). . . . . . . . . 172
5.5.2 The 2001 September 24 event (day 267 of year) . . . . . . 175
5.6 Heliospheric energetic particle reservoirs. . . . . . . . . . . . . . . . . 179
5.7 Influence of interplanetary structures on SEP propagation. . . . . 183
5.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
5.9 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
5.10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
6 Galactic and anomalous cosmic rays through the solar cycle: New insights
from Ulysses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
6.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
viii Contents
6.1.1 Particle populations in the heliosphere . . . . . . . . . . . . 195
6.1.2 Cosmic ray modulation . . . . . . . . . . . . . . . . . . . . . . 196
6.2 Selected cosmic ray observations. . . . . . . . . . . . . . . . . . . . . . 199
6.2.1 Observations close to Earth . . . . . . . . . . . . . . . . . . . 200
6.2.2 The transport equation . . . . . . . . . . . . . . . . . . . . . . 203
6.2.3 The diffusion tensor . . . . . . . . . . . . . . . . . . . . . . . . 207
6.2.4 Solar wind, magnetic field, and the current sheet. . . . . . 208
6.2.5 Size and geometry of the heliosphere . . . . . . . . . . . . . 210
6.2.6 Termination shock and anomalous cosmic rays. . . . . . . 211
6.2.7 Local interstellar spectra. . . . . . . . . . . . . . . . . . . . . . 212
6.2.8 Cosmic ray modulation models . . . . . . . . . . . . . . . . . 213
6.2.9 Modeling the 11-year and 22-year cycles . . . . . . . . . . . 214
6.2.10 The compound modeling approach to long-term modula-
tion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
6.3 Cosmic ray distribution at solar minima . . . . . . . . . . . . . . . . 216
6.3.1 Ulysses observations at solar minimum . . . . . . . . . . . . 218
6.4 The transition from solar minimum to solar maximum. . . . . . . 224
6.4.1 Galactic cosmic rays during the 1990–2000 A>0 solar
magnetic cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
6.4.2 MeV electrons . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
6.5 Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
6.5.1 Solar minimum. . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
6.5.2 Solar maximum . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
6.5.3 Insights on particle propagation in a turbulent astro-
physical plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
6.5.4 Cosmic ray modulation surprises from Ulysses . . . . . . . 238
6.6 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
6.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
7 Overview: The heliosphere then and now. . . . . . . . . . . . . . . . . . . . . 251
7.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
7.2 The known heliosphere in 1992 . . . . . . . . . . . . . . . . . . . . . . 253
7.2.1 The solar wind and the heliospheric magnetic field . . . . 254
7.2.2 Solar wind composition and ionization state . . . . . . . . 257
7.2.3 Energetic particles and cosmic rays . . . . . . . . . . . . . . 258
7.2.4 Interstellar and interplanetary neutral gas . . . . . . . . . . 260
7.2.5 Interstellar and interplanetary dust. . . . . . . . . . . . . . . 260
7.3 The known heliosphere after a solar activity cycle with Ulysses . 261
7.3.1 The global view . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
7.3.2 Coronal and heliospheric magnetic fields . . . . . . . . . . . 264
7.3.3 Composition and ionization state. . . . . . . . . . . . . . . . 267
7.3.4 Coronal mass ejections. . . . . . . . . . . . . . . . . . . . . . . 268
7.3.5 Energetic particles. . . . . . . . . . . . . . . . . . . . . . . . . . 268
7.3.6 Cosmic rays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
Contents ix
7.3.7 The heliosphere–interstellar medium interface . . . . . . . 274
7.3.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
7.4 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
7.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
Preface
Sinceitsinaugurationin1979andlaunchin1990,thejointEuropeanSpaceAgency
(ESA)/National Aeronautics and Space Administration (NASA) solar polar
Ulysses mission has produced transformational new insights into the dynamics of
theheliosphere.Themotivationforthisbookisthedesiretoprovideauniquerecord
of the heliospheric environment through a complete 11-year solar activity cycle,
from the Sun to the orbit of Jupiter. This is now possible, thanks to opportunities
provided by observations of the Sun using ground-based techniques as well as
important vantage points in space, including the unique out-of-ecliptic orbit of
Ulysses.Thecloseconnectionbetweenthesolarcycleandthestateoftheheliosphere
is well recognized; however, the just completed solar cycle 23 resulted in much
important progress in gathering and combining solar observations and in situ
observationsinspace.AlthoughtheEditorsandcontributingauthorsofthisvolume
areassociatedprincipallywiththeUlyssesmission,thebookisintendedtoprovidea
status report on contemporary understanding of the heliosphere that has been
achieved using the many sources of data and observations available since the early
to mid-1990s.
The story of the heliosphere is longer than that of space sciences: 2007 com-
memorates50yearsofspaceresearch,butalmost100yearsofheliosphericresearch.
Heliospheric research was born of cosmic ray research that started in 1912; the
connectionofthevariationsincosmicrayintensity,aswellasassociationsofsudden
decreasesincosmicrayintensityfollowingsolarflares,wasrecognizedbeforethefirst
measurements made in space. In the first decade and more following the launch of
Sputnik during the International Geophysical Year (5 October 1957), space around
the Earth was the new frontier, ever expanding as space probes moved farther and
fartherfromtheirEarthorigin.Thewealthofdataacquiredbynumerousspacecraft
inEarthorbit,butwhichprobedthemediumbeyondtheEarth’sownvolumeofspace
(the magnetosphere), gave a more and more detailed view of the interplanetary
medium and its connection with the Sun.
xii Preface
Itwasacosmicrayphysicist,LeverettDavis,whoin1955namedthevolumeof
spacearoundtheSuntheheliosphere.Davisexpressedinthiswaytheconnectionof
thevariationsintheintensityofcosmicrays(requiringaverylargevolume,compar-
able with the solar system) to solar activity as measured by the nearly periodic
variationsinthenumberofsunspots.Theapproximately11-yearperiodicityinboth
cosmicrayintensityandsunspotnumbersstronglyhintedataconnection.Itwassome
time, however, before the connection was correctly identified: by linking the con-
stantlyoutpouringplasmafromtheSunthatformedthebluish,ionictailsofcomets
(asnotedbyBiermann)withthesupersonicallyexpandingsolaratmosphereproposed
byEugeneParkerin1958.Finally,intheearly1960sthefirstwell-instrumentedspace
probesmeasuredasolarwindanditsembeddedmagneticfieldandlaidthebasisfor
quantitatively developing the concept of the heliosphere.
Itwasanothercosmicrayphysicist,JohnSimpson,whoalreadyin1959proposed
aspacemissionthatwouldcharttheinterplanetarymediumoutsidetheplaneinwhich
theplanetscircletheSun.Heandothershadrecognizedthattheintensityofcosmic
rayscanonlybeaffectedifathree-dimensionalvolumebreathesatthesamerhythmas
theSun.ThespacemissionthatSimpsonadvocatedinthelate1950sbecameareality
when,afteralongwait,theUlyssesspaceprobewaslaunchedin1990.Beforethen,in
the1970sand1980s,there wereseveralkeyinterplanetaryspacemissions—Helios1
and 2, Pioneers 10 and 11, Voyagers 1 and 2—that paved the way to the inner and
outerheliosphere,butstillonlyclosetotheeclipticplane.Theexplorationofthethird
dimension began with Ulysses.
Overthedecades,fromtheearly20thcenturyonward,theSunhasbeenobserved
with increasingly sophisticated instruments from both Earth- and space-based tele-
scopes.The11-yearactivitycyclebecameasubjectofintenseresearchasitspotential
effectsontheEarthanditstechnologieswererecognized.ThecomplexityoftheSun,
fromitsinteriortoitsatmosphere,isnowbewildering,asistherecognitionthatmany
orevenmostkeyphysicalprocessesoperateatspatialandtemporalscalesthatmay
needfurthergenerationsofobservatories(andobservers)toresolve.Butintermsof
the phenomenology of thesolar cycle, the richnessand variety ofobservationshave
brought their fruit: the development of the ‘‘activity’’ cycle can be observed and
cataloguedfromonesolarminimumtothenextandsuccessivecyclescanbecompared
to probe the underlying causes of solar variability. The best solar observations
through this most recent activity cycle have come from the SOHO spacecraft, with
importantcontributionsfromYohkohandmanycomplementaryobservationsfrom
ever more capable ground-based facilities.
Thelastcompletesolarcycle,cyclenumber23,hasbeenthebestobserved11-year
periodintheSun’shistory.InDecember2004,justasthatcyclewasapproachingits
close,theVoyager1spacecraftcrossedthefirstouterboundaryoftheheliosphere,the
terminationshock,atabout100timesthedistanceoftheSuntoEarth.Throughout
thecycle,spacecraftclosertoEarth,suchasACEinorbitaroundLagrangePoint1of
the Sun–Earth system, as well as WIND and even the aging IMP 8 spacecraft,
provided steady streams of observations about the properties of the interplanetary
mediumneartheeclipticplane.TheUlyssesspacecraft,which,aswewrite,isaboutto
celebrateits17thlaunchanniversary,hasprovideddatacoveringmorethananentire
