History of solar wind and space plasma physics revisited

0.19 MB·English

by  T. E. Girish

History of solar wind and space plasma physics revisited
T. E. Girisha, G. Gopkumara, P. E. Eapenb
aDepartment of Physics, University College, Thiruvananthapuram 695034, India email: [email protected]
bDepartment of Physics, St. Gregorius College, Kottarakara 691531, Kollam, India
Abstract
3
A paper published by Scottish geophysicist J.A. Broun in 1858 contained several pioneering and remarkable ideas in
1
0solar-terrestrial physics. He could anticipate more or less correctly the nature and origin of solar wind, solar magnetic
2
fields, sunspot activity and geomagnetic storms in the middle of the 19th century. Broun applied the experimental
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aresults of the behaviour of ionised gases in discharge tubes for the first time to Space Physics which may be considered
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9as the beginning of the astrophysicalplasma physics. In this contexthe attempted to explainthe plasma interactionsof

solar wind with the comet tails and earth’s magnetosphere. Most of the postulates or hypotheses put forwardby Broun
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h
pin 1858 and later in 1874 was rediscoveredduring the 20th century, after the advent of Space age.
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tKeywords: Solar wind, Plasma physics, Solar magnetic fields, Magnetosphere, Comet tails
s
i
h
.
s1. Introduction tronomer is well known for his discoveries of semi-annual
c
i variationsingeomagneticactivity(Broun,1848)andsolar
s
y Emergence of physical ideas of solar wind and space
sources of recurrent geomagnetic storms before Maunder
h
plasma physics during the 20th century significantly con-
p
(Broun, 1876). Broun served as the director of Mather-
[
tributed to our current knowledge of planetary sciences.

stom magnetic observatory in Scotland during the years
1
The quest for the causes of aurora and associationsof the
v
1842–1848andMaharaja’sobservatoryinTrivandrumdur-
1geomagneticvariationswithsolarphenomenalikesunspots
7 ingtheyears1852–1865(Clerke,2004). Duringhisservice
9inspiredthe developmentofsolar-terrestrialphysicsinthe
1 in Trivandrum (situated near magnetic dip equator) J.A.
.18th and 19th centuries (Parker, 1989). Kristian Birke-
1 Broun wrote a remarkable paper in December 1857which
0land’s Terrella experiments (1896–1913) were considered
3 was published in Philosophical Magazine as a letter next
1as the first study of that kind in space plasma physics
: year (Broun, 1858). This was one hundred years prior to
v(Rypdal and Brundtland, 1997). Ideas of transient parti-
i the publication of the hydrodynamic theory of the solar
X
cle emission from the Sun were developed since late 19th
r wind (Parker, 1960).
acentury (Goldstein, 1881; Mitra, 1952). However continu-
Inthisarticlewewilldiscussfirstaboutthepioneering
ous solar wind flow from the Sun were actively considered
ideasofBrouncontainedintheabovepaperaboutthena-
by space physicists only during early 1950’s (Biermann,
ture andoriginof solarmagnetic fields and sunspot activ-
1951). Weneedtorevisitthepresenthistoryofsolarwind
ityatatimewhensolarphysicswasjustemergingasare-
and space plasma physics when we consider the scientific
searchdiscipline. We willalsoexplainhowBrounperhaps
contributions of John Allan Broun during the 19th cen-
opened the studies on astrophysical plasma physics when
tury.
heappliedtheexperimentalresultsofelectricityandmag-
John Allan Broun, the Scottish geophysicist and as-
netism (gas dischargetube experiments) to space physics.
Preprint submittedto Planetary Space Science January 11, 2013
The nature of solar wind type medium filling the inter- • J.A. Broun was one of the earliest proponents
planetaryspaceanditsinteractionwithplasmabodieslike of the theory of possible physical connections
comets and earth’s magnetosphere as envisaged by Broun between planetary dynamics, sunspot activity
in his paper (Broun, 1858) during the middle of 19th cen- andoriginofsolarmagneticfieldswhichwasfol-
turywillbethendiscussed. Itisinterestingtofindthatex- lowedbyothersinthe19thcentury(De La Rue and Loewy
perimentalconfirmationtoBroun’spostulates/hypotheses 1865;De La Rue, Stewart and Loewy,1872). This
in1858andlaterin1874couldbepossibleonlyduringthe is also a topic of current interest (Hung, 2007).
second half of 20th century with the advent of space age. Planetsinoursolarsystemareknowntorevolve
the sun in orbits situated close (within ten de-
2. Broun’sideasofsolarmagneticfieldsandsunspot grees)totheheliographicequator(Novotny and Fairbridge
activity in the year 1858 1967).
(iii) “page 95: If the sun act as a magnet it is possible
After the discovery of sunspot cycle (Schawabe, 1844)
fromtheanalogyofourearth,thatitsmagneticpoles
the attempts to connect sunspot activity with geomag-
will not coincide with the poles of rotation; perhaps
netic phenomena waspurely statisticalor empiricalinna-
even the poles may have unequal forces. In such a
ture and lacked physical models to support the same. In
case, it might be expected that the fact could be
ordertoexplaincertainlawsofgeomagneticvariationsob-
determined from our magnetic observations.”
served in Europe and Trivandrum, Broun proposed some
newideasaboutsunspotactivityandsolarmagneticfields • Broun’s remarkable and intuitive perception of
with some physical insight in his Philosophical Magazine the nature of large scale solar magnetic fields.
paper (Broun, 1858). The relevant portions from the text During sunspot minimum and declining phases
of the above paper will be cited below (given within in- of the sunspot cycles large scale solar magnetic
verted comas). We have given our explanatory notes in fields often resembles a tilted dipole configura-
the modern scientific perspective for each citation which tion (Shultz, 1973; Zirker, 1977). North-south
are numbered serially in the small Roman numerals. The asymmetry in the strength of solar polar mag-
page numbers refers to the original paper of Broun. netic fields and differences in the epochs of re-
versals in northern and southern helio hemi-
(i) “page 94: Does not sun act as a magnet, perhaps
spheresarewelldocumentedinthesolar-terres-
as an electromagnet, the currents forming it being
trial literature of recent times (Babcock, 1959;
within its atmosphere?”
Makarov and Makarova, 1996). Broun’s idea
• The origin of solar magnetic fields is due to an
of inferring properties of solar magnetic fields
electromagnetic induction process involving an
fromgeomagneticdataisalsoacceptableinthe
electromagnetand currentsflowing in the solar
modern cotext (Lockwood, Stamper and Wild,
atmosphere. Thiscanbeconsideredasanearly
1999; Love, Rigler and Gibson, 2012).
anticipationofdynamomodels ofastrophysical
magnetic fields by Broun.
(ii) “page 94: Are not the solar spots disruptions of the
currentduetopositionsofplanetsintheplaneofits
equator?”
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3. Beginningofastrophysicalplasmaphysics: Broun’s ourofionisedgaseslikehydrogeninelectricdis-
ideasofsolarwindanditsinteractionwithcomets charge tubes under the action of external mag-
and earth’s magnetosphere. netic fields as observedby scientists of his time
like Plu¨cker in Germany and Micheal Faraday
Studiesontheelectricdischargelampsandelectricarcs
in England (Plu¨cker, 1858).
(Crowther, 1969; Maecker, 2009) inspired the investiga-
ThisisaninterestingexampleoftheBroun’sin-
tions on the dischargeof electricity through rarefiedgases
tuitiveguessoftheinteractionofinterplanetary
in the 19th century (Thompson, 2005). This later con-
magnetic field (carried by the solar wind) with
tributedtothe developmentofatomicphysicsandplasma
thecometaryplasmaatleasthundredyearsprior
physics. J.A. Broun was perhaps the first physicist to ap-
to the satellite era during which it was experi-
ply the results of discharge tube experiments in electro-
mentally confirmed (Biermann, 1963).
magnetism to space physics which may be considered as
(v) “page 97: Is not the zodiacal light the magnetic
the beginningofastrophysicalplasmaphysics. Inthissec-
aetherinaluminousstate,repelledbythesolarmag-
tionwewilldescribeaboutthesepioneeringideasofBroun
netic poles?
published in his philosophical magazine paper
Does not zodiacal light revolve around the sun?
(Broun, 1858). As in the previous section citations of rel-
If so, what is its period of revolution?
evant passages on the above paper will be presented here
Arenottheextentandtheintensityofzodiacallight
with our brief explanatory notes.
relatedtotheperiodsofspotsasCassiniandMairan
(iv) “page96: SirJohnHerschel,Ibelievehassomewhere
supposed?”
suggested electricity as the cause which directs the
• Scientists of the 19th century invoked the idea
tail of comets.... Are not comets formed by mag-
of an ether type media filling the interplane-
netic gases? Is not the tail of the comet due to the
tary space to felicitate any kind of energy (ex-
directive action of the solar magnet, the curvature
ample: sunlight) or physical action propagat-
of the tail, sometimes seen, being due to the posi-
ing through the same. J.A. Broun also shared
tion of solar magnetic poles relatively to the path of
a similar idea to explain the physical action of
the comet? Is not the condensation of comet, when
solar magnetic fields on distant objects in in-
approachingthe sun,aphenomenonsimilarto those
terplanetarymediumsuchascometaryplasma.
observedbyDr. FaradayandM.Plu¨ckerintheir re-
If one assumes an earth like magnetic field ex-
centresearchesontheactionofthepolesofamagnet
isting on the sun with a strength around 0.4×
on certain gases or liquids?.”
10−4 T it willbe reducedto 2.5×10−17 T near
• ScientistspriortoBrounsuggestedapolarforce earth by inverse square law variations. Like
probably of electrical nature from the sun act- Mairan (1754) Broun also believed that zodi-
ing on the comet tails during its passage to- acal light is a kind of gaseous discharge from
wards the sun (Mendis, 2006). Broun proposes the sun. According to him it is a magnetic ma-
that the observed changes in the tail of comets terial filling the interplanetary space and is re-
maybeduetotheactionofextendedsolarmag- leased from the sun due to repulsive action of
neticfieldsintheinterplanetaryspace. Hecon- the solar magnetic fields. Broun also assumes
sidersthisphenomenaanalogoustothebehavi- that such a gaseous discharge co-rotates with
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sun implying that is possibly a continuous out- electronsbyJ.J.Thompsonin1897(Thompson,
flow from our star. He also suggests that the 1897). Actually cathode rays was discovered
densityoftheaboveinterplanetarymaterial(as muchearlierthroughpioneeringexperimentscar-
known from intensity and size variations of the ried by (Plu¨cker, 1858) on the action of exter-
zodiacal light). can possibly change with the nalmagneticfieldonrarefiedgasesindischarge
phase of the sunspot activity cycle. tubes. The shape of light glows in these dis-
charge tubes (Geisslers tubes) used by Plu¨cker
(vii) “page97: Fromtheknownactionofthesunongases
for the above experiments surprisingly resem-
of comets, may we not infer some action of the sun
bled the shape of earth’s magnetosphere (see
onthegasesformingourownatmosphere?... Should
Fig.1). Plu¨cker’sexperimentalresultsservedas
notthesunactingasamagnetonthemagneticgases
aninspirationtoJ.A.Brountomodeltheinter-
formingouratmosphere,andbyinductionontheter-
action of extended solar magnetic fields (prop-
restrial magnet, cause the atmosphere to assume an
agating through a gaseous ether media in in-
ellipsoidal form, having the greater axis in or near
terplanetary space as assumed by him) with
the plane of equator?... If the form which the at-
the earth’s magnetic atmosphere (or magneto-
mosphereassumed,underthe influence ofterrestrial
sphere). According to Broun the shape of the
and solar magnets, were some what irregular (as in
earth’s magnetosphere is deformed and resem-
some figures assumed by magnetic liquids, between
bles anellipsoid withgreateraxisnear the geo-
polesofamagnetasinM.Plu¨cker’sexperiments)...
magnetic equator.
• Eventhough several models of the possible in-
(viii) “page 95: Is not the case that the magnetic distur-
teractions of solar wind particles with earth’s
bances coexists always with the spots; but it is not
magnetic field were developed during the first
impossiblethatduringtheformation ofthespotsthe
half of the 20th century (see Mitra, 1952, for
disturbance is produced that is to say at the period
details) the deformation of the earth’s magne-
when the supposed discharge of the sun’s electrical
tosphere from the dipole geometry (day side
atmosphereoccurs(wordsinitalicsformpartoforig-
compression and extended magnetic tail) due
inal text).
to interaction with the continuous solar wind
• Broun makes same comments on the solar ori-
flow was not known until the spacecraft age
gin of geomagnetic storms. He suggests two
(Kivelson and Russel, 1995). But Broun could
possibilities toexplainthe observedassociation
anticipate this discoveryat leasthundredyears
between sunspot activity and magnetic storms.
priortoitsexperimentalconfirmation. Hecould
It can be related to the phenomenon of forma-
also infer that the physical mechanisms behind
tion of sunspots itself. Another possibility is
interactionofextendedsolarmagneticfields(car-
that magnetic storms in earth occurs when an
riedbythesolarwind)withcometsandearth’s
electrical discharge from the solar atmosphere
magnetic atmosphereareidenticalor similarin
occurs. ThelatersuggestionofBrounissimilar
nature.
to the model of Goldstein (1881) who assumed
It is well known that search for the physical
particle emission from sunspots as the cause of
nature of cathode rays lead to the discovery of
the observation of aurora on earth.
4
Figure1: TheGeisslertubesandglowsshownasfringetypepatternsinsidethesameusedbyPlu¨ckerinhisdischargetubeexperiments(part
ofplateIofPlu¨cker,1858)
(ix) “page 94: After a magnetic disturbance there is a time. As a visionaryhe could find striking similarities be-
diminition of force shown on earth, which remains tween interaction of solar magnetic fields with cometary
for some days as if there had been a violent action or magnetospheric plasma and ionised gas behaviour un-
with the result of loss of energy.” derexternalmagneticfieldsindischargetubeexperiments.
This perhaps opened a new branch of study ‘astrophysi-
• Geomagneticstormoccurrencesinthemid/low
calplasma physics’ surprisinglyduring the middle of 19th
latitudes is characterised by a significant de-
century.
creaseinthehorizontalcomponentoftheearth’s
Scientists of the 18th century like Mairan (1754) and
magnetic fieldlasting upto 2–3daysduring the
early 19th century like Cassini suggested that interplane-
mainphaseofsuchmagneticdisturbances. They
tary space is filled with matter of solar origin and Zodia-
are now understood to be part of large energy
cal light (now understood to be an optical phenomena in
dissipation events in the magnetosphere–iono-
earth’s atmosphere) is visible manifestation of the same.
sphere systems as a consequence of solar wind-
Broun (1858) provided a physical basis to these ideas by
magnetosphereenergycoupling(Akasofu,1981).
proposing that ‘magnetic gases’ are continuously flowing
It is quite interesting to find that Broun could
outward from the solar atmosphere to the interplanetary
anticipate long ago (in 1858) that geomagnetic
medium by the repulsive action of solar magnetic fields
storms are indeed part of a huge energy dissi-
on these gases...Later in 1874 during the discussion of
pationphenomenaintheearthenvironmentin-
Trivandrumgeomagneticobservationsheproposedather-
volving strong or violent physical interactions.
modynamical mechanism of coronal expansion to account
for the solar wind outflow from the sun which is cited be-
4. Discussion
low (Broun, 1874).
Several decades prior to the dawn of modern atomic
“I believe the facts now certainly connected with solar
physics and plasma physics, Broun could propose several andlunarmagneticactioncannotbeexplainedwithoutthe
pioneering ideas in solar-terrestrialphysics which were re-
existence of an electric medium similar to through it may
discovered during the 20th century (Table 1). J.A. Broun
be denser than in which light and heat are propagated.
was a versatile genius who could think much ahead of his
As a footnote: The idea of such a medium was sug-
5
Table1: PioneeringideasofJ.A.Brounin1858anditsrediscoveryduringthe20thcentury
Broun’s ideas Rediscovery during the 20th century
1. Natureandoriginofsolarwind(Broun,1874,with Hydrodynamic theory (Parker, 1960) Satellite ob-
additions in) servations during 1958–62
2. Sunspot activity: possible connection with plane- Shuster (1905)
tary dynamics in the solar system
3. Nature of large scale solar magnetic fields:-
(a)originduetoanelectromagneticinductionpro- Dynamo theory of Larmor (1919)
cess in the sun
(b) tilted dipole configuration (Shultz, 1973)
(c)north-southasymmetryinsolarpolarmagnetic (Babcock, 1959)
fields
4. Solar wind and IMF plasma interactions:
(a) with earth’s magnetospherecausingdistortion Explorer satellite observations
in shape (Kivelson and Russel, 1995)
(b) with comet tails Biermann (1963), Neidner and Brandt (1978),
Neidner (1982)
5. Geomagnetic storm as a significant energy dissi- Solar-windmagnetosphereenergycouplingmodels
pation phenomena in the terrestrial environment Akasofu (1981)
6
gestedbyHerchelin1843(seeforeg.Steven Ruskin,2004). Broun, J.A., 1874. Observations of Magnetic Declination made at
Itisquitepossiblethattheremaybedensermediumaround TrivandrumandAgustiaMalleyintheobservatoriesofHisHigh-
ness MaharajahofTravancore inthe years 1852to 1869, Trivan-
the sun. I have long ago suggested that the zodiacal light
drumMagneticObservations-Vol1,HenryS.KingandCompany,
is formed in this medium by the passage of electric fluid
546.
(Broun, 1858). If M. Fayes theory of the repulsive action Broun,J.A.,1878.Phil.Trans.RoySoc.Lond.166,387.
ofsolarheat,whichblowsoutthecometarygasessomany Clerke, A.M., 2004. in Anita Mc. Cound (Eds.) Oxford Dictionary
ofNational Biography,OxfordUniversityPress,London,923.
millions ofmiles couldbe assumedthe sameactionshould
Crowther,J.G.,1969.AShortHistoryofScience,TheChancerPress,
blow off a part of solar gases.”
Suffolk,UK,153.
DeLaRue,W.,Loewy, B.,1865. Proc.Roy.Soc.Lond.14,59.
DeLaRue,W.,Stewart,B.,Loewy,B.,1872.Proc.Roy.Soc.Lond.
5. Conclusions
20,210.
1. JohnAllan Broun, the Scottish geophysicistcould pro- Goldstein,S.,1881.Wiedemanne. Ann.12,266.
Hung,C.C.,2007.Apparentrelationsbetweensolaractivityandsolar
pose several pioneering hypotheses/postulates in solar
tidescausedbyplanets,NASA/TM-2007-214817,GlennResearch,
terrestrialphysicswhicharepublishedin1858and1874.
Cube,Cleveland,1.
2. Broun could suggest physical mechanisms for continu- Kivelson, M.G., Russel, C.T., 1995. Introduction to Space Physics,
CambridgeUniversityPress,NewYork,5.
ous solar wind flow and solar coronal expansion in the
Larmor,1919.Rep.Brit.Assoc.87,159.
above years.
Lockwood, M.,Stamper,B.,Wild,M.N.,1999.Nature399,437.
3. BrounwasresponsibleforthebeginningofSpacePlasma Love, J.J., Rigler, E.J., Gibson, S.E., 2012. J. Geophys. Res. 39,
Physics in the middle of 19th century when we ap- L04102, doi.10.1029/2011 GLO50702.
Maecker, J., 2009. The Electric Arc, H Popp Matlab GmbH Publi-
plied the experimental results of the behavior ionized
cation,Germany,1.
gasesindischargetubes to Spacephysics. He couldex-
Mairan,De,1754.Trait´edel’AuroreBor´eale,2ndedn,Paris,264.
plainsolarwindinteractionswithcometailsandearth’s Makarov,V.I.,Makarova,V.V.,1996. SolarPhys.163,267.
Mendis, D.A.,2006. inTsurutani, et al.(Eds.) Recurrent Magnetic
magnetospheremuchbefore theSpaceageanddawnof
Storms, Corotating Solar Wind Streams, Geophys. M Ser. 167,
plasma physics. This preceded Birkeland’s Terrella ex-
AmericanGeophysicalUnion,Washington, 31.
perimentsinlaboratoryspacephysicsbyatleastfourty
Mitra,S.K.,1952.TheUpperAtmosphere,AsiaticSocietyPublica-
years. tion,Calcutta,445.
Neidner,M.B.Jr.andBrandt,J.C.,1978.Astrophys.J.223,655.
4. Broun’s postulates about nature and origin of solar
Neidner,M.B.Jr.,1982.Astrophys.J.Supp.Ser.48,1.
magneticfields,sunspotactivityandgeomagneticstorms
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