VOL. 79, NO. 31
JOURNAL OF GEOPHYSICAL RESEARCH
NOVEMBER 1, 1974
Mass EjectionsFrom the Sun' A View From Skylab
J. T. GOSLING,E. HILDNER, R. M. MACQUEEN,R. H. MUNRO, A. I. POLAND,AND C. L. Ross
High Altitude Observatory,National Centerfor AtmosphericResearch,Boulder,Colorado 80303
More than 30 instances
of suddenmassejectionsfrom the sun wereobservedwith the white light
coronagraph
experiment
aboardSkylabduringthefirst 118daysof themission.Typically,theseejections
appearas largemagneticloopsrootedat the sun,yet expandingoutwardthroughthe solarcoronaat
speeds
of the orderof 400 km s-•. The loopsalwaysappearto retaintheirmagneticconnection
to thesun.
Eighteenof theseejections
wereassociated
with activeanderuptiveprominences
andsurges;
onlythree
ejections
appearto havebeenflareinitiated.Associations
withground-detected
metricwavelength
type2
and4 radio burstsoccurfor about30%of theseevents;however,ground-detected
type2 and4 radio
burstsoriginating
nearthe limb are almostinvariablyaccompanied
by coronagraph-observed
ejections.
Pressureor MHD wavesrun out ahead of the transientmaterial ejecta;at times thesewavescan be
detectedby theireffectson nearbycoronalstructures.
For oneevent,thatof August10,1973,wemakethe
followingestimates:
(1) masscontent,4 x 10•5grams;(2) massflowrate, 1.1X 10•2gramss-•; (3) energy
content,8.4 • 10aøergs;and(4) energyflow rate,7.7 X 1026
ergss-•. Locally,thisrepresents
a significant
massandenergyinputto thesolarwind;wesuggest
thattheejections
arethecoronalcounterparts
of nonrecurrent(including shocks)solar wind disturbancesdetectednear the orbit of the earth.
Chapmanand Ferraro [1931]proposedmany yearsagothat
the observed correlation between solar activity and
geomagneticand auroral activity could be explainedif solar
activity sometimesresultedin the ejectionof ionized material
from the sun. In subsequent
years,modelsof sporadicmass
ejectionsfrom the sun and their 'frozen-in' magneticfields
have beeninvokedwith varyingdegreesof success
to explain
suchthingsasthe modulationin interplanetaryspaceof galactic and solar cosmicrays [e.g., McCracken, 1962; Gosling,
1964],the excessmassand helium abundanceof major solar
wind disturbances[e.g.,Hundhausen
et al., 1970;Hirshberget
al., 1972],and the outwardmotion of type4 radio bursts[e.g.,
Smerdand Dulk, 1971]. Recent observations[e.g., Stewart et
al.• 1974; Pinter, 1973; DeMastus et al., 1973; Riddle, 1970;
thesefeatureswith a discussion
of oneevent,the massejection
of August 10, 1973.This particulareventis oneof the brightest
and bestobservedout of approximately30 genericallysimilar
onesdetectedduring the first 118 daysof the Skylabmission.
Eight framesfrom a sequenceof more than 300 exposedduring the ejectionare displayedin Figure 1. The eventis first evident at 1332 UT on August 10 as a very bright overexposed
loop of materialextendingslightlyabovethe occultingdiskon
the westlimb of the sun (Figure 1, frame A). Examinationof
pictures taken in polarized light indicates that Thomson
scatteringof photosphericlight is responsiblefor most of the
radiance detected; however, particularly bright knots of
material are perhaps seen also in Ha emission. The initial
detectionof the loop is precededby the grounddetectionof an
Tousey,1973] of the sun have confirmedthe existenceof these
eruptive prominence on the west limb at north 13 at 1255 UT.
outbursts
of material
and have established
some of their
The prominencewasvisibleto groundobservers
in both wings
characteristicfeatures.In this paper we presentsome obser- of Ha and disappearedfrom their view at approximately1355
vations of massejectionsfrom the sun taken with the High UT, some 12 min after frame B was taken. However, no unAltitude Observatory'swhite light coronagraphexperiment usual motions or changesin the coronal structureabove the
aboard Skylab. (At least 39 transient eventswere detecteddur- westlimb are apparentin the hoursprior to the time of frame
ing the first 118 days of the Skylab mission.Here the term A. In the succeeding
minutesthe leadingloop progresses
outtransientis usedto describechangesin the coronaeasilydis- ward through the corona at an apparent radial speedof 400
cernible on a time scale of tens of minutes. However, some km s-•; it also expandsduring this outward progression,ultypes of transients are undoubtedly rearrangementsof timately achievinga width exceeding3.8 Rs as the front edge
material within the corona. Here we concentrate on those
passesbeyond the field of view of the coronagraph. (The
eventsthat obviouslyrepresentthe ejectionof material from measuredspeedof the leadingloop may not be the sameasthe
the sun.)
speedof the centerof massof the structure,sincematerialmay
The coronagraphwas externallyocculted,had a band pass flow undetectedalongthe loopsand becausethe apparentmofrom 3700to 7000•, and daily for a periodof 8 months tion is probably a superpositionof an expansionand outward
provided many picturesof the solar corona from 1.5 to 6 Rs motion.) The structure'sgeneral appearanceat the time of
from suncenter.The pictures,taken in both polarizedand un- frame C is that of one or more loops rooted in the sun, the
polarizedlight, are of a qualitycomparableto that of the best loopspresumablyoutliningthe distendedmagneticfield in the
obtained at solar eclipses.Instrumentalparametersas well as structure.At this stageof the developmentthe event appears
somepreliminary resultshave beendescribedby Mac Queenet similar to the June 10, 1973, event [MacQueenet al., 1974],
al. [!974].
which also follows an eruptiveprominenceseenat the limb.
AUGUST 10, 1973, EVENT
There are a number of features common to most of the mass
ejecta detectedby the Skylab coronagraph.Here we illustrate
Retarding the outward motion of the structure are solar
gravity, magnetic tension, the back pressureof the ambient
corona (which decreaseswith increasingheight as the density
decreases),and the transfer of momentum to the ambient corona. These forces are insufficient
Copyright¸ 1974by the AmericanGeophysical
Union.
to slow the motion
of the
August 10 event as it traversesthe coronagraphfield of view.
4581
4582
GOSLING
ETAL.'.
M^SSEJECTIONS
FROM
THESUN
A
N
C
B
D
Fig. la
Fig.1. A mass
ejection
fromthesunphotographed
at 1332,
1343,
1424,
1448,
1512,
1637,
1918,
and0138UT(frames
A-H,respectively)
onAugust
10and11,1973.
Thefieldofview
ofeach
frame
issixsolar
diameters.
Thesunisobscured
by
theocculting
diskatthecenter,
whose
effective
radius
is1.$Rs.Diffraction
rings
appear
around
theperiphery
ofthisdisk,
andtheshadow
extending
downward
fromthediskiscaused
byapylon
supporting
theocculter.
Thefaintannulus
ofabout
threesolardiameters
isaninstrumental
artifact.Theverystrongradialgradient
ofcoronalradiance
hasbeenattenuated
by
vignetting
within
theinstrument
andbydodging
ofthefinalprints.
Thefaintspot
nearthebottom
offrame
C iscaused
by
spacecraftcontamination.
retainsits magnetic
connection
to thesun.
Indeed,preliminary
measurements
(Figure2) indicate
thatthe yet the structure
loopspeeds
increase
withincreasing
height;thusthematerial This connection remains intact for the duration of the event;
thelowerendsof theloopsbecome
raysprojecting
is continuallybeingdrivenoutwardby forcesfrom below. ultimately,
thiswiththe findingof
About 2 hoursafter it first appears,the leadingedgesof the almostradially(frameH). (Compare
et al. [1974,Figure1, frameD] for the June
looppassbeyond
thefieldof viewof theinstrument
(frameF), MacQueen
GOSLINGET AL.:MASSEJECTIONS
FROMTHESUN
4583
{:.;?--
N
E
H
Fig. I b
1973, event.) The magneticfield lines in these rays are tion of massflow, and the dispersionof field lines are three
stretchedto connectwith the portion of the ejectionbeyond possiblecausesfor thisgradualfadingof the rays.Thereis no
the field of view of the coronagraph.
evidence
that anyof thematerialthat entersthecoronagraph
In thelatestages
of development
th• structure
of theAugust field of view ever returnsto the sun, althoughwithout in-
10eventmustbethat of a largemagnetic
bottleextending
far homogeneities,it is difficult to ascertainin which direction the
into interplanetaryspaceand rootedto the sun, similar in material is movingalong the loops.Certainly,the outward
manyrespects
to the magneticbottlesfirstenvisioned
by Gold speedof the outermostloop exceeds
the escapevelocity(250
[1959].In the daysfollowingthe timeof frameH the rays
graduallymer•e into other structures
and disappearas
km s-') at 6 Rs.
There is a largenet increasein the overallbrightness
of the
recognizable
entities.It is not possible
to identifythemat their coronaassociated
with theAugust10ejection.The percentage
eastlimb passage12-14 dayslater. Solar rotation, the cessa- changein intensityat 1424UT abovethe equatoron the west
4584
GOSLINGET AL.: MASS EJECTIONSFROM THE SUN
5OO
outermostloop never comesinto direct contactwith this ray,
implyingthat the changesin the ray are inducedby a pressure
or MHD wave running in front of the massejection. Such a
wave ultimately must steepen into a shock, but lacking
knowledgeof the sonicand Alfv6nicspeedsin the ambientco-
400
300
rona aheadof the ejections,
we cannotye_tdetermine
whether
200
the wave is a shock at the time of these observations.At least
I00
1.0
•
20
•
3.0
I
4o
5.0
r/ro
Fig. 2. Speed of the center of the outermost loop during the
August 10, 1973,massejection.The figure assumes
that the motion is
in the plane of the sky.
three radio observatorieswere monitoring the sun at the time
of this event (Solar GeophysicalData, 1973). None of these
observatorieshave reported radio burst activity in connection
with this massejection.Thus either the wave running aheadof
the material is not a shock, or conditions favorable for the
emissionand/or ground detectionof type 2 radiation are not
present here.
limb relative to that measured at 1140 UT (before the
GENERAL CHARACTERISTICS OF MASS EJECTIONS
prominenceeruption) is shownin Figure 3. Similar resultsare
obtainedat other timesduring the eventand for other latitudes
Most of the features of the August 10, 1973, event are comon the westlimb. Thus the motions describedabove represent
mon to almost all of the massejectionsor transientsobserved
true material and field motions and are not, for example,
with the Skylab coronagraph.Here we summarizethesecommerely a seriesof compressionand rarefactionwavesrunning
mon features and mention features more rarely observed.
outward from the sun.The amount of additionalmaterialpres1. The transientsusually take the form of magnetic loops
ent in the corona at 1424 UT as well as at other times can be
expandingoutward from the sun. Oftentimes,the material is
derived from the data. Here we provide an estimate of the
concentratedin clearly distinguishedloops; for other eventsit
number of additional electronspresentat 1424 UT by assumis more diffuselyspreadoverthe entireregionwithin the loop.
ing that the material is concentratedin the plane of the sky.
2. All looplikestructuresobservedwithin the field of view
The derived estimate, which should be accurate to within 20%,
of the coronagraph(1.5-6 Rs) eventuallyescapefrom the sun;
is 2 X 1039electrons. A nearly equal number of positively
the speeds
vary from eventto event,rangingfrom about200to
charged particles should be present. If we assumethat the
greater
than
1100km s-•. We haveno evidence
to supportthe
mean massper ion is 2 X 10-•'4gram (1.2 times that per pronotion [Schatten,1970; Hundhausen,1972] that expanding
ton), then the additional mass present in the corona at 1424
,
UT is4 X 10•5grams.
If weassume
thatall thismaterial
is looplikestructuresare everstoppedby magneticforces,solar
moving at 400 km s-•, then its kinetic energyis 3.2 • 1030ergs.
The gravitational energy at 4 Rs is -1.9 X 1030erg; if we
assumea temperatureof 106øK, then the enthalpy, which is the
sumof the internal energyplusthe work donein expandingthe
gas, is 1.4 X 1030ergs.The massflow rate is approximately 1.1
X 10•' grams s-•. Rates of energyflow are 9.2 X 10•'6ergss-•
(kinetic) and 4.0 X 10•'6ergss-• (enthalpy), whereaswork is being done againstgravity at the rate of 5.4 X 10•'6ergss-•. Later
in this paper we compare thesenumberswith estimatesof the
massand energycontent of high-speedsolarwind streamsand
flare-produced shock wave disturbancesat 1 AU.
The outward progressof the August 10, 1973, massejection
has a noticeableeffect on the preexistingcoronal structures
above the west limb. Of particular interest is the changed
appearanceof the coronal ray positionedimmediatelysouthof
the massejection.This ray is pushedaside(framesB-E) as the
ejectionmovesoutward, the bend in the ray keepingpacewith
the leading edge of the ejection. We note, however, that the
4o[
20
30
40
50
r/to
gravity, radiationof energy,or transferof momentumto the
ambient corona; that is, the structuresare never observedto
move sunward. However, we cannot eliminate the possibility
that some material drains back to the sun along the lower extremities of the loops.
3. The transient loops retain their connectionto the sun. It
is difficult to find positiveevidencefor magneticreconnection
within the field of view of the coronagraph:detached, closed
loops have not yet been identified.
4. The 'roots' of the magnetic loops generally persist as
recognizableentities for severaldays following an outburst of
material. They are seldom,if ever, distinguishableat subsequent limb passages.
5.
Pressure or MHD
waves run out ahead of the material
ejecta;at times,thesewavescan be detectedby their effecton
nearby coronal structures.
6. Looplike transients are most commonly found in
associationwith eruptive and active prominencesand surges.
Eighteen of the events have known associationswith these
phenomena;however, it is unlikely that all of the transient
material observed by the coronagraph is chromosphericin
origin--a fraction probably originates in the lower corona
overlyingthe chromosphericeruption.
7. Only three of the Skylab transientsdetectedduring the
first 118 days of the mission appear to have been flare initiated. One of these, associatedwith a 2B optical flare with
strongX ray emission,had material velocitiesin excessof 980
km s-•, had associatedtype 2 and 4 radio bursts,and gaverise
to a major interplanetary disturbanceat 1 AU.
8. At least16events
occurred
inconjunction
withnoother
Fig. 3. Percentagechangein intensity above the equator on the
westlimb at 1424UT on August 10, 1973,relativeto that measuredat signsof surfaceor limb activity. It seemslikely that thesemass
1140UT; If isthe intensitymeasuredat 1424UT, andI0 is the intensity ejecta originate on the back side of the sun.
,
measured
at 1140 UT.
9.
Unusual coronal activity prior to a transient abovethe
GOSLING ET AL.: MASS EJECTIONS FROM THE SUN
TABLE 1.
Transients
and Radio Bursts During the
First
118 Days of Skylab
Transients
and
Radio
Bursts
No.
of
Events*
Events
Total
transients
observed
38(+3)
Transient
events associated with
detectedñ type 2 (only) bursts
ground-
7(+2)
Transient events associated with
detected type 4 (only) bursts
ground-
2(+1)
Transient events associated with grounddetected type 2 and 4 burst pairs
Total transient
type 2 and/or
events with ground-detected
4 burst associations
Front
Transients
associated
Transients
associated
with
Side/Back
radio
Ha event
with
radio
Ha event
3
12(+3)
Side Transients
bursts
and
(front
side
bursts
and
with
9(+2)
events)
without
3(+1)
(back side events)
24
Radio
17
events
by coronagraph
Transients
observed
the
above
burstsõ
followed
within
3 hours
association
Classesof interplanetarydisturbances. There appear to be
two distinctly different classesof nonrecurrent solar wind disturbances
observations
in
earthward direction and possibly absorbed by intervening,
denser coronal plasma [Riddle, 1974].
Summarizing, we can say that ground-detected type 2
and/or type 4 metric radio burstsfrom sourcesaway from the
central meridian were almost invariably accompanied by
coronagraph-observedtransients. The conversewas not true.
The absenceof ground-detected type 2 bursts with the majority of coronagraph-observedevents implies either (1) that
shocksusually do not form closeto the sun, where they can
generate metric wavelength bursts, or (2) that conditions
favorable for the emissionof metric type 2 radio bursts(e.g., a
wave running into a streamer) are generally not present,
and/or (3) that conditions favorable for the detection of metric
type 2 radio bursts(e.g., negligiblerefraction by the intervening corona) are generally not present.
The absenceof ground-detectedtype 4 burstswith the majority of coronagraph-observedeventsimplies that typically,
MeV particles are not accelerated in conjunction with the
events.Certainly, the geometryof most eventsis favorable for
trapping MeV particles.
DISCUSSION
Radio Bursts Followed by Transients
Total ground-detected type 2 and/or 4
burst events reported during 118 days
burst
with
4585
12(+3)
detected near 1 AU.
Disturbances
that has received the most attention
*The values in parentheses refer to possible events.
Identification
was difficult
owing to poor temporal cover-
of the first class
occur about 10 times per year at the earth and are properly called flare-produced interplanetary disturbances
[Hundhausen,1972, chapter VI]. It is this classof disturbance
in the scientific literature.
Thesedisturbancesusuallyfollow large flares(2 or greater) acage.
companied by type 2 and (less often) type 4 radio bursts.
ñ'Ground detected'
means reported
in Solar Geovh¾sical
Characteristically, their signature at 1 A U includes a shock
Data (1973).
followed later by a large helium enrichment(•>15% relative to
õThe two radio burst events lacking a transient
association followed flare and/or surge activity within 20ø of
hydrogen)[e.g., Hirshberget al., 1972] and anomalouslylow
central
meridian.
solar wind temperatures[Goslinget al., 1973; Montgomery et
al., 1972]. Energetic solar protons (•>0.5 MeV) often accomregion from which material is ejectedis difficult to detector is pany such disturbances[e.g., Kahler, 1969]. Members of the
nonexistent.For example,we are aware of no instanceswhere secondclassof disturbance,accountingfor about two thirds of
a streamer 'collapsed' prior to a mass ejection, as has been all nonrecurrent interplanetary disturbances(J. T. Gosling,
suggestedby Brueckner [1972] for a mass ejection event unpublished data, 1974) usually have none of the above
detected by the Oso 7 coronagraph.
associationsexceptthat they may have shocksat their leading
10. Table 1 showsthat the relationshipof coronagraph- edges.Their solar origin has remained obscureuntil now.
observedtransientsand ground-detectedmetric type 2 and/or
We have establishedthat most of our observedmass ejectype 4 radio burstsis not simply one to one but is more com- tions do not follow large flares. (This is true even if we allow
plicated.The sectionof Table 1 on 'radio burstsfollowedby for the possibility that severalof our back side eventsfollow
transients' shows that if the coronagraph was observing large flares on the far side of the sun.) Further, the great mashortly after a type 2 or 4 burst and if the sourcewas near the jority of mass ejections do not give rise to ground-detected
limb, a coronal transientwas observed.Thus each ground- type 2 bursts,even when they originate in favorable positions
detectedtype 2 and/or type 4 burst from near the limb was ac- relative to the earth; nor do they give rise to type 4 bursts.
companiedby a transient,but the converseis not true; that is, Thus it appears unlikely that the majority of our observed
not all transientsare accompaniedby ground-detectedtype 2 massejectionslead to the first classof solar wind disturbances
and/or type 4 bursts.
at I AU, althougha few of our eventsundoubtedlydo so. We
If the lack of a visible chromospheric event with a suggestthat the majority of our observedmass ejectionsare
coronagraph-observedtransient indicates that the transient the coronal counterparts of the second class of nonrecurrent
originated from behind the limb and if the sources of interplanetarydisturbance,whosesolar origin was previously
coronagraph-observedcoronal transientslie with equal fre- obscure.
quency in front of and behind the limb, then the sectionof TaWe can add substanceto the aboveargumentsby comparing
ble 1 on 'front side-backsidetransients'indicatesthat ground the massand energyflow in the August 10, 1973,ejectionwith
detectionof type 2 and/or type4 burstsaccompanyinga 'back that of the two classes of disturbances described above. Table
side' transient is less likely than ground detection of those 2 has beenconstructedfor this purpose.This table showsthat
burstsaccompanyinga 'front side' transient. This result is not our estimatesof the massand energycontainedwithin the field
totally unexpected because radio emission from sources of view of the coronagraphat 1424 UT are comparableto the
behind the limb is expectedto be refractedaway from the correspondingestimatesfor nonrecurrent solar wind streams,
4586
GOSLING ET AL.: MASS EJECTIONSFROM THE SUN
TABLE 2.
Mass and Energy Content
Those
of
Nonrecurrent
and Flow Rates of the August 10,
Streams
and
Flare-Produced
Mass Content,
1973, mass
at 1424 UT
Nonrecurrent
stream
solar
at
1025 ergs s-1
77ô
2.7ô
(8.4)õ
1.3
2.1
35
41
1.2
70
1AUñ
81
(140)õ
*Derived from Figures 6 and 7 of Gosling ½t •.
[1972],
although some of the streams included in that study are recur-
rent, Flow rates assumecross-section area of 3.85 x 1025 cm2.
ñFrom Hundh•u$½m [1972, p. 205].
day.
õEquivalent
Energy Flow Rate,
(6.3)õ
shock wave
at
Compared With
1 AU
1030 ergs
112
2.2
at
Energy Content,
1 AU*
Flare-produced
disturbance
Disturbances
10lO g s-1
4
wind
1973, Mass Ejection
Wave
Mass Flow Rate,
1015 g
August 10,
ejection
Shock
energy release
Content assumesflow enhancement
lasts 2 days.
Flow rates assume that major enhancements of mass and energy flux pass a point
at solar
surface;
accounts for
change in gravitation
in 1
potential.
ôAssumes
that the temperatureis 106 øKand the conductionflux is negligible; kinetic, gravitation, and enthalpy
terms
are
included.
whereas they are factors of 9 and 17 times lower than the estimates for flare-producedshockwave disturbances.Note that
the massand energyflow rates (Table 2) must decreaseby a
port provided by R. Broussard and A. Csoeke-Poeckhand for the
criticalcommentson this manuscriptprovidedby A. J. Hundhausen.
The National Aeronauticsand SpaceAdministrationhas supported
this work under contract NAS5-3950.
The National
Center for At-
factor of about 60-90 in transit from the sun to the earth if mosphericResearchis sponsoredby the National ScienceFoundation.
transient ejecta such as that of August 10, 1973, are indeed
sources of nonrecurrent
streams.
Such a reduction
should
causeno conceptual difficulties, since flow rates are not conservedquantities. We expect decreasesin the flow ratesto arise
naturally from the broadening of the disturbance with increasingheliocentric distance.
Distribution of energyflux. Finally, it is of interest to examine the way that energyis distributedamongits variousflux
The Editor thanks H. Leinbach and W. M. Neupert for their
assistancein evaluating this paper.
components(kinetic,enthalpy,gravitation,andconduction)in
the normal coronalexpansionin contrastwith the way that it
is distributedamongthesecomponentsduring the August 10,
1973, ejection.Models of the normal expansionindicatethat
the heat conductionflux and the work doneagainstgravityare
the dominanttermsin the expansionin the innercorona,being
approximatelyequal but oppositein sign [e.g., Hundhausen,
1972, p. 71]. The enthalpy flux is approximately a factor of 2
lower, and the kinetic flux is negligibly small. On the other
hand, our bestestimatesof thesevariousenergyterms at 1424
UT on August 10, 1973, are: kinetic, 3.2 X 10•øergs;gravita-
Chapman, S., and V. C. A. Ferraro, A new theory of magneticstorms,
Terr. Magn. Atmos. Elec., 36, 77-97, 1931.
DeMastus, H. L., W. J. Wagner, and R. D. Robinson, Coronal disturbances, 1, Fast transient events observedin the green coronal
emissionline during the last solar cycle, Solar Phys., 31,449-459,
tion,-1.9 X 10søerg;enthalpy,1.4 >( 10søergs;conduction,
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Acknowledgments. Many people have contributedto the successof
this program. G. A. Newkirk, Jr., and J. A. Eddy played major rolesin
the initial conceptionand designof the instrument.The experiment
was constructed,tested, and supported in the field by Ball Brothers
Research Corporation, was integrated into the Apollo telescope
mount by the Marshall Space Flight Center, and was diligently
operated by the Skylab astronaut crews and mission control team at
the JohnsonSpaceCenter.The authorsthank all thesepeoplefor their
contributions.The authorsare especiallygratefulfor the scientificsup-
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(Received May 2, 1974;
accepted July 22, 1974.)