Feb 1, 1985 - the 0923 UT current sheet crossing is shown at ISEE 3. The expected ... (3) At 1436 UT the onset of the second major substorm began during a ..... gur; NAQ, Narssarssuaq; ST J, St. Johns; FSE, Fort Severn; BKC,. Back; LYN ...
JOURNAL OF GEOPHYSICAL
RESEARCH, VOL. 90, NO. A2, PAGES 1175-1190, FEBRUARY 1, 1985
Dynamics of the 1054 UT March 22, 1979, Substorm Event' CDAW 6 R. L. MCPHERRON
Institute of Geophysics and Planetary Physics,Universityof California,Los Angeles R. H. MANKA
National ResearchCouncil, Washington,D.C. Centerfor SpacePhysics,Rice University,Houston, Texas
The physicalprocesses involved in the transfer of energyfrom the solar wind to the magnetosphere, and releaseassociatedwith substorms,have been examinedin a sequenceof Coordinated Data Analysis Workshops(CDAW 6). Magnetic stormsof March 22 and 31, 1979, were chosento study the problem, usinga data basefrom 13 spacecraftand about 130 ground-basedmagnetometers. This paper describes the March 22 storm,in particular the large, isolatedsubstormat 1054 UT which followed an interval of magnetic calm. We summarize the observationsin the solar wind, in various regions of the magnetosphere,and at the ground, synthesizingthese observationsinto a description of the substorm development.We then give our interpretation of these observationsand test their consistencywith the reconnectionmodel. The substorm appears to have been generated by a southward turning of the interplanetarymagneticfield associatedwith a current sheetcrossing.Models of ionosphericcurrents derivedfrom grounddata show the substormhad three phasesof development.During the first phase,a two-celled convectioncurrent system developed in the polar cap as synchronousspacecrafton the nightsiderecorded an increasinglytaillike field and the ISEE measurementsshow that the near-earth plasma sheetthinned. In the secondphase,possiblytriggeredby suddenchangesin the solar wind, a one-celledcurrent systemwas added to the first, enhancingthe westwardelectrojet.During this phasethe synchronousorbit field becamemore dipolar, and the plasma sheet magneticfield turned strongly southwardas rapid tailward flow developedsoon after expansiononset, suggestingthat a neutral line formed in the near-earth plasma sheet with subsequentplasmoid ejection. In the third phase, which occurredafter interplanetarymagneticfield turned northward, the magnetosphericcurrent systemsdecayedas the plasmasheetexpandedand the flow turned earthward.The data from this event supportthe notion that substormsinclude two major processesof energydissipation:one directly driven by the solar wind and one driven by releaseof energystoredin the geomagnetictail. The near-tail data suggestthat one or more neutral lines formed earthward of the ISEE spacecraft.However, all the signaturesof plasma flow and energeticparticles can be explained only by postulating a complex seriesof events. While this reconnectionpicture representsthe interpretationsof many of the CDAW 6 participants,it is not a consensusviewpoint.
1.
INTRODUCTION
the ionosphere as a source of plasma, and the effects of this plasma on the substormprocess,as well as the role of ionoThe Enerqy Transfer Problem sphericconductivity. The primary goal of the Coordinated Data AnalysisWorkCDAW 6 was organized by a number of researcherswithin shop(CDAW6) is to tracetheflowof energy fromthes•)lar the spacephysicscommunity in an attempt to answer some of wind through the magnetosphereto its ultimate dissipationin these questions.It consistsof an ongoing sequenceof workthe ionosphere.Magnetosphericsubstormsplay an essential shops to define the questions,contribute data, discussand role in this energy transfer and as yet are not completely analyze the data, present papers at scientific meetings, and understood.A major questionrelated to substormsis the rela- finally, contribute papers to this collection. Facilities for this tive importance of energy dissipationdirectly driven by the workshop have been provided by the National Space Science solar wind and energy dissipation driven by the release of Data Center (NSSDC), the Lockheed Palo Alto Laboratories, energy stored in the geomagnetictail. Related questionsare and the European Space Operations Center. NSSDC has prowhich solar wind, magnetospheric,or ionosphericparameters vided the computer resourcesnecessaryto assemble the dicontrol geomagneticactivity and, quantitatively, what is the versedata required by the study in a common data base, and functional relation between these parameters and various to displaythesedata in a coordinatedmanner. measures of geomagnetic activity? Physically, we need to A study of magnetosphericsubstormsrequires data from a know which processesare responsiblefor the energy transfer global distribution of magnetic observatories,and an approacrossthe magnetopause,and which processestransfer or re- priate distribution of spacecraftwithin the magnetosphereand leasethis energywithin the magnetosphere.Field-aligned cur- solar wind. The assemblyof such a data set requires cooperrents play an important role in energy transfer within the ation of many individualsfrom many different countries.The magnetosphere,but details of the global current systemsand International Magnetospheric Study (IMS, 1976-1979; data their temporal development during substorms are not yet analysis phase, 1980-1985) has provided an ideal data base completelyknown. Other important questionsare the role of from which to begin. One of its primary goals was the acquisition of data
Copyright1985by the AmericanGeophysicalUnion. Paper number 4A8223. 0148-0227/85/004A-8223$05.00
useful in studies of the solar wind
interaction
with the magnetosphere.Major components of the IMS include the magnetometernetworks in North America, Europe, and Asia, ionospheric radars, and a comprehensive suite of 1175
1176
MCPHERRON ANDMANKA'DYNAMICS OFMARCH22, 1979,SUBSTORM x •
after•Bs
before •EE 3 /
--
/
200
/ /
/ /
/ /
_
/
/ / /
lOO
/' / /
/
•tsw:
/ /
-
79 min at 320 km/sec 57 m•n at 440
km/sec
/ / / /
y•
/
I -lOO
/
ISEE 1/2
Fig. 1. Locations of spacecraftmonitoring the solar wind at 1055 UT on March 22, 1979. The orientation of the IMF before and after
the 0923 UT current sheetcrossingis shownat ISEE 3. The expected solar wind travel time from ISEE
3 to the earth is also indicated.
Purposeof This Overview
One purposeof this paper is to presenta factual overviewof the 1054 UT March 22, 1979, substorm event, as a framework
for the material in the following papers as well as any future analysisutilizing the CDAW 6 data base.Another purposeis to presentour own descriptionof the magnetosphericdynamics associatedwith these observationsand an interpretation dynamicsassociatedwith theseobservationsand an interpretation of some of the mechanismsand causesof thesedynamics. Accordingly,our paper is divided into three principal sections: (section 2) the observationsof solar wind conditions, ground magneticactivity, effectsat synchronousorbit, effects in the near tail, and details of the 1054 UT substorm expansion phaseonset,(section3) a synthesisof the observations
into a descriptionof the substormdevelopmentand associated magnetosphericdynamics,and (section4) our own discussion and interpretationof the physicalreasonsfor thesedynamics, in terms of the magneticreconnectionmodel. Thus there is an evolution from a factual summary to substorm descriptions,to personalinterpretation. Our approach is to provide this characterizationof the event basedprimarily upon magneticdata though other observationsare utilized as appropriate. Subsequentpapers in this collection are devoted to detailedconsiderationof specificaspectsof the analysis. 2.
OBSERVATIONS OF THE MARCH 22, 1979, 1054 UT
newly dedicatedand alreadyexistingspacecraftsuchas ISEE 1, 2, 3, GEOS 1, 2, and others launchedby Japan and the Soviet Union.
The Substormsof March 22, 1979
SUBSTORM
Solar Wind Conditions
The locationsof spacecraftin the solar wind at 1054 UT on March 22, 1979, are shownin Figure 1. The solar wind monitor ISEE 3 was located 230 Re upstreamof the earth, 90 Re toward the dawnside of the magnetosphere.IMP 8 was
The first step in the CDAW 6 workshopsequencewas to roughly even with the bow shock,slightly to the duskside. choosesubstormeventsfor whichall of the major IMS space- Using the geometry shown and assuming solar wind discraft were operationaland convenientlysituatedfor studiesof continuities are carried earthward with the velocity of the substorms. It was alsorequiredthat major magnetometernet- solarwind, one obtains,for example,a delay betweenISEE 3 works be appropriatelylocatedand that the substormsbe well and IMP 8 of about 50 min at 1054 UT, when the postshock definedand tractable.Initially, a number of candidateevents solar wind speedis about 470 km/s. The delay betweenIMP 8 were consideredin order to determinewhetherthey satisfied and the magnetopausewould be only a few minutes if disthe multiple selectioncriteria. Eventually, two events were continuitiesare normal to the earth-sun line. The position of chosen,the first with North America in the midnightsector the tail monitors ISEE 1 and 2 are also presentedfor later and the secondwith Europe at midnight.For both eventsthe reference.These spacecraftwere located 14 RE behind the ISEE 1 and 2 spacecraftwereapproachingthe earth through earth and somewhat toward dawn from the midnight merithe tail in the vicinity of the plasmasheet.The first period, dian. 0600-2000 UT on March 22, 1979, is a moderate, well-defined Solar wind parametersobservedat IMP 8 are compared magneticstorm precededby a day of quiet conditionsin the with the AE index in Figure 2. Prior to about 0815 UT the solar wind and magnetosphere. The three major featuresof solar wind was relatively quiet with a velocity of the order of the storm are as follows: (1) At 0826 UT a sudden storm 340km/sand a densityof 10 cm-3. The GSM Z component commencement(ssc)(or perhaps better called a sudden imof the solar wind magneticfield had been weakly southward pulse,si) occurred,becauseof a shock in the solar wind; the on severaloccasionsbut related to little observablemagnetic shock was most likely causedby a solar flare on March 19 activity in the auroral oval. At 0747:23 UT an interplanetary [Tsurutani et al., 1984]. (2) At 1054 UT the onset of the first shockpassedISEE 3, causinglarge increasesin velocity,densubstormexpansion,the primarytopic of thispaperas well as sity and magneticfield strength.This shockreachedIMP 8 at the CDAW 6 analysisto date, began. This is an excellent 0821:20 UT, and the dayside of the earth at 0826, where it exampleof an isolatedsubstormfollowingan intervalof mag- causeda sudden increaseof the low latitude magnetic field. netic calm. This substorm was associated with a 70-min interAssumingpropagation of the shock along the earth-sunline, val of stronglysouthwardinterplanetarymagneticfield(IMF). thesetimes imply a velocity of 697 km/s, which should be (3) At 1436UT the onsetof the secondmajor substormbegan compared to the solar wind velocity of 320 km/s before the during a 3-hour interval of stronglysouthwardIMF. shock and 450 km/s behind. However, taking the distance The secondevent day, 1200 UT on March 31, 1979, to 0600
UT on April 1, 1979,illustratessubstormactivitygeneratedby a long interval of moderate,but fluctuating,IMF. This event is not discussed in this paper.
betweenISEE 3 and IMP 8 and projectingit along the shock normal, the requiredvelocityis n. At/At _• 480 km/s, which is slightlyfasterthan the postshocksolar wind velocity(J. King, personal communication,1983). At 0923 UT a seconddis-
MCPHERRONAND MANKA' DYNAMICSOF MARCH 22, 1979, SUBSTORM
continuityin the solar wind passedISEE 3, producinganother increasein the interplanetary magnetic field strength and a
1177
30 20
slight enhancementin the velocity. Accompanyingthese ½' ß• changeswas a decreasein densityand a suddensouthward •. turning of the magneticfield. Theseeffectsarrived at IMP 8 •a after 1008 UT, and about 16 min thereafter the AE index
10
0 -10
began to increasefrom a low baselinelevel as currentsbegan to flow in the auroral
oval.
20
The IMF remained southward at IMP 8 for 70 min and, at
the earth, producedmagneticactivity (as measuredby the AE index) exceeding1000 nT. At 1037 UT the field began to turn
• x
'•
0
less southward at IMP 8,andby1122UT, Bzpassed through •a zero to become northward. Magnetic activity in the auroral zone reached
a maximum
at 1135 UT.
Before
AE
had
-20
re-
turnedto background, a secondand longerintervalof south-
20
ward IMF began at about 1312 UT and lasted nearly 3 hours.
Duringthisintervalthe AE indexattainedevenlargervalues •' (exceeding1500 nT). Within the interval there was a second increasein density accompaniedby a sudden northward fluctuation
of the IMF.
The arrival
of these effects at IMP
0
>-
8 was
-20
quickly followedby the onsetof a major substormexpansion.
Variationsin the IMF recordedby IMP 8 immediatelyin front of the earth are displayedin Figure 3. In addition to the Z component variations mentioned above, the X and Y componentsof the field show an important physical feature in the solar wind, namely that the initial southward turning of the IMF was correlated with a crossingof the solar wind current sheet.Prior to the crossing,the IMF had been predominantly
20 S N
0
-20
06
08
10
outward from the sun, while afterward it was inward, as
12
14
Universal
16
18
20
Time
Fig. 3. Solar wind magnetic field as observed by IMP 5O
March 22, 1979. The solar wind current sheet crossed IMP UT
4O
and 1436 UT.
Northward
fluctuations
of the IMF
8 on
8 at 1010
at 1050 UT
and 1436 UT may have triggeredmajor substormexpansions. 3O
shownsystematicallyin Figure 1. This situation persisteduntil
2O
1436 UT
10
when
the northward
fluctuation
of the IMF
men-
tioned above reached IMP 8 and the spacecraftpassedback through the current sheetinto the region of outward field. 500
GroundMagnetic Activity on March 22, 1979
The character of ground magnetic activity on March 22, 1979, is summarizedin Figure 4 by plots of magnetic indices. The top two tracesdisplay A U (eastwardelectrojet)and AL (westwardelectrojet).Both indicesbegan to changerapidly at about 1020 UT, shortly after the first southward turning of the IMF was observedat IMP 8. The gradual decreasein AL was interruptedby the onsetof a substormexpansionat 1054 UT. A secondinterruption occurredat about 1123 UT in conjunction with a major intensification.AL reached its minimum value at 1133 UT, and thereafter increased until 1330 when
400
3OO
2O
the second interval
2000 t •
' -
•
IMF
caused it to decrease
quenceof an enhancedsolarwind dynamicpressurefollowing the interplanetaryshock.This situationpersisteduntil around 1010 UT, at which time Dst began to decrease.A decreasein ASYM begansomewhatlater at about 1047 UT. Both of these
1000
0
06
of southward
once again. The Dst and AS YM indicesare plotted in the bottom two traces.After 0826 UT both indices were positive as a conse-
08
10
12
Universal
14
16
18
20
Time
indices reached minimum values at 1212 UT, about 30 min
Fig. 2. Summary of solar wind plasma parameters at IMP 8 on March 22, 1979.Top tracesshow 5-min averagesof solar wind velocity and density. Middle trace shows 1-min values of the GSM Z componentof the IMP at IMP 8. Bottom trace presentsa 55-station
after the minimum in AL. The AS YM index recoveredrapidly, reachingits baselinevalue by the start of the secondsubstorm. The Dst index recoveredmore slowly, never reaching its baseline value before it decreasedagain in association with the
AE index calculated
second substorm.
at 1 min time resolution.
1178
MCPHERRONAND MANKA' DYNAMICSOF MARCH 22, 1979, SUBSTORM 1500
...........................
The geographiclocations of magnetic observatoriesused in the CDAW 6 study are plotted in Figure 5 (for detailed locations,seethe report by Kamide et al. [1983]). The Braunschweig chain in Scandinavia and the Izmiran and Sibizmir
1 ooo
chains in western USSR
were located in the noon to afternoon
sector. The Greenland
east and west chains were located
on
the prenoon side of the earth, while the Churchill chain, the Alberta
chain
and
the Alaska
chain
were
located
between
dawn and midnight. In the North American sector the Air Force GeophysicsLaboratory (AFGL) chain extended east-
-500
west -lOOO
at
subauroral
latitudes.
At
lower
latitudes
the
mid-
latitude chain encircledthe globe between 20ø and 50ø magnetic latitude.
Effectsof the IMF were observedin the polar cap soon after the southward turning passedIMP 8. Figure 6 presentsthe dawn-dusk and noon-midnightcomponentsof the equivalent current recordedat Thule, Greenland,closeto the geomagnetic pole. At approximately 1020 UT there was a sudden increasein the sunwardcomponentof the polar cap equivalent current (dashed line in Figure 6). This disturbance indicates the onset of enhancedconvectiondriven by the solar wind. Magnetic disturbancespersistedin the polar cap until about 1210 UT, approximately 50 min after the IMF had become
-15oo
northward
at IMP
8.
A secondinterval of enhancedconvectionbeganabout 1310 UT, shortly after the IMF turned southward for the second time. As in the first interval,convectionpersistedin the polar 06
08
lO
12
14
Universal
16
18
cap 40 min after the IMF became northward.
20
The responseof polar cap stationsto the southwardturning was not instantaneous,as demonstrated in high-resolution data plotted in Figure 7. Station NORD, locatedat the poleward end of the east Greenland chain, respondedabout 7 min
Time
Fig. 4. Magnetic activity indices for March 22, 1979. The top traces show the A U and AL AS YM
indices. The bottom
traces show the
and Dst indices.
NOON ß
..
. iiii'i'i'iiiiiiiiiiii'i' -'-'.'.'.'.'...-....... ,,'" .'
,-'"ø'l•lidlatitude:
....... -. ß
'",..
.,
.
,
.:
ß
'
ß
o
ß
.,
,--"•raunsch•veig .......
";",
,.
.
;-"Izmiran
..
.
. ß
.
..
.
,.
East
,•.
.
ß
' •0:301 ,
Sibizmir
60[ "•[
40 :
•,uror',al Zone •
iGree
,.
.
80
0 ß
.
ß
'.
'-,
,.,
•-
ß
ß
'"' •,
'...,.
-...
.
'"'
.--"Alberta." o'ø •
ß ,, -...,.,.,. ß....................,.,".,
..,-' AFGL
,' ...' ..
o
..
o .,o
Fig. 5. Polar plot showingobservatorylocationsat 1100 UT. Stationsare plotted as a functionof geographiccoordinates.Observatorychainsare connectedby linesand identifiedby a descriptivename.
MCPHERRONAND MANKA' DYNAMICS OF MARCH 22, 1979, SUBSTORM
1ooo
MRRCH 22,
1979
STRTION I THULE GEOMRGNET I C LRT I TUDE
8OO
1179
-
86.8 .......
600
SUNWARD
CURRENT
DAWNWAR
D CURRENT
400
200
0
-200
-4O0
I
I
I
I
I
I
I
I
I
I
I
I
7
8
9
10
11
12
13
14
15
16
17
18
TIME
(UT)
Fig. 6. Changesin the dawn-duskpolar cap magneticfield (courtesyof H. Kroehl).
later than the end of the southward turning recorded at IMP 8. While this delay is longer than the transit time expected using the location of IMP 8 and the orientation of the IMF discontinuity,it does representa relatively rapid coupling of energyfrom the IMF into the magnetosphere.In both intervals the end of polar cap disturbanceoccursduring the recovery of the auroral zone bays(compareFigure 4 with Figure 6). Traces of the H componentfrom selectedauroral zone stations are plotted in Figures 8 and 9. These traces reveal a number of important eventsduring the 1054 UT substorm. First, the start of bay activity in the auroral oval occurred between1020 and 1022 UT, the sametime that it began in the polar cap. Second,an apparent"precursor"bay was observed in the auroral oval between 1024 and 1050 UT. Third, the
suddenonset of a major substormexpansionoccurredat stations near midnight at about 1054 UT. The end of this expansion,as evidencedby the beginningof recovery of the negativebays, was between 1132 and 1152 UT. The entire substormwas over by 1300 UT. A stackplot of mid-latitude H tracespresentedin Figure 10 1000-1030
UT
MARCH
22,
also reveals several of the important events during the 1054 UT substorm. The first and most obvious is the si at 0826 UT
which produceda large, transientincreaseat all stations.The secondwas at approximately 1030 UT, when stationsin the dusk sectorbegan to record a decreasein H. The third was at 1054 UT, when a positive bay began at Newport (NEW). The onset of this bay was observed slightly later at Boulder, Tucson and Tahiti. It reachedmaximum developmentat 1120 UT, about 15 min earlier than in the auroral zone.
Observationsat SynchronousOrbit
The locations of spacecraftwithin the magnetospherea depicted in Figure 11. Six synchronousspacecraftwere operational during the 1054 UT substorm. The SCATHA and GEOS 2 spacecraftwere located just past noon. Spacecraft 1976-059 was near dawn, GOES 2 near 0400 LT, and 1977-
007 and GOES 3 near 0145 LT. The ISEE 1 and 2 spacecraft 06-20
UT March 22, 1979
1979
20
400
15
350
NORD
10
500 o,
,,
5
250
'i
o
200
15o
-10
100
-15
50
-20
........
0
-25
i
-30
i
i
i
i_j_l
_J_
,_J__L_I I L__• I1 i
i
i
-50
i
I
i
i
-100
Universal 10:00
10.05
10:10
10:15
UNIVERSAL
10:20
10:25
10:30
TIME
Fig. 7. High-resolutionplot of polar cap magneticfield responseto southward
IMF.
Time
H
Fig. 8. Stack plot of auroral zone H components. Traces are stackedby progressivewest dipole magneticlongitude.LRV, Leirvogur; NAQ, Narssarssuaq;STJ, St. Johns; FSE, Fort Severn; BKC, Back; LYN, Lynn Lake.
1180
MCPHERRON AND MANKA: DYNAMICS OF MARCH 22, 1979, SUBSTORM
06-20
solar wind pressureincreaseand consequentmagnetospheric compression. This begansuddenlyat 0826 UT, when the interplanetary shock passedthe earth, and ended almost as suddenly at 1008 UT, when the pressuredecreasedin conjunction with the current sheetcrossingand southwardturning of the IMF. During the 1054 UT substorm there were no changes that obviouslycorrelate with effectsin the midnight sector. However, suddendecreasesin magneticfield at 1140 UT and 1220 UT probably representencounterswith plasma injected
UT March 22, 1979
N'O•/ •',,,......•,,,,,,,,,,• CMO
earlier.
•e•' TIK •_
.
•
06
12
Universal
•
18
Time
Fig. 9. Continuationof H componentstackplot. NOW, Norman Wells; FSM, Fort Smith; CWE, Cape Wellen; CCS, Cape Chelyuskin'DIK, Dixon Island; KIR, Kiruna.
were on eccentric, inbound orbits in the 0200 LT meridian, about 14 Re behind the earth. Observationsmade by GEOS 2 near local noon at 1054 UT are summarizedin Figure 12. The H componentplotted in the
top panel is approximatelyparallel to the ambientfield and recorded variations in the magnitude of the field. The most obviousfeaturein thesedata is the increasein field magnitude, followingthe suddenimpulse,whichcorresponded to a major
Magnetic observationsrecordedin the postmidnightsector by the GOES spacecraftare presentedin Figure 13. The right panel of the figure display data from GOES 3, which at 1054 UT was located near 0145 LT. The radial component (V) showsthat the magneticfield at this location began to grow more taillike almost immediately after the southward turning of the IMF. This growth acceleratedrapidly at 1045 UT, with V reachinga maximum a little before 1054 UT. At 1054 UT there was a suddenchange in the field, which then rapidly returnedto a more dipolar configuration. Changesin the synchronousmagneticfield at a later local time were similar to those at 0145 LT, but considerablydelayed.The left panel of Figure 13 indicatesthat the growth of a taillike field did not beginthere until 1040 UT. Similarly,the dipolarization was also delayed, beginning at 1110 UT. The field at both locationsreturned to quiet levelsby about 1240 UT.
The synchronousspacecraft1977-007 was also located near 0145 LT and recordedchangesin the field configurationsimilar to the GOES observations.Figure 14 displaystime series of electrondifferentialfluxes(30-300 keV), a measureof magnetic field orientation, and east-westgradient anisotropiesfor energeticprotons (ions).The electronflux showsthree distinct events. The first is a sudden dropout of energetic electron
March 22, 1979 1436
1055
SJG
FRE
BOU
TUC
NEW
TAH
HON
GUA
0600
0900
1200
Universal
1500
1800
Time
Fig. 10. Stack plot of mid-latitude H components.Plotting conventionsare the same as in Figure 8. SJG, San Juan' FRE, Fredricksburg;BOU, Boulder;TUC, Tucson'TAH, Tahiti' HON, Honolulu' WKE, Wake Island' GUA, Guam.
MCPHERRON ANDMANKA.' DYNAMICS OFMARCH 22, 1979,SUBSTORM
1181
1100 UT MARCH 22, 1979
ß IMP
j j j JJ!
8
\\\\
/
ß
%\ \
BOWSHOCK
\ \
NOMINAL MAGN ETOPAUSE
ß
/ MAGNETOPAUSE
• GOES 2
AT 11• UT
X
GOES3 1977-•7
• ISEE2 ß ISEE
Fig. 11.
1
Locations ofspacecraft inside themagnetosphere shown ata timeshortly afteronset ofthe1054 UT expansion phase.
Thusthe injected fluxesat 1035UT. The secondis the beginningof the recovery tudesgreaterthanthat of the spacecraft. comefromoutside synchronous orbit. of electron fluxes a little before 1054 UT. The third is an particles
injection of electrons beginning at 1103UT. Changes in the
orientationof the magneticfieldcalculated from the electron Observationsin the Near GeomagneticTail At thetimeof the 1054UT expansion onsettheISEE 1 and
distributionfunctionare similarto thoseat the nearbyGOES
3 spacecraft, and gradientanisotropies showthat particle 2 spacecraft wereinbound in theplasma sheet in the0200LT fluxes(afterabout1100UT) engulfthe spacecraft fromalti- meridian approximately 13to 14Rsbehindtheearth,asillustratedin Figure11. The probablegeometry of the plasma sheetshortlybeforetheonsetis depicted in Figure15.Since MARCH 22, 1979
this onsetoccurredwithin a few minutesof the time that the
earth's dipoleaxiswasexactly perpendicular to theearth-sun line,it wouldbe expected that the plasmasheetwouldbe symmetric abouttheGSM equatorial plane.However, aswe
150
demonstratebelow, the neutral sheet crossedboth ISEE
spacecraft eventhough theywerelocated wellbelow theequatorialplane(seebottompanel). Ashasbeendiscussed byMc-
100
Pherronand Russell[1983], thesecrossingswere a conse-
quence ofa southward directed solarwindvelocity vector, and theplasma sheet wasrelatively thinat expansion onset. Based on thisinformation the plasmasheetis represented asa rela-
tivelythin regiondippingbelowthe equatorial plane.At various timesduringtheexpansion phasetheISEEspacecraft were locatedcloseto one or the other of the plasmasheet boundaries.
Magneticfieldobservations at ISEE 1 are compared to solarwindand groundmagnetometer datain Figure16. A
-50
verticaldashedline drawnat 1055UT designates the time of ,
,t i
,
i
i
I
i
[
i
expansion onset. It is apparent thatshortly afterthesouth-
•
wardturningof theIMF at IMP 8 theplasmasheetbeganto move downward acrossISEE 1, causingthe B,, component to
passthrough zeroandbecome positive pointing towardthe J
:
J
•
-50
earth.Subsequently, thespacecraft entered theboundary betweentheplasma sheetandthenorthlobe(suggested by the increase in fieldmagnitude andconfirmed by plasmaobservations[Paschmann et al., this issue]and by plasmaprobe measurements utilizingthe Berkeleyelectricfield detector
06
0•8
1•3 ' 1•2 UNIVERSAL
et al., thisissue]). At about1050UT the IMF 114' 116 ' 1•8 ' 20 [Pedersen TIME
of magnetic fieldnearlocalnoonin Fig. 12. GEOS 2 observations synchronous orbit.
turnednorthwardat IMP 8, and 5 min later a majorsubstorm
expansion onsetoccurred. Effectsof thisonsetwerenot seen in theISEE 1 magnetic fielduntil1107UT, whentheneutral
1182
MCPHERRON ANDMANKA: DYNAMICS OFMARCH 22,1979, SUBSTORM 09-13 GOES
UT MARCH 22, 1979
2
GOES
3
li , ß,-r-V-T--r-r--•--•--•v--r-•--• -.r-T--r--r-t---v--. v-1054
09
i,iIi ,,iii ,,iiiIi,Ij 10
11
UNIVERSAL
Fig. 13.
12
t..... I,,,,,I,,,,,I,,,ii_
09
TIME
10
11
UNIVERSAL
12
13
TIME
GOES2 and3 observations ofmagnetic fieldatsynchronous orbitinearlymorning hours.
sheetmovedupwardacrossISEE 1 and the field was observed meridianwaslocatedjust eastof Newport,whichwasat 0300
tobepointing southward at theneutral sheet (negative Bz).
LT.
The ISEE 2 spacecraftwas situatedsomewhatlower than The azimuthallocationof the expansiononsetin the auroISEE 1 and observedexpansioneffectssomewhatearlier. ral oval is somewhat harder to locate than its central meri-
Plasmaobservations fromISEE 2 aresummarized in Figure dian.Stackplotsof the D componentfrom the Albertaand 17.At 1058UT a burstof plasmawasobserved flowingtail- College chains(notshownhere)suggest thewestward surge wardat a velocity greaterthan500km/s.Thevelocity subsid- formed westof Alberta(since theAlbertatherewasno posied to about 200 km/s until 1118UT, whenthe flow direction tive spikein the D component), but considerably eastof reversed suddently and strongearthwardflow began.This Alaska(a strong positive D spikebeganaftera 10-mindelay). flow persisted until about 1145UT. Duringthe intervalof At Sitkaa positive D spikebegannearlyimmediately afterthe predominantly tailward flow there was a brief interval of expansion onset,suggesting the surgeformedjust east of
earthwardflow(1105to 1107UT).
Onsetof 1054 U T ExpansionPhase
A carefulstudyof high-resolutiondata revealsthat the ex-
Sitka.At this time,Sitka wasnearlyin the samelocaltime meridianastheISEE,GOES,and007spacecraft.
Thelatitude oftheexpansion onset canbedetermined fairly accurately fromlatitudeprofiles.Figure21 summarizes results
pansion onsetwasmorecomplex thansuggested by thepre- obtained fromtheAlbertachain.Asindicated in thefigure, ceding discussion. Band-pass-filtered (30-200s)fluxgatemag- the westwardelectrojetinitiallyformedbetween63ø and 66ø netometerdata from the AFGL magnetometer networkdis- magnetic latitude.As timeprogressed, theequatorial edgeof played in Figure 18 indicate a Pi 2 burst at 1055 UT. How- theelectrojet driftedequatorward to about60ø,whilethepoleever, the data also show there was an intensificationof the wardedgeremained fixed.Asa resultofthisbroadening, some expansion at 1104UT (alsoseeHughesand Singer[this of the morenorthernstations, e.g.,GreatWhale(GWC in issue]). Figure8),observed an apparent recovery of negative H perThe earliestindicationof theensuing expansion onsetwas turbations. Stations farthersouth,however, observed steadily recorded at synchronous orbitbyelectron detectors onspace- increasing negative H. At thetimeof theexpansion onset,the
craft 1977-007.As illustratedin Figure 19, electronfluxes centerof the electrojet waslocatedat about63ø magnetic latitude.Subsequently, itspolewardedgeexpanded northward thesynchronous magneticfieldbeganat thistime.Thesedata as shownin Figure21. The equatorward edgecontinued to alsodemonstrate that injectionof energetic electrons at this drift southward, reaching57ø at the end of the expansion location was associatedwith the 1104 UT intensificationof phase(1120-1140UT as definedby extremain mid-latitude theexpansion phaseratherthanwiththeearlieronset[Baker magnetograms of Figure10,or in the AL indexof Figure4). et al., thisissue;Fritz et al., 1984]. After 1140UT the polewardborderagainmovedrapidly The field-alignedcurrentsystemassociated with the 1054 northward, reaching 74ø, whereit remained throughout most
began to increase at 1052UT, suggesting thatsome change in
UT expansion onset wascentered at about0300LT. Figure20 of the recoveryphase. demonstrates thisby a stackplotof theD component from A "poleward leap"[Pytteet al., 1978]of magnetic activity thesubauroral zoneAFGL chainof magnetometers. At New- apparently occurred after1140UT as magnetic activitysudport(NEW)theperturbation after1054UT isweaklypositive, denlyappearedat the highest-latitude stationsin eachof the whileat RapidCity(RPC)it is strongly negative. At stations threeNorth American magnetometer chains.Figure22 illusVictoriaandSitkawestof Newport (notshown), thepertur- tratesthis phenomenon alongthe Churchillchain(bottom bationwasmorestrongly positive. Since theexpected ADsig- panel).The lowest-latitude stationWhiteshell (WHS)began natureof the substorm currentsystem is positivewestof its recovery at 1130, while a high-latitude station Baker Lake central meridian and negativeeast, we concludethe central
(BLC)suddenlybeganrecordingactivityat 1137UT. A simi-
MCPHERRONAND MANKA: DYNAMICSOF MARCH 22, 1979, SUBSTORM LOCAL 0200
TIME 0300
107 30-
'•5 keV
,,f,,
• I05
65-95
•
95-140 I40-200
LUI0• ......
• 200-30E
I0•
>145 >170 z o i-o
ke\
>220
o...
>295 >405
--,
•
45
0
1
I
,•E
o
I i000
IlOO
ø 12oo UT
22 MARCH 1979
Fig. 14. Spacecraft1977-007observations of energeticparticlesat 0130 LT in synchronous orbit (courtesyof D. Baker).
lar phenomenon occurred on the Alaska chain where lowlatitude stationsbegan recoveryabout 1130 while the highest-
latitudestation(JOP) (not shownin the figure)beganactivity at 1135.
Figure 22 also illustrates the discrete nature of this substorm expansion.In addition to the onset at 1054 UT and the intensification
at 1104 UT there was another at 1123 UT. This
intensificationis apparent along both the Alaska chain (top panel) and the Alberta chain (middle panel),where stationsat intermediatelatitudesrecordeda suddenonsetof activity. 3.
SYNTHESIS OF THE OBSERVATIONS: SUBSTORM DEVELOPMENT AND
MAGNETOSPHERIC DYNAMICS
As stated in the introduction,one major goal of this overview is to presentthe detailed time history of the first sub-
1183
storm on March 22, 1979,as determinedfrom magneticobservations. In this sectionwe describethis history in terms of a phenomenological modelof the physicalprocesses that appear to have taken place. Subsequentpapersexaminespecificaspectsof this and later substormsin greater detail; where relevant, we referencethesepapersto strengthenour arguments. The chronology of events occurring during the 1054 UT substormon March 22, 1979,is presentedin Table 1. Significant magnetic activity on March 22, 1979, began when an interplanetaryshock [Tsurutani et al., this issue] passedthe earth.This shockcompressed the magnetopause to about 7 Re
at the subsolarpoint [Wilken et al., 1983], generatingthe initial phaseof a magneticstorm which beganwith a sudden impulse at 0826 UT. The solar wind dynamic pressureremainedhigh until about 1008UT, when a decreasein density ended the initial phase and allowed the magnetopauseto move outward again. Coincident with this decreasewas a current sheetcrossingand associatedsouthwardturning of the interplanetarymagneticfield (IMF) which apparentlyinitiated energy transfer into the magnetospherevia some process which applies a portion of the interplanetaryelectric field •icrossthe magnetosphere[Tsurutani et al., 1984]. The effect of energy transfer in the form of enhanced convection was observedthroughoutthe polar cap and auroral zone shortly later [Kroehl and Kamide, this issue].Also coincidentwith the southwardturningof the IMF wasa southwardturningof the solar wind velocity vector [McPherron and Russell, 1983], which forcedthe tail downwardbeneaththe GSM equatorial plane. This was observedin the near tail as apparentmotion of the ISEE spacecrafttoward and acrossthe neutral sheet.At the same time, the tail current began to increaseand move earthward,causingequatorwarddrift of the electrojetsand an increasinglytaillike field at synchronousorbit near 0200 LT [Baker et al., this issue;Barfieldet al., this issue]. Accompanyingthe foregoingchangeswas an apparentthinning of the plasmasheet,which at 1030 UT causedenergetic protons at synchronousorbit to begin to drop out. A complete dropout occurred10 rain later as the spacecraftGOES 3 and 1977-007passedthrough a tailward directedcurrent sheet into the tail lobe [Baker et al., this issue;Fritz et al., 1984]. ISEE 1 magnetic field observations[McPherron and Russell, 1983] also supportthe notion of plasmasheetthinning as the field magnitudeincreaseddramatically(to •60 nT), and the spacecraftmoved into a low beta plasma [Lennartssonet al., this issue]near the northern boundaryof the plasmasheet. Coincidentwith the changesin the near-tail region,the currentsin the polar cap developedinto a convection-type,twinvortex system [Clauer and Kamide, this issue]. As evident from the ratio of A U to AL (greaterthan 1) the late afternoon vortex was more pronouncedthan the early morning vortex [Kamide and Baumjohann,this issue]. As the westwardelectrojetincreasedin strength,its equatorward edge drifted southward(cf. Figure 22). This seemsto have reducedthe currentover somestations,causingan apparent recoveryof the negativebay. This recoveryhas been interpretedby someCDAW 6 participantsas an earlier substorm. Careful examination
of all available
data shows that
none of the usual indicatorsof expansiononset(Pi 2, sudden intensification, synchronous dipolarization,tail field decrease) occurredin conjunctionwith thisportion of the event. The expansionphaseof the substormmay have begun as early as 1052 UT, as is suggested by the beginningof a recovery of particlefluxesat synchronousorbit. It definitelybegan by 1054UT as a suddendipolarizationof the field had begun.
1184
MCPHERRON AND MANKA' DYNAMICS OFMARCH 22,1979, SUBSTORM DAWN-DUSK PLANE THROUGH ISEE
Z(GSM)
I J• ISEE Z
•EE,
2/,ISEE1 Vns
NOON-MIDNIGHT
MERIDIAN
PLANE
Fig.15.Inferred geometry ofplasma sheet prior toexpansion onset at1055 UT,March 22,1979. Note that positions of ISEEspacecraft relative totheplasma sheet varygreatly through theevent.
March 22, 1979
By 1055UT, a Pi 2 burstand a suddenintensification of the
westward electrojet wereseenthroughout theearlymorning
I/Boulder
sector. Thisonsetmayhavebeentriggered by thenorthward turningof theIMF andsolarwindvelocity whichbeganat IMP 8 at 1052UT. Possibly the recovery of synchronous particle fluxesat 1052UT wascaused by thechange in tail geometry brought aboutbythenorthward turning. Thecurrent system associated withtheexpansion phase was
, I0•
distinctly differentfromthe presentearlier.As canbe seenin
theauroral zonestack plot,Figure8, theeastward electrojet wasdecreasing in strength, e.g.,at Tixie Bay(TIK), when suddenly the westward electrojet increased, e.g.,at College (CMO).Asshown byClauerandKamide [thisissue] andalso byKarnide andBaurnjohann [thisissue], thenewsystem consisted ofa single cellcentered in themorning hours. Thewestward surgeassociated withthisexpansion phase formedwellinto the morningsector,eastof Sitkanear0200 LT, but westof the Alberta chainnear 0300 LT. The central meridian of theexpansion phasecurrentsystem wasat about 0300LT, as can be seenfrom perturbations in the east-west magneticfield componentat subaurorallatitudes.The ISEE
spacecraft andthetwosynchronous spacecraft (GOES3 and 1977-007)werelocatednearlyin the samemeridianand were
0
08
probably justwestofthemeridian of surgeformation. Recoveryof the synchronous magneticfieldto a moredipolarconfiguration occurred rapidlynearthe meridianof ex-
•
09
IO
11
12
13
Untversol Ttme
Fig. 16. Magneticfieldobserved in theneartail at ISEE 2.
14
pansion onset. By 1057UT, particle fluxes werebackto predropout values, andthefieldinclination haddecreased significantly. At thistimethesynchronous spacecraft 1977-007 (and presumably GOES 3) reentered the plasmasheet,sinceeast-
MCPHERRONAND MANKA' DYNAMICSOF MARCH 22, 1979, SUBSTORM
1030-1200
UT
MARCH
22,
1185
1979
Np NEO. 1
-'"'"'; ......................... •'E: '"'"" x• '""' '"" '"' :'."""" .,'.... '""""'"'"'".
•EO. 1 108
Tp •.07
TE 106 600
Vp 400 200
+200
VX-20o
1
0.5
1030
1100
1200
1130
UNIVERSAL
TIME
observed at ISEE 2 in theneartail (courtesy of G. Paschmann). Fig. 17. Plasmaparameters
west gradientsin energeticprotons show a maximum flux earthward of the spacecraftafter this time (shown in bottom
the plasma sheetmust have been extremelythin during the interval 1057-1107 UT, sincethe two ISEE spacecraftwere in
panel of Figure 14). The deviationin the east-westmagnetic field componentat GOES 3 indicatesthis as well, having nearly returned to its presubstormbaseline.At 1104 UT, a secondPi 2 burst was seenon the ground, and "dispersionless"particle injection began at 1977-007.Proton gradients indicate these new particles arrived on field lines above (or tailward of) the spacecraft.Subsequently, there was a negative perturbationin the D component,which if causedby currents on a boundary above the spacecraft,indicatesfield-aligned
regionsof lobelike magneticfield on oppositesidesof the
GOES
corded
neutral
sheet.
Effects of the 1104 UT
substorm intensification
were not
observedin the magneticfield at either ISEE spacecraft.However, it may be noteworthythat a brief interval of moderate earthwardplasmaflow was seenat ISEE 2 between1105 and 1106 UT (seeFigure 17). The recoveryphaseof the substormin the near tail began about 1118 UT. At this time the plasma flow at both ISEE spacecraft reversed,becomingstronglyearthward.Also,shortcurrents inward, toward the auroral oval. In contrastto the foregoing,the field changesin the morn- ly after this time the stationsat the equatorwardedgeof the ing sectorof synchronousorbit were considerablydelayed. auroral oval began to recover,and high-latitudestationsre2 at 0412 LT observed a continuous increase in field
inclination until 1110 UT, at which time it suddenly de-
creased.As suggested by Nagai [1982], this delay is probably a consequenceof an expansiontoward morning of the eastward edgeof the substormcurrentwedge. The first effects of the 1054 UT expansion onset were observed in the near tail at 1057:30 UT. At this time the neutral
sheetpassedupward over ISEE 2, and very rapid tailward plasmaflow was seen[Paschmann et al., this issue].This flow wasaccompaniedby a stronglysouthwardmagneticfield [McPherron and Russell, 1983]. ISEE 1, which was above the neutral sheet, also recorded a tailward flow and field fluctuations. However, when the neutral sheet crossed ISEE 1 at 1107 UT, a southward field and tailward flow were present at ISEE 1 as well. As shown by McPherron and Russell[1983],
sudden
intensifications.
At
1124
UT
there
was a
suddendecrease in the densityof H + and He + + ionsat ISEE 1, as simultaneouslythe density of O + increased.Shortly thereafter, between 1128 and 1130 UT, the magnetic field
strengthdecreasedat both ISEE spacecraft,suggestingthey were suddenlydeep inside the plasma sheet.At 1134 UT a beam of oxygenions was observedflowing outward from the ionosphere[Lennartssonet al., this issue].These changesall suggest that the plasmasheetrapidlyexpandedafter 1118UT. 4.
DISCUSSION AND INTERPRETATION
OF
THE EVENT IN TERMS OF A MODEL
There are severalpossibleprocessesthat might explain the energytransferand release,and in fact this is one of the central problemsof magnetospheric physics. The readeris invited
1186
MCPHERRONAND MANKA' DYNAMICSOF MARCH 22, 1979, SUBSTORM
sphere.As discussedby Coroniti and Kennel [1972] and Akasofu and Kan [1973], there is no reason to expect a balance SUB between the rate at which flux is transported to the tail and the rate at which it returns to the dayside. However, if these rates are not balanced,flux is eroded from the dayside and accumulatesin the tail lobes.Other consequences include increasedflaring of the magnetopause,an increasein the tail current, a more earthward location of the tail current, and plasmasheetthinning. Most of these phenomena were observed in the 1054 UT substorm of March 22, 1979. As we demonstrated above, the southward turning of the IMF was quickly followed by the 1 100 1 115 1045 beginningof magnetic perturbations characteristicof a twoeelled convection system.At the same time the auroral oval moved southward(accumulationof flux in the lobes),and the _TPA i : i _ field at synchronousorbit becamemore taillike (strengthening SUB and earthward movementof tail current).In addition, fluxesof particlesat synchronousorbit disappeared(plasmasheetthinMCL ! i ning). It is impossiblefor sucha sequenceto continueindefinitely, as the dayside would be completely eroded, or the nightside plasma sheet would be exhausted of closed field lines. Some processmust occur which speedsup the return of flux to the daysideto bring the systeminto equilibrium.The variousphenomena that occur during the expansionphaseare apparently 1100 1115 1045 UNIVERSAL TIME manifestationsof this process. It has been suggested[Russellet al., 1971; McPherron et al., Fig. 18. Pi 2 burstsrecordedalong the AFGL subauroralmagne1973] that the expansion phase is caused by the sudden retometer chain, March 22, 1979 (courtesyof H. Singer).SUB, Sudbury' MCL, Mount Clemens;CDS, Camp Douglas. lease of energy stored in the tail lobes. This processhas been referred to as an "unloading process"[Akasofu, 1979]. In the unloadingprocess,the releaseof energydrives additional curto use the material in preceding sections to draw his own rents in the westwardelectrojetand particle precipitationinto conclusions.However, in this section of the paper we will the auroral oval. Some authors have suggestedthat the undiscussand interpret these data in terms of their consistency loading processis brought about by the formation of a nearwith one possible mechanism, reconnection on the dayside earth neutral line which reconnectsthe open flux accumulated and in the tail region of the magnetosphere. in the lobes [Russell and McPherron, 1973; Nishida and RussThe observationssummarized in the precedingsection are ell, 1978]. In one versionof this model, the "plasmoid"model, well organized by a "three-phase"model of magnetospheric the neutral line is initially of limited azimuthal extent and substorms [McPherron, 1979; McPherron et al., 1973]. In this forms on closed field lines inside the plasma sheet. As dismodel a southward turning of the IMF initiates a growth cussedby Russelland McPherron [-1973], this implies a conphaseduring which the solar wind drives a sequenceof events nected pair of "x-type" and "o-type" neutral lines. Initially, culminating in an expansion phase. At the beginning of the reconnection cutsonlythedosedfieldlinesforminga bubble expansion phase there is a sudden change in many of the processesinitiated during the growth phase and a large in1052 1103.6 107 ---is106 creasein energy dissipationas measuredby particle precipi106 , 105 tation and Joule heating. The expansion phase is terminated _: : 45-65 •is 105 by a suddenintensificationof activity at high latitudes [Kisa• r i / •30-45keV -• 104 beth and Rostoker, 1971] and the beginning of a recovery 104 1o3 phase during which the various growth and expansionphase 103 phenomenadie away. lO• O 102 =----• The various magnetosphericchangeswhich occur during --I • . • .................. -,a lO 10 the growth phase can be interpreted as manifestationsof a 106 lO5 driven process[Akasofu, 1979; Baker et al., 1984; G. Rostoker 105 et al., unpublishedmanuscript, 1984]. In a driven process, lO4 various phenomena are directly linked to the solar wind and 104 lO3 respond to its changes.The fact that the processis controlled 103 lO• by the solar wind magnetic field suggeststhat reconnection 102 between it and the earth's field may be responsiblefor the 1o 10 linkage [Dunfiey, 1961]. In the reconnection model of the 1 1 driven process,magneticflux from the daysideis transported to the nightside,where it reconnectsand returns to the day10:45 10:50 10:55 11:00 11:05 11:10 11:15 UNIVERSAL TIME side. A fraction of the solar wind electric field is imposed acrossthe magnetosphereas a result of dayside reconnection Fig. 19. Onset of expansionphaseshowedby electronflux at synchronousorbit, spacecraft77-007, March 22, 1979. and drives a two-celled current system in the polar iono1055
I 104
_
ß
ß .
,
_
ß
c
_
,
ß
ß
CDS•,,m•
_
ß
MCPHERRONAND MANKA: DYNAMICSOF MARCH 22, 1979, SUBSTORM
1187
CDS
, TP
10155
14•6 i
06
09
12
15
I$
Universal Time
Fig. 20. Stackplot of D componentsfrom subauroralzone AFGL chain,at 55ø geomagneticlatitude, March 22, 1979.
of plasma (plasmoid) around the o-type neutral line. As described by Hones [1979a, hi, this processwill continue until open field lines definingthe boundariesof the plasma sheetare reconnected(also see Hones and Schindler [1979] and Hones et al. [1973]). At this time the bubble of plasma is no longer connectedto the earth, and tension in the newly merged field lines connectedto the solar wind pulls the plasmoid downstream.
There are a number of expectedconsequences of the formation of a near-earthneutral line [Nishida et al., 1981]. First, in order to form the neutral line there must be a disruption of the sheetcurrent acrossthe tail. This can be accomplishedby diverting a portion of the current into the ionosphere as a localizedsegmentof westwardcurrent. Second,an x-type neutral line requiresa region of southwardmagneticfield inside the plasma sheettailward of the neutral line. In addition, the 8O
i
i
forceson plasma flowing into the neutral line from above and below are such that plasma will be ejectedboth eastward and tailward of the neutral line with high velocity. Movement of the plasmoid away from the earth leaves behind the x-type neutral line and a very thin plasma sheet [Fairfield et al., 1981]. Reconnectionof open field lines in the tail lobes causes a decreasein field magnitude [Caan et al., 1978]. Many of these phenomenawere observedduring the 1054 UT expansion phase [Fritz et al., 1984]. Subsequentto the expansion onset there was a rapid growth of the westward electrojetin the postmidnightsector.Simultaneously,the field at synchronousorbit became more dipolar as mid-latitude observatoriesdetected the magnetic perturbations of fieldaligned currentsconnectedto this electrojet(diversionof tail current through the ionosphere).In the plasma sheeta highvelocity burst of tailward flowing plasma was observedin as-
i
i
!
i
MARCH 22, 1979 75
7O
65
6O
11025UTI Westward
55 -
Jet
Begins to Grow
Recovery
Recovery
Peak Onset Strength
Peak
Onset
ooo
Onset
Strength 6oo
7oo
UT Fig. 21. Location of the westward electrojetin Alberta as inferred from latitude profiles of magnetic perturbations (courtesyof G. Rostoker).
1188
MCPHERRONAND MANKA: DYNAMICSOF MARCH 22, 1979, SUBSTORM
-400
TABLE 1. Magnetic Chronologyfor SubstormExpansionat 1054
i 1123
Alaska
UT, March 22, 1979
øI------.c.__ .....
-800•
Time, UT
I
0410-0425 0530-0540
0613 .
1123
0747 0821
.
-400
0826
-800
0900-1000
I
1137
ß Churchill__ .,•
O-
-400
-800 10
•
0923
/.low
•""-•-,,.,._.V•., ' •.,••.- -i
1008
½ •'"'•.jf ' L'"•/• high '
11 UNIVERSAL
I
12
Event Presubstorrn Brief interval of southward IMF at ISEE 3. Another southward interval. Isolated substorm at Great Whale River and AFGL 2.
Pi
Interplanetary shockpassesISEE 3. ShockreachesIMP 8 (At = 35 min) (compareto 57 min at v = 440 km/s). sscrecordedon nightsideby AFGL chain. Equatorial edge of oval moves south 2ø. IMF turns southward (-20 nT) at ISEE 3. Simultaneouschangesin solar wind flow. SouthwardIMF reachesIMP 8 (At = 54 min). Growth
Phase
Densitydecreases from 35 to 10 cm-3. 1000-1020
13
1010-1030Field decreasesby 50 nT at GEOS 2. 1010-1100
TIME
Fig. 22. High-latitude intensificationsof expansion,westwardelectrojet, March 22, 1979 (courtesyof G. Rostoker).
1020-1022
1024 1025
sociationwith a very strongpulseof southwardfield (implying tailward motion of a plasmoid). In fact, from the Berkeley electricfield data, in conjunctionwith the magneticfield and plasma data, there is clear evidencethat a plasmoid passed ISEE at about 1058 UT [Manka and Mozer, 1984]. Subsequently, lower velocity and a more weakly southward field were observedfor almost 20 min. Also, particle injection was observedat synchronousorbit. During this time the tail current sheet was extremely thin, and the central plasma sheet was not observedby either spacecraft(reconnectionof lobe field linesby stablenear-earthneutral line). Unloading of energy from the tail lobes must eventually cease,or come into equilibrium with the rate at which energy is tranported to the lobes by the solar wind. Otherwise,the tail lobeswould vanishduring the expansionphasejust as the daysideor nightsideclosedfield regionswould vanish during the growth phase. The end of the unloading processapparently initiates the recoveryphase. In the plasmoid model the recovery phase begins with suddentailward motion of the near-earth neutral line. As the neutral line passesthe near-earth spacecraft,there is a sudden reversalof flow direction and expansionof the plasma sheetat the spacecraftas they move into the closedfield region earthward of the neutral line [Forbes et al., 1981]. The tailward motion of the neutral line is projectedonto the ionosphereas a rapid poleward movement of auroral and magneticactivity [Pytte et al., 1978]. Subsequently,activity dies away as the currentsdriven by the unloadingand driven processes decay. These recovery phase phenomena were also observed during the 1054 UT substorm, although not as smoothly as suggestedby the model. A reversalof the plasma sheetflow at 1118 UT suggeststhe neutral line moved tailward of the ISEE spacecraftat this time. The intensificationof magneticactivity at higher latitudes at 1123 UT supports this interpretation. However, the suddenappearanceof magneticactivity at highest latitude did not occur until after 1135 UT, suggestingthe neutral line made its final retreat to the deep tail at this time. During the CDAW 6 workshop a number of problemswith the foregoinginterpretation were noted and alternative explanations considered.For example, Heikkila [1983] suggested that the precursor bay (1024-1045 UT) is an indication of an
1150 1152
earlier substormexpansiononsetand that there was no
1210
1028 1034:20 1037
Neutral
1038:40 1042 1050 1051
Neutral
sheet crosses down over ISEE
1.
IMP beginsto turn northward. sheet crosses down over ISEE
2.
Isolated bay reachesminimum and recovers. ISEE 1 appearsto reach north lobe. IMF briefly rotates northward at IMP 8. Expansion Onset
1054 1055
1055-1056
1057:30
Expansion onset,GOES 3 dipolarization. Beginground Pi 2 and positivebay at Fredricksburg. Suddenintensificationof negativebay at Meanook (eastof NEW near 0230 LT). ExpansionPhase Neutral sheetpassesupward over ISEE 2 (B:is southward below neutral sheet).Beginvery strongtailward flow at ISEE 2.
1058:30 1059
1104 1105-1107
ISEE 2 near lower plasmasheetboundary,suddenly recordsa 55-nT southwardB:. ISEE 2 nearly enterssouthlobe. Tailward flow appearsat ISEE 1 near upper plasma sheetboundary Particle injectionat spacecraft1977-007.Surgeappearsto have reachedCollege. Brief interval of apparent earthward flow at both ISEE.
1106:40 1107:30
1110
Neutral sheetpassesupward over ISEE 1 (B•is southward below neutral sheet). ISEE 1 near lower plasma sheetboundary. Dipolarizationof field completeat GOES 3. B• begins to increase at both ISEE.
1111
1115 1117-1118 1122 1123 1125 1129 1131-1133
1137
growth phase before the1054UT expansion onset. However,1300 1215 as we have discussedabove, this signaturewas probably pro-
Large amplitudeE field oscillations;T = 240 s (not seenin B) at GEOS 2. Nearly simultaneousonsetof bay activity around northern auroral oval. Begin growth of taillike field at GOES 3. Neutral sheetmovesdown at ISEE 1/2. Start isolated bay in morning oval. Neutral sheetcrossesdown over ISEE 1 (doesnot reach ISEE 2). Neutral sheetcrossesup over ISEE 1.
Begin dipolarization at GOES 2. IMF beginsto turn northward at IMP 8. Earthward flow beginsat ISEE 1 and 2. IMF
becomes northward
at IMP
8.
Intensification along Alberta chain. ISEE 2 well inside of plasma sheet. B• reachesmaximum at both ISEE. ISEE 2 temporarily in south lobe. ISEE 2 well insideplasma sheet. Burst of strong earthward-downwardflow. Maximum of mid-latitude positivebays.
PolewardLeap Electrojetactivity movesto high latitudes. RecoveryPhase End plasma sheetflows. Beginrapid recoveryfrom negativebays. End polar cap convection. Begin recoveryfrom positivebays. End all bay activity.
MCPHERRONAND MANKA: DYNAMICSOF MARCH 22, 1979, SUBSTORM
ducedby movementof a narrow westwardelectrojetequatorward of the normal auroral oval. G. Rostoker (personal communication, 1983) has suggestedthat the southward field in the plasma sheet at expansion onset was created by an outward line current emanatingfrom a westwardsurgeeast of the spacecraft.Although this might explain the initial southward field, it does not explain its persistence.Ground data clearly show that the surge propagated westward, and one would expect to see a distinct reversal of the z component as it passedover the ISEE spacecraft.In fact, the field remained southward for 15 min at ISEE 2, long after the surge had moved to premidnightlocal times. Huang et al. [1983] noted that there was a brief interval of earthward flow during the interval of southwardBz (1105-1107) and this is incompatible with the proposal that a neutral line was earthward of the ISEE spacecraftuntil about 1118 UT. We note, however, that this event
followed
soon after
the
1104
UT
intensification
which caused plasma injection at synchronous orbit and might have been causedby the formation of a secondneutral line tailward of the ISEE spacecraft.Another problem noted by G. Parks (personal communication, 1983) is that the tail field
turned
northward
somewhat
versal. Such an association
earlier
than
between northward
the flow
re-
field and tail-
ward flow has been observed by others [Caan et al., 1979; Hayakawa and Nishida, 1982] and is seenin numerical simulations [Sato et al., 1983]. A possibleexplanation for this phenomenon
is that the relative
orientations
of field and flow are
very dependenton position relative to the center of a localized neutral line. Another problem discussedin some detail by Paschrnannet al. [this issue] is that the timing of the flow reversal at the two spacecraftdoes not correspond to their assumedpositionsrelative to a singleneutral line. In our view, most of thesedifficultiescan be eliminated by postulating a more complex scenario than the one given above. First, it is likely that the initial neutral line (1054 UT) was spatially localized, probably east of the ISEE spacecraft. With time, this region expandedwestwardto engulf the spacecraft (1057:30 UT). Then, an additional neutral line may have formed (1104 UT intensification), tailward of the spacecraft (earthwardflow at 1105-1107 UT), and probably centeredin a different meridian. While these changeswere occurring, the entire tail was moving upward with wavesin the neurtal sheet as a result of the changesin the solar wind flow direction. If substormbehavior is as complexas suggestedabove, then it will be difficult given the limited observationsavailable with current spacecraftto prove conclusivelythat a near-earth neutral line is the only appropriate description.Missions involving many identical spacecraft,in conjunction with high time and spaceresolution imagesof auroral development,can possibly resolvesomeof the ambiguities.
1189
craft, 2 incoherent scatter radars, and more than 130 ground magnetometersprovides an excellentresourcefor this study. The March
22 event was chosen so that ISEE
1 and 2 were in
the tail and fortuitously were inbound through the plasma sheet and neutral sheet region just at the time of substorm onset, leading to the possible identification and analysis of what appears to have been a plasmoid ejection presumably associated with near-earth
neutral
line formation.
As we have
seen,the consistencywith the general reconnectionpicture is quite good, the major drawback being the lack of a quantitative physical model which describesthe reconnectionregion sufficientlywell to predict its physical extent, the amount of energytransferred,and the resultingplasma and field properties.
Some of the significant areas of research in the CDAW 6 analysis include a detailed analysis of the solar wind shock and solar wind coupling to the magnetosphere;analysisof the sscusing ground-basedand synchronousorbit data; quantitative analysis of the amount of energy coupled into the magnetosphereduring the substorm; a numerical analysis of the global electrojets,and associatedmagneticfield variations and electricpotentials as inferrred from ground magnetometersby the Kamide-Richmond-Matsushita method; an analysisof the Joule heating in the ionosphere;a detailed study of the variation of the energeticparticle population at synchronousorbit and in the tail; and a study of the highly dynamic (in space and time) region in the tail at about 12-14 R• during substorm onset. The details of these studieswill be presentedin the following papersin this issueand in future publications. Acknowledgments. The CDAW 6 sequence of workshops have been made possibleby support from NASA through the National SpaceScienceData Center, J. I. Vette, Director. Data utilized in the workshop were acquired as part of the International Magnetospheric Study and have been funded by a variety of national agenciesin various
countries.
The
World
Data
Center
A for Solar-Terrestrial
Physics,J. H. Allen, Director, has provided a significantportion of the ground magneticdata; the computational resourcesused in modeling the magnetic data were provided by the National Oceanic and AtmosphericAdministration and the National Center for Atmospheric Research.Data presentedin this report have been provided by a number of participants and the authors gratefully acknowledgethe many contributions of these individuals. Participation of R. H. Manka in CDAW 6 has been supportedby the National Oceanic and AtmosphericAdministrationand by National Aeronauticsand Space Administration contract NAS 5-27564. The participation of R. L. McPherron has been supported by National Science Foundation grant ATM 80-20376, Office of Naval Researchgrant ONR N0001482-K-0031, and by National Aeronautics and Space Administration grant NGL 05-007-004. We would like to thank D. Baker, W. Baumjohann, G. Rostoker, and H. Singer for helpful commentson preliminary versionsof thismanuscript.This is IGPP publication2265. The Editor thanks D. N. Baker and W. Baumjohann for their assistancein evaluatingthis paper. REFERENCES
5.
SUMMARY
The objective of the CDAW 6 analysisis to better understand the transfer of energy,from the solar wind to the magnetosphere,and its releaseassociatedwith substorms.Magnetic storms on two days, March 22 and 31, 1979, have been studied, though the analysis thus far has primarily concentrated on the first substorm (1054 UT) of March 22. The March 22 storm is characterizedby consistentcorrelations between solar wind variations and magnetosphericresponse, both substormshaving strong increasesin magnetospheric currentsfollowing sustainedintervals of southward IMF. In this paper we have describedthe developmentof a relatively isolated substorm (1054 UT) in the context of the solar wind and magnetosphericconditions.The CDAW 6 data base with data from approximately 43 experimentson 13 space-
Akasofu, S.-I. (Ed.), What is a magnetosphericsubstorm?,in Dynamics of the Magnetosphere,pp. 447-460, D. Reidel, Hingham, Mass., 1979.
Akasofu,S.-I., and J. R. Kan, Some new thoughtson magnetospheric substorms,Radio Sci., 8(11), 1049, 1973. Baker, D. N., S.-I. Akasofu, W. Baumjohann, J. W. Bieber, D. H. Fairfield, E. W. Hones, Jr., B. Mauk, R. L. McPherron, and T. E. Moore, Substorms in the magnetosphere,in Solar Terrestrial Physics--Presentand Future, edited by K. Papadopoulos and D. Butler, chap. 8, NASA, Washington,D.C., 1984. Baker, D. N., T. A. Fritz, R. L. McPherron, D. H. Fairfield, Y. Kamide, and W. Baumjohann, Magnetotail energy storage and releaseduring the CDAW 6 substormanalysisintervals, J. Geophys. Res., this issue. Barfield, J. N., C. S. Lin, and R. L. McPherron, Observations of
magneticfield perturbationsat GOES 2 and GOES 3 during the March 22, 1979 substorms:CDAW 6 analysis,J. Geophys.Res., this issue.
1190
MCPHERRONAND MANKA.' DYNAMICSOF MARCH 22, 1979, SUBSTORM
Caan, M. N., R. L. McPherron, and C. T. Russell, The statistical
signatureof magnetospheric substorms, Planet.SpaceSci.,26, 269, 1978.
Caan, M. N., D. H. Fairfield, and E. W. Hones,Jr., Magnetic fieldsin flowing magnetotailplasmasand their significancefor magnetic reconnection,J. Geophys.Res.,84, 1971, 1979. Clauer, C. R., and Y. Kamide, DP 1 and DP 2 current systemsfor the March 22, 1979, substorms,J. Geophys.Res.,this issue. Coroniti, F. V., and C. F. Kennel, Changesin magnetospheric configuration during the substormgrowth phase,J. Geophys.Res., 77, 3361, 1972.
Dungey, J. W., Interplanetary magnetic fields and auroral zones,
Lennartsson,W., R. D. Sharp,and R. D. Zwickl, Substormeffectson the plasmasheetion composition on March 22, 1979(CDAW 6), J. Geophys.Res.,this issue. Manka, R. H., and F. S. Mozer, Evidencefor a plasmoid in the near-earthgeotail at substormonset(abstract),Eos Trans. AGU, 65, 1051, 1984.
McPherron, R. L., Magnetosphericsubstorms,Rev. Geophys.Space Phys.,•7(4), 657, 1979. McPherron, R. L., and C. T. Russell,CDAW-6: Changesin the tail
magneticfield duringthe 1054UT March 22, 1979substorm(abstract),Eos Trans. AGU, 64(18),287, 1983. McPherron, R. L., C. T. Russell,and M.P. Aubry, Satellitestudiesof
magnetospheric substorms on August15, 1968,9, PhenomenologiPhys. Rev. Lett., 6, 47, 1961. cal model for substorms,J. Geophys.Res., 78, 3131, 1973. Fairfield, D. H., R. P. Lepping,E. W. Hones,Jr., S. J. Bame,and J. R. Asbridge,Simultaneous measurements of magnetotaildynamicsby Nagai, T., Observedmagneticsubstormsignaturesat synchronous altitude,J. Geophys. Res.,87(A6),4405, 1982. IMP spacecraft,J. Geophys.Res.,86, 1396, 1981. Forbes, T. G., E. W. Hones, S. J. Bame, J. R. Asbridge, G. Pasch- Nishida, A., and C. T. Russell,On the expectedsignaturesof reconnectionin the magnetotail,J. Geophys. Res.,83(A8),3890,1978. mann, N. Sckopke,and C. T. Russell,Evidencefor the tailward retreat of a magneticneutral line in the magnetotailduring sub- Nishida,A., H. Hayakawa, and E. W. Hones,Jr., Observedsignatures of reconnectionin the magnetotail,J. Geophys.Res.,86(A3), 1422, storm recovery,Geophys.Res.Lett., 8(3), 261, 1981. 1981. Fritz, T. A., D. N. Baker, R. L. McPherron, and W. Lennartsson, Implicationsof the 1100 UT March 22, 1979 CDAW-6 substorm Paschmann,G., N. Sckopke, and E. W. Hones, Jr., Magnetotail plasmaobservations during the 1054 UT substormon March 22, eventfor the role of magneticreconnectionin the geomagnetic tail, 1979(CDAW 6), J. Geophys. Res.,thisissue. in Magnetic Reconnection in Spaceand LaboratoryPlasmas,Geophys.Monogr.Set.,vol. 30, editedby E. W. Hones,Jr., pp. 203-207, Pedersen,A., C. A. Cattell, C.-G. F•ilthammar,K. Knott, P.-A. Linqvist, R. H. Manka, and F. S. Mozer, Electric fields in the plasma AGU, Washington,D.C., 1984. sheetand plasmasheetboundarylayer,J. Geophys. Res.,thisissue. Hayakawa, H., and A. Nishida, Statisticalcharacteristics of plasma Pytte,T., R. L. McPherron,M. G. Kivelson,H. I. West,Jr., and E. W. flowin the magnetotail,J. Geophys. Res.,87(A1),277, 1982. Hones,Jr., Multiple-satellitestudiesof magnetospheric substorms: Heikkila, W. J., The substormwith onsetat 1035 UT, 22 March, 1979 Plasma sheet recoveryand the poleward leap of auroral zone ac(abstract),Eos Trans.AGU, 64(18),286, 1983. tivity, J. Geophys. Res.,83(All), 5256, 1978. Hones,E. W., Jr., Plasma flow in the magnetotailand its implications Russell,C. T., and R. L. McPherron, The magnetotail and substorms, for substormtheories,in Dynamicsof the Magnetosphere, editedby SpaceSci. Rev., 15, 205, 1973. S.-I. Akasofu,p. 545, D. Reidel,Hingham, Mass.,1979a. Hones,E. W., Jr., Transientphenomenain the magnetotailand their Russell,C. T., R. L. McPherron, and P. J. Coleman,Jr., Magnetic field variationsin the near geomagnetic tail associated with weak relationto substorms,SpaceSci.Rev.,23, 393, 1979b. substormactivity,J. Geophys. Res.,76(7)1823,1971. Hones, E. W., Jr., and K. Schindler,Magnetotail plasmaflow during substorms:A surveywith IMP 6 and IMP 8 satellites,J. Geophys. Sato, T., T. Hayaski, J. Walker, and M. Ashour-Abdalla,Neutral sheetcurrent interruption and field-alignedcurrent generationby Res.,84(A12), 7155, 1979. three-dimensionaldriven reconnection,Geophys.Res. Lett., 10, 221, Hones,E. W., Jr., J. R. Asbridge,S. J. Bame, and S. Singer,Substorm 1983. variations of the magnetotail plasma sheet from XsM'-' 6 Re to Tsurutani, B. T., C. T. Russell,J. H. King, R. D. Zwickl, and R. P. XsM_• -60 Re, J. Geophys. Res.,78, 109, 1973. Lin, A kinky, inclinedheliospheric currentsheet:Causeof CDAW Huang, C. Y., G. Paschmann,T. Fritz, and D. H. Fairfield, Plasma substorms,Geophys.Res.Lett., 11(4),339, 1984. observationsin the geomagnetictail at substormonset(abstract), Tsurutani,B. T., J. A. Slavin, Y. Kamide, R. D. Zwickl, J. H. King, Eos Trans. AGU, 64(18), 287, 1983. Hughes, W. J.,andH. J. Singer,Mid-latitudePi 2 pulsations, geosyn- and C. T. Russell,Coupling betweenthe solar wind and the magnetosphere:CDAW 6, J. Geophys. Res.,this issue. chronous substormonset signaturesand auroral zone currents on Wilken, B., D. N. Baker, P. R. Higbie, T. A. Fritz, W. P. Olson, and March 22, 1979: CDAW 6, J. Geophys.Res.,this issue. K. A. Pfitzer, Magnetospheric configurationand energeticparticle Kamide, Y., and W. Baumjohann,Estimation of electricfields and effectsassociatedwith the SSC on March 22, 1979 (abstract),Int. currents from International Magnetospheric Study magnetometer Assoc.Geomagn.Aeron.Bull., 48, A9, 1983. data for the CDAW 6 intervals: Implications for substormdynamics,J. Geophys.Res.,this issue. R. H. Manka, National ResearchCouncil (JH608), 2101 ConstituKamide, Y., H. W. Kroehl, B. A. Hausman, R. L. McPherron, S.-I. tion Avenue,N.W., Washington,DC 20418. Akasofu, A.D. Richmond, P. H. Reiff, and S. Matsushita, NumeriR. L. McPherron, Institute of Geophysicsand Planetary Physics, cal modeling of ionosphericparametersfrom global IMS magneUniversityof California,Los Angeles,CA 90024. tometer data for the CDAW-6 intervals,Rep. UAG-88, World Data Center A for Sol.-Terr.Phys.,Boulder,Colo., Nov. 1983. Kisabeth,J. L., and G. Rostoker,Developmentof the polar electrojet during polar magneticsubstorms,J. Geophys.Res., 76(28),6815, 1971.
Kroehl, H. W., and Y. Kamide, High-latitude indicesof electricand magneticvariability during the CDAW 6 intervals,J. Geophys. Res., this issue.
(ReceivedJune25, 1984; revisedSeptember11, 1984; acceptedSeptember11, 1984.)
