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1. INTRODUCTIONInterplanetary coronal mass
ejections (ICME) also named ejecta cause thelargest geomagnetic
disturbances at Earth(e.g., Richardson et al., 2001). Their
effectmay be altered (enhanced or reduced) ifinstead of single
ejecta, we have a sequenceinteracting with each other. We focus on
theinterplanetary causes of two geomagneticalyactive intervals, one
during the maximum ofthe current solar cycle (March-April 2001),the
other at the maximum of cycle 21 (April1979).
The 2001 interval was dominated byactivity associated with the
largest sun spotgroup in 10 years, consisting of three ormore
active regions (ARs) centered near AR9393. For this period of
unusually intensesolar activity we discuss here energeticparticle,
radio, solar wind plasma andmagnetic field parameters observed by
theWind spacecraft. An unusual sequence offast ejecta accompanied
by a comprehensiveset of related signatures (long-lasting,intense
radio emissions, gradual solarenergetic particle (SEP)
enhancements,unusually strong magnetic fields andextreme plasma
conditions) were detected.In this paper we list the sequence
ofdisturbances during the extended interval ofMarch-April 2001. We
also compare part ofthis interval with April 1 to 7, 1979.
Thegeomagnetic response of the Dst index willbe contrasted.
2. INTERPLANETARY OBSERVATIONSFigure 1 shows the observations
at
Wind from March 26-April 26, 2001.
Solar-Heliospheric-Magnetospheric Observations on March23-April
26, 2001: Similarities to Observations in April 1979.
D. B. Berdichevsky1,2, C. J. Farrugia3, R. P. Lepping2, I. G.
Richardson4,2, A. B.Galvin3, R. Schwenn5, D. V. Reames2, K. W.
Ogilvie2, and M. L. Kaiser2
1L-3 Communications Analytics Corporation, Largo, Maryland
20774, USA2NASA Goddard Space Flight Center, Greenbelt, Maryland
20771, Mail Code 600, USA
3Space Science Center, University of New Hampshire, Durham, NH
03824, USA4Department of Astronomy, University of Maryland, College
Park, MD 20742, USA
5Max-Plank-Institut für Aeronomie, D 37191 Katlenburg-Lindau,
Germany
Abstract. We discuss the similarities and differences of two
intervals of extreme interplanetary solarwind conditions, separated
almost precisely by two solar cycles, in April 1979 and March-April
2001.The similarities extend to various data-sets: Energetic
particles, solar wind plasma and interplanetarymagnetic field. In
April 1979 observations were made by three spacecraft covering a
wide longitudinalrange (~ 70°) in the heliosphere. Data are
presented from Helios 2, located 28° East of the Sun-Earth lineat ~
2/3 AU, and from near the Earth. Observations of the 2001 interval
are from Wind. We examine thegeomagnetic activity during each
interval.
S2S1
(a)
(b)
(c)
(d)
(e)
( f )
(g)
1979/04/01-07
M C 2
H-CME
S3PP S4
1
1 0Dynamic Pressure
[nPa] (H+)
7 0
1
1 0B [nT]
Wind/mfi
7 0
- 9 0- 4 5
04 5θ
BGSE
[ ° ]
09 0
180270
φBGSE
[° ]
300
400500600700800
V
[kms-1
]Wind/swe
SS
(a)
(b)
(c)
(d)
(e)
( f )
(g)1 03
1 029 0 9 5 100 105 110 115
intensity (dB) relative to background
1 04
1 03
1 02
kHzWind/Waves
2001/03/26-04/26
M C 2
H-CME
DOY8 5
1 0-4
1 0-2
1 00
1 021 04
3 / 2 6 3 1 4 / 5 1 0 1 5 2 0 4 / 2 5
2 MeV p 2 MeV/n αααα 20 MeV p
Flux
(cm2sr s MeV/n)-1
Wind/Lemt
(cm2sr s MeV/n)
-1
Figure 1. Presented IMF and plasma observations are 5-min
averages. SEP: 2 MeV protons (black), 8 MeV α(green), and 20 MeV
protons (red) are 1-hour averages.The radio frequency spectrogram
shows 1-min averagewith color scale 0.1-20 decibels. For details
see text.
admin©2003AmericanInstituteofPhysics0-7354-0148-9/03/$20.00
admineditedbyM.Velli,R.Bruno,andF.Malara
adminCP679,
adminSolarWindTen:ProceedingsoftheTenthInternationalSolarWindConference,
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From top to bottom are plotted the totalmagnetic field and its
components in GSEcoordinates, the proton dynamic pressure(mpNpVSW),
bulk speed, SEP intensities atWind in the MeV range, and radio
signals inthe range 102−1.2 104 kHz. Theseobservations were made
while Wind wasexecuting a distant prograde orbit at (X1, Y1,Z1~) 0,
−240, 0 RE (GSE coordinates).Vertical lines in Figure 1 mark the
passageby Wind of 11 shock candidates. Solidvertical lines indicate
solar winddiscontinuities at shocks with MeV energeticparticle
enhancement, other shock passagesare marked with dashed-lines.
Another lessdistinct shocks may be present. An exampleis indicated
by the long-dashed vertical linelate on March 31. The onsets of the
SEPevents −two to three days prior to thepassage of the shock −
align with type IIIradio bursts (vertical radio
intensificationlines which are in the bottom panel).
Thoseassociated with the lift-off of five of the
CMEs that generated moderately strong SEPevents are indicated
with solid invertedtriangles between the two bottom panels.During
the interval in Figure 1, 11 haloCMEs were observed with
LASCO/SOHO,7 candidate ejecta intervals (suggested bythe slow
rotation of the IMF) may beidentified, and there were at least
3extended regions of very low, almostdisappearing solar wind plasma
(dynamicpressure was ≤ 1 nPa).
We will now focus on the periodMarch 28-April 1, 2001. During
this interval,SOHO LASCO and EIT observed signaturesof two full
halo CMEs directed towardEarth. One lifted off at ~ 1100-1200UT,
from~0° longitude on March 28, the other at~1030UT from ~ N20W19 on
March 29. Thespeed of the March 28 CME in the plane ofthe sky was
estimated at 500 km/s over thesouth pole and there was
negligibledeceleration. This CME is possiblyassociated with a flare
in AR 9397 [see e.g.,
Sun et al., 2002]. The March 29 halo CME
1
1 0
1 0 0N
p
[cm-3]
1
1 0B
[nT ]
7 0
-90-45
04 5θ
Bgse
[°]
09 0
180270
φBgse
[ ° ]
4 0 0
6 0 0
8 0 0
V
[kms-1]
1 0-2
1 00
1 02
3 / 3 0 4 / 1
2MeV H8MeV He20MeV H
Flux
(E str s n)-1
DAY (Mar 30-Apr 1, 2001)
SII
SI
(a)
(b)
(c)
(d)
(e)
( f )
(g)
2001/03/30-04/01
M C 2
H-CME
1 04
1 05
1 06 wi/swe
Lopez-expctdT
p
[K ]
SIII
0.010.1
11 0
1004 / 1ββββ
p
Wind/mfi
Wind/swe
Wind/lemt
1
1 0
100
Np
[cm-3]ISEE3-PLA
1
1 0B
[nT] ISEE3/MAG
7 0
- 9 0- 4 5
04 5
θB GSE
[° ]
09 0
180270
φBGSE
[° ]
400
600
800
V
[kms-1
]
1 0-3
1 0-1
1 01
1 03
5 6
4.2-6 MeV6 -11 MeV24-29 MeV
Flux H+
(cm2sr s MeV)
-1
IMP-8
Day (April, 1979)
S2
(a)
(b)
(c)
(d)
(e)
( f )
(g)
1979/04/04-06
M C 2
H-CME
1 04
1 05
1 06
ISEE3-PLAExpctd-Lopez
Tp[K ]
Tp
SI
Figure 2a: Observations for the period 00UT March 30 to06UT
April 1, lines are 5-min average. Starting from thetop: IMF
strength B, latitudinal, longitudinal orientationof B in GSE
coordinates, proton density Np, solar windspeed V, and proton
temperature Tp. The bottom panelscontain the intensity of 2 MeV
proton (black), 8 MeV α(blue) and 20 MeV proton (red).
Figure 2b: ISEE-3 observed for the period 06UT April4−12UT April
6, 1979, same as in Fig. 2a except thatbottom panel shows IMP-8
energetic proton chanels:4.2-6 MeV (black, higher flux), 6-10 MeV
(blue,medium), and 24-29 MeV (red, lower).
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had the much higher plane of the sky speedof ~1000 km/s with
apparently significantdeceleration. It was associated with an
X1.7flare in AR 9393. Figure 2a shows at Windthe total
interplanetary magnetic field, andcomponents in GSE coordinates,
the protondensity, bulk speed, temperature, andfinally energetic
particles in the MeV range.Figure 2a reveals two, almost
coincident,shocks, SI at 2330 UT on March 30 and SII at0111UT on
March 31. These are more clearlyidentified from the twofold
impulsive rise in
Tp panel. A third shock SIII was seen byWind 21 hours later.
What is therelationship between these three shocks andthe two halo
CMEs? Both the arrival timeand high speed of SIII at Wind exclude
anyassociation with the halo CMEs. The twofirst shocks are more
likely related to thehalo CMEs. Their proximity in time
isconsistent with the observation that thesecond halo CME twice as
fast as the firstone. Approximately six hours after theshocks SI
and SII are two distinct regions ofvery strong magnetic fields
(approximately~18 hours of ≥30 nT) of low variance, eachwith low
proton beta plasma (βp≤0.1,
illustrated in inset in Figure 2a). They areseparated by a
narrower region where thefield is weaker (10 nT at ~12-13UT)
andproton beta is high. These may be the ejectacorresponding to the
two halo CMEs. Theweakness of the first shock relative to thesecond
is in our view an indication that theejecta are in the process of
coalescing, andthe first shock in the process ofdisappearing. The
complex nature of theinterval is seen from the SEP profile
withspike at the strong shock SII and later at the
start of the first extended low βp region. A
decrease in the proton temperature (Tp) anda substantial drop in
the flux of MeVparticles help to identify the start of theejecta
interval in Figure 2a, indicated with avertical long-dashed
line.
Next we focus on a similar intervalon April 1-7 1979 in which
CMEs wereobserved in the process of overtaking eachother (Burlaga
et al., 1987), in observationsfrom Helios 2 (see Figure 3,
sameparameters as in Figure 2a). The location ofHelios 2 and 1 are
shown in Figure 4.
Helios 1 observes different solar windstreams, placing in that
way a limit to thelongitudinal extent of the ejecta observed
atEarth and Helios 2. There are at least fourshocks at Helios 2,
each preceding an ejecta.As during the March 27-April 1,
2001period, a single SEP event (associated to asun disk lift-off
location W43° (W15°) fromHelios 2 (Earth) at ~ 1100 UT on April
3,1979) was present (Richardson and Cane,1996). This was related to
the ejecta drivingshock S2. Did these ejecta observed in theinner
heliosphere eventually coalesce? Infact those associated with S2
and S3 haddone so by the time they arrived at Earth.Figure 2b shows
data from ISEE-3 (situatednear L1 point). Only one
shockcorresponding to S2 at Helios was still
1
1 0
100N
p
[cm-3]h2
24
1 0
3 0
7 0
B [nT]
h2
- 9 0- 4 5
04 5θ
SE
[ ° ]
09 0
180270
φSE
[ ° ]
300
400500600700800
V
[kms-1]
1 0-2
1 00
1 02
2 4 6
3-6 MeV6-11 MeV20-30 MeV
Flux H+
(cm2sr s MeV)-1
h2
Day [April 1979]
1979/04/01-07S1
(a)
(b)
(c)
(d)
(e)
( f )
(g)
M C 2
H-CME
1 04
1 05
1 06 PLA-Helios 2
Modfd-Lopez*
Tp
[K ]
PP S2 S3 S4Sun
Earth
H1
H2
Figure 3: Helio 2 data for the time period 12UT April 1-12UT
April 7, 1979, in the same format as in Figures 2aand 2b. The
bottom panel shows Helios 2 energeticproton chanels: 3-6 MeV (full
circles, higher flux), 6-11MeV (open squares, medium), and 20-30
MeV (fulltriangles, lower).
Figure 4. Shown are locations at approximately 68° ofHelios 1,
28° of Helios 2 on the interval April 1-9, 1979.Length of line
indicates the approximate displacement ofthe Helios spacecraft for
the interval and arrow thedirection of displacement.
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present at Earth. The disturbances in the Band V profiles are
now much attenuated.The shock S3 and a possible shock S4 atHelios
have dissipated. It is suggested thatthe ejecta passing Helios 2,
and drivingshocks S2, S3 and possibly S4 coalescedwithin about 0.3
AU downstream and 27°West of Helios 2, to form a
“complex-ejecta”,to use the terminology of Burlaga et al. 2002.
Both the March 30-April 1, 2001ISTP era events and the April
4-6, 1979Helios 2 events are related to solar CMEsthat followed in
quick succession (Sun et al.,2002; Burlaga et al., 1987).
Similarities inFigures 2a and 2b are: i) the shocks SII andS2
moving into low proton beta regions, ii)extraordinary heating and
extreme densitiesin the shocked regions, iii) sharp decrease ofthe
MeV SEP fluxes (~ 50%) at the beginningof the ejecta intervals,
indicated by verticallong-dashed line in Figures 2a and 2b.
Thereare also differences such as the latitudinalorientation of the
IMF, the attenuated
variations in IMF, V, Tp and SEP on April 5,1979 at Earth, in
Figure 2b when comparedwith those on March 31, 2001, in Figure
2a.
3. CONCLUSIONSWe have examined two intervals
separated by 22 years, where solar windconditions show some
stricking similarities,in particular the merging of multiple
ejecta.
How do the two events compare intheir geoeffectiveness? In 2001,
a great storm(minimum Dst < -380 nT, the largest of thecurrent
solar cycle) started on March 31 witha recovery phase lasting up to
April 5. TheKp index exceeded 6 for the whole day andreached
saturation at 9 UT. A second majorstorm was observed on April 11
(minimumDst
