The interplanetary and solar causes of geomagnetic activity

THE INTERPLANETARY AND SOLAR CAUSES OF GEOMAGNETIC ACTIVITY * BRUCE Jet

Propulsion

T. TSURUTANI,

Laboratory.

Institute

BRLCE

Califorma

Nationale

E. GOLDSTEIN

Institute

Institute

Institute,

University

CA 91 109, U.S.A

SP. Brazil

TANG

of Technology. SYCN

Geophysical

J. SMITH

Pasadena.

WAI.TER D. GONZALEZ dc Pesquisos Espacix~s, Sk JosL: dos Campos. FRANCFS _.

California

and EDWARD

of Technology.

Pasadena.

CA. 91 109. U.S.A

1. AKASOFL

of Alaska.

Fairbanks.

AK 99775-0800.

U.S.A

and ROGER

UCersity

R. ANDERSON

of Iowa, Iowa City. IA. IJ.S.A

Abstract-We present a review of recent work done on the topic of interplanetary and solar causes of gcomagnctic activity. During solar maximum (197% 1979). 9O”i;, of the major magnetic stcxms (D,, $ ~ 100 nT) are caused by large southward B. events associated with interplanetary shocks. Of these, roughly half of the R, events are located in the sheath and half assoclated with the driver gas. These two sources of southward IMFs often give magnetic storms a two-step prolilc. The sheath field events are generated in the interplanetary medium hctwccn the outer corona and the Earth from the “shocking” of the slow solar wind upstrcam of the high speed stream. In contrast, the driver gas cvcnts arc liclds which come from the solar source region. A correlation between the field orientation at the solar source and that at I a.u. was sought. hut none wah found. Thus, quantitative predictions of storm intensities l’rom solar observations appear to be very dilficult. Prominence eruptions are shown to be an important cause of the high speed solar wind streams that lead to magnetic storms. The other 10% of the magnetic storms arc not related to intcrplanctary shocks or high speed streams. hut to high density “non-compressional density cnhancemcnts”. Following magnetic storm5 arc “high-intensity long-duration .4E activity events” (HILDCAAs) that are series ofcontinuous aurora1 suhstorms that last from days to uccks during or after the storm’s recovery phase. HlLDCAAs can also occur indepcndcntly of magnetic storms. This continuous aurora1 activity is caused by the southward component of the magnrtlc ficld of interplanetary Alfvkn wuvcs. presumably through the process of magnetic reconnection with the Earth’s lield. These AIfvCn wave trains are often observed in the trailing portmns of high speed streams. From an analysis of a year’s data during solar maximum. it is found that the interplanetary medium IS “Alfcknic” approx. 60% of the time. There appear to bc no substantial diffcrenccs in magnetosphcric rcsponsc to Alfvinic or non-AlfvPnic interplanetary intervals. The magnetopause boundary layer is shown to contain broad-hand ELF;VLF plasma waves at least 85% of the time at all daysidc local times. Thcsc wa\es have suflicient amplitude to cause cross-lield difi’usion of magnetosheath plasma to form the low latitude boundary layer. Pitch angle scattering of the low latitude boundary layer particles is adequate to account for the daysidc aurora. The only intcrplanetary’mag~~closheuth parameter that appears to alt‘ect the wave intensities is the IMF H,. Although the waves arc present at almost all times. they are intensilied during southward IMF B, intervals.

Although it is well known that southward intcrplanetary magnetic fields (IMF) lead to geomagnetic activity through the process of magnetic reconnection

(Dungcy, 1961 ; Arnoldy. 1971 ; Foster c’/ LI/.. 1973; Tsurutani and Mcng, 1972 ; Baker c’t al.. 1983 ; Akasofu C/ trl.. 1985). little is known about the intcrplanetary and solar origins of these magnetic fields. If WC are to fully understand solar-terrestrial intcractions. WCmust trace the origin of the magnetic fields

*An invited paper presented at the First Latin American Conference on Space Geophysics, Aguas de Lindoia. Brazil, 20 25 November. 1988.

Sun. Recently.

the authors

their attention

on this important

INTRODUCTION

into

I09

interplanetary

space.

and

eventually

back

to the

of this article have focused topic.

Their

findings,

110

B. T.

TSURUTANI et

the limitation of the results to date, and remaining major problems, will be briefly reviewed.

BACKGROUND

INFORMATION

al.

ALfvbn wave (rotatIonat discontinuty)

FOR INTERPLANETARY

PHENOMENA

IBI t-_-p A brief review is provided to give readers a background on major interplanetary features (shocks, high speed streams, non-compressional density enhancements, hehospheric current sheets, discontinuities, Alfven waves, and magnetic clouds) that may be related to geomagnetic activity. This review will be brief, and by no means complete. We shall suggest references for further reading. For readers who have a background in this area, this section can be skipped without loss of continuity.

High speed streams and collisionless shacks The predominant source of high speed streams during solar maximum is coronal mass ejections (CMEs) associated with solar flares or with prominence eruptions. During solar minimum, the main source is coronal holes, which when they are long lasting lead to corotating interaction regions (CIRs) in interplanetary space (Smith and Wolfe, 1976) ; because the velocity of the high speed streams (500-1000 km s- ‘) is much greater than the normal solar wind (350450 km s- ‘), and this velocity difference is greater than the local magnetosonic wave speed (- 70-100 km s- ‘), a collisionless shock forms at the interaction front. As the upstream plasma crosses the shock it is, via plasma instabilities, heated, compressed and accelerated (in the shock frame). There is therefore a substantial increase in density, convection speed, and therefore, ram pressure (mNV,‘,) across the shock. In the above expression m is the ion mass, N the density and V,, the solar wind velocity. When this pressure pulse is incident upon the magnetosphere, the magnetosphere is abruptly compressed until pressure balance is again achieved. This magnetic compression can be detected world-wide on the ground and is called a suddenimpulse (SI). If the pressure increase is followed by a magnetic storm, it is called a storm sudden commencement (SSC).

Discontinuities and Alfi& waves Of the various types of discontinuities hypothesized by Landau and Lifschitz (1960), there are principally only two types (besides shocks) which are of importance to space plasma physics. They are tangential and rotational discontinuities. A tangential discontinuity

Tangential discontlnulty

N,,T,,B,

B;n

N,,T,,B,

= 6;;

=0

FIG. I. SCHEMATIC OF AN ALFV~N WAVE (TOP) AND TANGENTIAL DISCONTINUITY (BOTTOM).

A

is pictorially illustrated in the bottom half of Fig. 1. The plasma density and temperature and the magnetic field direction and magnitude may be entirely different on the two sides of the discontinuity. The prime requirement (definition) is that there is no normal component across the discontinuity surface, i.e. the fields on both sides are parallel to the plane of the discontinuity. Alfven waves are illustrated in the top half of Fig. 1. For isotropic plasmas, Alfven waves are transverse and non-compressional. If these waves are highly steepened and have an abrupt phase change, they are called rotational discontinuities. Rotational discontinuities therefore conserve field magnitude and (ideally) have a normal component equivalent to the ambient field. Heliiospheric current sheet In 1978 it was discovered that the interplanetary magnetic field comes outwards from one hemisphere of the Sun and returns in the other hemisphere (Smith et al., 1978). A schematic is given in Fig. 2. The field reversal occurs in what is called the heliospheric current sheet. This was previously called a “sector boundary” (Wilcox and Ness, 1965) before the threedimensional configuration was understood. The offset of the current sheet rotation axis from the Sun’s rotation axis gives the familiar “two-sector” pattern as the Sun rotates relative to inertia space. Presumably

The interplanetary

and solar causes of geomagnetic

FIG. 2. CONFIGURATION OF THEHELIOSPHERE CURRENTSHEET (FROMSMITHrt d., 1978, J. gmphys. Res. 83,717, COPYRIC;HT BY THE AMERICAN GEOPHYSICAL UNION).

warps or wiggles in the current sheet gives rise to four, six, etc. (even number) sectors per solar rotation. If there is no reconnection (no normal B component) across the current sheet, it is a tangential discontinuity. If the fields on both sides connect across the current sheet, then the discontinuity is rotational in nature. The same situation exists for the neutral sheet (which separates the two lobes in the Earth’s magnetic tail) and for the Earth’s magnetopause (which separates the interplanetary medium from the magnetosphere). If the heliospheric current sheet is swept up and compressed by a high speed stream and the magnetic fields near the current sheet are tilted so that they have a substantial North-South component, the intense distorted fields can lead to geomagnetic activity through reconnection with the Earth’s northwardlydirected fields. A schematic of the cause of the C’DA W6 substorms is illustrated in Fig. 3.

A phenomenon called a magnetic cloud has been discovered in the interplanetary medium (Klein and

15$E -3

FIG. 4. ONE POSSIBLECONFIGURATION OF A “MAGNETIC CLOUD” (FROMKLEIN AND BURLAGA, 1982, J. geophys. Rex 87,613. COPYRIGHT BY THEAMERICANGEOPHYSICAL UNION).

Burlaga, 1982). See Fig. 4 for their schematic. Magnetic clouds are large (>0.25 a.u.) regions characterized by intense magnetic fields that have their principal axes rotated in a plane. This configuration is consistent with a large magnetic loop or bubble. Interplanetary coronal mass ejections (CMEs) The canonical picture of the evolution of a CME in interplanetary space is given in Fig. 5, taken from Bame et al. (1979). Extending from the Sun outwards are attached magnetic fields giving the form of a “tongue” (Gold, 1962). If the fields are closed, one then has a magnetic bubble or cloud. This driver gas region is characterized by low proton densities and temperatures and high intensity, smooth magnetic fields. There is often a lumpy distribution of enriched helium present. For a further discussion, see Zwickl et ul. (1983). The boundary between the shocked plasma (sheath) and the driver gas is a discontinuity. This discontinuity is believed to be tangential in nature. Between the shock wave and the discontinuity is the shocked solar wind plasma, which has been swept up by the high speed stream. This region can be characterized by compressed AlfvCn waves, discontinuities and locally generated waves and turbulence. INTERPLANETARY

SOURCE OF SOUTHWARD

FOR MAGNETIC

FIG. 3. SCHEMATICOF THE “KINKY” HELIOSPHERIC CURRENT THATCAUSEI)THE C‘DAW-6 SURSTORMS (FROMTSURIJTANI cv Cd., 1984. Gwphys. Rex. Left. 11, 339. COPYKIC;HTBY THF AMERICANGEOPHYSICAL UNION).

III

activity

B,

STORMS

Southward B, The origins of interplanetary southward B, leading to major (Dsr < - 100 nT) magnetic storms is an important question, for both understanding the solar source and interplanetary evolution of the solar wind, and for obtaining advanced warning of an impending storm hours to days in advance by utilizing interplanetary and solar observations. In Gonzalez and Tsurutani (1987), it was deter-

B. T.

TSUK~JTANI

A possible geometry piasma drlvlng a shock

c,t 01 of wave

beyond

lowest

siege

T-depresslo;

n u

SC

Sun 01 A ( OKONAL MASS IJl’(‘TIOI
FIG.

5. COY~IGIJKAI~O~

mined

that

storms

of

clcctric

field

E11rth.s than

I),,

must

bc larger

rcfcrencc

other

(which val.

did

GIUSC

dctcrmincd They

Akxofu.

1081).

1986)

I”

M urayuma.

pressure

and

magnctosphcric planctnry &,.

is strong

scale but

important (1082).

the solar role.

21s

In

field

that

the

All

of

txni

previously

similar

scvcrul

wxys

: the

abow

the

(I I northward the

Mac5ol;11 intcrwith

cocfficicnts.

thcrc

is not (B.

pressure supgcsted

the

I978 :

1, is the in

only

and

+ IO nT

1989)

bctwecn 37

h.

the

Although nuturc iblc

large

north\+at-d

by Murayama

high

pl;isnia

density

fbr

arc

nine

analyses

or

cor-

lag

lime

cvcnt is

is 0

&36

h. the

it SCCIT~S plainsthe the

s;~mc origins number

cvcnts xrc >llmost

ol

identical.

physical

random

bctwccn

the

concerning

bccausc

so with

diffcrcncc

it

I~I

rcpions

the

field

cvcnts,

similar

the rcsponsiblc

dots

cvcnts

the

nccdcd

IMF

events:

one:

;

zmd two

events.

cvcnts. ;lrc

have

th;tt

them

IMP

and

and

and southwnrd

principal

southward

IMF

southward

IMF

fur gcnctxting The

southward

may

it sccm5 possible an

with

in

the s~mc

cvcnts) shocks

for

southw:lrd

about

IO southhxrd

shock,‘NCDE

they

;IS

dcpcndcncc).

vs

IMF cvenls

field

xc

to

polxity

northward

southward

ofcvcnts

of. the northward

th:lt

h). Thcsc

similar in

Ihlloncd

1‘urthcr

Thus

,’ also pl:iys

number

numbers

while

3

opposite

nine

and

responding

>

to the

Tsurutani

cbcnts,

associated

(NCDEs).

T

and

R, events

but

events

northward

;irc

in Gonzalez

northward

cvcnls.

wcrc

cross-corrcl;ltcd

rcconncction wind

1986: above.

southward

intcr-

out

wcrc

cbcnts

1’1 c/l..

angle

polar

correlation

cvidcncc

(Barfatrc

thcrc

(R, >

[or

A!asof~~,

((I:?)

when

large

function

xnd

to Murayarnu.

coordinates.

in

this

the

pointed

that

were

criteria

cf (I/..

(19X7)

in the

Thcrc

within

coupling

It WIS also

longer

thcsc

(Gonznlcr

sin”

II the

magnctopausc thut

storms)

19X6).

parumctcrs.

rcsultcd

thcrc

‘YR

last

‘WHAT llhs PKOI~A~;I\TEI~70 1 a.u. (IIwM BAW A~II:KI(.,~\ GI:OIWYSI(~,~I Uwoh).

Ihr

2ind in the

cvcnts

meeting

: i: (Pcrr;luIt

:md 11’ ‘c-B, (similar

LZIM’:~ :und

txni

m:l_jor analysts

wcrc

I~LIS~

fields

1%~ THI

duskward

’

ni

met thcsc criteria.

the best-fit

IO storms.

The

5niV

cvcnts

dctailcd

criteria

nT.

IO intcrplanctxry

studied

not

than

thcsc

intcrplanctary

Marc

ha\c

of the

of’data

intcrplnnctary

< ~ 100

frame.

3 h. E;tch

500 days no

21rc simple

thcrc intensity

(C‘ME)

process

orientations.

northward

;md

is the cfTcccctivcncss ofco~rpling

The interplanetary and solar causes of geomagnetic activity

113

Event summary

(a 1 Shocked

southward fields l

Causes of IO magnetic storms quite diverse l

(b)

Shocked current sheet

4 storm lntenslf Ications to D,, < -100 nT due to driver gas southward fields

l

I or 2 kinky hellospherIc

l

I shock

. 2or 3 turbulent l

( c 1 Turbulence,

FIG.

)

event

sheath fields

field around NCDE

waves or dlscontinultles l

(d

I draped

current sheets

field lntenslflcatlon

Draped magnetic

4 driver gas/5 7. A SUMMAKY

sheath/I

NCDE

OF THE SOUTHWARD

10 MAJOR MAGNETIC

fields

IMFs

THAT

CAIJSEI)

STOKMS.

Five out of 10 were sheath fields. four were driver gas fields, and

(e

1 Driver

one was associated with a non-compressive enhancement (NCDE) event.

density

gas fields Magnetic torque

FIG. 6. THE VAKIOLS (D,,

<

-100

nT)

INTEKPLANETAKY

MAGNETIC

STORMS

CAUSES OF IO MAJOR THAT

OCCUKK~.D

IN

1978-1979.

to the magnetosphere. For the northward events. D,, is zero or the magnetosphere is in the recovery phase of a storm. AB is typically O-200 nT. For southward events, D,, < - 100 nT. The magnetosphere thus essentially responds like a diode (as was suggested by Burton ct d.. 1975).

SOLAR

SOURCES

01; iW2GNETIC

STORMS

The interplanetary and solar causes of the IO magnetic storms (lY78~lY79) arc studied in Tsurutani c/ rll. ( IYXXa) and Tang cat(I/. (IYXY). rcspcctivcly. It is found that thcrc arc a whole variety ofintcrplanctary and solar causes. The interplanetary uuscs arc schematically illustrated in Fig. 6. Within the sheath region, the compression of pre-existing southward tields or a heliospheric current sheet can lead to magnetic storms. There arc also casts where turbulence. waves or discontinuitics with the sheath arc associated with southward IMFs. which in turn GILISC magnetic storms. The waves or turbulcncc could tither bc COIII-

pressed interplanetary fields or could be locally gencrated. It is not certain which is the correct process, at this time. Within the driver gas, the magnetic fields are intense and free of directional discontinuitics. These fields arc often oriented southward which. through magnetic reconnection, causes magnetic storms. These fields arc sometimes followed by northward fields, or vice versa. This general South/North or North/South configuration is consistent with a bubble or loop. Finally, one case (out of 10) did not involve a high speed stream or a shock. The solar wind velocity was average (400 km s- ‘) but the density was extraordinarily high (_ 35 cm ‘). Intense southward magnetic ficlds wcrc associated with this cvcnt. The plasma event is called a non-comprcssional density enhancement or NCDE (Gosling ct cd., 1977). Although this phenomenon created the southward fields for only one event out of the IO (IO% of the magnetic storms studied), it is an important component. and the solar origin and its evolution in intcrplanetary space need to be bcttcr understood. The summary of Tsurutani 1’1rr/.‘s (19X&) work is given in Fig. 7. The bottom line indicates that roughly half of the southward fields rcsponsiblc for storms arc in the sheath behind intcrplanctary shocks and the other half arc &Ids within the driver gas. This ratio was found from a study using data near solar maximum (1978~lY7Y). Presumably during solat minimum when thcrc is 21 paucity of CMEs, it is expected that the majority of southward field events will have sheath or sheath-like plasma origins. During the latter phase of the solar cycle. it is belicvcd the coronal holes probidc the majority of high speed

114

B. T.

TSURUTANI

et

al. EVENTst

TABLE ~.THESOLARPHENOMENARESPONSIBLEFOKTHEINTEKPLANETAKYSOUTHWAKD~~

Solar origin Shock (U.T.) I 2 3 4 5 6 7 8 9 IO

Cause of southward

27 Aug 1978 (02) 28 Sept 1978 (21) 25 Nov 1978 (12) 21 Feb 1979 (02) 9 March 1979 (05) 28 March 1979 (08) 3 April 1979 (09) 24 April I979 (23) 29 Aug 1979 (05) 17 Sept 1979 (NCDE)

B:

Driver gas (SE) Driver gas (SW) Shocked-E,

Event Prominence

2/M3 flare Prominence

Driver gas (SW) Distorted sheath fields

l/MI

Distorted

sheath

Draped

sheath

gas

flare

Solar field

23 Aug N15ElS

North-west*

27 Sept N27W19

East*

20 Nov N35W50

South-east

18 Feb

_*

5 March

Nl IE38

2/X1 flare

26 March

N5W78

l/Ml

30 March

S25E31

Prominence

fields

fields/driver

eruption

(Flare)

fields

Driver gas (SE) Distorted sheath fields Distorted

eruption

Date/location

flare eruption

2/X2 flare X2 flare

22 April S25EO 26 Aug N5WI I4 Sept > E90

I

East North-east West* West, South-west South-east,

South-west _*

6)

*Driver gas events. _FFrom left to right are the event times, the causes of the southward B_. the types of solar events, the date and locations of the solar events, and the orientations of the photospheric fields at the solar sources.

however, such studies have not been performed and should be done in the near future.

streams;

Solar origins of’southward IMFs The location and type of solar source for the major magnetic storm events are given in Tables 1 and 2. TABLE 2. INFORMATION CONCERNING THE INTEKPLANETAKY SHOCKS PRECEDING THE SOUTHWAKU B: EVENTS*

Shock date

Mach number

Storm D,, (nT)

I

24 April 1979

3.5

- 140

2

27 Aug 1978

3.3

-220

3 4 5 6 7 8 9

29 Aug 21 Fcb 2X Mar 2X Sept IO Mar 3 April 25 Nov

2.3 2.2 I.5 1.3 1.1 I.0

-I40 - 110 -120 -215 -140 -200 -150

1979 1979 1979 1978 1979 1979 1978

I .o

Solar

source

Prominence eruption Prominence eruption 2/X2 flare (flare) 2/X1 flare 2iM3 fare I;Ml flare l/Ml flare Prominence eruption

* From left to right are the dates of detection for the shock at ISEE(I a.u.), the magnetosonic Mach number of the shock (calculated by the Abraham-Schrauner method), the magnetic storm peak D,,, and the solar source. The most intense shocks are associated with prominence eruptions.

These are taken from Tang et al. (1989). One major point of the tables is that there is no obvious correlation between the strength of the solar source and the strength of the magnetic storm. Storms with -220 nT < D,, < -200 nT are caused by M-class flares or prominence eruptions. The most intense flares, X-class events, are associated with only -200 nT < D,, < - 100 nT storms. Another interesting feature is that the highest Mach number interplanetary shocks (events I and 2) are associated with relatively weak solar events : prominence eruptions. From the growing evidence of the importance of the latter type of solar event (Joselyn and McIntosh, 1981 ; Sanahuja rt al., 1983) it is important that more effort be placed into understanding the physical processes involved in their formation and their evolution in interplanetary space.

Can solar photospheric observations be used to predict interplmetary,fiel~.~~~ To predict the field magnitude and orientation in the sheath region, knowledge of the upstream slow solar wind, the properties of the high speed stream, and the interaction between the two are needed; because the origin of the slow solar wind is not at all well understood (and therefore the details of which

The interplanetary and solar causes of geomagnetic activity

are almost totally unknown), the possibility of being able to predict the turbulent sheath fields remains remote at this time. Tang et al. (I 989) have compared the orientations of the solar photospheric field to those in interplanetary space for interplanetary B, events where driver gases are the cause of the southward BZevents. If the two orientations are the same or similar [as Pudovkin and Cherkov (1976) and Pudovkin et ul. (1979) have suggested], then if one can determine which solar events will cause high speed streams that will reach the Earth and what the direction and duration of the magnetic field will be, then it would be possible to predict (in advance) the strength of impending magnetic storms. However, the Tang et d. (1989) results (Table 1) indicate that there is apparently no correspondence between the orientation of the photospheric field at the site of the solar source and the orientation in interplanetary space. There are several possible causes for this finding : the driver gas fields detected in interplanetary space may come from regions well above the photosphere, or as the high speed stream propagates through interplanetary space, the gross magnetic field shape and orientation is not maintained. Effort in determining which of the above possibilities is the correct one will be an important step in helping to solve the storm predictability problem. It should also be noted that the above work was only limited to a 500-day study near solar maximum. The causes of magnetic storms during solar minimum need to be studied and understood.

COMMENTS

ON

“GREAT”

SOLAR

FLARES

It is often thought that “great” solar flares lead to “great” magnetic storms (the “big flare syndrome”, Kahler, personal communication, 1988 ; Eselevich ef al., 1988). However, there is a growing body of works that have shown that this is not correct (Joselyn and McIntosh, 1981 ; Sanahuja et al., 1983; Tang et cd., 1989). One has to ask why this general misperception is held? The Gonzalez et ul. (1989) article shows that the predominant interplanetary parameter leading to geomagnetic southward storms is B,, or more prccisely the two interplanetary parameters V,, and -B; giving the interplanetary electric field through many different possible coupling functions (see Gonzalez et ul., 1989, for a detailed discussion). Thus the larger the flare, perhaps the higher the velocity of the high speed stream (V,,) and the larger the compressional magnetic field behind the shock (up to a maximum roughly four times the upstream ambient field). How-

115

ever, this indicates nothing concerning the NorthSouth component of the magnetic field. One might expect to statistically get larger southward B, and therefore magnetic storms from large solar flares. [Tsurutani et al. (1988b) indicate less than 20% of the 55 high speed streams led by shocks in 1978-1979 caused storms with D,, < - 100 nT. This implies that statistically, the IMF was “correctly” oriented for “sufficient” duration only in one out of six cases.] Gonzalez ef al. (1989) also point out that the ram pressure term (PuVV~~), can also be an important parameter when there are large pressure changes (previously discussed in depth by Murayama, 1982, 1986). This can lead to substantial solar wind energy transfer to the magnetosphere. This term may be even more important for great solar flares where the velocities can exceed 1000 km s ‘. What can we say about the importance of major flares? Do they sometimes cause great storms or great aurora1 activity, and why? These questions cannot be answered at this time, essentially because little work has been done on this particular topic. WC can speculate that higher magnetic fields and higher velocities should stutisticul/y lead to large - V,,BI. Multiple solar flare events could lead to extraordinarily high interplanetary magnetic fields because the shock associated with a second flare can compress the driver gas fields of the first flare. It should also be pointed out that the ram pressure at these very high velocities may become an important source of energy because of the V:,, dependence. At this time, we do not know if this occurs or not. Research on this topic is needed. It is strongly recommended that persons studying these topics first start with great magnetic storms, and then work backwards to the Sun to find the interplanetary and solar causes. If one conversely started with major solar flares and then looked at the Earth’s magnetosphere, there will be many flares without consequential storms. As an example, the August 1972 flare created a solar wind velocity > 1500 km s ’ and an interplanetary magnetic field of > 100 nT at I a.~. However, this extraordinary interplanetary event only caused a weak ns7 2 - 141 nT (however a K, z >9+). This is because the field was primarily oriented northwards throughout the high speed stream.

SUBSTORMS

In our studies, it was noted that after some magnetic storms, intense, continuous aurora1 electrojet (AE) activity sometimes followed for days. We formulated criteria for these events and called them HILDCAAs. This acronym stands for high intensity (peak AE >

13. T. TSUKIJTAN~ rf &.

II6

c

1

5

0” -2oc

I 26

27

28

29

August

30

I 31

1

2

1978

.I..--.-

3

Sept

-

4

1978

FIG. 8. AN CXAMPII: Ok A HIGH INTtNSlTY LONG I>lJKATION (‘ONTINUOIJS ,dE ACTIVITY EVENT. The HILDCAA is denoted by a horizontal bar above the next-to-botwm panel. The event occurred after an interplanetary shock (beginning or27 August) and a large southward B; (end of27 August and beginning of 2X April) which caused a major magnetic storm (bottom panel. 18 August). The HILDCAA event is accompanied by large fluctwtions in the magetic field components (4th and 5th panels from the top).

1000 nT), tinuous

long-dur~~tion

(AE

not

(must

to drop

or more),

AE activity.

arbitrary;

however,

gent rcquircmcnts.

;-4X

200 nT

h). con-

Figure

for

between the X-components

2 h

C’lcarly the above criteria

by placing thcsc relatively WC obtained

500 days of study (Tsurutani One example

last

below

arc

strin-

seven cvcnts within and Gonzalez,

19X7).

is shown in Fig. 8. ‘The HILDCAA

indicated

by a horizontal

magnetic

storm

bar in the /lE

panel. The

is caused by a large southward

event on 27.~28 August and

1978. The HILDCAA

starts on 29

Augusi

Scptcmbcr.

The HILDCAA

the tiuctuations

is

lasts

5_

cvcnt

until the l~~~inllin~ of4 cvcnt is associated with

of the IMF

components.

Figure 9 illustrates a HILDCAA slrcum.

It is, however,

in the intcrplanctary

tuations

cvcnl which is not

The fluctuations

associated magnetic

with

Ii&i

rckttion

(IMF). interval

the nature of the IM F ~uctll~lti~~ns,

and Cionzalcz

of ;I HILDCAA

peak correlation

( 19X7) examined

bct\+ccn the solar wind velocity.

of B and V,,

for an IX h

event (26 May

coefficient

is quite high,

1979). The > 0.8. and

occurs at zero lag. This is consistent with the intcrplanetary

fluctuations

being AlfvCn

cvcnt the waves wcrc dctcrmincd outwards

waves.

In this

to be propagating

from the Sun. Belcher and Davis (197l),

a classical work,

dctcrmined

that continuous

in

Alfv&n

waves were often dctcctcd in the trailing

portion

high speed streams (such as the cx~mplc

in Fig. 8).

F-towcvcr. they noted

that

Alfvbn

of strczms (Fig. 9). At I au., propnguting Tsurutani

outwards

waves could

of bc

wcrc correlated

the cor-

V,,,, :tnd 8.

the waves ac typicaily

from the

and Gonzalct

Sun.

(1987)

All seven of the

HILDCAA

events

with Alfvbn ~IIVCS. All of the Alfvtn

waves wcro determined

to be propagating

outwards

from the Sun. To dctcrminc

by a bar).

To d~t~rlliin~ Tsurutani

Iluc-

start and stop almost simultaneously

with the beginning and end oft hc I-i I LDCAA (indicated

inlcrval

dctcctcd over 50% of the time and also indepcndcntly

associated with ;I magnetic storm or ;I high speed solar wind

10 is an example of the ~Ol-r~J~~tioncoefficient

if the mechanism

fctr cncrgy transfci

from the solar wind to the rn~~~n~t~~spilcrcis magnetic rcconncction

associated

with

the southward

poncnts nfthc Alfvt’n waves, Tsurutani

com-

and Gonr.:rlcz

The interplanetary and solar causes of geomagnetic activity

kj

600 . ..-.._I

I---_.,*

=_

(1987) pcrformcd cross-correlation analyses between the IMF r-component and the AE indicts. For the majority of events analyzed. the correlation cocfficicnts wcrc anomalously low. The authors hypothcsizcd that thcrc could bc several possible reasons for this finding : (I ) bccausc ISEE- was often at the wings of the halo orbit (about the L1 libration point)

r26

c c.

Mav

117

1979

00:

I8 UT

during the HILDCAA events (WC Fig. II. from Tsurutani and Baker. 1979), it is possible that the Alfvi-n waves detected at ISEEdid not have the same phase and amplitude as those that impinged up on the magnetosphere ; (2) a mechanism other than reconnection was the responsible mechanism (Tsurutani et rrl.. IOX8c); or (3) reconnection is the mcchanism. but because the magnetosphere was in a highly turbulent state. aurora1 activity was not directly correlated to peomagnctic activity. An example of this Cypc is well documented in the second CDA W-6 event (Tsurutani c’t trl.. 1985). Other interesting questions :IISO arose associated with Alfvcn W;IVCS.Since the Alfvi-n waves often have a quasi-periodic appearance. are thcrc casts whcrc thcrc is rcsonancc bctwccn the AIf& waves and the magnctosphcre. c.g. when the Alfvt;n wavelength is comparable to the width of the magnetosphere or the distance from the nose of the magnetopause to the tail rcconncction line? Another question is. “If the southward turning of the IMF causes reconnection and the onset ofsubstorms and the northward turning causes the cessation of reconnection and the cutoff 01 gcomagnctic activity. then is the duration of substorms (the “typical” duration of -I 3 h) directly due to the period of Alfvkn waves?” Are there pcriodicitics in Ihc interplanetary magnetic field?

B.

118

T.

TSURUTANI

et al.

Halo orb& around Sun-Earth tibratioi? point To Sun

FIG. 1I

THE ISEE-

OKBIT .ABOUTTHE SW-EARTH

To answer this question, we examined interplanetary IMP-8 data for the HILDCAA intervals. Examples of the cross-correlation results for B_ vs AE are given in Figs 12-15. In the top of each panel, a full 18 h of data are examined. The bottom panel illustrates the results for the same events, but for shorter intervals ranging from 2: to 6 h. Figure 12 illustrates that using the near-Earth IJWP8 data, there is a strong correlation between the southward component of the Alfvkn waves (- B_ only used) and AE. There is a peak correlation coefficient located min lag. For the shorter 6 h interval, a at -40-60 maximum C.C. of -0.8 is obtained. The other intervals examined (Tsurutani rt al., 1990a) also indicated high correlation coefficients between B, and AE. Thus it is apparent that the lack of correlation in the ISEEAE analyses was due to the unfavorable location of the ISEE spacecraft and the relatively small wavelengths of the AlfvCn waves. Figures 12-15 show a variation of lime lags for different HILDCAA events. In Fig. 12, AE is delayed (with a 5 min uncertainty) from B; by about 4060 min. In Fig. 13, the delay is -45 min. Fig. 14, -20 min, and almost zero for Fig. 15. This is something of a puzzle as all of these am-oral events are very intense (by definition of a HILDCAA event). It is generally thought (Bargatze er rrl., 1985; Akasofu et al., 1985) that during intense aurora1 events, the magnetosphere is “directly driven”. Long time lags (30.-60 min) should not occur, however Tsurutani it (~1. (l99Oa) have found both long and short time delays for HILDCAA events. The last

LIHRATIONPOINT, L 1.

Zft, ;egff:ember 1978

oO:oO

-

l&O0

UT.

FIG. 12. C~OSS-~~RR~L.~TIONWTWEEN ~~JTHWA~V AND AE.

IMF f3,

The interplanetary

and solar causes of geomagnetic

I-

119

activity

16 June 1979 167

Doy

0O:OO - 18:OO U.T.

06.00-0900

U.T.

o-02-0.4

-

-0 6 -08-I

-80

I I I -20 0 20 Log (mm)

I

II

40

60

Fro. 13. SAME AS FIG.

12.

I

I

-60

-40

-OSl_

-I_ Log

FIG. 14. SAME figure (16) is curious because of the very short time delay. A schematic illustrating some of the interplanetary features discussed in this review is given in Fig. 16. The principal interplanetary regions that have been found to lead to major geomagnetic activity are indicated. Behind the shock are the compressed sheath plasma and fields, which during solar maximum cause roughly half of the magnetic storms with DST < _ 100 nT. The other half of the major magnetic storms are caused by southward fields in the driver gas. Since there is no (known) relationship between the fields in the two regions, some magnetic storms have two separate main phases, one due to the sheath fields and a second due to driver gas fields. Largeamplitude outwardly propagating AlfvCn waves are found in the trailing portions of high speed streams. If southward components are present in the magnetic field, each southward dip leads to high latitude aurora1 activity. Typical aurorai act&y Since AlfvCn waves are frequently present in the interplanetary medium (Belcher and Davis, 1971), the

(mm) AS FIG.

12.

question arises as to whether most substorms are associated with Alfvttn waves or to tangential discontinuities, turbulence, etc. To answer this question, Tsurutani et al. (1990a) examined nearly one year (1979) of IMP-8 interplanetary data divided up into 12 h intervals. The correlation coefficients of the Xcomponent of V and B at zero lag were calculated for each 12 h and the results were binned into five equal intervals, shown in Table 3. The peak AE-_B correlation coefficient was calculated and the average lag of AE from -B, was determined. The average of all of the events within each bin was calculated and the standard deviation determined (in parentheses). If one assumes that a O&l.0 V,- B,Ycorrelation coefficient indicates an AIfvCnic interval and a O-O.4 correlation coefficient indicates a “non-Alfvenic” interval, then it is clear there are far more Alfvenic (55) than non-Alfvenic intervals (27). Roughly 2/3 of all intervals are Alfvenic. The last two values in the table indicate that the correlation coefficient with AE is slightiy higher for non-Alfvenic intervals and the delay time is also slightly longer, but these differences

B. ?-.

120

TsuKCTANl

TABLL:

27 September 1978 Day 270

/

3. STA i,STl<‘S

Ol- THt

0,: ‘TWF: INTEKPLAiXETAKY GCOMAGiX;I:TI(‘

(a)

OR-

PI d.

00

00-

l&O0

U

T.

i\l.tdNI(.lTY.

NON-/\LbV6VI
Mt~I~ItIM ANI)

THE COKKtLATIOY

AC’TIVI I Y IOK I)AYS

1

‘TO

3 13. 1979*

-. IkfP-8 interplanetary 1979 ,4E- R,c.c. Med. AE-- B. Ia& No. I2 h 1’, -B, C.C. [ave.], (SD.). m1n xt zero Ing intervals (“4,) (SD.) 11 (13.6)

0 0.2

0.2 0.4 0.4 0.6

13(14.8) IO (il.4)

0.6 0.8 0.8 I.0

27 (30.7) ‘6 (29.5)

0.64 0.72 0.54 0.60 0.64

so 1421 ( IX) 35 [40] ( 16) 45 [39] (34) 50 [47] (71) 35 [34] (14)

(0.18) (0.13) (0.X) (0.18) (0. I’))

* Twelve-hour intervals 01‘ interplanetary data were analyzed to determmc the IMF U, solar wind I’, correlntion ~ocfticients. The cvcnts were binned into five equal intcrv:lls bused on their oorrclation coefkicnts. From Icft-to-right are the cross-rctrrel;ttion coefficients, the number of I3 h interv;tls. the corrctatioo between A E and the sttuthward component oi’B_ (the S.D. is given in parentheses). and lhc lap OF ,4 E I‘rom B..

rcct

will require :I careful study with perhaps a

or not

much larger intcrplanctary

-_f

(

,

,

,

(

,

,

d:ita set.

Other

,

pllysical processes besides magnetic rcconand ram pressure variations may bc important in causing gcomagnctic xtivity. The daysidc z_wxxa

no&on

-60

-40

-20 0 20 Lag (mm)

40

15. SAMI: AS FK;.

ik.

60

60

is bclicvcd to bc continuously

t 2.

appear lo midnight

vary in intensity sector aurora.

present and does not its greatly as the ncitr-

Viscous

interaction

at the

ln~l~nct~~p~~usc boundary layer may pl:ty an inip~rt~lnt are within

the standard

deviations

role in the cause of the dayside aurora.

of the events

Figure 17. taken from Gurnctt it ol. (1979). illustratcs six crossings of the magnctopausc low latitude wave boundary layer. Thcsc crossings arc indiciltcd by vertical crosshatchings. The top panel displays the

analyzed. It

appears

intervals

possible

have

responses

that

slightly

; however,

Alfvbnic/non-All”&nic

different

to dcterminc

magnetospheric

whcthcr

this is cor-

Tangential

Driver gas

Trailing portion of high speed stream f-‘lC;.

16.

A

(‘0LLISIONLI:SS

SCHtMATK’ SHO(‘K

YroKMs, 11: THAWrdfit.i~s

01: THE (THAT AK]:

fY,-kKPLANbThKY

I-EATlIKES

C‘ALJSliS A SuDlIFY I)IKE(“TI:I~

STOKM OK A STOKM INTENSII‘I(‘ATION

IMI’IJLSE),

SUFFIC~I:NTLY

IF I)IKt<‘Tl:l~

01, THE PIIC;H 3v3.1)

xx

I‘H~AKII).

SOUTHWAKL)).

STK~AM

THAT

LEAI)

SHLATH AND

l.IbLIX

i)Ki~hK

Sheath

TO

Gl.OMAC;P;t:l-I(‘

(THAT tins

(‘AN

h(‘TlVITY

CAtJSI‘

~I~:LI)S (THAT

CAN

AL~V~N WAVES 114‘ THI: TKADING

(THAT ('AN CA~JSI: HILDCAAS).

: A

MA<;NiiTlC‘ cAusI:

A

I’OKT102i

144C

1500

l45C Time UT ISEE - 1 Day 314, 1977

FIG.

17. SIX

(TARF.N

bmhf

C’KOSSINGS OK GUKNFTT

PAKTIAL

CI cd.. I%“?.

CKOSSfN
Ob THE

hlACi’VLTOPAtJSE

Re.\. 84. 7043.

C‘OPYKIGHT

LOW

LATITC’I>F

13~ THF

BOUNDAKY

LAYER

AMEIU~AN &OPHYSI(.AL

IJYION).

There are intense wvcs

at each crossing.

The W~VCSare hroadbcnded, extending from 3 lo 500 Hz in the rna~nctic component :tnd from 3 Hz to 10 kHz in the electric component.

20 ISEE-I wave electric spectrum channels, the middle. the 16 wave magnetic spectrum channels and the bottom panel, the magnetic field components in magnetopause-normal coordinates. The top two panels indicate that the waves present in the boundary

layer arc intense and very broad-banded. The enhanced intensities in the electric channels extend from 3 Hz to 10 kHz and the magnetic component extends from 3 to -500 Hz. the electron cyclotron frequency. Gurnctt et d. (1979) have argued that

122

B. T.

TSUKUTANI

et al.

Localtime IhI

Fro. 18. WAVE

Latitude Id@

INTENSITY ASA FUNCTION OF LOCAL TOME.

Each point represents

the first 1 min average pause crossing.

FIG. 19. WAVE

INTENSITY AS A FUNCTION LATITUDE.

of a magneto-

the waves must be composed of an electromagnetic whistler mode component and an electrostatic component. The latter waves have a k perpendicular to B,,. Numerous plasma instabilities have been proposed to explain the waves. The leading candidates are a velocity shear plus non-linear cascading @‘Angelo, 1973) for the electromagnetic waves and the lower hybrid drift instability (Huba et al., 1977, 1981 ; Lemon and Gary, 1977; Gary and Eastman, 1979) or the electrostatic Kelvin Helmholtz instability (Lakhina. 1987) for the electrostatic emissions. The difficulty in determining the correct sources is partly caused by the broad-band nature of the waves plus the lack of any distinct peaks in the spectra. There are also many sources of free energy available. The latter makes a narrowing down of the number of possible instabilities (by elimination of potential free energy sources) very difficult. A statistical study of the magnetopause waves was conducted using about I50 magnetopause crossings. It was found that enhanced plasma waves were detected for 85% of the crossings. It is possible that waves were present for the other 15% of the cases, but the intensities were comparable to or less than the magnetosheath wave intensities, so the boundary layer emissions could not be distinguished. Figures 18 and 19, from Tsurutani et al. (1990b) give the wave intensity dependences 011 local time and latitude. Each point is a one minute average of the electric channel of the LOO0 Hz wave intensity. This channel is representative of the wave property at other frequencies. Figure 18 illustrates that, although there is a two order of magnitude variation in intensity, there is essentially a constant average wave intensity as a function of local time. Figure I9 illustrates that there is no latitude dependence in wave intensity

OF SPACECRAFT

throughout the limited latitude range covered by the spacecraft, - 2.0” to f 26.0’. When many magnetopause events are averaged together, the wave intensity and spectral shape are constant as a function of local time. This is shown in Figs 20 and 21. The local time chosen for “local dawn” is 5-8 h, “noon”, 11-l 3 h, and “dusk”, 16-l 9 h. Three frequencies are shown for the electric spectra (IO’, lo’, 10’ Hz). All three curves lie almost on top of each other. Two frequencies are shown for the magnetic spectra (IO’ and IO’ Hz). These three lines he essentially on top of each other. A power-law fit to the above spectra was made. “) nT* Hz- ’ and I,,,,,,,, = 3 x IO-’ .f -IL’

Magnetopause crossings -6-

-Dawn -8

_-

-

5:8 LT

-----

Noon

II.13

-.-.I

Dusk

16.19 LT.

(57events)

L.T. (13 events1 (IQ events)

-10 -

‘I” p

-12-

"z B

-14-

-16-

-18 100

I

I

I

IO’

102

IO3

Freqtmcy

I 104

I 105

(Hz)

FIG.20. ELECTROSTATICWAVESPECTRALSHAPEASAFUNCTION OFLOCAL TIME.

J 106

Magnetopause

signiticant expression pendicular (1974):

crowngs

cross-field difusion. By starting with the for the Pederscn mobility of particles perLO B,, given by Schultz and Lanzcrotti

e QTC,, “’ - B,, I +(QT,,,)“ where e is the electron or ion charge, B,, the ambient magnetic ficld, R the cyclotron fl-cqucncy and T,,, the effcctivc particle collision timcs. Tsurutani and Thornc (I 982) derived cross-tield diffusion rates based on rcsonanl wave particle interactions :

FIG.21. SAhll

-

Dawn

5.8

-----

Noon

II.13

LT

(57

events)

-.-.-

Dusk

16 19 LT(l9wents)

LT113events)

.AS PI<;. 20. I S(‘l.l’r FOK Tttt M'A\t

MA(;iit.rl(

<'Ohll'(lZI N I.

V’ cm ' H/ ‘_ These fits are useful to calculate the magniludc of waves particle interactions. The only parame~cr studied which had an cfi-ct on the intensity of the WIVCS was the tnagnctoshcath - .!S;.The more negative 8,. the greater the intensity ol’thc waves. This is shown in Fig. 32. It ih not ihought that thcsc waves arc substorm depcndenl. The waves arc almost always present (> 85%). cvcn when the interplanetary magnetic field is northward. II is more likely that southward IMFs C~LIXC the plasma instability generating the waves to be triggered tnorc easily or driven more strongly.

Y--0.0079%12.85 r7=Ot16 f

where U,,. E,, arc the wave magnetic and clcctric atnplinudes at the resonant frequency. I’ the particle velocity and D,,,,!, the Bohm diffusion rate. /I ,,,,,, = E QcB,,. whcrc Qy.,, = I. In the above expression for D, /it\ and 1) , ,j, it was assumed that R_ 7,,, >> I. Using typical low latitude boundary layer parametcrs as R,, G 50 nT, 1%’ = 30 cm I, it is found that I kcV protons can diffuse ~1 a rate of z 4 x IO’ km’ with lhe electrostatic waves. s ’ from interaction Tsurutani and Thornc (1982) concluded that the magnctopause waves were sutficienl to diffuse niagnctosheath plasma across the magnctopausc sufficiently rapidly to account for the Ihrtnation of the low IaLitttdc boundary layer.

Figure 23 illustrates the U. C. Bcrkclcy cncrgctic electron and proton llux for the six boundary layet crossings shown in Fig. 17. From the middle panel of the tigurc. it is clear that - I kcV solar wind protons have cay xccss to the boundary layer regions. - I and -6 keV electrons and - 6 keV protons arc cnhanccd in these regions. The IWO cncrgy channels Ihr the electrons and I,I the protons wet-c used to form crude E-folding spectra of the particles :

J, = 3 x IO’E(keV) J,, = lO’E(kcV)

“cm

’ “cm :s ‘sr ‘s

‘sr

’ kcV

‘kcV

II

‘.

given by Tsurutuni ct rrl. ( I98 I). If one integrates the spectra down to the actual peak in flux, which occurs a~ 100 300 eV, it is determined that the precipitalion rate is g I .O -1.2 erg cm ’ s ‘_ For comparison. the daysidc aurora1 rate is 1 I .Oerg cm ’ s ‘.

RE

7 9

1’::

u-r

14

i‘ ‘i

12 2

ISEE-

i

c

-I ISEE-

‘”

E!

3 IA E a

x F

..;.‘.

o

a’

_-.._ _ . . . . . x.:

.’ 5

-0”

_

.r--..........

,__-_-.-.*.‘a

0

-%.-$J& .-. .

:

o

.,C .

&,..

1430

.‘_’

.. .

. . .._.

:f

.

.;,.

.. ..

’ I..

.-.’

“x

It.

-

IO0

: 60

1450

6 m N

‘.;

/ 440

. ..,,.

i50”

m

The interplanetary

and solar causes of geomagnetic activity

CONCINSIONS

Gold.

T.

(1962)

Magnetic

125 storms.

S[xwc

Sri.

RN.

1,

I 00.

The purpose was t.o present a brief review of oltr &ork in these areas. give what is known and what has been learned and, most importantly. what is not known and how one could possibly approach the problem efficiently and with greater certainty in obtaining results. It is hoped WC have achieved some or our goals in this paper. ~lf,krln,rlcc!yt,t,jc,irl,s-We

the urganizers of the First $ace Geophysics (in particular Dr Jose Marques cia Costa. the C~~nv~n~r). for giving us this opportunity to organize this talk and present it at Latin

their

Amentan

Jnccting.

Propulsion

thank

~onfcrrnce

Portions

on

of

this

work

Laboratory, California under contract with NASA.

were

done

ut

the

Jet

lnstitutc of Technology.

HF:I;EKENCES Akasofu, S. I. ( 1981) Energycoupling between the solar wind and the rn~1~~~~1~1sp~~er~. Sixwc .%i. Kw. 28. I 1I. Akzwfu. S. 1.. Olmsted, c’.. Smith, E. J., Tsurut;mi. B. T.. Okida, R. and Baker. D. N. (1985) Solnr wind variation5 and gcomagnctic storms : ;I sludy of mdividual storms bawd on high time rcrolution ISEEData. ./. gc~op/t,r\. Kcs. 90. 325.

Bclcher. J. W. and Davis, L.. Jr. (lY71) Large :Jmpl~t~d~ AlI‘vkn M’~\CS Jn the interplanetary mcdlum, 2. .I. {]w/)/IJ’.Y. Rc.\. 76. 3533. Burton. R. K., McPhcrron. R. L. and Russell. c‘. T. (197.5) An empirical relationship hetueen interplanetary conditions and II,, .J. ~JPoJJ/~~,s.Rtcv. 80. 41-04. D‘Angclo, N. (1Y7i) Ultralow frfquency Huctuations at the p&r cusp h~)uJ~~i~lrie~,,1. ~/~~~~J/~~..~. Ret. 78, 1%. thnpcy. J. W. (1961) lntcrpl;1netarq nxtpnetic lield and the aurora1 zones. P/JJY. Rm. hrr. 6, 47. Ewlvich. V. Ci.. Fainshtein. V. G. and Filippov. M. A. (19X8) On the problem ofgeocffectivcness of sporadicphenomena 011 the Sun. !‘/r/Wr. ~~,/W SC,;. 36. 101 5. Foster, J. C.. Fairfield, D. 11.. Ogilvic. K. W. and Rosenberg. T. J. (1971) Relationship of interplanetarypatxmcters and occurrence of magnclosphcric substcxms. .I. ,gcwph,~~.s. Rcs. 6Y7l.

Gonzale7. W. U., Gcnzalez. A. L. C. and Tsurutani, B. T. (IYXY) Comment on “Large Scale Response octhe M~~netosph~r~ to a Southward Turning of the Intcrplanetary Magnetic &Id” by Sauvaud. J. A. rt ai. j. ycw~Il>~.\. Kc.v. 94, 1547. Gonzalez. W. 0. and Tsurutani, B. T. (1987) Criteria 01 intcrplanctary paramelcrs causing intense magnetic storms (DST c - 100 nT). f’/ww/. S[xw Sci. 35. I IO I Gon/alcc. W. D.. Tsurutani. B. T.. Gonzalw. A. L. C., Smith, E. J.. Tang. F. and Akasofu, S. 1. (IYXY) Solar windJll~~~l~el~~~pherecoupiing during intcnsc magwxc storms ( 197s 1979). J. gcw$~j.\. Rev. Y4. 8835. (;oslinf. J. T.. Hildncr, E.. Asbridgc. J. R., Bamc, S. J. and Feldman. W, C, (1977) Noncompressive density enhanccmalts in the solar wind. .J. ,qlcw,d~yv.Ra. 82. 5005. Gurnctt, D. A.. Anderson. R. R.. Tsurutam, B. T.. Smith. E. J., Paschmunn. G., Hacrcndcl, G.. Bamo S. J. and Russell. C. T. (197’)) Plasma wave turbulence at the magnctopause : observ;ltions from /SEE I and 2. J. gcopl~j,,\. Rtcs. 84, 7043.

Hubn, J. D.. Glad& N. T. anii Drake. J. I;. ( 1% I ) On the role of the lower hybrid drift Instability in substorm dynamics. J. ~/cwp/i~~~. Ret. X6. 5XX I. Hubn. J. D.. Gladd. N. T. and Papadopoulos, K. (1977) The lower-hybrid-drift instability as ;I wurcc of ~~O~AOUS rcsistivily for mngnctic ticld reconnection. C;cwpl~~.r.Rc.s. f.c,r/. 4, 125.

M11r~ly~~nl~l.T. paramctors

( Ic)t(l)c’oupling and

~~~Ill~J~ncti~

function

bctwecn

solar

wind

indices. Km. Gco,ph~\. .Spmy

J%i*.s. 20 1 6’3. Per&tilt.

P. and Akasol’u. S. I. (197X) A study ofgcomagnctic (;co~~/Jvs. J. R. u.\Ir. SW. 54. 547. Pudovkin, M. I. and C’hcrtkov. A. D. (lY76) Magnetic field of the solar wind. .S‘r)/w P/I),.\. 50, 213. Pudovkin. M. I.. Zaitseva, S. A. and Bcncvslenska. E. E. (lY7Y) The structure and paramctcr of flare streams. .I. p~p/~p. RLJS.84, 6649. Sanahuja, B., Domingn, V., Wenzcl. K. P.. Josclyn. J. A. and Kepplcr. E. (1’38.3) A large proton went associated solar fil;Jmcnt activity. S&w Pi7~x. 84. 32 I StOrJllS.

126

B. T. TSIJKUANI

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Tsurulani, B. T.. Gould, T.. Goldstein. B. E.. Gon/ale7. W. D. and Sugiura. M. (I99Oa) Intcrplanctar) Alfv&n WIIVCSLund ;turoriil (substorm) activity : I,VP-8. /. ~JC/CY~/~I~.C. RN. (in press). Tsurut;mi. B. T. and Mcng. C. I. ( 1971) Intcrplanctary magnetic licki variations and substorm xtivlty. J. c~cwp/i)-.\. k\. 77. 2964. Tsurutani, B. T.. McPhcrron. R. L. and Gonz;~le/. W. D. ( I9XXc) Aurora1 hypotheses. .S~~icv~e~239. 127X. Tsurutani, B. T.. Russell. C‘. T.. King. J. Fl.. Zwickl. R. D. and Lin. R. P. (10x4) A kinky heliosphcric current sheet : c;lusc 01‘(‘fId M’6 substorms. ~c~I/II‘\. lie\. I.cif. I I. 339. Tsurutani. B. T.. Slovin. J. A.. Kamide. Y.. Zuickl. R. D.. King. .I. H. xnd Russell. C. T. (19X5) Coupling bctwcen the solar wind and the mngnetosphcrc : C‘DA CZ 6. ./. ~JC'O/'/'~'V. Rex 90. I 1’)I Tsurutani. B. T., Smith. E. J.. Thornc. R. M.. Anderson. R. R.. Gurnctt. 0. A.. Parks. G. K.. Lin. C. S. and Russell. C. T. (19x1) Wave particlc interactions ;~t the m;ifnctopa~~sc : contributions to the daysidc ;Iuror:t. (+oq,/rd,.v Rc.c. Lv//. 8. I X3. Tsurutani, B. T. and Thorne, R. M. (1983) Dilt‘uvon praccsscs in the magnetopause boundary layer. G~II/II’~. Rc.\. /.?I/. 9. 1247. Wilcox. J. M. ;Ind Ness. N. F. (196.5) Qu;tsi-stationary corotating structure in the interplanetary medium. ./. q(‘o/I/I!,.\. Ru. 70. 5793. Zwickl, R. D.. Ahbridge. J. R.. Bame. S. J.. Feldman. W. C.. Gosling, J. T. :~nd Smith. E. J. (1983) Plusma propcrtics ol’driver gas Ihllowinp intcrplnnetary shocks obscr\ed by /SEE-3. So/r/r IC’/m/ birc. p. 71 I. NASA C’onf. Publ. (‘Pxx).