Magnetospheric Studies Using the UKS Data 

Grant No. NAGS-536 

(NASA-C3- 180273) C!AGNE?OSPBEEXC STUDIBS N87- 15822 

CSING TEE DKS CA'IA Semiannual Status 

EG;FOX~, 15 Hay 19t5 - 75 Nov. 1586, 

(California Univ-) 62 p CSCZ 048 Unclas 

G3/46 13543 

C. T. Russell and R. C. Elphic 

Institute of Geophysics and Planetary Physics 

University of California 

Los Angeles, California 90024 

March 31, 1987 

Report for Period May 15, 1985 - November 15, 1986 

Prepared for 

Goddard Space Flight Center 

Greenbelt, Maryland 20771 

. 
1. Introduction 

This ffsemiannual report" covers the three reporting periods from 

the initiation of grant NAG5-536 in May 1985 to November 15, 1986. . 

The purpose of the grant is to analyze the magnetic field data from 

the UKS spacecraft and hence learn more about the solar wind 

interaction with the earth's magnetosphere and about the magnetosphere 

itself. In order to undertake this task, we have to first reduce the 

data from essentially raw experimenter data records to engineering 

units. 

date has been minimal and the effort has proceeded much more slowly 

Then the data can be analyzed. The support for this effort to 

than would be optimum. 

The UKS spacecraft was launched in August 1984 as part of the 

AMPTE mission. It co-orbits the earth with the IRM spacecraft in an 

orbit that reaches an apogee of close to 19 earth radii. The 

magnetometer is of a design identical to that of ISEE-1 and -2. 

time resolution of the plasma data is an order of magnitude better 

than on ISEE-1 and -2. 

understanding of the bow shock, upstream waves, interplanetary shocks 

and the magnetopause. Furthermore, the existence of four spacecraft 

(the two ISEE's and the UKS-IRM pair) in the region of the solar wind 

interaction with the earth's magnetosphere permits a series of very 

critical correlative studies. We can examine the evolution of waves 

in the foreshock, the varying structure of the bow shock along the 

boundary, simultaneous behavior of the magnetopause in the north and 

south hemisphere and MHD waves in the magnetosphere and magnetosheath 

simultaneously. 

The 

These improvements can lead to a better 

-2- 
H,is tory 

UCLA refurbished, tested and calibrated its ISEE spare unit and 

delivered it to D. J.Southwood of Imperial College, London for 

installation on the UKS spacecraft. 

of the instrument on the spacecraft. 

data reduction software to Imperial College as well as advice on 

instrument operations and data reduction. 

initial copies of the telemetry data and requested money from NASA to 

enable us to reduce and analyze these data. 

about one quarter of the requested amount of money. 

requested support for this effort and again were awarded only $30K. 

This support is less than that provided guest investigators to study 

already reduced data. 

in order to use it has impaired the amount of science we have been 

able to accomplish. 

We also aided in the integration 

We provided copies of our ISEE 

In 1985 we were provided 

We received only $30K, 

In 1986 we again 

The fact that we also have to process the data 

Data Reduction 

In 1985 we attempted to process the preliminary experimenter data 

tapes. We were able to be successful on half of these tapes but were 

unsuccessful because of formatting errors and other undetermined 

errors on the data tapes. We could not afford to find the errors in 

these data sets and were unable to process half of the data. 

In 1986 we received a new set of definitive data, this data is 

much improved but again we have run out of money before we could 

process all of it so that only half of the definitive tapes have been 

processed. 

-3- 
Team Support 

During 1986 we supported the principal investigator D. J. 

Southwood by attendance at UKS team meetings twice and full AMPTE 

science meetings twice. 

Software Development 

Software was developed to process and display the AMPTE/UKS data 

based on the data reduction algorithms for the ISEE magnetometer. We 

have not been able to afford to write programs to display or list any 

orbit/attitude data. 

Research Efforts 

Upstream Waves. We have examined intervals of the joint occurrence 

of waves at ISEE and UKS in the foreshock region and found that the 

waves vary markedly with position. 

handedness of the waves vary with amplitude. 

presented at COSPAR and published in the COSPAR journal (Russell et 

al., 1986). A copy of this paper is attached. A more detailed 

examination of these waves was prepared and sent to JGR (Russell et 

al., 1987). It is now in press. A copy of this paper is attached. 

We have also found that the 

These results have been 

We have begun a collaboration with Fred Scarf and Bob Strangeway 

on the CCE plasma wave observations of the bow shock on 1 November 

1984. UKS was situated upstream of the bow shock, and can provide 

input parameters to determine the shock characteristics such as 

instantaneous B and Mach number. Larry Zanetti at APL is also 

studying the CCE 

providing UKS upstream data as well as ISEE-1 solar wind and 

Bn 

1 November bow shock observations, and we are 

-4- 
magnetosheath data from a somewhat different local time. This event 

promises to be well-supported observationally. 

Magnetopause Studies 

Another AMPTE/ISEE study begun 1986 centered on the nearlysimultaneous crossing of the dayside magnetopause at two widely 

separated sites on 19 September 1984. 

event is attached. The IMF was southward at this time and the 

spacecraft observed two important, related phenomena. First, between 

1545 and 1600 UT, both UKS and ISEE observe a decrease in field 

strength, together with an inward tilting of the field at UKS (seen in 

the B 

south of the equator. Second, flux transfer events (FTE’s) are 

observed nearly simultaneously at the two widely separated sites. 

A preprint of a paper on this 

component) north of the equator and an outward tilting at ISEE 

n 

This paper is in preparation for JGR. 

Another collaborative magnetopause study centers on 4 September 

1984, when IRM and UKS pass through a highly compressed magnetopause. 

ISEE provided continuous upstream data during the event, and 

fortuitously, the SABRE radar in Britain was able to monitor 

ionospheric flows at the strongly displaced dayside auroral zone. 

During this event FTE’s were observed at UKS and IRM, and ionospheric 

flow disturbances are observed by SABRE correlated with the FTE’s 

Other ISEE/AMPTE Studies 

There are many other joint studies that can be undertaken with the 

ISEE and AMPTE data. 

other groups and we will advise and assist as required. 

Some of these are being actively pursued by the 

One such 
study begun in 1986 centers on an isolated plasma flow and field event 

observed by IRM on 28 March 1985 in the magnetotail. This IRM event 

coincides with disturbances observed in the ionosphere by EISCAT near 

the IRM footprint. 

Baumjohann on the IRM plasma and field data, and has also supplied 

supporting ISEE data for several IRM/CCE magnetotail study intervals. 

The lack of resources prevent us from pursuing this as vigorously as 

we should. 

Rick Elphic has been working with Wolfgang 

-6- 
*a POOR QUALITY Adv Space Res Vol. 6. No 1. pp. 85-88. 1986 

Pnnted in Great Bntaia All rights reserved. 

SIMULTANEOUS OBSERVATION OF 

UPSTREAM WAVES WITH ISEE AND 

AMPTE 

C. T. Russell,* J. G. Luhmann,* R. C. Elphic* and 

D. J. Southwood** 

'Institute of Geophysics and Planetary Physics, University of 

California, Los Angeles, CA 90024, U.S.A. 

**Blacker! Laboratory, Imperial ColIege, London, U. K. 

ABSTRACT 

0273-1177K36 60.00 + SO 

Copynght @ COSPAR 

Measurements obtained by ISEE-2 and the UKS spacecraft upstream of the Earth's bow shock are 

examined. 

frequency range. 

in different regions of space. 

similar at high frequencies and least similar at low frequencies. The position dependent 

nature of the upstream waves indicates that comparisons between ground-based measurements 

and in situ observations must be undertaken with some caution. 

Simultaneous observations show that upstream waves are excited over a broad 

Even when peaked spectra occur the peaks can occur at different frequencies 

Generally the spectra seen at the two locations are most 

INTRODUCTION 

Energetic particles are observed to flow back toward the Sun on field lines that connect to 

the Earth's bow shock,. The 

first is leakage from the magnetosheath /1,2/. If the thermal speed of particles in the 

magnetosheath exceeds their drift speed, some of them can propagate back upstream. 

second mechanism is reflection by the bow shock /3,4,5/. 

motion reversed by the combined action of the magnetic gradient and the electric potential 

jump across the shock. 

approaches the bow shock. 

the interplanetary electric field. Thus, the ion foreshock boundary lags behind the 

electron foreshock boundary. 

These energetic beams are accompanied by waves which grow on the free energy available in 

the beam-like particle distributions. Since the properties of the beams vary with position 

in the foreshock because of both source variations and propagation effects, and since waves 

have finite growth times we expect that the properties of the upstream waves should vary 

also. In fact, it has been known for some time that the properties of upstream MHO waves 

are quite position dependent /6/. However, our understanding of how the wave properties 

vary has been built up from many individual events under varied solar wind conditions. It is 

not always possible to ascertain what changes are due to the location of the observer and 

what are acts to the different solar wind conditions. 

The launch of the AMPTE mission in August 1984 with its two spacecraft that went into the 

solar wind,.UKS and IRM,combined with the ISEE-1 and -2 spacecraft which had been launched 

in 1977, has allowed us to begin to probe spatial variations in the upstream waves under 

constant solar wind conditions. for this purpose we need study the data from only one 

spacecraft of each pair. We will choose to use the ISEE-2 /7/, and the UKS magnetometer 

data /8/ and solar wind data from the UKS three-dimensional ion instrument /9/. 

Two mechanisms have been proposed for these returned beams. 

The 

Energetic ions can have their 

Electrons have the greatest speeds and are observed first as one 

Ions, moving more slowly upstream, are swept back somewhat by 

OBSERVATIONS 

We have reviewed all data obtained by ISEE-2 and the UKS while they were both returning data 

in the solar wind during October and November 1984. From these observations we selected 

for further study intervals during which one or both spacecraft were observing upstream 

waves and the interplanetary magnetic field was moderately steady. 

nature of the observations with four examples. 

October 19, 1984. Figure 1 shows the simultaneous measurements obtained by ISEE-2 ana UKS 

on day 293, 1984 from 0840 to 0848 UT. The right-hand two panels show the time series at 

one-second resolution. The top panel on the left shows the power spectrum summed over all 

three sensors. The bottom panel shows the location of the spacecraft relative to the foreshock boundary in the 8-V plane. 

displaced from each other. 

A. Johnstone (personal communication, 1986) to scale the shock location. 

Below we illustrate the 

The B-V planes for the two spacecraft are parallel but 

We have used the solar wind data supplied by M. Smith and 

85 
86 C. T. Russell et al. 

oc1 'OBER 19. 1984 

t 

%+-7Ydo, 

Frequency (Hertz) o I 

BX 

BY 

82 

b 842 844 846 848 

Universal Time 

Fig. 1. The magnetic field power spectra, 

time series and foreshock geometry on 

October 19, 1984 at both ISEE-2 and UKS. 

In this'example ISEE-2 is outside the foreshock region and UKS is behind the foreshock 

boundary. 

band from ZOO-seconds to 2-second periods. 

are left-hand elliptically polarized, with an ellipticity of 0.73. 

The power spectrum at UKS is enhanced over that' at ISEE over the entire spectral 

The waves at the peak of the spectrum at UKS 

Fig. 2. 

time series and foreshock geometry on 

October 30, 1984. 

The magnetic field power spectrum, 
. 

1 

p.~r,:p- PSC .: OSilUi..Nb I .-1b E3 

OF POOR QUALm 

Simultaneous Upstream Waves 

NOVEMBER 5. 1984 ___- -___ 

-0 

L 

10% '''(02 ''70 eo, 0- 

Frequency (Hertz) lo - 

5 /r:NF.,v ?$,-. - - 'lex n 2 or--

Y -'A I I 1 ,- 01, *(a< ( . . ' , *.-. -A. .-BY 

u- 

"5- 1 I 

f o-b'-~ -- -_c-:BZ 

mm- IO' 

.#' --I 

ISEE-2 

,I I 

5-t ,-L,-- *, Hk - -- .,#I 

'122s 1227 1229 1231 1?33 

universal Time 

Fig. 3. 

time Series and foreshock geometry on 

November 5, 1984 from 1225 to 1233 UT. 

The magnetic field power spectrum, 

NOVEMBER 5. 1984 

10- - 

o- .- O: 

f 10- 

CD-5 - a- ISEE-2 1 

Fig. 4. 

time series and foreshock geometry on 

November 5, 1984 from 0925 to 0941 UT. 

The magnetic field power spectrum, 

October 30, 1984. 

foreshock with the bow shock. 

identical, but at low frequencies there is an almost complete absence of upstream waves at 

ISEE. It is possible that this difference is due to the presence of upstream electrons at 

ISEE but no upstream ions while at UKS both are present. 

0.08 Hz are right-handed almost circularly polarized waves propagating at a small angle to 

the magnetic field. The low frequency waves peaking at about 0.025 Hz at UKS are also 

right-handed with an ellipticity of 0.34. 

Figure 2 shows the observations on day 304, 1984 from 1352 to 1400 UT. 

TStE and UKS 1 ie close to the bow shock with ISEE close to the point of tangency of the 

Here the power spectra at frequencies above 0.1 Hz are 

The high frequency waves above 
88 C. T. Russell er al. 

November 5, 1984(A). 310 from 1225 to 1233 UT 

this time ISEt and UKS are nearly coincident in the B-V plane display but in fact are close 

to 10 Earth radii apart. The time series in the right-hand two panels and the power 

spectra show that the signals observed by the two spacecraft are. quite similar. 

locations the signals are right-hand polarized with an ellipticity of about 0.6. 

Figure 3 shows the observations on day 

At both 

I 

At 

November 5, 1984(8). 

0925 to 0941 UT. Now the two spacecraft are well separated in the B-V plane. The spectra 

are qualitatively similar but they do differ at the lowest frequencies. 

they have different peak frequencies. 

polarized while the waves at UKS are right-hand polarized. 

DISCUSSION AND CONCLUSIONS 

Figure 4 shows the observations three hours earlier on day 310 from 

In particular, 

Furthermore, the waves at ISEE are left-hand 

From our examination of those cases in which one spacecraft is in front of and the other 

spacecraft behind the foreshock as illustrated in Figure 1, it is clear that the enhancement 

in the power spectrum of upstream waves occurs across the entire frequency spectrum 

measured not just at around 0.03 Hz. This observation is important to those studying the 

source of Pc 3, 4 waves in the dayside magnetosphere. The upstream wave source has a 

broad spectrum. The narrow bandedness of the terrestrial emissions must have its source in 

the resonance of magnetospheric field lines. 

Another observation of importance to those studying Pc 3, 4 waves is that spectral peaks 

may occur at different frequencies at different locations in the foreshock region. 

if one is conducting a correlative study between a ground observing site and a space 

observation and one observes a different frequency wave at the two locations, this does not 

imply that the ground-based signal does not have its origin in space. The signal observed 

on the ground might very well have propagated from some other region of the foreshock where 

tile wave properties were different. 

We note that the B-V coordinate system is a useful one for ordering the foreshock data. 

However, its success here should not be taken to imply that the wave properties depend only 

on the location of the spacecraft in this plane. In fact, when all observations of the 

upstream region are examined it becomes clear that the properties depend on the full threedimensional geometry of the interaction. 

Thus, 

ACKNOWLEDGMENTS 

We wish to thank E. W. Greenstadt for the use of his program for displaying the 5-V 

geometry of the bow shock and foreshock region and to M. A. Smith and A. Johnstone for the 

use of their data prior to publication. 

and Space Administration under research contracts NAG5-536 and NAS5-28448. 

This work was supported by the National Aeronautics 

REFERENCES 

D. A. Tidman and N. A. Krall, Shock Waves in Collisionless Plasmas, 175pp, 

J. P. Edmiston, C. F. Kennel, and D. Eichler, Escape of heated ions upstream of 

quasi-parallel shocks, Geophys. Res. Lett., 9, 531, 1982. 

B. U. 0. Sonnerup, Acceleration of particles reflected at a shock front, 

J. Geophys. Res., 74, 1301, 1969. 

G. Paschmann, N. Sckopke, J. R. Asbridge, S. J. Bame, and J. T. GosLing, Energization of solar wind ions by reflection from the earth's bow shock, 

J. Geophys. Res., 85, 4689, 1980. 

s. J. Schwartz, M. F. Thomsen, and J. T. Gosling, Ions upstream of the earth's 

bow shock: A theoretical comparison of alternative source populations, 

J. Geophys. Res., 88, 2039, 1983. 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

C. T. Russell and M.M. Hoppe, Upstream waves and particles, Space SCi. Rev., 

- 34, 155-172, 1983. 

C. T. Russell, The ISEE-1 and -2 fluxgate magnetometers, IEEE Trans. Geosci. 

Elect., GE-16, 239-242, 1978. 

8. D. J. Southwood, W. A. C. Mier-Jedrzejowicz, and C. T. Russell, The fluxgate 

magnetometer for the AMPTE UKS subsatellite, IEEE Trans. Geosci. Remote 

Sensing, GE-23, 301-304, 1985. 

A. J. Coates, J. A. Bowles, R. A: Gowen, B. K. Hancock, A. D. Johnstone, and 

S. J. Kellock, AMPTE UKS three-dimensional ion experiment, IEEE Trans. Geosci. 

Remote Sensing, GE-23, 287-292, 1985. 

9. 
Upstream Waves Simultaneously 

Observed by ISEE and UKS 

C. T. Russell, J. G. Luhmann, and R. C. Elphic 

Institute of Geophysics and Planetary Physics 

University of California, Los Angeles, CA 90024 USA 

D. J . Southwood 

Blackett Laboratory, Imperial College, London SW7, 2 BZ UK 

M. A. Smith, A. D. Johnstone 

Mullard Space Science Laboratory 

Holmbury St. Mary, Dorking, 

Surrey, RH5,6NT UK 

October 1986 
Abstract 

Measurements obtained in the solar wind by ISEE-2 and the United 

Kingdom Subsatellite UKS have been examined for observations of 

upstream waves. These data reveal that the waves in the foreshock 

region are enhanced at: a1.l frequencies from at least .003 Hz to 0.5 

Hz. The wave spectra generally have a spectral peak but this peak is 

usually broad and the peak frequency depends on the position of the 

spacecraft. 

similar at high frequencies and least similar at low frequencies. 

Generally the spectra seen at the two spacecraft are most 

The 

geometry of the interaction is displayed in the plane containing the 

magnetic field and the solar wind velocity and the spacecraft 

location. However, this coordinate system does not order all the 

observed wave properties. It does not clearly explain or order the 

handedness of the waves, or their direction of propagation. 

clear that the upstream region is inherently three-dimensional. The 

It is 

position dependent nature of the upstream waves indicates that 

comparisons between ground-based measurements and in-situ observations 

must be undertaken with some caution. 

Introduction 

Our present understanding of the ULF waves obsemed upstream of the 

earth's bow shock is built upon many individual observations under 

varying solar wind conditions. From these individual observations we 

have developed a model of how the properties of the waves depend on 

the location of the observer relative to the magnetic field line 
tangent to the bow shock or more specifically a boundary somewhat 

behind the tangent field line known as the foreshock boundary. 

variability of the solar wind properties from Observation to 

The 

observation limits our ability to determine precisely the spatial 

dependence of the properties of the waves. However, the launch of the 

AMPTE mission in August 1984 with its two spacecraft, IRM and UKS, in 

a highly elliptic orbit extending well into the solar wind, allows us 

to make observations of the upstream waves simultaneously with those 

obtained by the ISEE-1 and -2 spacecraft whose orbits also extend 

upstream of the shock. 

18.7 earth radii (Re). 

The apogee of the UKS and IRM spacecraft is at 

The apogee of the ISEE-1 and -2 spacecraft is 

23 Re. 

The two spacecraft of each of these pairs are separated from each other 

by only a few hundred kilometers in the near apogee region. 

purpose of studying the spatial variations of the properties of the 

waves we need to examine only the data from one spacecraft of each 

For the 

pair. We will choose to use the ISEE-2 data and the UKS data, using 

the magnetic field data from the ISEE-2 fluxgate magnetometer 

(Russell, 1978) and from the UKS fluxgate magnetometer (Southwood et 

al., 1985) and the solar wind data from the UKS three-dimensional ion 

experiment (Coates e t a l . , 1985). We note that the UKS fluxgate 

magnetometer was originally the spare unit for the ISEE-2 spacecraft 

and hence the two magnetometers are identical instruments. Any 

differences observed in the spectral properties of the waves observed 

with these instruments arise from the waves themselves. 

-2- 
Upstream waves have been studied for almost two decades beginning with 

Greenstadt et al. (1968) and Fairfield (1969). They have been found 

in front of the bow shocks of Mercury (Fairfield and Behannon, 

1976), Venus and Jupiter (Hoppe and Russell, 1982) and 

interplanetary shocks (Russell et al., 1983). These upstream waves 

are clearly generated by MHD instabilities in the back-streaming 

particles that accompany these waves. 

arise from either of two mechanisms. First, some fraction of the 

incoming ions may be reflected by the bow shock (Sonnerup, 1969; 

Paschmann et al., 1980; Schwartz et al., 1983). Second, ions heated 

by their passage through the bow shock may escape back upstream if 

their thermal energy is great enough (Tidman and Krall, 1971; 

Edmiston et al., 1982). It is probable that both these mechanisms are 

operative with varying relative strengths upstream of the bow shock, 

probably depending in part on the angle of the interplanetary 

magnetic field to the shock normal at the source of the upstreaming 

particles. Thus the properties of the beams should depend on location 

within the foreshock because of variations in the source of the beams. 

In addition, the beams should evolve with distance from the shock due 

to the presence of the MHD instabilities that generate the waves. As 

we will see below the properties of the waves are also quite 

spatially dependent. 

These energetic particles can 

Finally, we note that there is much evidence that the waves generated 

in the upstream region are convected through the bow shock and 

magnetosheath and couple into the magnetosphere exciting dayside Pc 3- 

4 magnetic pulsations. For a recent review of this topic the 

-3- 
interested reader is referred to the paper by Odera (1986). 

Observations 

We have examined all the available UKS and'ISEE-2 magnetic records in 

October and November 1984 while both spacecraft were returning 

measurements in the solar wind. From these data we have selected 

intemals of from 8 to 16 minutes long during which the interplanetary 

magnetic field was fairly steady in direction. 

intervals both ISEE and UKS were in the upstream wave region. 

picked two periods with only one satellite in the upstream wave reigon 

to further illustrate the nature oE the upstream waves. 

During most the these 

We 

October 19, 1984. Figure 1 shows the simultaneous measurements 

obtained by ISEE-2 and UKS on 10/19/84 (day 293) from 0840 to 0848 UT. 

On the right-hand side are the two time series at one-second . 

resolution in solar ecliptic coordinates. 

On the left-hand side in the top panel is the power spectrum of the 

waves summed over the three sensors. 

the geometry of the obsemations. 

containing the solar wind velocity, the interplanetary magnetic field 

direction and the spacecraft. The B-V planes for the two spacecraft 

differ but have been superimposed here under the assumption that the 

nature of the waves observed depends only on the relative location of 

the spacecraft in the B-V plane. The foreshock location has been 

sketched in under the assumption that the upstream beams have an 

The bottom left-hand panel shows 

The plane shown is the B-V plane 

-4- 
energy of 1.2 times that of the incoming solar wind protons 

(Greenstadt and Baum, 1986). In order to scale the size of the bow 

shock we have used the solar wind parameters measured by the UKS threedimensional plasma analyzer. These data, together with the location 

of the spacecraft and magnetic field direction in solar ecliptic 

coordinates are given in Table 1. 

will resemble that of Figure 1. 

The format of the following figures 

In this example ISEE-2 is outside the foreshock region and UKS is 

within it. 

that at ISEE over the entire spectral band from 200 second period to 

2 second period. The waves at the peak of the spectrum seen at UKS 

are left-handed polarized, propagating at 23O to the magnetic field 

according to the spectral analysis.technique of Means (1972): The 

waves are elliptically polarized with an ellipticity of 73%. 

percent polarization is moderate, 58%.. These parameters are 

summarized in Table 2. 

We see that the power spectrum at UKS is enhanced over 

The 

October 23, 1984. Figure 2 shows the simultaneous measurements 

obtained by ISEE-2 and UKS on 10/23/83 (day 297) from 0845 to 0853 UT 

in the same format as Figure 1. 

magnetic field has rotated so that it is nearly orthogonal to the 

usual spiral angle. In this situation UKS is outside the foreshock 

and ISEE-2 is inside the foreshock. We note that the solar wind 

density of 7 cme3 used in Table 2 and in constructing Figure 2 was 

assumed so that both spacecraft were in front of the bow shock in 

Figure 2. 

In this example the interplanetary 

The ion instrument was not in the proper mode to return an 
accurate measure of the solar wind density at this time. 

example ISEE observes the upstream waves and UKS has a much reduced 

In this 

. 

spectrum. Again we see an enhancement in the upstream waves region 

over the entire frequency spectrum. The waves at the peak of the 

spectral enhancement are right-handed here and not left-handed as in 

the previous example. 

the magnetic field, 44*, and are only weakly polarized, 36%. There is 

a slight enhancement of the waves at high frequencies above 0.1 Hz. 

The waves are propagating at a large angle to 

We believe this is due tqnatural emissions possibly associated with 

electrons returning along field lines which connect to the shock but 

upstream of the foreshock boundary (Feldman et al., 1983). 

October 30, 1984. 

1984, ISEE and UKS both lie close to the bow shock but ISEE lies 

In this example, from 1352 to 1400 UT on day 304, 

close to the point of tangency of the foreshock boundary with the 

bow shock. Figure 3 shows that at frequencies above 0.1 Hz both 

spectra are identical. Yet at low freqencies there is an almost 

complete absence of waves at ISEE. 

as discussed in the previous example. 

This phenomenon may be the same 

Upstream electrons might be 

generating waves at both ISEE and UKS but either the ions present at 

ISEE, and upstream of ISEE, had not had enough time to generate 

measureable waves or the bow shock was somewhat smaller than 

. 

sketched and only electrons and not ions were present at ISEE. The 

waves at high frequencies, above .08 Hz are almost identical in all 

their properties. They are right-handed, almost circularly 

polarized waves, c - .9l,.propagating at a small’ angle to the 

magnetic field, 18-20°, and highly polarized, 80-98%, as shown in 

-6- 
Table 2. The low frequency waves that peak at about .025 Hz at UKS 

are also right-hand polarized with an ellipticity of 0.34, are 

propagating at large angle to the magnetic field, 65O, and are 

moderately well polarized, 74%. 

November 5A, 1984. As indicated in Table 1, from 1225 to 1233 on day 

310 ISEE-1 and UKS lay about 12 Re apart. 

Figure 4, the two spacecraft lay very close as projected in the B-V 

plane. Examination of the wave forms on the right-hand side of Figure 

4 show the time series to be quite different. 

spectral densities are similar. Their spectra almost lie on top of 

one another with UKS, which is slightly closer to the foreshock-bow 

shock tangency, being slightly below ISEE at the lowest frequencies. 

Nevertheless, as shown in 

However, their power 

As shown in Table 2 the waves at the peak of the spectrum are righthanded ellipically polarized with ellipticities of about 0.6, 

propagating at moderate angles to the field, 14O and 37O and have 

weak percent polarizations, 21 and 57%. At frequencies near 0.1 Hz the 

waves have very similar amplitudes at the two spacecraft but are 

decidedly different in polarization. At AMPTE the waves are left 

handed polarized with an ellipticity of -0.35 but at ISEE they are 

right-hand polarized with a polarization of 0.89. At both locations 

the waves are propagating nearly along the field. 

November 5B, 1984. Three hours earlier than the above event, the 

magnetic field orientation was sufficiently different that ISEE and UKS 

became well separated in the foreshock as shown in Figure 5. 

spectra at the two locations are different but only at the lowest 

Now the 

-7- 
frequencies. Above .03 Hz the spectra are identical. The lower 

spectral densities are observed at ISEE which is further from the 

shock. 

given in Table 2.' The waves have a large angle of propagation to the 

field 36O and 59O, and are weakly polarized. The waves differ 

markedly in their polarizations. 

while at UKS they are right-hand polarized. This is true whether the 

entire bandwidths of the two peaks are analyzed or the exact same bands 

of frequencies are analyzed at the two spacecraft. 

near 0.1 Hz, the waves become more circularly polarized, propagate 

more nearly along the field, are more highly polarized and are more 

The properties of the waves at the peaks of the two spectra are 

At ISEE they are left-hand polarized 

At higher frequencies 

similar in their properties than near the peak of the wave spectrum 

October 6, 1984. 

from 1228 to 1244 as shown in Figure 6. 

closer to the bow shock. 

A similar geometrical situation is found on day 280 

However, here ISEE-2 is 

Again the spectra are nearly identical at 

high frequencies. The waves at the spectral peaks near .06 Hz are 

propagating at a small angle to the magnetic field, 9O at UKS and 19O 

at ISEE and are only weakly polarized at UKS, 32%, but more strongly 

polarized at ISEE, 76%. The waves are left-hand polarized at both 

locations with the ISEE waves being the more circularly polarized. 

October 14, 1984. The major difference between this event from 0829- 

0840 on day 288 and the previous one is that ISEE-2 is further from 

the bow shock. 

frequencies. 

The spectra now coincide only at the very highest 

The waves at both locations are propagating at a large 

angle to the magnetic field, 53O at UKS and 80° at ISEE. The waves 

-8- 
are right-handed at UKS with an ellipticity of 0.45 and are nearly 

linearly polarized at ISEE with an ellipticity of -0.16. 

locations the waves have moderate percent populations, 40% at UKS and 

At both 

68% at ISEE. 

locations of the two spacecraft are very close, only 0.8 Re apart. 

We note that in this example the B-V planes through the 

October 29, 1984. This example from 1213 to 1229 UT on day 303, as 

shown in Figure 8, is not unlike the previous example. The principal 

difference is that the B-V planes through the two spacecraft here are 

8.4 Re apart. 

the field direction than at ISEE, 1S0 at UKS but 72O at ISEE. The 

waves at UKS are almost right-hand circularly polarized with an 

eccentricity of 0.77 and at ISEE are almost linearly polarized with 

an eccentricity of -.12. The UKS waves.have a low, 20% percent 

polarization while the waves at ISEE have a moderate percent 

polarization of 58%. 

The waves at UKS are propagating much more closely to 

October 27, 1984. On day 301 from 0722 to 0738 UT ISEE and lkS were 

again similarly situated but spread somewhat farther apart in the BV plane as illustrated in Figure 9. 

planes, however, was half that of Figure 8. Here the spectra are more 

The separation of the two B-V 

closely aligned especially at the higher frequencies. At both 

locations we observe waves propagating nearly along the magnetic 

field with right-hand polarization. 

November 26, 1984. In our last example from 0704 to 0712 on day 331 

shown in Figure 10, ISEE was nearly radially upstream of UKS. Here the B- 

-9- 
V planes are almost coincident. The waves seen at UKS downstream from 

ISEE are much larger than those seen at ISEE. One possible 

explanation of this is that UKS is right at the bow shock and that the 

oscillations seen at UKS are in fact the pulsations associated with 

the quasi-parallel shock. The waves seen at ISEE are highly polarized 

with an 88% polarfzation, are left-handed with an ellipticity of - 

0.67 and are propagating at an angle of 31O to the magnetic field. 

The waves seen at UKS are also moderately polarized with a 68% 

polarization but are right-hand polarized with an ellipticity of 

0.64. 

magnetic field. 

The UKS waves are propagating at an angle of only 12O to the 

Discuss ion 

The availability of simultaneous observations in two quite separate 

regions of the foreshock gives us very useful insight into the nature 

of the waves upstream of the bow shock. 

our examination of those cases in which one spacecraft is beyond the 

foreshock boundary such as on October 19 and 23, that the enhancement 

in the power spectrum takes place at all frequencies, not just in the 

spectral band centered at around 0.03 Hz. This fact is important for 

those studying Pc3, 4 waves in the dayside magnetosphere. 

not to be appreciated that the upstream wave spectrum is broad. 

these waves are convected to the magnetopause and couple to the 

magnetosphere they can excite a wide range of frequencies in the 

magnetosphere. The narrow band emissions seen there must be a 

magnetospheric effect and not a reflection of a narrow band source. 

First, it is evident from 

It seems 

If 

- 10- 
There are certainly spectral peaks in the upstream waves. Almost 

every spectrum had a distinguishable spectral enhancement or peak. 

However, the peaks seen simultaneously at different spacecraft were not 

necessarily at the same frequency. 

5) and October 6 (Figure 6) clearly illustrate this difference. This 

position-dependent spectrum may explain why different ground observing 

sites have different responses to the interplanetary magnetic field. 

The variability of the dependence of the period of waves seen at 

various ground stations on the strength of the interplanetary 

magnetic field and the apparent differences between the dependence 

seen on the ground and at arbitrary locations in the foreshock led 

Green et al. (1983) to call into question whether upstream waves are a 

major source of magnetospheric Pc 3-4 pulsations. However, before 

these conclusions can be drawn one must compare ground data with the 

waves in space that will be convected to the magnetopause. 

The events of November 5 (Figure 

The B-V coordinate system used herein is a convenient system in which 

to visualize the spacecraft positions and it provides much order to 

the data. However, it does not order all the wave properties. We 

have examined the handedness of the waves, their angle of propagation 

to the magnetic field and their percent polarization as a function of 

position in the B-V plane and have found no ordering. 

that waves properties are determined by the three-dimensional nature of 

the interaction. 

properly exhibit the angle between the IMF and the shock normal 

because the shock normal is not necessarily a vector in the B-V 

Thus, we feel 

For example the B-V plane diagrams do not 

-11- 

~ -~ 
plane. 

We have also looked for correlations between parameters. 

Specifically we examined the correlation between eccentricity and 

percent polarization and between angle of propagation and percent 

polarization and found no correlation. We did, however, find one 

correlation between eccentricity and the fractional amplitude of 

the waves, the square root of the power in the peak of the spectrum 

normalized by the background magnetic field strength. 

correlation is shown in Figure 11. 

This 

When the fractional amplitude is 

0.3 or below the waves are left-handed in the spacecraft frame and 

when they are above 0.3 in amplitude the waves are right-handed in the 

spacecraft frame. 

We emphasize that these left and right handed waves are not two 

separate populations occuring under different solar wind conditions 

but that both polarizations occur simultaneously in different regions 

of the foreshock. 

polarizations are the waves illustrated in Figures 5, 7, 8, and 10. 

This obsentation is consistent with the analysis of Hoppe and Russell 

(1983) who showed that the narrow band waves were generally righthanded. We understand these differences in terrns of both resonant 

and non-resonant instabilities as discussed by Sentman et al. (1981). 

Examples of this simultaneous occurrences of the two 

Conclusions 

We have examined a number of examples of simultaneous magnetic field 

-12- 
measurements in the upstream region ahead of the bow shock using the 

identical magnetometers flown on ISEE-2 and UKS. On field lines 

behind the ion foreshock boundary, waves appear over the entire 

frequency range from .003 to .5 hz. Their power spectra are generally 

peaked. However, the peak frequency is position dependent. Generally 

spectra are most similar at the two spacecraft at the higher 

frequencies. The B-V plane is useful for ordering the observations to 

first order but this coordinate system does not order all the wave 

properties such as percent polarization, handedness, or direction of 

propagation. Thus the upstream wave region is inherently threedimensional. 

upstream waves indicates that caution must be exercised when comparing 

simultaneous measurements on the ground and in space, or even 

comparing statistical properties, for only a. fraction of the waves in. 

the upstream region convect against the magnetopause. 

The positional dependence of the spectral peak of the 

Acknowledgements 

We wish to thank E. W. Greenstadt fo the use of his program for 

displaying th B-V geometry of the bow shock and foreshock region. 

This work was supported by the National Aeronautics and Space 

Administration under contracts NAGS-536 and NAS5-28448. 
References 

Coates, A. J., J. A. Bowles, R. A. Gowen, B. K. Hancock, A. D. 

Johnstone and S. J. Kellock, AMPTE UKS three-dimensional ion 

experiment, IEEE Trans. Geosci. Remote Sensing, GE-23, 287-292, 

1985. 

Edmiston, J. P., C. F. Kennel and D. Eichler, Escape of heated ions 

upstream of quasi-parallel shocks, Geophys. Res. Lett., 9, 531, 

1982,. 

Fairfield, D. H., Bow shock associated waves obsewed in the far 

upstream interplanetary medium, J. Geophys. Res., 74, 3541, 

1969. 

Fairfield, D. H. and K. W. Behannon, Bow shock and magnetosheath 

waves at Mercury, J. Geophys. Res., 81, 3897, 1976. 

Feldman, W. C., R. C. Anderson, S. J. Bame, S. P. Gary, J. T. 

Gosling, D. J. McCornas, M. F. Thornsen, G. Paschmann and M. M. 

Hoppe, electron velocity distributions near the earth’s bow 

shock, J. Geophys. Res., 88, 96-110, 1983. 

Green, C. A., T. J. Odera and W. F. Stuart, The relationship between 

the strength of the IMF and the frequency of magnetic 

pulsations on the ground and in the solar wind, Planet. Space 

Sci., 31, 559-567, 1983. 

-14- 
Greenstadt, E. W., and L. W. Baum, Earth's compressional foreshock 

boundary revisited: Observations by the ISEE-1 magnetometer J. 

Geophys. Res., submitted, 1986. 

Greenstadt, E. W., I, M Green, G. T. Inouye, A. J. Hundhausen, S. J. 

Bame and I. B. Strong, Correlated magnetic field and plasma 

obsemations of the earth's bow shock, J. Geophys. Res., 73, 

51, 1968. 

Hoppe, M. M. and C. T. Russell, Particle acceleration at planetary 

bow shock waves, Nature, 295, 41-42, 1982. 

Means, J. D., Use of the three-dimensional covariance matrix in 

analyzing the polarization properties of plane waves, J. 

Geophys. Res., 77, 5551, 1972. 

Odera, T. J., Solar wind controlled pulsations: A review, Rev. 

Geophys., 24, 55-74, 1986. 

Paschmann, G., N. Sckopke, J. R. Asbridge, S. J. Bame, and J. T. 

Gosling, Energization of solar wind ions by reflection from the 

earth's bow shock, J. Geophys. Res., 85, 4689, 1980. 

Russell, C. T., The ISEE-1 and -2 fluxgate magnetometers, IEEE Trans. 

Geosci. Remote Sensing, DE-16, 239-242, 1978. 
Russell, C. T., E, J. Smith, B, T. Tsututani, J. T. Gosling and S. J. 

Bame, Multiple spacecraft observations of interplanetary 

shocks: Characteristics of the upstream ULF turbulence, in 

Solar Wind Five (edited by M. Neugebauer), pp. 385-400, NASA 

Conference Publication 2280, Washington, D.C., 1983. 

Schwartz, S. J., M. F. Thomsen and J. T. Gosling, Ions upstream of 

the earth's bow shock: 

source populations, J. Geophys. Res., $8, 2039, 1983. 

A theoretical comparison of alternative 

Sentman, D. D., J. P. Edmiston and L. A. Frank, instabilities of low 

frequency, parallel propagating electromagnetic waves in the 

earth's foreshock region, J. Geophys. Res:, 86, 7487-7497, 

1981. 

Sonnerup, B. U. O., Acceleration of particles reflected at a shock 

front, J. Geophys. Res., 74,1301, 1969. 

Southwood, D. J., W. A. C. Mier-Jedrzejowicz and C. T. Russell, The 

fluxgate magnetometer for the AMPTE UKS subsatellite, IEEE 

Trans. Geosci. Remote Sensing, GE-23, 301-304, 1985. 

Tidrnan, D. A. and N. A. Krall, Shock Waves in Collisionless Plasmas, 

175 pp., Wiley-Interscience, New York, 1971. 

-16- 
Figure Captions 

Figure 1. The magnetic power spectra, time series and foreshock 

geometry.on October 19, 1984 (day 293). The upper right-handed panel 

shows the magnetic field at one second resolution in solar ecliptic 

coordinates obtained by the UKS satellite. 

shows the corresponding measurements obtained by the ISEE-2 spacecraft. 

The upper left panel shows the power spectrum obtained through a Fast 

The lower right-hand panel 

Fourier Transform of the displayed time series. 

three sensors has been summed. 

from ISEE-2. The lower right-hand panel shows the location of the 

spacecraft in the B-V plane, the plane containing the magnetic field, 

the solar wind velocity vector and the spacecraft. 

The power from all 

The heavy line corresponds to the data 

The B-V 

- planes of the two spacecraft are in fact different but have been 

superimposed for easy comparison'of the relative position of the 

spacecraft. The information on spacecraft position, the vector 

magnetic field, and the solar wind density and velocity used to 

construct this panel is given in Table 1. 

Figure 2. The magnetic power spectra, time series and foreshock 

geometry on October 23, 1984 (day 297). 

Figure 3. The magnetic power spectra, time series and foreshock 

geometry on October 30, 1984 (day 304). 
Figure 4. The magnetic power spectra, time series and foreshock 

geometry on November 5, 1984 (day 310) from 1225 to 1233 UT. The B-V 

planes through ISEE and UKS are separated by 8.3 RE at this time. 

Figure 5. The magnetic power spectra, time series and foreshock 

geometry on November 5, 1984 (day 310) from 0925 to 0941 UT. The B-V 

planes through ISEE and UKS are separated by 5.1 RE at this time. 

Figure 6. The magnetic power spectra, time series and foreshock 

geometry on October 6, 1984 (day 280). 

and UKS are separated by 5.8 RE at this time. 

The B-V planes through ISEE 

Figure 7. The magnetic power spectra, time series and foreshock 

geometry on October 14, 1984 (day 288). 

and UKS are separated by 0.8 RE at this time. 

The B-V planes through ISEE 

Figure 8. The magnetic power spectra, time series and foreshock 

geometry on October 29, 1984 (day 301). 

and UKS are separated by 8.4 RE at this time. 

The B-V planes through ISEE 

Figure 9. The magnetic power spectra, time series and foreshock 

geometry on October 27, 1984 (day 301). 

and UKS are separated by 4.3 RE at this time. 

The B-V planes through ISEE 

Figure 10. The magnetic power spectra, time series and foreshock 

geometry on November 26, 1984 (day 331). 

and UKS are separated by 0.8 RE at this time. 

The B-V planes through ISEE 
Figure 11. The ellipticity of the waves near the peak of the power 

spectrum as a function of the fractional amplitude of the waves. 

ellipticity is determined using the Means (1972) technique and is 

defined as being the ratio of the minor to major axis of the 

perturbation ellipse. The orientation of the normal to the 

perturbation ellipse is determined from the quadrature power in the 

Means technique. 

total power under the spectral peak divided by the background field 

strength. 

in Table 2. 

The 

The fractional amplitude is the square root of the 

The bandwidth used in this analysis is given for each event 

-19- 
Table 1 

Parameters used in Calculating Foreshock Geometry 

GSE Location (RE) 

Event ISEE 

October 19 (21.3, 4.6, -1.8) 

October 23 (13.7,-2.2,-5.4) 

October 30 (14.2,-3.8,-5.2) 

November 5A (20.0, 1.0, 1.3) 

November 5B (21.0, 0.2, 0.5) 

- 

October 6 (11.1, 0.2,-5.3) 

October 14 (20.5, 4.8,-3.2) 

October 29 (17.7, 4.2, 2.2) 

October 27 (14.0, 5.3, 3.3) 

- UKS 

(11.1, -7.4, 0.4) 

(15.9,-8..0, 0.2) 

(12.5,-9.9, 0.2) 

(15.8,-10.2,-0.2) 

(15.0,-10.8,-0.1) 

(14.0,-4.7, 0.5) 

(18.3, -4,2, 0.1) 

(16.4,-4.8,-0.3) 

(17.2,-7.6,-0.1) 

B(nT) N(~rn'~) V(kms") 

(-10.4,9.3,-1.0) 7.1 540 

(-4.9,-0.9, 2.4) 7.0* 650 

(3.9,-2.5, 1.8) 6.0 360 

(4.3, 0.1, 1.7) 4.0 550 

(4.1,-0.2,-0.1) 3.9 565 

(8.5,-5.7, 0.0) 3.8 565 

(4.2,-1.3, 0.6) 1.5 550 

(6.0,-0.8, 0.9) 6.2 435 

(4.9,-1.5,-0.1) 4.0 440 

November 26 (17.5,-10.4,-3.2) (12.2,-10.0,-0.6) (2.4, 0.1, 0.2) 4.2 3 70 

"Assumed value 

-20- 
Table 2 

Wave Properties at Spectral Peaks 

Event Spacecraft 

October 19 

October 23 

October 30 

November 5A 

November 5B 

October 6 

October 14 

October 29 

October 27 

November 26 

UKS 

ISEE 

UKS 

UKS+ 

ISEE+ 

UKS 

ISEE 

UKS 

UKS+ 

ISEE 

UKS 

ISEE 

UKS 

ISEE 

UKS 

ISEE 

UKS 

ISEE 

UKS 

ISEE 

+ Not used in Figure 11 

Frequency Weighted Propagation EccenBand (Hz) Frequency (Hz) Angle 

.018- .082 

.019 - .039 

.015-. 034 

.08 - .27 

.OS- .27 

.01- .05 

.02-. 05 

.02-..03 

.03 - .05 

.03 - -05 

.04-. 07 

.OS - .07 

.Ol- .05 

.01- .05 

.01- .04 

.01- .04 

.02- .04 

.02 - .05 

.02 - -05 

.01- .03 

.051 

.030 

.025 

.12 

.16 

.033 

.038 

.025 

.035 

.036 

.054 

.062 

.02a 

.029 

.028 

.02a 

.032 

.036 

.030 

.oia 

23O 

440 

65O 

200 

17O 

370 

14O 

36O 

41O 

590 

90 

190 

530 

80° 

15 O 

72O 

13O 

100 

120 

31O 

tr ic i ty 

- .73 

.59 

.34 

.91 

.94 

.67 

.61 

.57 

.6a 

- .34 

- -47 

- .75 

.45 

- ,16 

.77 

- .12 

.58 

.63 

.64 

- .67 

Percent 

Polarization 

58 

36 

74 

a0 

98 

21 

57 

45 

36 

50 

32 

76 

40 

68 

20 

58 

61 

31 

88 
Fiaure 1 
Frequency (Hertz) 

- E 10 t‘i !? 

ISEE-2 1; 

Universal Time 

Figure 2 
.. 

OCTO BER 30, 1984 

I I I I I I? 

3 BY 2-5 E d) I’ ‘Y 

..I 05 

Y 

g0 

L 

2-5 

z 

5 

.o Ll I I I I I I I !J 
MSEE-2 

NOVEMBER 5, 1984 

,. - Ll. n. ii 

Og25 1227 I 1229 ' 12k1 ' 1243 7 

Universal Time 
I. 

w 

SER 5, 1984 

I- UKS : 

0 

Universal Time 
OCTOBER 6, 1984 

I I I I I I 

h" 

I-0 

c 

--lo BY 

D 

Q) 

Lo 

0 --lo 

- 

.- 

BZ ..I 

UKS 

p1 = ti 

1228 1232 I I I I 1236 1240 I I I 1244 I 

Universal Time 

Figure 6 
MI SEE-^ 

OCTOBER 14, 1984 

BX 

BY 

I -. 

ISEE-2 4 

i 

I I I I I I I I 829 831 833 835 837 839 

Universal Time 
OCTOBER 29, 1984 

L 

Y 

90 a 

i -4 

a0 

0 

C 

a 

.- 

d 

r" -4 

4 

1212 1216 1220 1224 1228 I I I I I I I 

Universal Time 

Figure 8 
OCTO 

WKS 

1BER 27, 1984 

rt I I I I I I I 11 

722 726 I I 730 I I 734 I ‘ ’ 1j 

738 

Universal Time 

Figure 9 
NOVEMBER 26, 1984 

Frequency (Hertz) 

E SIB* 

E I.. 

BZ 

0 

704 706 708 71 0 71 2 

Universal Time 

5k k 
W 0. a 

Q) 

w 

0.4 

0 

-0.4 

0 0 

0 

e 

0 0.2 0.4 

Frdc t i o n al Amp 1 it u d e 

0.6 
SIMULTANEOUS MEASUREMENTS OF THE MAGNETOPAUSE AND FLUX 

TRANSFER EVENTS AT WIDELY SEPARATED SITES BY AMPTE-UKS AND 

ISEE-1 AND 2 

R. C. Elphic' and D. J. Southwood2 

I Institute of Geophysics and Planetary Physics, University 

of California, Los Angeles 

' B 1 ackett Laboratory, Imperial College, London 

November 10 1986 

1 
Abstract. 

UKS and IRM spacecraft, pairs crossed the dayside 

m%netopause at nearly the same universal time and mwnetic 

local time but at much different latitudes. This 

fortuitous occurrence a1 lows the magnetopause and flux 

transfer events (FTE'sj to be studied at two widely 

,+p44%it~+ sites at the same time. The magnetopause crossing 

locations and inferred normals indicate that no single 

simple symmetric magnetopause surface can describe the 

boundary at this time. Flux transfer events (FTE's) are 

observed at both locations, those at UKS having standard 

normal component signatures, while those at ISEE have 

On 19 September 1984 the ISEE-1 and 2 and AMPTEreverse signatures. The FTE's at UKS, closer to the 

equator, appear to have less helicity, or "twistedness" than 

those at ISEE far to %ha sou%h. FTE disturbances exhibit 

little coherence between sites. While within the 

magnetosphere, the spacecraft observe a coherent field 

rarefaction coupled with a' tiltj we speculate that the 

signature is associated with dayside magnetopause 

reconnecti on. 

2 
Introduction 

Our understanding of the magnetopause has increased 

substantially in recent years, not least because of the ISEE 

spacecraft mission and associated activities. ISEE 1 and 2 

measurements were important in opening up the investigation 

of the small sc5le (< 1 RE, Earth radius) structure of 

phenomena in the boundary vicinity and in particular in 

distinguishing space from time variation. The ISEE 

separations rarely exceeded about 1 RE and there have been 

few opportunities to examine magnetopause phenomena on 

longer spatial scales. Opportunities arose for correlative 

studies on larger scale lengths in the fall of 1984 when the 

AMPTE IRM and UKS spacecraft joined ISEE 1 and 2 in orbits 

with similar apogee distances and local time but different 

orbital inclination. 

On 19 September 1984 the ISEE-1 and 2 and AMPTE--UKS and IRM 

spacecraft pairs crossed the dayside magnetopause 3t nearly 

the same universal time (1600 UTIand magnetic local time 

(1100 LT). This interval provides an opportunity to compare 

the magnetopause and flux transfer events (FTE’s) at the two 

sites. In this paper we shall compare the magnetopause 

location and orientation, the boundary structure and FTE 

occurrence and structure at the two sites. 
Magnetopause Location and Orientation 

At the time considered here, AMPTE and ISEE spacecraft were 

outbound from perigee and in the dayside magnetosphere. 

Figure 1 shows the trajectories of the spacecraft in GSM 

coordinates. Tick marks on the trajectories occur every 

fifteen minutes. At 1600 the spacecraft were separated by 

only 1 Re in Y GSM, but by 6 Re in Z GSM. ISEE and AMPTE 

could thus sample, respectively, the off-equatorial and 

near-equatorial manetopause in the northern and southern 

hemispheres at roughly the same magnetic local time. Also 

shown in Figure 1 are filled circles showing the initiai 

magnetopause locations seen by AMPTE and ISEE. 

The dashed line shows the nominal position of the 

magnetopause as given by Fairfield (1971). The magnetopause 

position recorded at both locations is well inside its 

average position 

Figure 2 gives an overview of UKS and ISEE-1 and 2 4-second 

resolution magnetic field data between 1545 and 1645 UT. We 

have examined the five second resolution IRM data for this 

period; TJKS and IRM are so close that the records are 

effectively identical throughout. We shall only use UKS 

data here. The field components are displayed in a boundary 

normal coordinate system in which the L component is aligned 

with %he mean magnetospheric field orientation at each site. 

In the GSM system, the L coordinate unit vectors are (0.568, 

-0.003, (3.823); (-0.485, 0.307, 0.819) at ISEE and AMPTE 

4 
the mean field is in a GSM (X,Zi meridian plane tilting at 

about 40' to the Z axis away from Earth; at the AMPTE 

spacecraft, the field tilts in the (X,Zj plane at 3 similar 

angle, but towards the Earth and with a small Y component. 

The normal direction was fixed using the tangential 

discontinuity assumption, i. e., it is along the normalized 

cross-product, of the mean magnetospheric and magnetosheath 

fields. The unit vector magnetopause normal for UKS is 

(0.883. -0.015, 0.4691 in G5M while for ISEE-1/2 it is 

(0.808, -0. 191, -0.558). 

Figure 2 shows that prior to the first UKS magnetopause 

encounter at 1559 IJT, the magnetic field behavior at the 

ISEE and AMPTE spacecraft is similar; a depression in the 

total field is followed by a rise in strength before rJKS 

meets the boundary. The depression is accompanied by s 

negative perturbstion in Bn a% IJKS, above %he equator, and a 

larger positive one at ISEE, well below the equator. There 

are 3lSO srnaller excursions in the Bm component at each 

site, which are also in antiphase. 

Evident coherent behavior between the spacecraft ceases orice 

UKS crosses the magnetopause at 1559. Two more magnetopause 

encounters follow 3% 1602 and 1611. FTE signatures are 

observed at -1600, 1604, 1607, and possibly at 1614 and 1630; 

the CrKS tracking period ended shortly afterwards. ISEE-2 

crosses the magnetopause at 1625, 1626, and 1632, and very 
clear FTE si&!riatures in Bn can be seen at 1616, 1622, 1627, 

1636, 1638 and 1641. There may also be FTE’s at 1620, 1625 

and 1630. Some 1200 km behind ISEE-2 along the orbit, ISEE1 does not cross the magnetopause until after 1634, although 

all the ISEE-2 FTE’s show up in the ISEE-1 data as well. 

MaeneIzapause ShaEsle 

Commonly the magnetopause is described as a conic of 

rotation about the Sun-Earth line. Figure 3 shows the rJKS 

and ISEE trajectories rotated into the plane containing the 

spacecraft position and the Sun-Earth line. Also shown are 

the projections of the two magnetopause normals into this 

plane. From the position of the magnetopause and its normal 

at that point it is possible to determine the conic section 

(with Earth at one focus) that fits that position and 

normal. These are shown for UKS and ISEE as the dotted and 

solid curves, respectively. 

It can clearly be seen that the magnetopause is distorted in 

shape. At 1600, when [JKS first encounters the magnetopause, 

ISEE-1 and 2 are still well inside the boundary, whereas the 

UKS-derived magnetopause places ISEE outside the 

magnetopause at this time. Likewise when ISEE cro:;ses the 

miNnctopause near 1630, rJKS is outside the boundary, while 

the ISEE-derived magnetopause places lTKS inside the 

boundary. Moreover, up to 1630, little FTE ac%ivity is seen 

at UKS suggesting that the spacecraft remains well outside 

the boundary. No symmetric conic of a single eccentricity 

1 

6 
can account for the magnetopause position and shape at this 

time. 

The field perturbations in the normal direction prior to 

1559 seen at both spacecraft sites could reflect a change in 

magnetopause shape. The direction change at UKS is not 

great but at ISEE, farther from the equator, the direction 

changes by about 15' in the meridian tilting away from the 

Earth. The field at UKS, above the equator, tilts more 

towards the Earth. 

One potential explanation is that reconnection is initiated 

on the dayside magnetopause somewhere near noon at about 

1545 when the perturbation starts. The gradual tilting in 

the field at both ISEE and AMPTE spacecraft results from the 

equatorial part of the local field lines being sucked 

towards the reconnection site. The rarefaction in field 

strength could result from the same effect. As the 

reconnection rate drops, field tilt decreases and 

compression increases. The net erosion of the magnetopause 

has moved the boundary very close to IJMS which exits very 

soon after. Field compression is often seen immediately 

sd jacent to the magnetopause; this is the first evidence 

that it is a temporal rather than spatial effect. 

FTE Occurrence and Structure 

It is clear from Figure 2 that FTE activity is present, 

simultaneously at, ISEE-1/2 in the southern hemisphere ant3 

7 
AMPTE-IJKS in the northern hemisphere. There is no one-toone correspondence evident between individual events 

detected at the two sites. The Russell and Elphic (1978) 

connected tube hypothesis suggests that one might expect a 

simple relation. If, as has been proposed (Russell et al., 

1985; Southwood et al., 1986), FTE's originate in the 

equatorial region, lJKS should observe the signatures of 

northward moving tubes first. There could be a time delay 

(of up to a minu%e or so> before ISEE-1/2, roughly 2 Re 

farther from the subsolar point, observes the southern 

counterpart. In the 4-second time series data in Figure 2, 

none of the UKS FTE's has an unambiguous ISEE counterpart at 

the expected time. However, the picture is not simple. 

Close examination of the records reveals a variety of 

smaller amplitude disturbances on various time scales; more 

sophisticated analysis is needed. 

Complicating the comparison of FTE occurrence are the 

differences in amplitude at each site. The range of peakto-peak Bn amplitudes for the five FTE's seen on [JKS extends 

from 15 to 38 nT, with a mean of 26 nT: the five largest 

ISEE-2 amplitudes range from 20 to 53 nT, with a mean of 39 

nT. In the Russell and Elphic interpretation (and many 

developments of it>, when a spacecraft grazes a FTE, the 

observed Bn signatures is due to the disturbance or 

"draping" field around the FTE flux tube (Farrugia et al., 

1986). However, the Bn signature is also detected within 

the open part of the tube where, as pointed out by Cowley 
(1982) and Paschmann et al. (19823, it indicates the 

presence of field-aligned currents within the FTE twisting 

the field. The events seem of similar duration at the two 

sites (thus the smaller Bn does not reflect smaller crosssection). The FTE’s observed at the ISEE location seem to 

be more twisted up than those at the UKS location. 

In addition to the lower amplitude of the signals at TJKS, 

there is another important distinction between events 

cle%ected at the %wo sites. The FTE Bn variations shown in 

the UKS plot are all standard (Sj bipolar signatures, i. e., 

a positive followed by a negative excursion. The ISEE Bn 

signatures are all reverse (R) signatures, negative followed 

by positive excursions. This is consistent with the earlier 

statistical results (Rijnbeek et al., 1984; Berchem and 

Russell, 1984; Southwood et al., 1986) which showed that S 

(R) events were predominant above (below) the equator. 

Summary and Discussion 

This paper presents the f ir5t reports of simultaneous 

measurements at the magnetopause from spacecraft separated 

by more than 10,000 km. In the case reported here, the 

spacecraft, the ISEE 1/2 pair and the UKS/IRM pair of the 

AMPTE mission, are near the noon meridian but at very 

different latitudes. Our preliminary s%udy shows that the 

measurements have fulfilled some expectations but that 

important questions remain for further study. 

9 
Magnetopause location and shape, as inferred from boundary 

normals, suggests that the boundary cannot be 

instantaneously represented by a simple symmetric conic 

surface. At the time that UKS exits the magnetosphere, the 

conic section magnetopause predicts ISEE in the sheath when 

it is still in the magnetosphere. When ISEE later exits, 

the lJKS position predicted by the appropriate conic section 

is inside the magnetosphere and thus again inconsistent. 

The first exit of rJKS from %he magnetosphere is preceded by 

a signature that is similar at both spacecraft. A dip in 

field strength accompanied by a bending of the field 

corresponds to the outward displacement of the plasma and 

field in the equatorial regions. This in turn is followed 

by an increase in field at both spacecraft before UKS leaves 

the magnetosphere. We speculate that this is symptomatic of 

a sustained magnetopause erosion. 

Whilst the spacecraft were in the magnetopause vicinity 

FTE’s were observed at both sites. Those in the north at 

[JKS show standard Bn signatures indicative of a northwar!i 

travelling flux tube, while those at ISEE in the south have 

reverse Bn signatures expected for southward travel ling 

perturbations . 

The FTE’s at UKS have smaller amplitude Bn signatures and 

are fewer in number than the FTE’s at the ISEE location. We 

thus kiave an individual instance consistent with the survey 

results of Southwood et al. ( 1986; which found a much lower 

10 
. 

rata of FTE occurrence at rJKS than in the first years of 

ISEE operation where ISEE was aghin at higher mean latitude. 

Southwood et al. (19861 and also ‘Saunders et al. (19861, who 

specifically compared the UKS results with the ISEE 

statistics, have argued that the survey result was due to 

the lower average latitude of the UKS measurements. 

We have argued that the larger Bn signature is likely to 

imply that the field becomes more twisted as events move 

away from the equator. More analysis is required to confirm 

that the actual duration of events is similar at each site 

before the conclusion is secure. 

There is no evident one-to-one correspondence.of FTE’s seen 

at the two sites. In light of the disturbed nature of the 

field near the boundary and potential systematic amplitude 

anti duration differences beeween sites we intend to 

investigate this question further. The question has a 

bearing on whether FTE’s are due to connected tube formation 

(patchy reconnection: Russell and Elphic, 1978) or whether 

they are a manifestation of tearing mode phenomena (Lee and 

Fu, 1985). In the Lee and Fu picture, tearing islands 

forming at the equatorial magnetopause could rleve10p in the 

nclrth and south independently and convect away 

independently: no correspondence would necessari ly be seen 

between the [JKS and ISEE FTE’ s, 
We wish to thank C.T. Russell for helpful discussions. IRM 

data w3s kindly provided by H. Luehr and W. Baumjohann. 

This work was supported by NASA grants, NAGS--536 and NAS5- 

28448. Work at Imperial College, including provision of the 

AMPTE-UKS. magnetometer, was funded by the IJ. K. Science and 
I3e fererlces 

Berohem, J., and C.T. Russell, Flux transfer events on 

the magnetopause: Spatial distribution and 

controlling factors, J. Geophys. Res., 89, 

6689, 1984 

Cowley, S. W.H., The causes of convection in th.e Earth’s 

magnetosphere - a review of developments 

during the IMS, Rev. Geophys. Space Phys., 

20, 531, 1982 

Fairfield, D.H., Average and unusual locations of the 

Esrth’s magnetopause and bow shock, J. 

Geophys. Res., 76, 6700, 1971 

Farrugis, C.J., R.C. Elphic, D.J. Southwood, and 

S.W.H. Cowley, Field and flow 

perturbations outside the open field region 

in flux transfer events. 1. Theory, Planet. 

Space Sci., 1986 

Lee, L. C. and Z. F. Fu, A theory of magnetic: flux 

transfer at the Earth’s magnetopause, 

Geophys. Res. Lett., ’ 12, 105, 1985 

Psschmann, G., G. Haerendel, I. Papamastorskis, N. 

Sckopke, S. J. Bame, J. T. Gbsling and C. T. 

Russell, Plasma and msgne%ic field 

characteristics of magnetic flux transfer 

events, J. Geophys. Res., 87, 2159, 1982 

Ri jnbeek, R.P., S. W. H. Cowley, D. J. Southwood and C. T. 

Russell, A survey of dayside flus transfer 

events observed by ISEE 1 and 2 

magnetometers, J. Geophys. Res., 89, 786, 

1984. 

Russell, C.T. and R.C. Elphic, Initial ISEE 

rn,ubnetometer results : rnagnetxpause 

observations, Space Sci. Rev., 22, 681, 

1978 

Russell, C. T. , J. Berchem and J. Luhmann, Or1 the source 

region of flux transfer events, Adv. Space 

Res., 5, 363, 1985 

m amriders, M. A. , D. .J. Southwood, R. P. Rijnbeek, W. A. (2. 

Mier-Jedrzejowics, and M. W. Dunlop, . 

De%ection of FTE’s by the AMPTE-TJKS 

magnetometer, Adv. Space Res. ~ (in press), 

1986 

13 
SolJthwood, D..J. M.A. Saunders, M.W. Dunlop, W.A.C. 

Mier-Jedrzejowicz, and R. P. Rijnbeek, A 

survey of flux transfer events recorded by 

the UKS spacecraft magnetmmeter, Planet. 

Space Sci. , ( in press), 1986 

14 
Figure Captions 

Fig. 1. Trajectories of ISEE-1 and 2 and AMPTE-TJKS on 19 

September 1984 in GSM coordinates. Time ticks are shown 

every 15 minutes, with hours indicated to one side. Filled 

circles indicate the first encounter wi%h the magnetopause. 

The average magnetopause position according to Fairf ield 

(1971) is shown by %he dashed curve. 

Fig. 2. Time series of UKS (top) and ISEE-1 and 2 (bold and 

thin %races, respectively in %he battorn panel j in boundary 

normal coordinates. Data paints (derived from a centered 12 

second average) are plotted every 4 'seconds. 

Fig. 3. UKS and ISEE trajectories rotated into the plane 

containing the spacecraft position and the Earth-sun line. 

Also shown are the magnetopause crossing positions, derived 

normal directions and inferred magnetopause shapes for ISEE 

(solid curve) and UKS (dotted curve). 
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