The density structure of the plasmapause region was investigated using the two satellites, ISEE-1 and DE-1 to obtain complementary radial and latitudinal profiles. Data from the plasma wave receivers were to be used to obtain total electron density, and from the ion mass spectrometers to determine thermal plasma morphology

Olsen, R. C.

English

NASA Technical Reports Server

I .* 
J 
4. Fli&l Report: NAG5-568 
NASA/GSFC 
PLASMASPHERE AND MAGNETOSPHERE STRUCTURE 
FROM ISEE-1 AND DE-1 
I!. c. Olsen 
Physics Department 
The University of Alabama in Huntsville 
Huntsville, Alabama, 35899 
October 15, 1987 
(NASA-CR-181372) PLASMASPHEBE AND 887- 299 84 
HAGNETOSPHiiRE STRUCTUaE FROH ISEE-1  Akid U E - 1  
Fiaal Eieport (Alabama Univ.) 31 p A v a i l :  
NTIS HC AQ3/MF A O ?  CSCi 1/48 Unclas 
G3/46 6102695 
https://ntrs.nasa.gov/search.jsp?R=19870020551 2020-03-20T10:00:19+00:00Z
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I. Introduction - 
The purpose of this grant has been to investigate the 
density structure of the plasmapause region, using the two 
satellites, ISEE-1 and DE-1 to obtain complementary radial and 
latitudinal profiles. Data from the plasma wave receivers 
were to be used to obtain total electron density, and from the 
ion mass spectrometers to determine thermal plasma morphology. 
This program was partially successful, in that the 
general relationships derived from ISEE-1 could be applied tc 
the DE-1 data. A frustratingly small percentage of the data 
overlapped in truly helpful ways, however. In general, it 
could be counted on that one of the satellites would be off at 
the wrong time, or in the wrong instrument modes. This points 
out the need for strong coordination efforts in future 
programs to insure that complementary data sets are available 
(e.g. POLAR and WIND, with GEOTAIL). Operational duty cycles 
of greater than 50% will be necessary, if overlaps are not 
specifically planned. 
- 11. Radial Structure 
Electron density profiles were obtained for over 25 sets 
of orbits where the ISEE-1 satellite passed through perigee 
near DE-1. Several dozen more oribts were analyzed, and 
proved unsuitable for various reasons. The first major result 
to arise from the analysis of the ISEE-1 data was the (re)- 
discovery of the L-4 density profile exhibited by the 
* 
Page 3 
plasmapause region ( Chappell et al, 1970). This has been 
emphasized in the way the data are plotted, as shown in Figure 
1. Figure la shows an ISEE-1 density profile from April 19, 
1982 (day log), with density plotted vs. L .  This is an 
outbound segment at local dusk (18-21 LT). A sharp 
plasmapause is found at L = 2.7, 18 LT, 18 degrees magnetic 
latitude. After that, the decline is slower, in fact L-4 as 
indicated by the solid line, which is normalized to 100 cm-3 
at L = 4 . 5 .  This latter set of values, used generally 
throughout our analysis, is chosen for convenience in 
comparing with f i E - i  d a t a ,  and is coiisistezt with  recezt 
findings by R. R. Anderson that the normal radius for a 100 
cm-3 isodensity contour is L - 4 . 5  (Huntsville Modeling 
Conference, October, 1986). If the data are normalized by 
L-4, Figure lb results. The data form a nearly horizontal 
line, at least from L - 3 to 5 ,  with a slight shift upward 
from L - 5 to 7. This shift is real ( i.e. not a statistical 
fluctuation), and not atypical. 
Even when the density profile is not constant over large 
ranges of L, it is often true that L-4 profiles are applicable 
piece-wise. Figure 2 shows an example from June 1, 1982 (day 
152), at 17 LT. The normalized density profile is flat from L - 3 to L - 5.8, then drops sharply, and is again flat from L = 
6.0 to 7.0. Such structures are attributed to a plasmasphere 
boundary subject to intermittent erosion (due to substorms), 
followed by refilling at constant rates. Sharp boundaries 
such as the one found here are therefore indicative of 
substorm activity which did not disturb the plasma inside the 
L = 5.8 boundary. 
This work also allowed for the (re)discovery of detached 
plasma regions (Chappell, 1974). This is illustrated in 
Figure 3, again a normalized density profile vs. L. These 
data are from March 26, 1982 (day 85). The satellite is in 
the 20-22 LT sector, moving outbound, and dropping in magnetic 
latitude from +15 to -2 degrees. Plasmasphere densities (i.e. 
greater than 100 cm-3) are found inside L - 4.3. There are 
then lower plateaus, followed by a return to the initial 
profile from L - 6.05 to 6.50. It can be seen that plotting 
these ‘normalized’ densities emphasizes the differences 
between true boundaries, and the more gradual spatial 
gradients which exist as equilibrium structures. 
The goal of establishing the nature of the plasmapause 
topology requires complementary passes through the 
plasmapause. This was effectively achieved only twice in 
1982, according to our surveys of the data. Both examples are 
illustrated here. Both show L-4 dependences f o r  the ISEE-1 
radial profiles, and latitude independent profiles from DE-1. 
Figure 4 shows the ISEE-1 and DE-1 orbits in latitude vs L 
plots. These data from March 16, 1982 (day 75). ISEE-1 
passes is at 2040 LT at L = 3, 2141 at L = 4, and 2206 LT at L 
= 5. DE-1 stays between 2240 and 2300 LT during this period. 
As a result, the field lines crossed by ISEE-1 early during 
its orbit, co-rotate to the nominal DE-1 region. Figure 5 
shows the ISEE-1 density profile, with L-4 profile overlaid. 
Page 5 
The agreement is particularly good in the L - 4 to 5 range. 
I f  this normalization is applied to the DE-1 data, Figure 6 
results. The density profile is flat from -40 to +15 degrees, 
where it starts to break up. The rise at 15 degrees latitude 
has no apparent counterpart in the ISEE-1 data, the subsequent 
fall reflects the drop in density after L - 5 in the ISEE-1 
profile. 
The second conjunction which proved useful was on Hay 6, 
1982 (day 126). This example was used in the article on 
plasma heating (Olsen, et a1 , 1987). Figure 7 shows the 
ISEE-1 and DE-1 orbits. ISEE-1 moves radially outward, and 
down in magnetic latitude, as it rotates from 16 to 19 MLT. 
DE-1 approaches the equator from the opposite hemisphere, in 
the 19-20 HLT range. The ISEE density profile, shown in 
Figure 8, shows a sharp plasmapause density gradient at L = 
3.7, with two regions of gradual slope at either side. The 
density profiles were least-square-fitted (LSF), with results 
indicated on the figure. The inner region drops quite 
sharply, with the outer region dropping a little more sharply 
than normally found in the outer plasmasphere. If this latter 
information is applied to the DE-1 latitude profile, Figure 9 
results. The normalized density is found to be flat from -38 
to +8 degrees. 
As a result of this work, the regular analysis of DE-1 
data was modified to include regular plots of 'normalized' 
density profiles. It was found that flat latitude profiles 
such as these were common, if not in the majority. The cases 
Page 6 
which showed a clear latitude structure, which could be 
seperated from radial structure, were somewhat rare. In 
particular, it was difficult to find clear cases of latitude 
structure in the limited set which included complementary ISEE 
and DE data. As a consequence, the following cases use only 
DE data. 
111. Latitude Structure -
Two forms of latitudinal structure have been found in the 
data. First, a latitude structure with a local minimum at the 
magnetic equator was found to be a persistent feature of the 
normalized density profiles. Second, there was occasionally 
evidence of a density dropoff with latitude at 40-50 degrees 
magnetic latitude. Both features are indications of, 
plasmasphere filling processes. 
- A. Equatorial Density Minimum 
The density minimum at the magnetic equator is an effect 
associated with plasma heating at the equatorial plasmapause 
(Olsen et al, 1987). By means of the techniques developed 
under this grant, it is now possible to demonstrate the 
existence of the density minimum unambiguosly. 
The first example comes from January 8, 1982. The orbit 
is illustrated in Figure 10, a projection of the DE-1 orbit in 
SEI coordinates into the 0300 local time plane. Only DE-1 data 
are available from this time. ISEE-1 was in the right region, 
at the right time, to provide useful, complementary data, but 
A 
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was not operating. The satellite passes out through the outer 
plasmasphere as it crosses the equator, passing through a 
region of heated plasma, indicated by the cross-hatched area 
in Figure 10. Figure 11 shows the electron density, 
normalized for radial distance, plotted versus latitude. The 
normalized density drops by a factor of 3, over a latitude 
range of about 10 degrees, centered at the equator. The 
actual density profile (not shown), also shows the local 
minimum at the equator, with roughly equal values for the 
electron density on either side. 
Figure 12 is a color spectrogram for the hydrogen data 
from the Retarding Ion Mass Spectrometer (RIMS) on DE-1, with 
the plasma wave data (PWI) shown in the bottom half. The 
heating process noted above in the orbit plot, is shown here 
by the large red area in the top panel, which is the Retarding 
Potential Analysis (RPA) for the H+ measured along the spin 
axis (nominally 90 degree pitch angle). Higher fluxes, and 
higher retarding voltages, are indicative of heating. The 
middle panel is the spin axis for the integral H+ flux. This 
plot shows a progression from isotropic, rammed plasma, to a 
pancake distribution (peaked at 90/270 degrees), back to 
isotropic, and finally field-aligned (peaked at 0/180 
degrees). 
On March 15, 1982 (Day 741, the satellite was outbound, 
rising up to the equator from the southern hemisphere while 
skimming the L = 3 field line, crossing the equator at L = 
Page 8 
3.4, finally crossing the plasmapause at L = 4.5 at 16  degrees 
magnetic latitude. The density profile vs. L is shown in 
Figure 1 3 .  The dip at L = 3.4 coincides with the equator 
crossing, with the plasmapause occurring at L - 4.5. The 
normalized density profile is shown in Figure 14. This 
emphasizes the drop in density, which is almost a factor of 3. 
The thermal plasma data (not shown) again show heating 
effects. The cold isotropic H+ and He+ ions show a 
temperature increase, but apparently remain largely isotropic. 
_. m e  third exampie OF a density minimum OCL'UCS in a regfori 
of substantially lower plasma density, on July 18, 1982 (day 
1 9 9 ) .  The orbit for DE-1 is shown in figure 1 5 .  DE-1 is in 
the mid-afternoon sector, and stays near L = 4.5 for a 
substantial portion of the equator passage. The density data 
are shown in Figure 1 6 .  The electron density (lower panel) 
shows a nearly monotonic variation, with only faint 
indications of a local minimum at lower latitudes. Once the 
data are normalized, however, it is clear that the region from 
-20 to +20 degrees magnetic latitude is a region of reduced 
density. RIMS data (not shown) indicate that the plasma away 
from the equator is field-aligned, while at the equator the 
plasma pitch angle distribution is peaked near 9 0  degrees 
(e.9. pancake). This latter distribution (along with RPA 
analysis) is indicative of heating, again. 
Page 9 
The three cases illustrated here illustrate the idea of a 
local minimum in the plasma density near the magnetic equator. 
This minimum is associated with heating of the thermal plasma,. 
particularly ions (electrons not being observed on DE). The 
third case, above (day 199), with field- aligned ions 
disappearing at the equator, can be interpreted as a result of 
enhanced (positive) plasma potentials, reflecting the low 
energy (few ev) ion beams. This interpretation has been 
suggested previously for similar observations (Olsen et a1 
1987). The observations at lower L (higher density) are 
ixterpreted ir! B similar wzyi Heating of the low energy ions 
results in an increase of the plasma potential (of a volt or 
two). The ion density is then reduced (exp (-9 phi/kT)), and 
the electrons follow ( basically a barometric law). Such 
effects will not be observed if the density is too high 
(heating damped) or too low (associated plasma temperatures 
are larger than the plasma potentials). The effect appears to 
be limited to a density range of 20-300 cm-3. 
- B. High/Low latitude Plasmapauses 
Variations in the plasmapause L-shell often appear to 
vary with latitude in DE data, but such effects are difficult 
to seperate out from anticipated processes such as local time 
(azimuthal) structures co-rotating past the satellite. (This 
was the point of combining the two satellite data sets.) One 
example of the high/low latitude structure which is often 
observed is shown from August 27, 1982 (Day 239). Figure 17 
shows the orbit for this pass. The satellite is near noon, 
Page 10 
local time, moving inward radially, and upward in latitude. 
Figure 18 shows the L-profile for the density. The satellite 
crosses the plasmapause at L = 5.5, at -22 degrees magnetic 
latitude, at 16 UT. The density increases as the satellite 
moves in to L = 4, then decreases with the same profile until 
1845 UT, at L - 4.3, at +35 degrees magnetic latitude. At 
this point, the plasmapause is again encountered. The 
normalized density profile, shown in Figure 19, emphasizes 
this behavior. These data suggest a plasmasphere which 
extends to greater L at low latitude. Such a feature has been 
suggested by statistical surveys of the RIMS data (J. L. 
Green, private communication, 1983). Such a structure might 
be expected if the plasmasphere begins filling from the 
equator down. Unfortunately, these data do not rule out a 
simple explanantion in the form of a local time structure 
(over almost 3 hours, or 45 degrees azimuth) rotating by the 
satellite. 
IV. References -
1. Chappell, C. R . ,  K. K. Harris, and G. W. Sharp, The 
morphology of the bulge region of the plasmasphere, - J. 
Geophys. - Res., 75, 3848-3861, 1970. 
2. Chappell, C. R., Detached plasma regions in the 
magnetosphere, - J. Geophys. 2, Res - 79, 1861-1870,1974. 
3. OlSen, R. C. S. D. Shawhan, D. L. Gallagher, J. L. 
Green, and C. R. Chappell, Plasma observations at the 
earth's magnetic equator, - J. Geophys. Res., __ 92, 2385-2407, 
Page 11 
1987 
- V. Programmatics 
Publications submitted or published based on work under 
this contract are listed below. A publication tentatively 
titled, "The density minimum at the earth's magnetic equator" 
by Olsen et al, is under preparation for submission to JGR. 
Data have been provided to P. M. E. Decreau to extend 
previous work (ref 1 below) to the local dawn region. This 
grant led to cooperative experiments recently conducted using 
LL ,lC w w - 1  --^e- 2 L-- -e 
stimulate waves observable by the University of Iowa plasma 
wave experiment. Results from these latter experiments will 
be considered as the telemetry is processed. 
u ~ ~ r v c r ~ r ~ y  V I  Calf fo i i i ia  (UCB) eleetisc ~ G E  OE ISEE-1, t~ 
This work was completed after the principal investigator 
moved to the Naval Postgraduate School, Monterey, California. 
The work there was supported by an internal grant from the 
Research Foundation of the Naval School. 
1. Decreau, P. M. E., D. Carpenter, C. R. Chappell, R. 
H. Comfort, J. L. Green, D. A. Gurnett, R. C. Olsen, 
and J. H. Waite, Latitudinal plasma distribution in the dusk 
plasmaspheric bulge: Refilling phase and quasi- equilibrium 
state, - J. Geophys. Res., 91, 6929-6943, 1986. 
2. Comfort, R. H., Plasmasphere thermal structure as 
measured by ISEE-1  and DE-1, Adv. Space Res., 6, 31-40, 1986. - -  
3. Olsen, R. C. S. D. Shawhan, D. L. Gallagher, J. L. 
Page 12 
Green, and C. R .  Chappell, Plasma observations at the 
earth's magnetic equator, - J. Geophys. - Res., 92, 2385-2407, 
1 9 8 7 .  
A )  
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APRIL 19, 1982 
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MARCH 26, 1982 
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FIGURE 6 
DE-1 AND ISEE-1 
MAY 6,1982 
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FIGURE 7 
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UT 
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96 
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70 8 1  
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- 601 
3 
DY NAM ICs EXPLORER 1 
MAY 16,1982 
ELECTRON DENSITY ADJUSTED TO L = 4.3 
MAGNETIC LATITUDE (A:) 
FIGURE 9 
DYNAMICS EXPLORER 1 
JANUARY 8,1982 
SM COORDINATES 
6 
1936 UT 7 'PLASMASP*"SE L = 3.9 TO 4.0
20 UT INNER PLASMASPHERE 
L < 3.0 
FIGURE 10 
4 
1000, I I I 
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10 I I 1 I I I I 
-40 - 20 0 2 0  40 
MAGNETIC LATITUDE (DEGREES) 
FIGURE 11 
DYNAMICS EXPLORER 1 
JANUARY 8,1982 
MAGNETIC EQUATOR 
PLASMA WAVE I W R U M E N T  I - ELECTRIC ANTENNA 
- 5 0  
- 10 
- 1.0 
. 0.1 
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RAM 
-90 
- la0 
1000 
100 
10 
2 
DYNAMICS EXPLORER 1 
MARCH 15, 1982 
0330 - 0520 
D A Y  74 
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23.0 MLT 
X = - 30 to t 24 
R = 2.3 to 4.4 
UT 
W 
0 
0 
0 
- 
Q 0 0 0  
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0 
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L 
5 6 
FIGURE 13 
DYNAMICS EXPLORER 1 
MARCH 15, 1982 
0330-0520 UT 
I I 
0 
0 0 
8 0 
0 
0 0 
0- 8 
0 
0 
0 
I I 
-40  -20 0 + 20 
MAGNETIC L A T I T U D E  
FIGURE 14 
L = 6  
DYNAMICS EXPLORER 1 
JULY 18,1982 
16 UT 
SM COORDINATES 
15 MLT 
DAY 199 
FIGURE 15 
i. . .  
. 
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fr 
FIGURE 16 
DYNAMICS EXPLORER 1 
AUGUST 27, 1982 
I 1521 UT 
SM COORDINATES 
12 MLT 
DAY 239 
. 
FIGURE 17 
1000 
DYNAMICS EXPLORER 1 
1520-1853 UT 
I i 
AUGUST 27, 1982 
?i 0 0 - 
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1 
4 5 6 7 
1 
FIGURE 18 
DYNAMICS EXPLORER 1 
AUGUST 27, 1982 
1000 L I I I 1 
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12 MLT 
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0 
* 
I I I I I I I I 
- 40 - 2 0  0 2 0  40 
MAGNET IC LATITUDE 
FIGURE 19 


Plasmasphere and magnetosphere structure from ISEE-1 and DE-1

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