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Geomagnetic and Solar Cycle Dependence of the Ring Current Ions
GEOMAGNETIC AND SOLAR CYCLE OF T H E R I N G C U R R E N T I O N S
DEPENDENCE
S. Y. Fu,IQ. G. Zong2Z. Y. Pu 3 L. Xie 4
1Department of Geophysics, Peking University, Beijing, 100871, China 2Center .for Space Physics, Boston University, MA 02215 3Space Weather Lab, CSSAR, CAS, Beijin9, 100080, China 4Department of Geophysics, Peking University, Beijin9,100871, P.R. China
ABSTRACT Observations obtained from CRRES/MICS in the solar maximum show that both the ring current composition and the location of the maximum ion flux can be influenced by geomagnetic activity and solar cycle. Both the number and the energy density ratio of O +, He ++ and He + ions increase during geomagnetic active times, whereas that of H + exhibits an obvious decrease. It is also interesting to compare with AMPTE observations which were made in the solar minimum. The abundance of the ring current H + is apparently lower in the solar maximum than in the solar minimum. In contrast, the abundance of both O + and He ++ ion is higher in the solar maximum. In addition, the average location of the maximum number density of the energetic ions is about 0.5 RE lower in solar maximum than that in solar minimum. INTRODUCTION In the past years, two of the most important in-situ ring current observation were made by AMPTE which launched in 1981, solar minimum and CRRES satellite which was operated during 1990 - 1991, solar maximum. Based on the instrument ability of distinguishing different ion species, it is recognized that the variation of the ion composition may play an important role in the formation and decay of a storm. By using the data obtained by AMPTE, the locations of the maximum number density for different ion species have been found to be at about L--4, 5.2, 5.7 and 7 for H +, O +, He + and He ++ ions, respectively during geomagnetic quiet period. These positions would move inward, to the lower L shells during storm periods (Gloeckler and Hamilton, 1987). The relative contribution of ion species to the ring current during low and high geomagnetic activities has been identified by both case study (Gloeckler and Hamilton, 1987, Krimigis et al 1985; Hamilton et al 1988) and statistical study (Daglis et al, 1993). However, the solar cycle dependence of the radial ion distribution and the relative abundance in the ring current region are still unclear. Based on CRRES/MICS measurements in 1991, we studied the averaged ring current property during both quiet and active time in the solar maximum. Further, a comparison between the solar maximum and solar minimum observations is made.
-421 -
S. Y. Fu et al.
OBSERVATIONS Radial Profiles of Number Density and Energy Density In Figure 1, the radial profiles of number densities for O +, He +, He ++ and H + in the quiet and active time ring current are shown on the left side. The percentage of the accumulated energy of the different ion species to the whole ring current versus L value are shown on the right side. Dst index is used as a criterion to assemble the data for quiet (Dst<30 nT) and storm (Dst>50 nT) times in which the averaged Dst are about 7 nT and 70 nT, respectively.
1
lO
100
IDstl>5OnT ,.., 100 E
+
.~0 aID
9 ++ 9
9
ai_ 10=
+:o~:
~ ~
~
a)
5
E
&
= 10~
+++++
, ...................
, .........
, .........
"
IDstl>50 nT
, .......
/ H +
+
He* ,, H e ++ x
o'.
0 §
55 &~A
i
........
H* . o He+~ He++5
a
9
|
i
Z
10 4
0
1
2
3
~_
5
6
7
........
1
....
*n'~ E
'~ "
+ + + + + ++
1
+ + +oo
~176176
1
~'10
i
---
I
t
9
I
I
9
9
o
~"
o 0 o -~
~
I
, .
.
.
.
2
.
3
.
.
..
.
.
.
4
.
5
L
.
.
.
.
.
.
.
.
6
7
,D=,:30n;
. . . . . . . . . . . . . . . . . . . . . . . .
80-].-
+ +
60
+
+ + + + + +
++
1
o
10"4[
1
2
3
~_
5
6
7
1
2
3
~.
5
6
7
Fig. 1 (Left) Radial profiles of number density of O+,He+,He ++ and H + in the quiet and active time ring current. (Right) Percentage of the accumulated energy below L of the ions to the whole ring current. Four different symbol lines represent the contribution of the four species. The solid line shows the total accumulated energy. The energy range is 54 keV/e-426 keV/e. From Figure 1 we can see that during quiet times, there exist two different number density peaks in the radial profiles, one is at about L - 3 for H + and He ++ ions and the other is around L - 4 . 5 for O + and He + (bottom-left panel in Figure 1). During geomagnetic activity, the position of the maximum number densities for O + and He + move inward and all four species concentrated in the region L - 3 ,,~ 4 (top-left panel in Figure 1). Although O + and He + show an obvious inward motion during active times, the total accumulated energy versus L shell (the solid lines in right panels) remains unchanged. More than 80% of the total ring current is still in the region 2.5 < L < 5. However, the relative contribution of different ion species changes a lot, as we can see from the right panels in Figure 1. The H + contribution falls from 80% to < 60% as the magnitude of Dst becomes larger than 50 nT, and that of O + increases from 10% to 30~
-422 -
Geomagnetic Activity and Solar-Cycle Dependence of the Ring Current Ions Energy Density,of the ring current The accumulated percentages of energy densities for each ion species are displayed in Figure 2. The top two panels are for the outer ring current (L=6) and the bottom two panels for the inner ring current (L=4). On the basis of Figure 2, following points can be made: 1. The outer part of the ring current contains about 65% H + and 20% O +, and less than 10% He + and He ++. Ions which carry the main energy density in this region are in the energy range below 200 keV/e.
1 0 0 ~, - -
80 .-.. ~
9
'
'
100~
,
6
H+ +
i IDstl<30nT +
W
+
+
+
+
He++=
+
O"
.
,
k=6
9
o
o
o
oo
9
o
9
9
+
9 +
~ ~
ioo
~ ~!
+
:
++ + o
o
9
i
~
I
M
+
9
; ~]~ ~
He++ ,, He ,=
~o"
,,,) o
lOO
o O
i
l
o
,.,
9
9
]l
m
I i
~
IDstl>50 nT
+ + + + -i
i
~
'~176 i 80~ L=4
!
9
F_JQ (keV/e)
E/Q (keY/e)
IDstl<30nT
o ~ m
9
'
L=4
+ +
IDstl>50nT
n" 40 o
+
.
~" .o~-
9
§
o ..
.
H+
80 f
He+ "
++ + . + + +
60~-
.
t-
§ o
,
§ §
~, 4o~-
§
a m
m
§ +
+§
+
+ 20
§
....
~..: 0_L~
+
+
+
+
o
~
~
~
+++ +
.~;
.
+
+
o
o~
9
9
=. x ~. l~ li . i~ I~R
A i~ !! ~ It
100
E/Q(keV/e)
E/Q (keV/e)
Fig. 2 Accumulated energy density below E/Q in the inner (L=4) and in the outer (L=6) ring current for quiet and ctive times. 2. In the inner part of the ring current, high energy H + ions contribute a large amount of energy density, especially in quiet times. For example, about 20%s of the total energy density in the inner region comes from H + with energy range from 200 to 400 keV. 3. During active times, the contribution of O + ion can be as high as 30%s in the inner region and 35%s in the outer region. While the contribution of H + ions are 55% and 45%, respectively. 4. The He ++ ions show an increased importance in the outer region during active times (increases from <10% to 15%), whereas they show no obvious change in the inner ring current. 5. Contrary to He ++ ions, the contribution of He + ions shows little variation at L=4 and L=6. Ion Composition Dependence on Solar-Cycle In order to provide an overview of the ion composition variations in the ring current regions, the density ratios derived from the energy range (54 keV/e to 426 keV/e) at the inner (L=3-4) and outer idng current (L=5-6) during quiet conditions (J Dst 1<30 nT) and storm times (I Dst 1>50 nT) are given in Table 1. The composition results obtained by CHEM onboard AMPTE are also presented for comparison. The total
-423 -
S. Y. Fu et al.
Table 1. C o m p a r i s o n of f r a c t i o n a l n u m b e r a n d e n e r g y density for ring c u r r e n t ion species
[I
H§ O§ He .-+ He "
Solar Maximum I1 Solar Minimum Number Density Ratios(% to Total) i Number Density Ratios(% to Total) .... L=3-4 L=5-6 L=3-4 L=5-6 Quiet a Storm b Quiet a Storm b Quiet c Storm d Quiet c Storm d 89 65.9 74.5 53.3 " 96.3 77.3 91.1 75.4 7.1 27.8 17.8 37.2 2.2 17.4 4.2 18.9 2.27 2.54 2.86 6.2 0.14 0.5 0.5 1.1 1.47 3.77 4.77 3.25 0.75 1.3 3.2 0.78
n+ O+ He++ He +
Energy Density Ratios(% to Total) Energy Density Ratios(% to Total) L=3-4 L=5-6 F' L=3-4 L=6.4-6.8 Quiet a Storm b Quiet a Storm b Quiet Storm Quiet e Storm y 86 74 87 64.2 69.3 46.7 6 21 4.6 23.2 16.2 35.4 1 3 6.5 7.3 6.96 13 4 0 1.78 5.2 7.43 4.7 ,,
a. b. c. d. e. fi
IDstl<30 nT, Energy Range 50-426 keV/e. (MICS) IDstl>50 nT, Energy Range 50-426 keV/e. (MICS) IDstl<18 nT, Energy Range 1-315 keV/e. (from Table III in (Gloeckler and Hamilton, 1987) ) IDst[>51 nT, Energy Range 1-315 keV/e. (from Table III in (Gloeckler and Hamilton, 1987) ) AE<30 nT, Energy Range 10-100 keV/e. (from Fig.7 in (Daglis,1993)) AE>700 nT, Energy Range 10-100 keV/e. (from Fig.7 in (Daglis,1993))
energy density at the inner and outer ring current is 100 and 25.7 keV/cm 3 during quiet times and 180 and 30.7 keV/cm 3 during active times. The corresponding total number densities are 0.53 and 0.24 cm -3 at quiet times and 1.13 and 0.3 cm -3 at active times, respectively. Similar to the observations of AMPTE, the ionospheric origin O + ions measured by CRRES/MICS show a tremendous enhancement during storm times compared to relatively quiet times. The energy density ratio of H + to the total energy density in the inner ring current falls from 87% to < 64%, whereas O + increases from 4.6% to 23%. It should be emphasized, however, that the O + contributions to the ring current at L=6 for quiet and active times are 16.2% and 35.4% respectively, which is reasonable higher than those values 6% and 21% reported by AMPTE satellite in the solar minimum. He ++ and He + have also a higher fraction than in the solar minimum. The abundance of He ++ can even reach 12% of the total energy density during active times. As we can see from Table 1, only for H + ions the percentages (number density ratio to the total) are at a lower value in both quiet and active times compared with the solar minimum phase. DISCUSSION and CONCLUSIONS It was suggested that the ring current might consist of two belts located at different positions (e.g., Akasofu, 1963). Later investigations indicated that a belt at smaller radial distances is mostly constituted by O + ions and a belt located outside consists mostly of protons (Williams and Hamilton,1985; Hamilton, 1988).This study shows locations of the maxima number density in the radial profiles show a displacement for different ion species duringquiet times. The H + and He ++ ions concentrate at lower L shell than O + and He + ions. Both the positions of the maximum flux of O + and He + move into lower L-shells in the early stage of a storm and then move back to higher L-shells in the recovery phase. However, the positions for H + and He ++ do not show any dependence on Dst. This may be indicated that there are two ring current belts not only by radial distance, but also by different ion composition. The spacial variations of these ring current ions are closely associated with the composition variation during geomagnetic activity. The maximum flux location
-424 -
Geomagnetic Activity and Solar-Cycle Dependence of the Ring Current Ions of the quiet time ring current in the solar maximum is found to be 0.5 RE inward than the observation made in solar minimum (Gloeckler and Hamilton, 1987). This implies that the average convection electric field in the solar maximum maybe stronger than that in solar minimum since the enhanced convection electric field is thought to be responsible for the charged particle moving across the magnetic field from the tail plasma sheet into the inner magnetosphere. The noteworthy result is that the flux of H + ions is apparently lower in the solar maximum than that in the solar minimum, on the other hand, both O + and He ++ are higher in the solar maximum. This result seems to be consistent with the outflow flux of the ionospheric origin ions which varies from solar minimum to solar maximum. It has been shown that the outflow flux e.g. O + could be one order higher in the solar maximum as enhanced solar irradiation e.g. F10.7 flux varied from solar minimum to solar maximum whereas the flux of H + shows independent of the solar activity (Cannata and Gombosi, 1989). Also, the observation in the geosynchronous orbit shows there is no correlation between the He ++ ion flux and the solar activity (Young et al. 1982). Although the variation of helium abundance in solar wind is of only 1% difference between the solar maximum and the solar minimum (Ogilvie et al. 1974), However, evidences have also shown that the high helium abundances in the solar wind are often associated with CMEs and interplanetary shocks and its frequency of occurrence is in phase with the solar cycle (Borrini and Gosling, 1982). On the other hands, it is widely known that CMEs and interplanetary shocks are often interplanetary causes of geomagnetic storms (e.g. Gosling, 1987) and therefore, the solar events like CME, interplanetary shocks may lead to a relatively high abundance of He ++ observed in the ring current. ACKNOWLEDGEMENT This work was supported by the grant number 40144015, partly by CNSF grants 49984002, 49834040 and Chinese Research project G20000784. REFERENCES Akasofu, S.-I., S. Chapman, and D. Venkatesan, The main phase of great magnetic storms, J. Geophys. Res., 68, 3345-3350, (1963). Borrini, G., J. T. Gosling, S. J. Bame, and W. C. Feldman, Helium abundance enhancements in the solar wind, J. Geophys. Res., 87, 7370-737, (1982). Cannata, R. W., and T. I. Gombosi, Modeling of the solar cycle dependence of quiet-time ion upwelling at high geomagnetic latitudes, Geophys. Res. Lett., 16, 1141-1144, (1989). Daglis, I. A., E. T. Sarris, and B. Wilken, AMPTE/CCE CHEM observations of the ion population at geosynchronous altitudes, Ann. Geophys., 11,685-696, (1993). Gloeckler, G., and D. C. Hamilton, AMPTE ion composition results, Phys. Scr., T,18, 73-84, (1987). Gosling, J. T., D. N. Baker, S. J. Bame, W. C. Feldman, R. D. Zwickl, et al., Bidirectional solar wind electron heat flux events, J. Geophys. Res., 92, 8519-8539, (1987). Hamilton, D. C., G. Gloeckler, F. M. Ipavich, W. Stiidemann, B. Wilken, et al., Ring current development during the great geomagnetic storm of February 1986, J. Geophys. Res., 93, 14,343-14,355, (1988). Krimigis, S. M., G. Gloeckler, R. W. McEntire, T. A. Potemra, F. L. Scarf, et al., Magnetic storm of September 4, 1984: a synthesis of ring current spectra and energy densities measured with AMPTE/CCE, Geophys. Res. Lett., 12, 329-332, (1985). Ogilvie, K. W., and J. Hirshberg, The solar cycle variation of the solar wind helium abundance, J. Geophys. Res., 79, 4595-4602, (1974). Williams, D. J., Dynamic of the Earth's ring current: Theory and observation, Space Sci. Rev., 42, 375-396, (1985). Young, D. T., H. Balsiger, and J. Geiss, Correlations of magnetospheric ion composition with geomagnetic and solar activity, J. Geophys. Res., 87, 9077-9096, (1982).
-425 -
DEPENDENCE
S. Y. Fu,IQ. G. Zong2Z. Y. Pu 3 L. Xie 4
1Department of Geophysics, Peking University, Beijing, 100871, China 2Center .for Space Physics, Boston University, MA 02215 3Space Weather Lab, CSSAR, CAS, Beijin9, 100080, China 4Department of Geophysics, Peking University, Beijin9,100871, P.R. China
ABSTRACT Observations obtained from CRRES/MICS in the solar maximum show that both the ring current composition and the location of the maximum ion flux can be influenced by geomagnetic activity and solar cycle. Both the number and the energy density ratio of O +, He ++ and He + ions increase during geomagnetic active times, whereas that of H + exhibits an obvious decrease. It is also interesting to compare with AMPTE observations which were made in the solar minimum. The abundance of the ring current H + is apparently lower in the solar maximum than in the solar minimum. In contrast, the abundance of both O + and He ++ ion is higher in the solar maximum. In addition, the average location of the maximum number density of the energetic ions is about 0.5 RE lower in solar maximum than that in solar minimum. INTRODUCTION In the past years, two of the most important in-situ ring current observation were made by AMPTE which launched in 1981, solar minimum and CRRES satellite which was operated during 1990 - 1991, solar maximum. Based on the instrument ability of distinguishing different ion species, it is recognized that the variation of the ion composition may play an important role in the formation and decay of a storm. By using the data obtained by AMPTE, the locations of the maximum number density for different ion species have been found to be at about L--4, 5.2, 5.7 and 7 for H +, O +, He + and He ++ ions, respectively during geomagnetic quiet period. These positions would move inward, to the lower L shells during storm periods (Gloeckler and Hamilton, 1987). The relative contribution of ion species to the ring current during low and high geomagnetic activities has been identified by both case study (Gloeckler and Hamilton, 1987, Krimigis et al 1985; Hamilton et al 1988) and statistical study (Daglis et al, 1993). However, the solar cycle dependence of the radial ion distribution and the relative abundance in the ring current region are still unclear. Based on CRRES/MICS measurements in 1991, we studied the averaged ring current property during both quiet and active time in the solar maximum. Further, a comparison between the solar maximum and solar minimum observations is made.
-421 -
S. Y. Fu et al.
OBSERVATIONS Radial Profiles of Number Density and Energy Density In Figure 1, the radial profiles of number densities for O +, He +, He ++ and H + in the quiet and active time ring current are shown on the left side. The percentage of the accumulated energy of the different ion species to the whole ring current versus L value are shown on the right side. Dst index is used as a criterion to assemble the data for quiet (Dst<30 nT) and storm (Dst>50 nT) times in which the averaged Dst are about 7 nT and 70 nT, respectively.
1
lO
100
IDstl>5OnT ,.., 100 E
+
.~0 aID
9 ++ 9
9
ai_ 10=
+:o~:
~ ~
~
a)
5
E
&
= 10~
+++++
, ...................
, .........
, .........
"
IDstl>50 nT
, .......
/ H +
+
He* ,, H e ++ x
o'.
0 §
55 &~A
i
........
H* . o He+~ He++5
a
9
|
i
Z
10 4
0
1
2
3
~_
5
6
7
........
1
....
*n'~ E
'~ "
+ + + + + ++
1
+ + +oo
~176176
1
~'10
i
---
I
t
9
I
I
9
9
o
~"
o 0 o -~
~
I
, .
.
.
.
2
.
3
.
.
..
.
.
.
4
.
5
L
.
.
.
.
.
.
.
.
6
7
,D=,:30n;
. . . . . . . . . . . . . . . . . . . . . . . .
80-].-
+ +
60
+
+ + + + + +
++
1
o
10"4[
1
2
3
~_
5
6
7
1
2
3
~.
5
6
7
Fig. 1 (Left) Radial profiles of number density of O+,He+,He ++ and H + in the quiet and active time ring current. (Right) Percentage of the accumulated energy below L of the ions to the whole ring current. Four different symbol lines represent the contribution of the four species. The solid line shows the total accumulated energy. The energy range is 54 keV/e-426 keV/e. From Figure 1 we can see that during quiet times, there exist two different number density peaks in the radial profiles, one is at about L - 3 for H + and He ++ ions and the other is around L - 4 . 5 for O + and He + (bottom-left panel in Figure 1). During geomagnetic activity, the position of the maximum number densities for O + and He + move inward and all four species concentrated in the region L - 3 ,,~ 4 (top-left panel in Figure 1). Although O + and He + show an obvious inward motion during active times, the total accumulated energy versus L shell (the solid lines in right panels) remains unchanged. More than 80% of the total ring current is still in the region 2.5 < L < 5. However, the relative contribution of different ion species changes a lot, as we can see from the right panels in Figure 1. The H + contribution falls from 80% to < 60% as the magnitude of Dst becomes larger than 50 nT, and that of O + increases from 10% to 30~
-422 -
Geomagnetic Activity and Solar-Cycle Dependence of the Ring Current Ions Energy Density,of the ring current The accumulated percentages of energy densities for each ion species are displayed in Figure 2. The top two panels are for the outer ring current (L=6) and the bottom two panels for the inner ring current (L=4). On the basis of Figure 2, following points can be made: 1. The outer part of the ring current contains about 65% H + and 20% O +, and less than 10% He + and He ++. Ions which carry the main energy density in this region are in the energy range below 200 keV/e.
1 0 0 ~, - -
80 .-.. ~
9
'
'
100~
,
6
H+ +
i IDstl<30nT +
W
+
+
+
+
He++=
+
O"
.
,
k=6
9
o
o
o
oo
9
o
9
9
+
9 +
~ ~
ioo
~ ~!
+
:
++ + o
o
9
i
~
I
M
+
9
; ~]~ ~
He++ ,, He ,=
~o"
,,,) o
lOO
o O
i
l
o
,.,
9
9
]l
m
I i
~
IDstl>50 nT
+ + + + -i
i
~
'~176 i 80~ L=4
!
9
F_JQ (keV/e)
E/Q (keY/e)
IDstl<30nT
o ~ m
9
'
L=4
+ +
IDstl>50nT
n" 40 o
+
.
~" .o~-
9
§
o ..
.
H+
80 f
He+ "
++ + . + + +
60~-
.
t-
§ o
,
§ §
~, 4o~-
§
a m
m
§ +
+§
+
+ 20
§
....
~..: 0_L~
+
+
+
+
o
~
~
~
+++ +
.~;
.
+
+
o
o~
9
9
=. x ~. l~ li . i~ I~R
A i~ !! ~ It
100
E/Q(keV/e)
E/Q (keV/e)
Fig. 2 Accumulated energy density below E/Q in the inner (L=4) and in the outer (L=6) ring current for quiet and ctive times. 2. In the inner part of the ring current, high energy H + ions contribute a large amount of energy density, especially in quiet times. For example, about 20%s of the total energy density in the inner region comes from H + with energy range from 200 to 400 keV. 3. During active times, the contribution of O + ion can be as high as 30%s in the inner region and 35%s in the outer region. While the contribution of H + ions are 55% and 45%, respectively. 4. The He ++ ions show an increased importance in the outer region during active times (increases from <10% to 15%), whereas they show no obvious change in the inner ring current. 5. Contrary to He ++ ions, the contribution of He + ions shows little variation at L=4 and L=6. Ion Composition Dependence on Solar-Cycle In order to provide an overview of the ion composition variations in the ring current regions, the density ratios derived from the energy range (54 keV/e to 426 keV/e) at the inner (L=3-4) and outer idng current (L=5-6) during quiet conditions (J Dst 1<30 nT) and storm times (I Dst 1>50 nT) are given in Table 1. The composition results obtained by CHEM onboard AMPTE are also presented for comparison. The total
-423 -
S. Y. Fu et al.
Table 1. C o m p a r i s o n of f r a c t i o n a l n u m b e r a n d e n e r g y density for ring c u r r e n t ion species
[I
H§ O§ He .-+ He "
Solar Maximum I1 Solar Minimum Number Density Ratios(% to Total) i Number Density Ratios(% to Total) .... L=3-4 L=5-6 L=3-4 L=5-6 Quiet a Storm b Quiet a Storm b Quiet c Storm d Quiet c Storm d 89 65.9 74.5 53.3 " 96.3 77.3 91.1 75.4 7.1 27.8 17.8 37.2 2.2 17.4 4.2 18.9 2.27 2.54 2.86 6.2 0.14 0.5 0.5 1.1 1.47 3.77 4.77 3.25 0.75 1.3 3.2 0.78
n+ O+ He++ He +
Energy Density Ratios(% to Total) Energy Density Ratios(% to Total) L=3-4 L=5-6 F' L=3-4 L=6.4-6.8 Quiet a Storm b Quiet a Storm b Quiet Storm Quiet e Storm y 86 74 87 64.2 69.3 46.7 6 21 4.6 23.2 16.2 35.4 1 3 6.5 7.3 6.96 13 4 0 1.78 5.2 7.43 4.7 ,,
a. b. c. d. e. fi
IDstl<30 nT, Energy Range 50-426 keV/e. (MICS) IDstl>50 nT, Energy Range 50-426 keV/e. (MICS) IDstl<18 nT, Energy Range 1-315 keV/e. (from Table III in (Gloeckler and Hamilton, 1987) ) IDst[>51 nT, Energy Range 1-315 keV/e. (from Table III in (Gloeckler and Hamilton, 1987) ) AE<30 nT, Energy Range 10-100 keV/e. (from Fig.7 in (Daglis,1993)) AE>700 nT, Energy Range 10-100 keV/e. (from Fig.7 in (Daglis,1993))
energy density at the inner and outer ring current is 100 and 25.7 keV/cm 3 during quiet times and 180 and 30.7 keV/cm 3 during active times. The corresponding total number densities are 0.53 and 0.24 cm -3 at quiet times and 1.13 and 0.3 cm -3 at active times, respectively. Similar to the observations of AMPTE, the ionospheric origin O + ions measured by CRRES/MICS show a tremendous enhancement during storm times compared to relatively quiet times. The energy density ratio of H + to the total energy density in the inner ring current falls from 87% to < 64%, whereas O + increases from 4.6% to 23%. It should be emphasized, however, that the O + contributions to the ring current at L=6 for quiet and active times are 16.2% and 35.4% respectively, which is reasonable higher than those values 6% and 21% reported by AMPTE satellite in the solar minimum. He ++ and He + have also a higher fraction than in the solar minimum. The abundance of He ++ can even reach 12% of the total energy density during active times. As we can see from Table 1, only for H + ions the percentages (number density ratio to the total) are at a lower value in both quiet and active times compared with the solar minimum phase. DISCUSSION and CONCLUSIONS It was suggested that the ring current might consist of two belts located at different positions (e.g., Akasofu, 1963). Later investigations indicated that a belt at smaller radial distances is mostly constituted by O + ions and a belt located outside consists mostly of protons (Williams and Hamilton,1985; Hamilton, 1988).This study shows locations of the maxima number density in the radial profiles show a displacement for different ion species duringquiet times. The H + and He ++ ions concentrate at lower L shell than O + and He + ions. Both the positions of the maximum flux of O + and He + move into lower L-shells in the early stage of a storm and then move back to higher L-shells in the recovery phase. However, the positions for H + and He ++ do not show any dependence on Dst. This may be indicated that there are two ring current belts not only by radial distance, but also by different ion composition. The spacial variations of these ring current ions are closely associated with the composition variation during geomagnetic activity. The maximum flux location
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Geomagnetic Activity and Solar-Cycle Dependence of the Ring Current Ions of the quiet time ring current in the solar maximum is found to be 0.5 RE inward than the observation made in solar minimum (Gloeckler and Hamilton, 1987). This implies that the average convection electric field in the solar maximum maybe stronger than that in solar minimum since the enhanced convection electric field is thought to be responsible for the charged particle moving across the magnetic field from the tail plasma sheet into the inner magnetosphere. The noteworthy result is that the flux of H + ions is apparently lower in the solar maximum than that in the solar minimum, on the other hand, both O + and He ++ are higher in the solar maximum. This result seems to be consistent with the outflow flux of the ionospheric origin ions which varies from solar minimum to solar maximum. It has been shown that the outflow flux e.g. O + could be one order higher in the solar maximum as enhanced solar irradiation e.g. F10.7 flux varied from solar minimum to solar maximum whereas the flux of H + shows independent of the solar activity (Cannata and Gombosi, 1989). Also, the observation in the geosynchronous orbit shows there is no correlation between the He ++ ion flux and the solar activity (Young et al. 1982). Although the variation of helium abundance in solar wind is of only 1% difference between the solar maximum and the solar minimum (Ogilvie et al. 1974), However, evidences have also shown that the high helium abundances in the solar wind are often associated with CMEs and interplanetary shocks and its frequency of occurrence is in phase with the solar cycle (Borrini and Gosling, 1982). On the other hands, it is widely known that CMEs and interplanetary shocks are often interplanetary causes of geomagnetic storms (e.g. Gosling, 1987) and therefore, the solar events like CME, interplanetary shocks may lead to a relatively high abundance of He ++ observed in the ring current. ACKNOWLEDGEMENT This work was supported by the grant number 40144015, partly by CNSF grants 49984002, 49834040 and Chinese Research project G20000784. REFERENCES Akasofu, S.-I., S. Chapman, and D. Venkatesan, The main phase of great magnetic storms, J. Geophys. Res., 68, 3345-3350, (1963). Borrini, G., J. T. Gosling, S. J. Bame, and W. C. Feldman, Helium abundance enhancements in the solar wind, J. Geophys. Res., 87, 7370-737, (1982). Cannata, R. W., and T. I. Gombosi, Modeling of the solar cycle dependence of quiet-time ion upwelling at high geomagnetic latitudes, Geophys. Res. Lett., 16, 1141-1144, (1989). Daglis, I. A., E. T. Sarris, and B. Wilken, AMPTE/CCE CHEM observations of the ion population at geosynchronous altitudes, Ann. Geophys., 11,685-696, (1993). Gloeckler, G., and D. C. Hamilton, AMPTE ion composition results, Phys. Scr., T,18, 73-84, (1987). Gosling, J. T., D. N. Baker, S. J. Bame, W. C. Feldman, R. D. Zwickl, et al., Bidirectional solar wind electron heat flux events, J. Geophys. Res., 92, 8519-8539, (1987). Hamilton, D. C., G. Gloeckler, F. M. Ipavich, W. Stiidemann, B. Wilken, et al., Ring current development during the great geomagnetic storm of February 1986, J. Geophys. Res., 93, 14,343-14,355, (1988). Krimigis, S. M., G. Gloeckler, R. W. McEntire, T. A. Potemra, F. L. Scarf, et al., Magnetic storm of September 4, 1984: a synthesis of ring current spectra and energy densities measured with AMPTE/CCE, Geophys. Res. Lett., 12, 329-332, (1985). Ogilvie, K. W., and J. Hirshberg, The solar cycle variation of the solar wind helium abundance, J. Geophys. Res., 79, 4595-4602, (1974). Williams, D. J., Dynamic of the Earth's ring current: Theory and observation, Space Sci. Rev., 42, 375-396, (1985). Young, D. T., H. Balsiger, and J. Geiss, Correlations of magnetospheric ion composition with geomagnetic and solar activity, J. Geophys. Res., 87, 9077-9096, (1982).
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