AMPTE/CCE observations of the plasma ... - Wiley Online Library

GEOPHYSICAL RESEARCH LETTERS, VOL.

AMPTE/CCE

OBSERVATIONS

DURING

OF THE

THE SEPTEMBER

12, NO. 5,

PLASMA

PAGES 321-324,

COMPOSITION

4, 1984 MAGNETIC

MAY 1985

BELOW

17 keV

STORM

E.G. Shelleyl, D. M. Klumparl, W. K. Peterson•, A. Ghielmetti• H. Balsiger2,J. Geiss2,and H. Rosenbauer3 •Lockheed Palo Alto Research Laboratory, 3251 Hanover Street, Palo Alto, CA 94304 2PhysikalischesInstitut, University of Bern, 3012 Bern, Switzerland 3Max-Planck-Institut fur Aeronomie, D-3411 Katlenburg-Lindau, F.R.G. Abstract: Observations from the Hot Plasma Composition Experiment on the AMPTE/CCE spacecraft during the magneticstorm of 4-5 September1984 reveal that significant injection of ions of terrestrial origin accompanied the storm development. The compression of the magnetosphereat storm suddencommencementcarried the magnetopause inside the CCE orbit clearly revealing the shocked solar wind plasma. A build up of suprathermal ions is observed near the plasmapause during the storm main phase and recovery phase. Pitch angle distributions in the ring current during the main phase show differences

the AMPTE/CCE

betweenH + and O + that suggestmassdependentinjec-

low energy portion of the inner ring current distribution while the ions below about 1 keV generally characterize the

essentiallyall equatorial pitch angles. Electrons from 50 eV to 25 keV were simultaneously measured. The instrumentation is describedmore fully by Shelley et al. [1985]. Figure 1 is a compositespectrogramof the HPCE observationsfor three orbits. The various individual spectrogram panels are defined in the figure caption. Figure 2 displaysdusk sector

radial profiles for H + and O + partial number densities. Ions between 1 keV and 17 keV typically characterize the

tion, transport and/or loss processes.

thermal and suprathermal populations. During the pre-storm outbound pass beginning at 2215 UT on September 3 the magnetospheric particle fluxes were relatively weak and unstructured. The apparent elec-

Introduction

GEOS-1 made the first ion composition measurements in the near equatorial magnetosphere beginning in 1976 [Balsiger et al., 1983]. This was followed in 1977 by the ISEE-1 which extended ion composition well into the plasma sheet [Sharp et al., 1983]. Other spacecraftproviding equatorial or near equatorial ion composition measurements include GEOS-2 in geosynchronous orbit [Balsigeret al., 1983], PROGNOZ-7 in a highly inclined, highly elliptical orbit [Lundin et al., 1983], and SCATHA in a nearly geosynchronous orbit (5.3 Re x 8.3 Re) [Johnson et al., 1983]. With the exception of the SCATHA instrumentation which had an energy range up to 32 keV/e, all of the above measurements were limited to _

=

ol

i0.1 =•. p'_/ L •.•'

0.01l

fI=' i •0

{

SEPT 5. 0338-0•0 UT

I 30

PITCH

I

• 50

{

ANGLE

I •0

-_

j

q

• / 90

•0

SEPT 0338-0•10UT

I

I 30

PITCH

I

I, 50

•0

90

ANGLE

Fig. 3. Normalized pitch angle distributionsof 12-17 keV H + and O + ring current ions during the main phase of the storm.

32z4

Shelleyet al.: 1-17 keV Ion Composition

storm and to vary systematicallywith solar cycle [Young et al., 1982]. Nevertheless,detailed studiesof individual events such as this one can elucidate the physical processes that take part in the dynamicsof the magnetosphere. The striking differences in the energy distributions of the terrestrial O + and He + observedduring the storm suggest different source locations and/or transport and

D.T. Young for their contribution to the successof the HPCIE experiment. This research is funded by NASA

energization processes. The higherenergyof the O + might suggest injectiondeeperin the tail while the He + is either

Balsiger, H., J. Geiss, and D.T. Young, The Composition of Thermal and Hot Ions Observed by the GEOS-1 and GEOS-2 Spacecraft, Energetic Ion Composition in the Earth's Magnetosphere, R. G. Johnson, ed., Terra Sci. Publ. Co., Tokyo, 195, 1983. Johnson,R.G., R.J. Strangeway,E.G. Shelley,J.M. Quinn and S.M. Kaye, Hot Plasma Composition Resultsfrom the SCATHA Spacecraft, Energetic Ion Composition in the Earth's Magnetosphere, R.G. Johnsoned., Terra Sci. Publ. Co., Tokyo, 287, 1983. Lundin, R., B. Hultqvist, N. Pissarenko, and ^. Zacharov, Composition of the Hot Magnetospheric Plasma Observed with the PROGNOZ-7 Satellite, Energetic Ion Composition in the Earth's Magnetosphere, R.G. Johnson ed., Terra Sci. Publ., Co., Tokyo, 307, 1983. Scarf, F.L., CCE Plasma Wave Observations during the Storm of September 4-5, 1984, Geophys. Res. Lett., (this issue), 1985. Sharp, R.D., R.G. Johnson, W. Lennartsson, W.K. Peterson and E.G. Shelley, Hot Plasma Composition Results from the ISIEIE-1 Spacecraft, Energetic Ion Composition in the Earth's Magnetosphere, R.G. Johnson ed., Terra Sci. Publ. Co., Tokyo, 231, 1983. Shelley, E.G., A. Ghielmetti, E. Hertzberg, S.J. Barrel, K. Altwegg-Von Burg, and H. Balsiger, AMPTE/ CCIE Hot Plasma Composition Experiment (HPCE), to be publ. in ISEE Trans. Geosci. and Remote Sensing, May, 1985. Williams, D.J. and M. Sugiura, The Charge Composition Explorer and the 4-7 September 1984 Geomagnetic Storm, Geophys. Res. Lett., (this issue) 1985. Williams, D.J. and L.R. Lyons, The Proton Ring Current and its Interaction with the Plasmapause; Storm Recovery Phase, J. Geophys. Res., 79, 4195, 1974. Young, D.T., H. Balsiger, and J. Geiss, Correlation of Magnetospheric Ion Composition with Geomagnetic and Solar Activity, J. Geophys. Res., 87, 9077, 1982.

directly injected or is detached from the plasmasphere.On the other hand the pitch angle distributions of the higher

energycomponentof the O + (Figure3) suggest that a large fraction of these ions have been injected into the equato-

rial magnetosphereearthward of the plasma sheet, perhaps at the substorminjection boundary. We find a some-

what similar problem in interpreting the He ++ distributions which are inferred to be of solar wind origin

and might be expectedto have been transported inward from the plasma sheet. If that were the case we would expect not only the low energy (_