Physics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sm31b06r&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SM31B-06
Physics
2720 Energetic Particles, Trapped, 2778 Ring Current, 2788 Storms And Substorms
Scientific paper
The ion composition observations by the Polar spacecraft from the last solar minimum to the present are compared to similar observations by CRRES in the previous cycle. The Magnetospheric Ion Composition Spectrometer (MICS) was onboard CRRES and is part of the Polar CAMMICE experiment. The MICS sensor provided mass and charge state composition data for the energetic (1-425 keV/q) ions including H+, He+, He++, and O+. The 5-minute average number densities for each species are computed by mapping the MICS fluxes down to the magnetic equator using the measured pitch angle distributions and integrating the equatorial spectrum over the energy range 1-200 keV/q. Approximately 3.5 years of the Polar mission in the rising part of the solar cycle are used for the database. The densities are analyzed statistically with the solar EUV index F10.7 and various geomagnetic indices such as Kp and Dst. The results are compared with a similar study of the ion composition in the energy range 0.9-15.9 keV/q measured by the GEOS 2 satellite during geomagnetically quiet periods [Young et al., 1982], and with the recent survey of the relative composition measured by Polar averaged over all times [Pulkkinen et al., 2000]. It is found that ion densities at L ~ 6-7 during relatively quiet intervals show correlations to the EUV and geomagnetic activity similar to the results of Young et al. [1992]. At lower L the correlation of the ion density with the EUV and activity levels increases substantially, due in part to the extremely low energetic ion densities during the quiet intervals of solar minimum. This may be interpreted as a combination of the solar cycle effects on 1) the ring current source population; and 2) the processes which transport the ions to lower L. The behavior of the ion composition during geomagnetic stormtime is also investigated by restricting the density database to those intervals with the Dst index below a threshold value. Paradoxically, the Polar data shows that the measured stormtime ion density has little correlation with the EUV or the activity level. As the threshold in Dst is lowered, corresponding to storms of higher intensity, the correlations of both the H+ and O+ ion density with F10.7 and Kp tend to disappear. This result may indicate that the Young et al. [1982] model of ion density as a function of F10.7 is inappropriate for simulation of geomagnetic storms.
Fennell Joseph F.
Grande Marco
Pulkkinen Tuija I.
Roeder James L.
Turner Niescja Evonne
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