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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, A07206, doi:10.1029/2005JA011559, 2006

A statistical comparison of hot-ion properties at geosynchronous orbit during intense and moderate geomagnetic storms at solar maximum and minimum

Jichun Zhang

Space Physics Research Laboratory, University of Michigan, Ann Arbor, Michigan, USA


Michael W. Liemohn

Space Physics Research Laboratory, University of Michigan, Ann Arbor, Michigan, USA


Michelle F. Thomsen

Los Alamos National Laboratory, Los Alamos, New Mexico, USA


Janet U. Kozyra

Space Physics Research Laboratory, University of Michigan, Ann Arbor, Michigan, USA


Michael H. Denton

Los Alamos National Laboratory, Los Alamos, New Mexico, USA


Joseph E. Borovsky

Los Alamos National Laboratory, Los Alamos, New Mexico, USA


Abstract

Hot-ion measurements at geosynchronous orbit from the Los Alamos Magnetospheric Plasma Analyzer (MPA) instrument during geomagnetic storms at solar maximum (July 1999–June 2002) and at solar minimum (July 1994–June 1997) are collected, categorized, and analyzed through the superposed epoch technique. To investigate this source of the storm-time ring current, the local time (LT) and universal time (UT) dependence of the average variations of hot-ion fluxes (at the energies of ∼30, ∼17, ∼8, and ∼1 keV), density, temperature, entropy, and temperature anisotropy are examined and compared among four storm categories, i.e., 44 intense storms and 120 moderate storms, defined by the pressure corrected Dst (Dst*), at the two solar extrema. All the hot-ion parameters are highly disturbed around Dst*min; they show distinct peaks or minima and display obvious increase or decrease regions, whose locations do not change much with levels of geomagnetic activity and solar activity. It is also found that intense storms at solar minimum always have the highest (lowest) average peak value (minimum) in each hot-ion parameter. Around Dst*min in each storm category, hot ions are clearly denser near dawn than those near dusk. On the nightside and in the afternoon sector, temperature and entropy during solar minimum storms are usually higher than those during solar maximum storms; there is actually no clear temperature and entropy enhancement during solar maximum storms. During each type of storm, hot ions are isotropic on the nightside but anisotropic (T per /T par > 1) close to noon.

Received 2 December 2005; accepted 20 April 2006; published 26 July 2006.

Keywords: Magnetospheric physics; geosynchronous orbit; magnetospheric plasma sources.

Index Terms: 2162 Interplanetary Physics: Solar cycle variations (7536); 2788 Magnetospheric Physics: Magnetic storms and substorms (7954); 2730 Magnetospheric Physics: Magnetosphere: inner; 2764 Magnetospheric Physics: Plasma sheet; 2740 Magnetospheric Physics: Magnetospheric configuration and dynamics.

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Citation: Zhang, J., M. W. Liemohn, M. F. Thomsen, J. U. Kozyra, M. H. Denton, and J. E. Borovsky (2006), A statistical comparison of hot-ion properties at geosynchronous orbit during intense and moderate geomagnetic storms at solar maximum and minimum, J. Geophys. Res., 111, A07206, doi:10.1029/2005JA011559.