Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - A statistical comparison of hot-ion properties at geosynchronous orbit during intense and moderate geomagnetic storms at solar maximum and minimum.
AU - Zhang, Jichun C.
AU - Liemohn, Michael W.
AU - Thomsen, Michelle F.
AU - Kozyra, Janet U.
AU - Denton, Michael H.
AU - Borovsky, Jospeh E.
N1 - Copyright (2006) American Geophysical Union.
PY - 2006
Y1 - 2006
N2 - 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.
AB - 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.
KW - storm geosynchronous lanl DCS-publications-id
KW - art-782
KW - DCS-publications-personnel-id
KW - 123
U2 - 10.1029/2005JA011559
DO - 10.1029/2005JA011559
M3 - Journal article
VL - 111
SP - 1
EP - 16
JO - Journal of Geophysical Research
JF - Journal of Geophysical Research
SN - 0148-0227
IS - A07206
ER -