Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsa23b1472y&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SA23B-1472
Physics
[2415] Ionosphere / Equatorial Ionosphere, [2427] Ionosphere / Ionosphere/Atmosphere Interactions, [2431] Ionosphere / Ionosphere/Magnetosphere Interactions, [2479] Ionosphere / Solar Radiation And Cosmic Ray Effects
Scientific paper
The Space Environment Research Center (SERC), Kyushu University has deployed the MAGnetic Data Acqusition System (MAGDAS) at 50 stations along the 210- and 96-degree magnetic meridians (MM) and the magnetic dip equator, and several FM-CW radars along the 210-degree MM during the International Heliophysical Year (IHY) period of 2005-2009 (see http://magdas.serc.kyushu-u.ac.jp/ and http://magdas2.serc.kyushu-u.ac.jp/). The MAGDAS project for space weather will be continued during the Post IHY, i.e., the International Space Weather Initiative (ISWI) period of 2010-2012. The goal of MAGDAS project is to become the most comprehensive ground-based monitoring system of the earth's magnetic field. By analyzing these new MAGDAS data, we can perform a real-time monitoring and modeling of the global (e.g., Sq, EEJ) current system and the ambient plasma mass density for understanding the electromagnetic and plasma environment changes in geospace during helio-magnetospheric storms. In order to examine the propagation mechanisms of transient disturbances, i.e., sc/si, Pi 2, and DP2, relations of ionospheric electric and magnetic fields are also investigated by analyzing the MAGDAS magnetic data and the Doppler data of our FM-CW ionospheric radar. A new EE-index (EDst, EU, and EL) was proposed by SERC for real-time and long-term geo-space monitoring. The basic algorithm to obtain EE-index was constructed by Uozumi et al. (2008). EU and EL mainly represent the range of the EEJ (equatorial electrojet) and CEJ (equatorial counter electrojet) components, respectively. The baseline levels of EU and EL are obtained by averaging the H-component magnetic variations observed at the nightside (LT = 18-06) MAGDAS/CPMN (Circum-pan Pacific Magnetometer Network) stations along the magnetic equator. The baseline value is defined as EDst and its variations are found to be similar to those of Dst. We examined relationships among the EEJ amplitude, the F10.7 solar radiation flux, the solar wind parameter, Ap-index and the ionospheric conductivity. The followings were clarified:(1) The EEJ amplitudes of several-hrs period are controlled by the interplanetary electric field (Ey = - Vsw x BIMF). (2) The EEJ and Sq current oscillate with two dominant periods of (a) 14.5 days and (b) semi-annual on the global scale, where the Sq current component shows clear annual variation. (3) The 14.5-days EEJ variation is amplified during winter. (4) The peaks of the semi-annual EEJ variation are found in spring and autumn. (5) The amplitude of the EEJ variation depends on the 11-years solar activity (i.e., F10.7 solar radiation flux). (6) The semi-annual EEJ variation is similar to that of Ap-index. (7) The EEJ variation is not dependent on the geographic longitude, but the ionospheric conductivity depends on that. (8) In the F10.7 solar radiation flux and the solar wind parameter, we could not find (a) 14.5-days and (b) semi-annual variations. These results suggest that (1) the 14.5-days EEJ variation may be caused by a tidal wave in the atmosphere, and (2) the semi-annual EEJ variation is caused by the geometrical seasonal variation of geo-dipole axis to the Sun, which may produce changes in the ionosphere dynamo and not in the ionospheric conductivity.
Abe Sumiyoshi
Uozumi Teiji
Yamazaki Yasuhiro
Yumoto Kiyo
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