Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm31a2081u&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM31A-2081
Physics
[2704] Magnetospheric Physics / Auroral Phenomena, [2721] Magnetospheric Physics / Field-Aligned Currents And Current Systems, [2752] Magnetospheric Physics / Mhd Waves And Instabilities, [2790] Magnetospheric Physics / Substorms
Scientific paper
The formation of a substorm current wedge (SCW) is one of the fundamental processes in the expansion phase of the magnetospheric substorm [e.g. McPherron et al., 1973]. Uozumi et al. [2011] found that the ground Pi 2 timeseries had high coherencies with simultaneously observed AKR timeseries, regardless of whether the Pi 2 timeseries were associated with upward FAC or downward FAC; this fact suggests that the upward SCW and the downward SCW oscillated in a synchronized manner. This aspect was deduced from ground observations, and should be verified by a simultaneous observation on the ground and in the magnetosphere. In order to clarify the timing relation of Pi 2s that are associated with SCW oscillations, we made a comparative study by combining the ground and satellite data. We analyzed simultaneous ground-satellite observation of Pi 2 pulsation at the ETS-VIII geosynchronous orbit [Koga and Obara, 2008] and at MAGDAS/CPMN [Yumoto and the MAGDAS Group, 2006] high-, middle- and low-latitude stations. We picked up a Pi 2 event that exhibited a high coherency in the waveform among the ground and satellite Pi 2. A typical Pi 2 occurred around 1121UT on July 28, 2008. MLT of each ground station and ETS-VIII at the occurrence of the Pi 2 was as follows: TIK: 19.5h, KUJ: 20.0h, ETS-VIII: 20.8h, ZYK: 20.9h, MGD: 21.0h, PTK: 21.5h and WAD: 3.7h. Characteristics of the Pi 2 event are summarized as follows: (1) the initial deflection of the ground Pi 2s and magnetic bay variations in the D (eastward) component indicate the signature of the upward (at TIK, ZYK, MGD and PTK) and downward (at WAD) FAC of the SCW. (2) Pi 2 oscillated in- or 180deg out-of-phase among the D on the ground and N (eastward) components at the geosynchronous altitude (correlation coefficient: |Υ|> 0.75, phase delay: |ΔT|<10s). (3) Pi 2 oscillations in the H (northward) and P (parallel to the earth rotation axis) component exhibited phase (time) difference among them (|ΔT| < ~50s). By taking into account that the polarity of the D and N components Pi 2 oscillations were demarcated by the direction of the SCW FAC (upward or downward) and the sign of the geomagnetic latitude (northern- or southern-hemisphere), the present results indicate that the entire part of the SCW system (MLT span: ~8h) oscillated in a synchronized manner. This observational fact suggests that the substorm current wedge (SCW) is main source of global Pi 2 occurrence. On the other hand, the time differences in the H and P components Pi 2 can be explained by a characteristic of Pi 2 propagation in the magnetosphere, which was examined by Uozumi et al. [2000, 2009, 2011]. We will present other Pi 2 events that have the same characteristics, and also present results of statistical analyses.
Abe Sumiyoshi
Baishev D. G.
Ikeda Atsushi
Imajo S.
Kawano Hideaki
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