HR: 0830h
AN: SM41B-0573    [PDF]
TI: Polar distributions of small-scale magnetic disturbances derived from the Akebono magnetometer data
AU: * Hasunuma, T
EM: hasunuma@pat.geophys.tohoku.ac.jp
AF: Department of Geophysics, Graduate School of Science, Tohoku University, Aramaki-Aoba, Aoba-ku, Sendai, Miyagi, 980-8578 Japan
AU: Fukunishi, H
EM: fuku@pat.geophys.tohoku.ac.jp
AF: Department of Geophysics, Graduate School of Science, Tohoku University, Aramaki-Aoba, Aoba-ku, Sendai, Miyagi, 980-8578 Japan
AU: Takahashi, Y
EM: yukihiro@pat.geophys.tohoku.ac.jp
AF: Department of Geophysics, Graduate School of Science, Tohoku University, Aramaki-Aoba, Aoba-ku, Sendai, Miyagi, 980-8578 Japan
AU: Nagatsuma, T
EM: tnagatsu@crl.go.jp
AF: Communications Research Laboratory, 4-2-1 Nukui-kita, Koganei, Tokyo, 184-8795 Japan
AU: Kataoka, R
EM: ryuho@pat.geophys.tohoku.ac.jp
AF: Department of Geophysics, Graduate School of Science, Tohoku University, Aramaki-Aoba, Aoba-ku, Sendai, Miyagi, 980-8578 Japan
AB: In the cusp and its vicinity, burst-like disturbances of magnetic and electric fields are often observed on Freja, FAST, and Akebono spacecraft. Recent studies suggest that these small-scale disturbances are signatures of the dispersive Alfv$\acute{e}$n waves (DAW) and the ionospheric Alfv$\acute{e}$n resonator (IAR) excited in the topside ionosphere. These disturbances would play a key role in the energy coupling between the magnetosphere and the ionosphere. The purpose of this study is to obtain the polar distributions of these small-scale disturbances and their contributions to field-aligned currents from the Akebono magnetometer data. We analyzed the magnetometer data of 2596 passes in 1991 during the periods when the Akebono satellite was located above an altitude of 5000 km with the FFT method. The obtained polar maps show that the region of intense magnetic disturbances in the frequency range 0.0156-0.125 Hz covers the local time sector from the dayside cusp to the dawnside. In contrast, no intense disturbances are found on the nightside and duskside region. It is also found that in the altitude region from 5000 to 8000 km intense magnetic disturbances are observed over a wide latitude range from the auroral oval to the polar cap, while in the altitude region above 8000 km, these disturbances are concentrated in the dayside cusp region and its vicinity. We will discuss the origins of such day-night and dawn-dusk asymmetry and altitude dependency.
DE: 2724 Magnetopause, cusp, and boundary layers
DE: 2736 Magnetosphere/ionosphere interactions
DE: 4275 Remote sensing and electromagnetic processes (0689)
DE: 6030 Magnetic fields and magnetism
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting