TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 65 (No. 5), pp. 411-433, 2013

ULF waves in the outer magnetosphere: Geotail observation 1 transverse waves

Susumu Kokubun

Formerly, Solar-Terrestrial Environment Laboratory, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 447-8507, Japan

(Received April 2, 2012; Revised December 21, 2012; Accepted December 24, 2012; Online published June 10, 2013)

Abstract: A survey of ULF waves in the Pc 5 frequency range during the six year period (1995-2000) has been made for the field line resonance waves in the outer magnetosphere, using plasma flow and magnetic field measurements with the Geotail spacecraft. On the morning side a series of wave trains often appears during several hours. In contrast such a series of wave trains with a long duration is rarely observed in the afternoon to evening sector. Most of waves in the afternoon sector are isolated, of which duration is approximately one hour. The existence of a set of preferential frequencies and the pronounced dawn-dusk asymmetry of wave occurrence and wave features, which were found in ground-based and ionospheric measurements of geomagnetic ULF pulsations, were statistically confirmed. It is also noted that the background plasma flow is sunward in the evening sector without exception. Transverse waves are generally observed in the condition of plasma β below 1.5. High β cases are mostly associated with events on the dusk side. As for the relation to solar wind conditions, Pc 5 waves tend to occur under the condition of more radial than the average IMF spiral angle, or of low cone angle.
Key words: Pc 5 waves, dawn-dusk asymmetry of occurrence, radial IMF.

Corresponding author E-mail: kokubun@pop21.odn.ne.jp

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