LONG-DURATION WHISTLER WAVES IN THE MAGNETOSHEATH - WAVE CHARACTERISTICS AND THE POSSIBLE SOURCE REGION

A type of whistler waves termed ''long-duration whistler waves'' (LDWW ) in ELF range (1 similar to 64 Hz) in the magnetosheath is studied ac cording to the wave characteristics and generation based on data obser ved by the search coil magnetometer onboard the Geotail satellite. LDW W are band-limited emissions near the lower hybrid frequency typically lasting several tells of minutes. Orientations of wave normal are det ermined front waveform data of vector magnetic field with an assumptio n of plane waves and are observed to be fairly well organized in a cer tain duration of LDWW. Ambiguity in propagation directions is removed by comparison of the phase relation between magnetic components and on e component of electric field, The propagation vectors of LDWW are sta tistically aligned along the ''Parker spiral'' but are primarily rever sed in the dusksides and in the dawnsides of tile magnetosheath: that is, one is sunward, and the other is antisunward. This outstanding asy mmetry strongly suggests that the bow shock region is the common sourc e region with waves propagating away from the bow shock along the drap ed magnetic field in the magnetosheath, Electrons composing a type of distribution function in Aat-topped shape are concurrently observed du ring a series of LDWW events and are likely to yield a favorite condit ion for LDWW propagating a long path free from attenuation caused by w ave particle interactions.