科研之友
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摘要
Pi2 pulsations observed in the inner magnetosphere have been explained as radially trapped fast mode waves in the plasmasphere (i.e., plasmaspheric resonance). This model suggests that these waves can be globally detected at all local times in the inner magnetosphere when azimuthal propagation is allowed. There are no reports of Pi2-associated fast mode waves on the dayside in the inner magnetosphere, however. In this case study we focus on a Pi2 pulsation that was observed by the low-latitude Bohyun station (L = 1.35) in the postmidnight sector (MLT = 3.1) at 1853 UT on 27 February 2008. During the Pi2 event, Time History of Events and Macroscale Interactions during Substorms (THEMIS)-E was near the dawnside inner magnetosphere (MLT = 5.1 and L = 2.6), and THEMIS-D was near the duskside inner magnetosphere (MLT = 17.8 and L = 3.1), which are transition regions between nightside and dayside. On the dawnside, THEMIS-E observed poloidal oscillations characterized by the azimuthal component of the electric field (delta E(y)) and the radial (delta B(x)) and compressional (delta B(z)) components of the magnetic field. These components had high coherence (>0.8) with a low-latitude Pi2 pulsation at Bohyun. We confirmed that the poloidal oscillations are radially standing fast mode waves excited by plasmaspheric resonance. On the duskside, however, no poloidal oscillations in the Pi2 frequency band were detected at THEMIS-D, indicating that the plasmaspheric resonance may not establish itself globally. We suggest that there is strong longitudinal attenuation of fast mode waves near the duskside, which may be due to complicated duskside plasmapause structures. In addition, a well-defined, trapped fast mode oscillation would be expected as a two-dimensional mode structure near the meridian plane of a source region.
- 出版日期2010-12-10
