Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009jgra..11412206l&link_type=abstract
Journal of Geophysical Research, Volume 114, Issue A12, CiteID A12206
Physics
8
Magnetospheric Physics: Mhd Waves And Instabilities (2149, 6050, 7836), Magnetospheric Physics: Magnetosphere: Inner, Magnetospheric Physics: Electric Fields (2411), Magnetospheric Physics: Solar Wind/Magnetosphere Interactions
Scientific paper
Ultralow frequency (ULF) waves in the Pc4 and Pc5 bands are ubiquitous in the inner magnetosphere and have significant influence on energetic particle transport. Investigating the source and characteristics of ULF waves also helps us better understand the interaction processes between the solar wind and the magnetosphere. However, owing to the limitation in instrumentation and spatial coverage, the distribution of ULF waves in local time and L shell in the inner magnetosphere has not been completely studied. The recent Time History of Events and Macroscale Interactions During Substorms (THEMIS) mission provides unique opportunities to investigate the spatial distribution of ULF pulsations across different L shells with full local time coverage in the inner magnetosphere during solar minimum, with both electric and magnetic field measurements. Pc4 and Pc5 pulsations in the electric field observations are identified throughout 13 months of measurements, covering 24 h in local time. The pulsations are characterized as either toroidal or poloidal (including compressional) mode, depending on the polarization of the electric field. Subsequently, the pulsations' occurrence rate and wave power distributions in radial distance and local time are recorded. While the distributions of both Pc4 and Pc5 events vary greatly with radial distance and local time, Pc4 events are more frequently observed in the inner region around 5-6 RE and Pc5 events are more frequently observed in the outer region around 7-9 RE, which suggests that the field line resonance is an important source of the ULF waves. In the flank regions, the wave power is dominated by the toroidal mode, likely associated with the Kelvin-Helmholtz (KH) instability. In the noon sector, the Pc5 ULF wave power is dominated by the poloidal mode, likely associated with the solar wind dynamic pressure disturbance. The KH instability plays an important role, suggested by our observations, during the solar minimum when the solar wind dynamic pressure is relatively weak. We also find that the contributions to the Pc5 ULF wave power from the external sources are larger than the contributions from the internal sources. These statistical results are important in characterizing Pc4 and Pc5 waves and also important for any efforts to model the transport of energetic particles in the magnetosphere.
Angelopoulos Vassilis
Bonnell Jerry
Elkington Scot R.
Ergun Robert
Glassmeier Karl-Heintz
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