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POLAR observations

Figure 3 displays the radial electric field component (tex2html_wrap_inline448) and an azimuthal magnetic field component (tex2html_wrap_inline438) measured by POLAR instruments on January 10, 1997, 21-24 UT, while moving from the northern polar cap toward the equator at 05:30 MLT. At 21:53 UT, POLAR began to observe B-field oscillations whereas E-field oscillations were not observed before 22:10 UT presumably due to the unfavorable orientation of the E-field long booms. The B-field perturbations appear mainly in the azimuthal direction (tex2html_wrap_inline438), and the electric field oscillates in the radial direction (tex2html_wrap_inline448); wave signals in other components are weak. The background magnetic field is oriented along the z-axis, and therefore we conclude the observed wave is a toroidal mode. Both components are observed at L shells from 9.0 to 6.6. The observed wave periods vary in the 150-250 s range, corresponding to wave frequencies of 4-7 mHz.

Figure 4 presents bandpass-filtered time series data for the 21:50-23:10 UT interval. Here we have used a Butterworth band-pass filter at 5tex2html_wrap_inline4562 mHz to remove noise from the data shown in Figure 3. The E- and B-field components are clearly 90tex2html_wrap_inline446 out of phase, indicating that the observed mode is a standing wave.



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Next: GEOTAIL observations Up: Observations Previous: Solar wind observations

© 1998 AGU