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Modulation of Electromagnetic Ion Cyclotron Waves by Pc5 ULF Waves and Energetic Ring Current Ions
Author(s) -
Kakad Amar,
Kakad Bharati,
Omura Yoshiharu,
Sinha Ashwini K.,
Upadhyay Aditi,
Rawat Rahul
Publication year - 2019
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2017ja024930
Subject(s) - physics , emic and etic , cyclotron , ring current , computational physics , sweep frequency response analysis , ion , ultra low frequency , magnetometer , magnetic field , search coil , geophysics , atomic physics , magnetosphere , acoustics , magnetic flux , quantum mechanics , sociology , anthropology
Abstract We present a ground observation of modulations of strong electromagnetic ion cyclotron (EMIC) waves by short and long periodicities at Indian Antarctic station, Maitri. The signatures of these waves were evident in the magnetic field variations recorded by an induction coil magnetometer during the interval 4.7–7.2 UT on 17 September 2011, a moderately disturbed day. These waves were preceded by a gradual increase in the solar wind dynamic pressure, which started at 3.88 UT. The discrete rising tone EMIC waves were observed in the Pc1 frequency band (∼0.5–0.9 Hz). The investigation of the periodicities of the observed wave spectrogram shows the presence of short (≈2.4 min) and long (≈39–69 min) periodicities. Our analysis shows that the short periodicities are associated with the Pc5 Ultra Low Frequency (ULF) waves generated by magnetic field line oscillations, while long periodicities might be associated with the ring current drifting ions. A new method, based on the cross‐correlation technique, is adopted to determine sweep rates of the discrete rising tones. The average sweep rates estimated in the range of 0.44–1.9 mHz/s are relatively low as compared to the past reports of sweep rates derived from the satellite observations of EMIC waves. We found that the higher sweep rates are associated with the stronger EMIC waves on the ground, which is in agreement with the theoretical studies. This suggests that the theoretically proposed dependence of sweep rate on strength of EMIC wave in the generation region is retained even during the propagation of these waves to the ground.