Variation of Magnetospheric Ultra-Low Frequency Wave Power Spectrum during the 27-28 May 2017 Challenge Event: LFM-RCM Simulation Results

The 27-28 May 2017 storm has been chosen as a GEM Challenge event which is characterized by an extended period of strongly southward IMF (~-20 nT) following another eight hours of enhanced solar wind dynamic pressure. The LFM global magnetosphere model coupled with the RCM ring current model was used to explore the ULF wave power spectrum in the magnetosphere during this challenge event. We analyzed the power spectrum distribution in the equatorial plane and in the frequency range of 1-15 mHz (Pc4-5) and 15-50 (Pc3-4) mHz for the radial and azimuthal component of electric field and parallel component of magnetic field. The integrated Pc4-5 power in the radial electric field component started to show up on the magnetopause after the enhanced dynamic pressure arrived around 16 UT of May 27, and stronger power was seen inside the magnetopause after the southward turning of IMF at ~22 UT of May 27. Compressional mode power shows similar behavior in the Pc4-5 range during different phases of the storm. The Pc3-4 band ULF wave power is generally lower than that of the lower frequency band. Eigenmode analysis shows signatures of field line resonance near 12 MLT. It is suggested that the compressional mode fluctuations get resonantly coupled with the toroidal mode field line resonance.