Ground Pi-2 pulsations comprise superpositions of various modal components of shear and fast Alfven waves, field line resonance, and plasmaspheric resonances. These complex waveforms, hard to resolve with Fourier transforms are successfully characterized by wavelet techniques. Wavelet detection employs decomposition and reconstruction modes to characterize time-frequency components. Hence, suitable for the examination of the locality and complexity of natural signal patterns. The current study presents the automatic detection of Pi-2 pulsations using Daubechies and Morlet wavelet transforms. In the study, distinct Pi-2 events from CPMN stations along 210${^\circ}$ magnetic meridian were detected. Global Pi-2 pulsations with harmonious H oscillations and discrete D bays in the sub-aurora zone suggest a common source with diverse tunneling paths. Scalograms of Pi-2 undulations of the frequency band of 6.7-22 mHz were observed despite different kinds of Pi-2s. Auroral Pi-2s were highly localized in local time with clear H and D bays, implying magnetospheric-ionospheric current couplings. Latitudinal and longitudinal Pi-2 propagations are exemplified by 180${^\circ}$ phase-shift (polarization) in EWA and group delay in the mid-latitudes of the northern hemisphere. Overall, Pi-2 wave power from high to low latitudes declined with peak amplitudes of 15 nT to less than 1 nT, respectively. Finally, external influences from sea currents causing signal attenuation due to the station's proximity to the sea were also identified. To conclude, the accuracy and efficiency of wavelet analysis with no computation hassle render it a valuable tool for the study of space events in the magnetospheric community.

Due to differences in solar illumination, a geomagnetic field line may have one footpoint in a dark ionosphere while the other ionosphere is in daylight. This may happen near the terminator under solstice conditions. In this situation, a resonant wave mode may appear which has a node in the electric field in the sunlit (high conductance) ionosphere and an antinode in the dark (low conductance) ionosphere. Thus, the length of the field line is one quarter of the wavelength of the wave, in contrast with half-wave field line resonances in which both ionospheres are nodes in the electric field. These quarter waves have resonant frequencies that are roughly a factor of 2 lower than the half-wave frequency on the field line. We have simulated these resonances using a fully three-dimensional model of ULF waves in a dipolar magnetosphere. The ionospheric conductance is modeled as a function of the solar zenith angle, and so this model can describe the change in the wave resonance frequency as the ground magnetometer station varies in local time. The results show that the quarter-wave resonances can be excited by a shock-like impulse at the dayside magnetosphere and exhibit many of the properties of the observed waves. In particular, the simulations support the notion that a conductance ratio between day and night footpoints of the field line must be greater than about 5 for the quarter waves to exist.

The RBSP and the Arase satellites have different inclinations and sometimes they fly both near the equator and off the equator on the same magnetic field line, simultaneously. Such conjunction events give us opportunities to compare the electron density at different latitudes. In this study, we analyzed the plasma waves observed by Arase and RBSP-A or B during the three conjunction events during and after the 7 Sep 2017 storm event. The electron number density at the satellite positions were estimated from frequencies of the UHR emissions obtained by the HFA/PWE onboard the Arase and the Waves instrument onboard RBSP, respectively. During the three conjunction events, the satellites passed through the plume, inner trough (the narrow region with low electron density between main body of the plasmasphere and the plume), plasmatrough with variable electron density, and partially-refilled plasmasphere. The power-law index m for the inner trough and plume was inferred to be 6~8 and ~0, respectively. This is interpreted to mean that the trough was close to collisionless and the plume was near diffusive equilibrium. In the plasmatrough with the varying density, both the high-density and low-density regions had m~0. The low-density portion of this region may have a different origin from the inner trough, because of the different m-indices. For the partially-refilled plasmasphere in the storm recovery phase, the power-law index m showed negative values, meaning that the density in the equatorial plane was higher than at higher latitudes.