Observations of increasing EMIC waves frequency with the increasing solar cycle

Electromagnetic ion-cyclotron (EMIC) waves are important to the dynamics of the radiation belts and are detected at a variety of L-shells during storm and quiet times. During periods of increased solar activity and storm like conditions, the plasmasphere erodes and the ring current expands inward to lower L-shells. The overlap between the cold plasmasphere ions and hot ring current ions can lead to a temperature anisotropy and generation of EMIC waves. The generation region location may be inferred from ground-based magnetometer measurements with higher frequencies indicating the waves were generated in a stronger magnetic field closer to Earth. Observations with an induction-coil magnetometer located in Halley Bay, Antarctica (L = 4.5) show an increasing number of ground observed EMIC waves rising or originating above 1 Hz from 2007 to 2012. In addition, when waves at higher frequencies are observed it is generally higher in power than the lower frequency waves, which could lead to more effective scattering of energetic particles. The waves have a seasonal dependence and grow in number, intensity, and spectral frequency during the winter months. The increasing activity of the Sun and solar wind could be causing an increase in temperature anisotropy at lower L-shells leading to higher frequency and higher power waves observed on the ground.