Statistical Distribution of Observations of Pc1 Pearl Pulsations by the Van Allen Probes and Poynting Flux Analysis from 11th October 2013

Abstract:

Pc1 pearl pulsations are a time-modulated electromagnetic wave in the Pc1 band of the ULF spectrum. They are believed to be a subclass of electromagnetic ion cyclotron (EMIC) waves, and so are generated through the ion cyclotron instability. However, the exact cause of their modulated structure is still a topic of debate. The previously held idea of ionospheric reflection between conjugate hemispheres has been discredited due to several observations of a similar modulation period on the ground as in the magnetosphere as well as numerous in situ observations of unidirectional poynting flux. However, there still exist examples of events exhibiting bidirectional poynting flux which would suggest a reflecting wave packet. We will show analysis from one such event observed in October of 2013 using both in situ and ground-based data. The Van Allen Probes spacecraft, launched in August of 2012, have offered us an unprecedented view into the equatorial magnetosphere where the generation region of EMIC waves is thought to reside. As of August of 2014, the spacecraft will have undergone one full precession around Earth, allowing for observations spanning the full range in MLT. We therefore present here a statistical analysis of EMIC waves, both pearl pulsations and unstructured, observed within the first two years of the Van Allen Probes mission.