Event Details

Van Allen Probes EMFISIS Measurements of Whistler Mode Waves: Observations, Theory, and Modeling

The Van Allen Probes EMFISIS instrument provides observations of the wave magnetic and electric fields in both the whistler mode chorus and plasmaspheric hiss frequency range. Recent results from this comprehensive dataset are presented. A statistical survey of plasmaspheric hiss wave parameters reveals a two-population structure – one more field aligned and one more oblique. The distribution of this oblique population is shown to be similar to that observed for oblique chorus waves, albeit at smaller radial distances. The feasibility of a direct link between these two wave modes is tested, and confirmed, using ray-tracing simulations. Also presented are results detailing how the measured electric field compares with the electric field calculated using cold plasma theory and magnetic field observations. The structure of discrepancies is consistent with the formation of a plasma sheath around the electric field sensors – which may be modeled as a voltage divider with complex impedance. The antenna-shorting factor and anomalous gain effects from the spin-axis antennas are also identified and considered. The resultant density-dependent model may be used to correct electric field observations for these effects, and is subsequently demonstrated to be as accurate as the methodology permits. Finally, we present a method of estimating electron densities from observations of plasmaspheric hiss. Once calibrated against the density from the upper hybrid line, these calculated densities are demonstrated to yield a high degree of accuracy, as well as providing density estimates under conditions where other methods are subject to observational limitations.