Electron density spatial distribution and ion mass from coordinated observation of Arase and Van Allen Probes

Electron density spatial distribution and ion mass are obtained using coordinated observation of Arase and Van Allen Probes.

The PWE-HFA onboard Arase (EMFISIS onboard Van Allen Probes) observes radio and plasma waves in a frequency range from 0.01 to 10 MHz (from 10 Hz to 400 kHz). We can determine in-situ electron number densities by measuring upper hybrid resonance frequencies. Due to the difference of inclination of orbits of Arase and Van Allen Probes, we can measure electron number densities at different magnetic latitudes on the same field line by utilizing data obtained by both Arase and Van Allen Probes. Such data sets provide information of field aligned density distributions.

On the other hand, The MGF onboard Arase measures the static magnetic field and low-frequency magnetic field variations. From the MGF data, we obtain field line resonance (FLR) frequency and estimate equatorial plasma mass densities. Solving the FLR wave equation, we assume power-low density distribution with value of power low index which is estimated from the above-mentioned electron density measurements. Furthermore, we derive average ion mass from mass density and electron density with the assumption of quasi-neutrality of plasma.

This is first report of coordinated observation of Arase and Van Allen Probes to estimate the field aligned electron distribution and plasma mass densities.