M. Yamauchi (IRF)Date:
AniaraMass-loading energy extraction from the solar wind to the planetary system for additional ion escape
Swedish Institute of Space Physics
According to Cluster hot ion statistics, the amount of escaping ions (O+ number density about 1% of the solar wind) can no longer be ignored in terms of mass density because escaping ions occupies about 20% of the solar wind. In fact, Cluster observed substantial deceleration of the solar wind H+ while acceleration of O+ in plasma mantle. Using conservation of anti-sunward momentum in case of inelastic mixing of O+ into the H+ flow, energy conversion becomes proportional to total mass flux of O+ (into the incident solar wind and to the square of the solar wind velocity (u_sw^2), but not dependent on the injection area or solar wind density. Applying the observed O+ value and area, this means 10^10-11 W, and is large enough to explain the electric current system flowing in the cusp region, which is the most intense current system in the dayside. Since the ion heating due to the Joule heating of such an ionospheric current system is the main driver of the ion outflow, the entire cycle constitute a positive feedback energy extraction, explaining the observed exponential dependence of the escaping flux to Kp or solar wind velocity.
The present positive feedback model requires only the magnetic connectivity to the load: ionosphere for the Earth's case. This means that the concept should be applied to all unmagnetized body with sufficient atmosphere that can form a region (ionosphere or its equivalent) to consume the electric energy to heat ion. One possible application is comet. If the mass-loading region is magnetically connected to the region close to the cometary coma, energy extraction could be higher, reducing the solar wind energy more and extra acceleration of O+ beyond the gyromotion might occur. Possible candidate of such process in Rosetta/ICA observation will be discussed. Created 2017-10-05 08:52:59 by Mats HolmströmLast changed 2018-04-27 09:21:46 by Mats Holmström