Studying ionic composition in open field regions using a 16 moments multi-species fluid model

Spectroscopic observations of the solar atmosphere reveal regions of the solar corona that are enriched in the abundance of heavy element with low-first ionisation potential (examples of low ‘FIP’ i.e. with <10 eV are Fe, Mg) relative to photospheric abundances. This enhancement in the abundance of low-FIP elements by a factor of three or four, called the ‘FIP effect’, is still not well understood. Moreover enriched abundances of low-FIP elements are also observed in the slow solar wind, which could give us more insights on its origins. An inverse-FIP effect corresponding to a decreased abundance of low-FIP elements has been measured in the atmosphere of M-type stars.

Turbulent mixing of the chromosphere combined with the ponderomotive force caused by Alfvén waves propagating in these atmosphere could give a mechanism that might explain the FIP effect. Diffusive theories including the thermal force exerted on the ions due to a collision frequency gradient has also a role to play on minor ion extraction from the chromosphere.  Our goal is to study and compare these effects using  ISAM, a new 1D 16 moments multi-fluid model taking into account collisional effects of the different heavy ions. In this work we use profiles from 3 different solar wind types simulated using ISAM in which we propagate Alfvén waves with a Shell Model of Alfvén-wave turbulence. We then compare the FIP bias obtained from these 3 types of wind.

This work has been funded by the ERC SLOWS SOURCE − DLV − 819189