Simulating the FIP effect in coronal loops using a multi-species kinetic-fluid model

By Nicolas Poirier et al. 2020, Astrophysical Journal

    The goals of this study are the following:

  • Reviewing the physics and verifying that the ionization fractions of all modeled elements agree with observations.
  • Investigating which physical mechanisms extract heavy ions and how they contribute to the FIP effect. We will in particular see how the thermal and ponderomotive forces play a role in the FIP effect.
  • Making diagnostics of FIP biases and comparing the results with typical values from other studies but also observations (e.g. Hinode, Ulysses).
Snapchots from a combined EUV movie of loops above an active region during the solar flare of July 19th 2012. Raw observations taken by the Atmospheric Imaging Assembly (AIA) instrument onboard the Solar Dynamics Observatory (SDO) NASA mission. All credits to NASA for the data and Miloslav Druckmüller for the processing. The original full time resolution movie is available in the author's webpage

Coronal loops are large scale structures that can extend far up to the high corona (~2.0/2.5 Rs). They are closed magnetic flux tubes situated beneath helmet streamers. One should not confuse them with smaller loops above active regions, the latter being much more visibles especially in EUV images (see figure 1).

Coronal loops being magnetically anchored at both sides to the Sun, the plasma remains confined inside at opposite to solar wind plasma that is ejected into the interplanetary space along open field lines. However they are still candidates at supplying the slow solar wind via magnetic reconnection. In fact coronal loops adjacent to open flux regions may exchange material, hence supplying the slow solar wind with plasma that was initially confined inside coronal loops. This is a reason why the modeling of coronal loops is highly relevant to the SLOW_SOURCE project, in order to investigate the origin of the slow solar wind.

As discussed in the composition aspects of the slow solar wind in “About the slow wind”, coronal loops are good candidates as a possible source of the slow solar wind because of their similar compositions. The composition is measured in situ for the slow wind whereas it is observed remotely by EUV spectrometry for coronal loops. They both show an enrichment in specific heavy ions which have a low First Ionization Potential (FIP). As a consequence, understanding the FIP effect and its origins is a key point in the project that requires special attention. This is a challenging topic that probably involves multiple physical effects such as: turbulence, waves, kinetics effects, radiative transfer and chemistry.

This work follows up on another study from Victor Réville et al. , Investigating the origin of the FIP effect with a shell turbulence model, recently accepted in Frontiers in Astronomy and Space Sciences.