| Presentation Title: | Plasma Composition and Wave Activity in a Solar Active Region |
| Author(s): | T. Mihailescu, D. Brooks, M. Laming, D. Baker, L. Green, A. James, D. Long, L. van Driel-Gesztelyi, M. Stangalini |
Abstract:
The plasma composition of the solar corona exhibits an overabundance of elements with a low first ionization potential (FIP) compared to those with a high FIP. This enhancement of low-FIP elements is believed to take place in the chromosphere and is characterised by the FIP bias parameter. Typically, the strongest enhancement is observed in active regions and is believed to be a result of wave activity within the active region. In this work, we study the plasma composition in an active region following an episode of significant new flux emergence into the pre-existing active region, which separates it into two loop populations with different ages and properties. We use Hinode EIS data to estimate the FIP bias using two diagnostics: Si X 258.375 A/S X 264.233 A (temperature of approximately 1.5 MK) and Ca XIV 193.874 A/Ar XIV 194.396 A (temperature of approximately 4 MK). The preexisting loops (those that had formed before the flux emergence) show significantly higher FIP bias values in the Ca/Ar diagnostic than the Si/S one, but this pattern is not observed in the emerging loops (those created by the flux emergence). This result can be interpreted in the context of the ponderomotive force model, which proposes that the plasma fractionation is generally driven by Alfvén waves. Matching spectroscopic observations with predictions from simulations of the ponderomotive force suggests that the different plasma composition patterns observed in the two sets of loops depend on the properties of the Alfvén waves driving the enhancement - in particular, on whether the waves are resonant or not resonant with the loop and the chromospheric height at which they deposit their energy.