FIP stands for First Ionization Potential. It's the energy required to remove the first electron from a neutral atom.
Low-FIP elements: These are easily ionized (≤ ~10 eV).
Examples: Mg (7.6 eV), Si (8.2 eV), Fe (7.9 eV), Ca (6.1 eV)
High-FIP elements: These require more energy to ionize (> ~10 eV).
Examples: O (13.6 eV), C (11.3 eV), N (14.5 eV), Ne (21.6 eV)
The FIP effect is the enhancement of low-FIP elements (like Mg, Si, Fe) in the solar corona compared to their abundance in the photosphere.
In simpler terms:
In the solar corona, there are relatively more atoms of elements that are easy to ionize (low-FIP), and fewer of those that are harder to ionize (high-FIP).
FIP bias is a measure of this enhancement — how much more abundant low-FIP elements are in the corona compared to the photosphere.
It’s often expressed as a multiplication factor:
| Photospheric Abundance | × FIP Bias = | Coronal Abundance |
|---|---|---|
| (baseline) | (e.g., ×2) | (enhanced) |