Flocculi are those mottled, cloud-like patches you see best in H-alpha or Ca II K light — they’re magnetic field regions showing up in the chromosphere. But the “bright vs dark” thing? That’s about how plasma and magnetic fields are interacting in slightly different ways.
Let’s break it down cleanly.
🌞 Bright Flocculi
These show up as lighter, glowing patches.
What they are:
- Regions of enhanced magnetic field strength
- Often found around active regions or near sunspots
- Associated with plage (especially in Ca II K)
Why they’re bright:
- Magnetic fields heat the chromospheric plasma locally
- Increased temperature → increased emission
- So they radiate more strongly in H-alpha or Ca II lines
In short:
Strong magnetic field + local heating = brighter emission.
They’re basically magnetic “hot spots.”
🌑 Dark Flocculi
These look like darker, filamentary or patchy structures.
What they are:
- Cooler, denser plasma suspended in magnetic fields
- Often connected with filaments or fibril structures
- Can be part of the magnetic canopy over quiet Sun
Why they’re dark:
- Cooler plasma absorbs more background light
- Seen in absorption against the bright chromosphere
- Line-of-sight geometry matters a lot
In short:
Cooler material + absorption = darker appearance.
They’re more like magnetic clouds rather than heaters.
⚖️ The Key Physical Difference
| Feature | Bright Flocculi | Dark Flocculi |
|---|---|---|
| Magnetic Field | Strong & concentrated | Structured but often supporting suspended plasma |
| Temperature | Slightly hotter | Slightly cooler |
| Appearance | Emission | Absorption |
| Association | Plage / active regions | Filaments / fibrils |
One subtle but important point
It’s not that one is “magnetic” and the other isn’t.
Both are magnetic phenomena.
The difference is:
- Are we seeing heated chromospheric plasma emitting?
- Or cooler material absorbing background light?
If you’re observing in H-alpha and seeing mixed bright and dark mottling, that’s often the magnetic network transitioning between heating zones and fibril canopies. The dynamic contrast can shift noticeably over 10–20 minutes as small-scale fields evolve.