First glimpse inside a sunspot

[RealityCheck01]

In another thread Michael mentioned an interesting news article with nice science behind it:
First glimpse inside a sunspot 7 November, 2001

By analysing sound waves travelling inside the Sun, a US team of scientists has produced the first detailed image of what goes on inside a sunspot.
The picture that emerges is of fast-moving streams of hot, electrically charged gas converging into a gigantic vortex that reaches below the solar surface.
...
"What we found is that sunspots are not static but consist of very strong, downward flows of plasma - electrically charged gas - travelling toward the interior of the Sun at speeds of about 4,800 kilometres per hour (3,000 miles per hour)," Kosovichev said.
...
When the sound waves reach a point about 4,800 km (3,000 miles) below the surface, however, their speed increases significantly, indicating that the roots of a sunspot are hotter than their surroundings.

The paper looks like Investigation of Mass Flows beneath a Sunspot by Time-Distance Helioseismology by Junwei Zhao, Alexander G. Kosovichev and Thomas L. Duvall, Jr.

This is at least one sunspot basically acting as a giant eggbeater and mixing up the surface of the Sun to a depth of 16,000 km.

The thread is closed so I cannot add this observation to the list of reasons why Michael's idea about a solid iron ferrite surface at 4800 km is wrong. But maybe Michael can tell us why the detection of hot plasma flowing through the depth of 4800 km below this sunspot is evidence for his solid surface as he claims?
The paper has Figure 3 (Vertical cuts through the sunspot center) with the plasma flow below the middle of the umbra going down to ~7,000 km.

 

[Lilly Owl]

Very cool.

 

[RealityCheck01]

It gets cooler !
When astronomers look at the photosphere in general, they calculate that the temperature increase with depth from ~5777 K at the top to ~9400 K at 100 km below the top.
However the magnetic fields that create sunspots reduce the plasma temperature to 3000–4500 K. Below the sunspot astronomers refer to the Wilson depression (~1000 km) and it's temperature difference from the photosphere temperature.

It is clear that magnetic inhibition of convection is most effective within 1.5 Mm of the photosphere (Thomas & Weiss 1992). The temperature difference,

T, between the sunspot umbra and the mean undisturbed atmosphere at the level of the Wilson depression, is about 9000 K, but

T decreases rapidly with depth. The estimated value of

T falls to 500 K at a depth of 2 Mm and then to 25 K at a depth of 6 Mm (Meyer et al. 1974).