In regions of very strong magnetic fields on the Sun, what happens to magnetic pressure compared to the surrounding atmospheric pressure?

• A. Magnetic pressure increases, while surrounding pressure decreases
• B. Magnetic pressure decreases, while surrounding pressure increases
• C. Both increase
• D. Both decrease

Answer: (A)

Magnetic pressure grows with the square of the magnetic field, so when the field is very strong, P_mag becomes large. In a region like a sunspot, this strong magnetic pressure needs to be balanced by the surrounding gas pressure across the boundary. That means the gas pressure inside the magnetized region drops relative to the outside so that the total pressure matches what’s outside. So in those regions, magnetic pressure increases while the surrounding (gas) pressure decreases, leading to a higher magnetic influence compared to the surrounding atmosphere. This also helps explain why sunspots are cooler and darker—the strong magnetic field suppresses energy transport by convection.