Convective collapse
= Convective collapse
A compressible intensification mechanism for a thin, nearly vertical <flux tube> in a superadiabatic atmosphere. An unstable downflow drains material and lowers internal gas pressure; approximate lateral balance $p_i+B^2/(2\mu_0)=p_e$ then permits the tube to contract and its field to strengthen at nearly conserved <magnetic flux>. It relies on compressibility and thermal evolution, which are absent from a strict <Boussinesq approximation>. Dynamic photospheric structures need not satisfy thin-tube equilibrium, so this mechanism does not explain every intense field concentration.