Abstract
Recent studies of sunspots have shown that there is a critical value (Bcrit) of the vertical component of the magnetic field (Bver) that triggers umbral mode of convection, i.e., only umbral convection is allowed in regions with Bver > Bcrit .We study the existence of a Bcrit in other magnetic structures, such as pores. The evolution of Bver on the pore boundary during its lifetime shows the role of Bver on the stability of pores.